Updated on 2024/05/19

写真a

 
SAKAI Tatsuya
 
Organization
Academic Assembly Institute of Science and Technology CHIKYU SEIBUTSU KAGAKU KEIRETU Professor
Faculty of Science Department of Science Professor
Title
Professor
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Degree

  • Ph.D ( 1997.3   The University of Tokyo )

Research Areas

  • Life Science / Plant molecular biology and physiology

Research History (researchmap)

  • Niigata University   Faculty of Science Department of Biology Bioregulatory Science   Professor

    2014.4

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  • Niigata University   Headquarters for Strategy and Planning Office for Promoting the Cultivation of Young Researchers   Associate Professor

    2010.2 - 2014.3

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  • Japan Science and Technology Agency

    2007.10 - 2011.3

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  • RIKEN

    2000.10 - 2010.1

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  • 日本学術振興会   特別研究員(PD)

    1998.4 - 2000.9

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Research History

  • Niigata University   Faculty of Science Department of Science   Professor

    2017.4

  • Niigata University   Abolition organization Bioregulatory Science   Professor

    2014.4 - 2017.3

  • Niigata University   Headquarters for Strategy and Planning Office for Promoting the Cultivation of Young Researchers   Associate Professor

    2010.2 - 2014.3

Education

  • The University of Tokyo   Graduate School, Division of Science   Plant Biology

    - 1997.3

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    Country: Japan

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Papers

  • Photosensory adaptation mechanisms in hypocotyl phototropism: how plants recognize the direction of a light source Reviewed

    Ken Haga, Tatsuya Sakai

    Journal of Experimental Botany   2023.1

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    Authorship:Corresponding author   Publishing type:Research paper (scientific journal)   Publisher:Oxford University Press (OUP)  

    Abstract

    Plants recognize the direction of a light source and exhibit phototropic responses. Physiological studies have predicted that differences in the light intensity received by the cells on the irradiated and shaded sides of a coleoptile or hypocotyl cause differences in the amounts of photoproduct. This hypothetical photoproduct appears to regulate a signaling pathway that controls cell elongation in which cells under lower light intensity elongate more than those under higher light intensity. This results in a bending growth toward a light source and has been proposed as the photoproduct-gradient model of phototropism. In this review, we summarize recent findings on the photosensory adaptation mechanisms involving a blue-light photoreceptor, phototropin1 (phot1), ROOT PHOTOTROPISM2, NONPHOTOTROPIC HYPOCOTYL3 (NPH3), and another photoreceptor family, the phytochromes. The current evidence demonstrates that, in addition to the transition of the phot1–NPH3 photoreceptor complexes to their active state, the presence of a certain population of the phot1–NPH3 complexes showing a steady state, even in a light environment, is essential for recognition of the light source direction in phototropism. This is consistent with the photoproduct-gradient model, and a dissociation state of the phot1–NPH3 complex would be considered an entity of the hypothetical photoproduct in this model.

    DOI: 10.1093/jxb/erad015

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  • The phosphorylation status of NONPHOTOTROPIC HYPOCOTYL3 affects phot2-dependent phototropism in <i>Arabidopsis</i> Reviewed

    Taro Kimura, Ken Haga, Tatsuya Sakai

    Plant Signaling & Behavior   17 ( 1 )   2022.1

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    Authorship:Corresponding author   Publishing type:Research paper (scientific journal)   Publisher:Informa UK Limited  

    DOI: 10.1080/15592324.2022.2027138

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  • Intragenic complementation at the Lotus japonicus CELLULOSE SYNTHASE-LIKE D1 locus rescues root hair defects. Reviewed International journal

    Bogumil Karas, Loretta Ross, Mara Novero, Lisa Amyot, Sayaka Inada, Michiharu Nakano, Tatsuya Sakai, Shusei Sato, Jeremy D Murray, Paola Bonfante, Krzysztof Szczyglowski

    Plant Physiology   186   2037 - 2050   2021.5

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    Language:English   Publishing type:Research paper (scientific journal)  

    Root hair cells form the primary interface of plants with the soil environment, playing key roles in nutrient uptake and plant defense. In legumes, they are typically the first cells to become infected by nitrogen-fixing soil bacteria during root nodule symbiosis. Here, we report a role for the CELLULOSE SYNTHASE-LIKE D1 (CSLD1) gene in root hair development in the legume species Lotus japonicus. CSLD1 belongs to the cellulose synthase protein family that includes cellulose synthases and cellulose synthase-like proteins, the latter thought to be involved in the biosynthesis of hemicellulose. We describe 11 Ljcsld1 mutant alleles that impose either short (Ljcsld1-1) or variable (Ljcsld1-2 to 11) root hair length phenotypes. Examination of Ljcsld1-1 and one variable-length root hair mutant, Ljcsld1-6, revealed increased root hair cell wall thickness, which in Ljcsld1-1 was significantly more pronounced and also associated with a strong defect in root nodule symbiosis. Lotus japonicus plants heterozygous for Ljcsld1-1 exhibited intermediate root hair lengths, suggesting incomplete dominance. Intragenic complementation was observed between alleles with mutations in different CSLD1 domains, suggesting CSLD1 function is modular and that the protein may operate as a homodimer or multimer during root hair development.

    DOI: 10.1093/plphys/kiab204

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  • The Phosphorylation Status of NPH3 Affects Photosensory Adaptation During the Phototropic Response. Plant Physiology, in press. Reviewed

    Taro Kimura, Ken Haga, Yuko Nomura, Takumi Higaki, Hirofumi Nakagami, Tatsuya Sakai

    Plant Physiology   187   981 - 995   2021.5

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  • Arabidopsis ROOT PHOTOTROPISM2 Is a Light-Dependent Dynamic Modulator of Phototropin1 Reviewed

    Taro Kimura, Tomoko Tsuchida-Mayama, Hirotatsu Imai, Koji Okajima, Kosuke Ito, Tatsuya Sakai

    The Plant Cell   32   2004 - 2019   2020

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    Authorship:Corresponding author   Language:English   Publishing type:Research paper (scientific journal)  

    DOI: 10.1101/862649

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  • Low-fluence blue light-induced phosphorylation of Zmphot1 mediates the first positive phototropism Reviewed International journal

    Hiromi Suzuki, Tomokazu Koshiba, Chiharu Fujita, Yoshio Yamauchi, Taro Kimura, Toshiaki Isobe, Tatsuya Sakai, Masato Taoka, Takashi Okamoto

    Journal of Experimental Botany   70 ( 20 )   5929 - 5941   2019

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    Phototropin1 (phot1) perceives low- to high-fluence blue light stimuli and mediates both the first and second positive phototropisms. High-fluence blue light is known to induce autophosphorylation of phot1, leading to the second positive phototropism. However, the phosphorylation status of phot1 by low-fluence blue light that induces the first positive phototropism had not been observed. Here, we conducted a phosphoproteomic analysis of maize coleoptiles to investigate the fluence-dependent phosphorylation status of Zmphot1. High-fluence blue light induced phosphorylation of Zmphot1 at several sites. Notably, low-fluence blue light significantly increased the phosphorylation level of Ser291 in Zmphot1. Furthermore, Ser291-phosphorylated and Ser369Ser376-diphosphorylated peptides were found to be more abundant in the low-fluence blue light-irradiated sides than in the shaded sides of coleoptiles. The roles of these phosphorylation events in phototropism were explored by heterologous expression of ZmPHOT1 in the Arabidopsis thaliana phot1phot2 mutant. The first positive phototropism was restored in wild-type ZmPHOT1-expressing plants; however, plants expressing S291A-ZmPHOT1 or S369AS376A-ZmPHOT1 showed significantly reduced complementation rates. All transgenic plants tested in this study exhibited a normal second positive phototropism. These findings provide the first indication that low-fluence blue light induces phosphorylation of Zmphot1 and that this induced phosphorylation is crucial for the first positive phototropism.

    DOI: 10.1093/JXB/ERZ344

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  • Deetiolation Enhances Phototropism by Modulating NON-PHOTOTROPIC HYPOCOTYL3 Phosphorylation Status Reviewed

    Sullivan, Stuart, Kharshiing, Eros, Laird, Janet, Sakai, Tatsuya, Christie, John M.

    Plant Physiology   180 ( 2 )   1119 - 1131   2019

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    DOI: 10.1104/PP.19.00206

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  • Determination of Auxin Flow During Phototropic Responses Using Fluorescent Auxin Analogs. Reviewed

    Sakai T

    Methods in molecular biology (Clifton, N.J.)   1924   157 - 163   2019

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    Authorship:Lead author, Corresponding author  

    DOI: 10.1007/978-1-4939-9015-3_12

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  • Roles of AGCVIII Kinases in the Hypocotyl Phototropism of Arabidopsis Seedlings Reviewed

    Ken Haga, Lena Frank, Taro Kimura, Claus Schwechheimer, Tatsuya Sakai

    Plant and Cell Physiology   59 ( 5 )   1060 - 1071   2018.5

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:Oxford University Press  

    Regulation of protein function by phosphorylation and dephosphorylation is an important mechanism in many cellular events. The phototropin blue-light photoreceptors, plant-specific AGCVIII kinases, are essential for phototropic responses. Members of the D6 PROTEIN KINASE (D6PK) family, representing a subfamily of the AGCVIII kinases, also contribute to phototropic responses, suggesting that possibly further AGCVIII kinases may potentially control phototropism. The present study investigates the functional roles of Arabidopsis (Arabidopsis thaliana) AGCVIII kinases in hypocotyl phototropism. We demonstrate that D6PK family kinases are not only required for the second but also for the first positive phototropism. In addition, we find that a previously uncharacterized AGCVIII protein, AGC1-12, is involved in the first positive phototropism and gravitropism. AGC1-12 phosphorylates serine residues in the cytoplasmic loop of PIN-FORMED 1 (PIN1) and shares phosphosite preferences with D6PK. Our work strongly suggests that the D6PK family and AGC1-12 are critical components for both hypocotyl phototropism and gravitropism, and that these kinases control tropic responses mainly through regulation of PIN-mediated auxin transport by protein phosphorylation.

    DOI: 10.1093/pcp/pcy048

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  • Asymmetric Auxin Distribution is Not Required to Establish Root Phototropism in Arabidopsis. Reviewed

    Kimura T, Haga K, Shimizu-Mitao Y, Takebayashi Y, Kasahara H, Hayashi KI, Kakimoto T, Sakai T

    Plant Cell Physiol.   159 ( 4 )   823 - 835   2018.4

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  • Involvement of PP6-type protein phosphatase in hypocotyl phototropism in Arabidopsis seedlings Reviewed

    Haga, Ken, Sakai, Tatsuya

    Plant Signaling and Behavior   13 ( 11 )   e1536631   2018

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    DOI: 10.1080/15592324.2018.1536631

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  • Yucasin DF, a potent and persistent inhibitor of auxin biosynthesis in plants Reviewed

    Tsugafune, Shinichi, Mashiguchi, Kiyoshi, Fukui, Kosuke, Takebayashi, Yumiko, Nishimura, Takeshi, Sakai, Tatsuya, Shimada, Yukihisa, Kasahara, Hiroyuki, Koshiba, Tomokazu, Hayashi, Ken-ichiro

    SCIENTIFIC REPORTS   7   2017.10

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:NATURE PUBLISHING GROUP  

    The plant hormone auxin plays a crucial role in plant growth and development. Indole-3-acetic acid (IAA), a natural auxin, is mainly biosynthesized by two sequential enzyme reactions catalyzed by TAA1 and YUCCA (YUC). TAA1 is involved in the conversion of tryptophan to IPA, and YUC catalyzes the conversion of IPA to IAA. We previously demonstrated that yucasin inhibits AtYUC1 enzyme activity and suppress high-auxin phenotype of YUC overexpression plants, although yucasin displayed weak effects on the auxin-related phenotype of wild-type plants. To develop more potent YUC inhibitors, various derivatives of yucasin were synthesized, and their structure-activity relationships were investigated. Yucasin difluorinated analog (YDF) (5-[2,6-difluorophenyl]-2,4-dihydro-[1,2,4]-triazole-3-thione) was identified to be a more potent YUC inhibitor than the original yucasin. YDF caused an auxin-deficient phenotype in Arabidopsis wild-type plants that was restored with auxin application. YDF was found to be highly stable regarding metabolic conversion in vivo, accounting for the potent activity of the inhibition of IAA biosynthesis in planta. Photoaffinity labeling experiments demonstrated that yucasin-type inhibitors bind to the active site of AtYUC1. YDF is a promising auxin biosynthesis inhibitor and is a useful chemical tool for plant biology and agrochemical studies.

    DOI: 10.1038/s41598-017-14332-w

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  • The ARM Domain of ARMADILLO-REPEAT KINESIN 1 is Not Required for Microtubule Catastrophe But Can Negatively Regulate NIMA-RELATED KINASE 6 in Arabidopsis thaliana Reviewed

    Ryan C. Eng, Laryssa S. Halat, Samuel J. Livingston, Tatsuya Sakai, Hiroyasu Motose, Geoffrey O. Wasteneys

    PLANT AND CELL PHYSIOLOGY   58 ( 8 )   1350 - 1363   2017.8

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:OXFORD UNIV PRESS  

    Microtubules are dynamic filaments, the assembly and disassembly of which are under precise control of various associated proteins, including motor proteins and regulatory enzymes. In Arabidopsis thaliana, two such proteins are the ARMADILLO-REPEAT KINESIN 1 (ARK1), which promotes microtubule disassembly, and the NIMA-RELATED KINASE 6 (NEK6), which has a role in organizing microtubule arrays. Previous yeast two-hybrid and in vitro pull-down assays determined that NEK6 can interact with ARK1 through the latter protein's Armadillo-repeat (ARM) cargo domain. To explore the function of the ARM domain, we generated fluorescent reporter fusion proteins to ARK1 lacking the ARM domain (ARK1 Delta ARM-GFP) and to the ARM domain alone (ARM-GFP). Both of these constructs strongly associated with the growing plus ends of microtubules, but only ARK1 Delta ARM-GFP was capable of inducing microtubule catastrophe and rescuing the ark1-1 root hair phenotype. These results indicate that neither the ARM domain nor NEK6's putative interaction with it is required for ARK1 to induce microtubule catastrophe. In further exploration of the ARK1-NEK6 relationship, we demonstrated that, despite evidence that NEK6 can phosphorylate ARK1 in vitro, the in vivo distribution and function of ARK1 were not affected by the loss of NEK6, and vice versa. Moreover, NEK6 and ARK1 were found to have overlapping but non-identical distribution on microtubules, and hormone treatments known to affect NEK6 activity did not stimulate interaction. These findings suggest that ARK1 and NEK6 function independently in microtubule dynamics and cell morphogenesis. Despite the results of this functional analysis, we found that overexpression of the ARM domain led to complete loss of NEK6 transcription, suggesting that the ARM domain might have a regulatory role in NEK6 expression.

    DOI: 10.1093/pcp/pcx070

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  • Red/Far Red Light Controls Arbuscular Mycorrhizal Colonization via Jasmonic Acid and Strigolactone Signaling Reviewed

    Maki Nagata, Naoya Yamamoto, Tamaki Shigeyama, Yohei Terasawa, Toyoaki Anai, Tatsuya Sakai, Sayaka Inada, Susumu Arima, Masatsugu Hashiguchi, Ryo Akashi, Hideyuki Nakayama, Daisuke Ueno, Ann M. Hirsch, Akihiro Suzuki

    PLANT AND CELL PHYSIOLOGY   56 ( 11 )   2100 - 2109   2015.11

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:OXFORD UNIV PRESS  

    Establishment of a nitrogen-fixing symbiosis between legumes and rhizobia not only requires sufficient photosynthate, but also the sensing of the ratio of red to far red (R/FR) light. Here, we show that R/FR light sensing also positively influences the arbuscular mycorrhizal (AM) symbiosis of a legume and a non-legume through jasmonic acid (JA) and strigolactone (SL) signaling. The level of AM colonization in high R/FR light-grown tomato and Lotus japonicus significantly increased compared with that determined for low R/FR light-grown plants. Transcripts for JA-related genes were also elevated under high R/FR conditions. The root exudates derived from high R/FR light-grown plants contained more (+)-5-deoxystrigol, an AM-fungal hyphal branching inducer, than those from low R/FR light-grown plants. In summary, high R/FR light changes not only the levels of JA and SL synthesis, but also the composition of plant root exudates released into the rhizosphere, in this way augmenting the AM symbiosis.

    DOI: 10.1093/pcp/pcv135

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  • Distinct Characteristics of Indole-3-Acetic Acid and Phenylacetic Acid, Two Common Auxins in Plants Reviewed

    Satoko Sugawara, Kiyoshi Mashiguchi, Keita Tanaka, Shojiro Hishiyama, Tatsuya Sakai, Kousuke Hanada, Kaori Kinoshita-Tsujimura, Hong Yu, Xinhua Dai, Yumiko Takebayashi, Noriko Takeda-Kamiya, Tatsuo Kakimoto, Hiroshi Kawaide, Masahiro Natsume, Mark Estelle, Yunde Zhao, Ken-ichiro Hayashi, Yuji Kamiya, Hiroyuki Kasahara

    PLANT AND CELL PHYSIOLOGY   56 ( 8 )   1641 - 1654   2015.8

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    The phytohormone auxin plays a central role in many aspects of plant growth and development. IAA is the most studied natural auxin that possesses the property of polar transport in plants. Phenylacetic acid (PAA) has also been recognized as a natural auxin for &gt;40 years, but its role in plant growth and development remains unclear. In this study, we show that IAA and PAA have overlapping regulatory roles but distinct transport characteristics as auxins in plants. PAA is widely distributed in vascular and non-vascular plants. Although the biological activities of PAA are lower than those of IAA, the endogenous levels of PAA are much higher than those of IAA in various plant tissues in Arabidopsis. PAA and IAA can regulate the same set of auxin-responsive genes through the TIR1/AFB pathway in Arabidopsis. IAA actively forms concentration gradients in maize coleoptiles in response to gravitropic stimulation, whereas PAA does not, indicating that PAA is not actively transported in a polar manner. The induction of the YUCCA (YUC) genes increases PAA metabolite levels in Arabidopsis, indicating that YUC flavin-containing monooxygenases may play a role in PAA biosynthesis. Our results provide new insights into the regulation of plant growth and development by different types of auxins.

    DOI: 10.1093/pcp/pcv088

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  • PINOID functions in root phototropism as a negative regulator Reviewed

    Ken Haga, Tatsuya Sakai

    PLANT SIGNALING & BEHAVIOR   10 ( 5 )   2015.5

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:TAYLOR & FRANCIS INC  

    The PINOID (PID) family, which belongs to AGCVIII kinases, is known to be involved in the regulation of auxin efflux transporter PIN-FORMED (PIN) proteins through changes in the phosphorylation status. Recently, we demonstrated that the PID family is necessary for phytochrome-mediated phototropic enhancement in Arabidopsis hypocotyls and that the downregulation of PID expression by red-light pretreatment results in the promotion of the PIN-mediated auxin gradient during phototropic responses. However, whether PID participates in root phototropism in Arabidopsis seedlings has not been well studied. Here, we demonstrated that negative root phototropic responses are enhanced in the pid quadruple mutant and are severely impaired in transgenic plants expressing PID constitutively. The results indicate that the PID family functions in a negative root phototropism as a negative regulator. On the other hand, analysis with PID fused to a yellow fluorescent protein, VENUS, showed that unilateral blue-light irradiation causes a lower accumulation of PID proteins on the shaded side than on the irradiated side. This result suggests that the blue-light-mediated asymmetrical distribution of PID proteins may be one of the critical responses in phototropin-mediated signals during a negative root phototropism. Alternatively, such a transverse gradient of PID proteins may result from gravitropic stimulation produced by phototropic bending.

    DOI: 10.1080/15592324.2014.998545

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  • Arabidopsis ROOT PHOTOTROPISM2 Contributes to the Adaptation to High-Intensity Light in Phototropic Responses Reviewed

    Ken Haga, Tomoko Tsuchida-Mayama, Mizuki Yamada, Tatsuya Sakai

    PLANT CELL   27 ( 4 )   1098 - 1112   2015.4

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:AMER SOC PLANT BIOLOGISTS  

    Living organisms adapt to changing light environments via mechanisms that enhance photosensitivity under darkness and attenuate photosensitivity under bright light conditions. In hypocotyl phototropism, phototropin1 (phot1) blue light photoreceptors mediate both the pulse light-induced, first positive phototropism and the continuous light-induced, second positive phototropism, suggesting the existence of a mechanism that alters their photosensitivity. Here, we show that light induction of ROOT PHOTOTROPISM2 (RPT2) underlies photosensory adaptation in hypocotyl phototropism of Arabidopsis thaliana. rpt2 loss-of-function mutants exhibited increased photosensitivity to very low fluence blue light but were insensitive to low fluence blue light. Expression of RPT2 prior to phototropic stimulation in etiolated seedlings reduced photosensitivity during first positive phototropism and accelerated second positive phototropism. Our microscopy and biochemical analyses indicated that blue light irradiation causes dephosphorylation of NONPHOTOTROPIC HYPOCOTYL3 (NPH3) proteins and mediates their release from the plasma membrane. These phenomena correlate closely with the desensitization of phot1 signaling during the transition period from first positive phototropism to second positive phototropism. RPT2 modulated the phosphorylation of NPH3 and promoted reconstruction of the phot1-NPH3 complex on the plasma membrane. We conclude that photosensitivity is increased in the absence of RPT2 and that this results in the desensitization of phot1. Light-mediated induction of RPT2 then reduces the photosensitivity of phot1, which is required for second positive phototropism under bright light conditions.

    DOI: 10.1105/tpc.15.00178

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  • Yucasin is a potent inhibitor of YUCCA, a key enzyme in auxin biosynthesis (vol 77, pg 352, 2014) Reviewed

    Nishimura T, Hayashi K- I, Suzuki H, Gyohda A, Takaoka C, Sakaguchi Y, Matsumoto S, Kasahara H, Sakai T, Kato J- I, Kamiya Y, Koshiba T

    PLANT JOURNAL   81 ( 4 )   649   2015.2

  • PINOID AGC Kinases Are Necessary for Phytochrome-Mediated Enhancement of Hypocotyl Phototropism in Arabidopsis Reviewed

    Ken Haga, Ken-ichiro Hayashi, Tatsuya Sakai

    PLANT PHYSIOLOGY   166 ( 3 )   1535 - +   2014.11

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    Several members of the AGCVIII kinase subfamily, which includes PINOID (PID), PID2, and WAVY ROOT GROWTH (WAG) proteins, have previously been shown to phosphorylate PIN-FORMED (PIN) auxin transporters and control the auxin flow in plants. PID has been proposed as a key component of the phototropin signaling pathway that induces phototropic responses, although the responses were not significantly impaired in the pid single and pid wag1 wag2 triple mutants. This raises questions about the functional roles of the PID family in phototropic responses. Here, we investigated hypocotyl phototropism in the pid pid2 wag1 wag2 quadruple mutant in detail to clarify the roles of the PID family in Arabidopsis (Arabidopsis thaliana). The pid quadruple mutants exhibited moderate responses in continuous light-induced phototropism with a decrease in growth rates of hypocotyls and normal responses in pulse-induced phototropism. However, they showed serious defects in enhancements of pulse-induced phototropic curvatures and lateral fluorescent auxin transport by red light pretreatment. Red light pretreatment significantly reduced the expression level of PID, and the constitutive expression of PID prevented pulse-induced phototropism, irrespective of red light pretreatment. This suggests that the PID family plays a significant role in phytochrome-mediated phototropic enhancement but not the phototropin signaling pathway. Red light treatment enhanced the intracellular accumulation of PIN proteins in response to the vesicle-trafficking inhibitor brefeldin A in addition to increasing their expression levels. Taken together, these results suggest that red light preirradiation enhances phototropic curvatures by up-regulation of PIN proteins, which are not being phosphorylated by the PID family.

    DOI: 10.1104/pp.114.244434

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  • The Phototropic Response is Locally Regulated Within the Topmost Light-Responsive Region of the Arabidopsis thaliana Seedling Reviewed

    Kazuhiko Yamamoto, Tomomi Suzuki, Yusuke Aihara, Ken Haga, Tatsuya Sakai, Akira Nagatani

    PLANT AND CELL PHYSIOLOGY   55 ( 3 )   497 - 506   2014.3

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    Phototropism is caused by differential cell elongation between the irradiated and shaded sides of plant organs, such as the stem. It is widely accepted that an uneven auxin distribution between the two sides crucially participates in this response. Plant-specific blue-light photoreceptors, phototropins (phot1 and phot2), mediate this response. In grass coleoptiles, the sites of light perception and phototropic bending are spatially separated. However, these sites are less clearly distinguished in dicots. Furthermore, the exact placement of the action of each phototropic signaling factor remains unknown. Here, we investigated the spatial aspects of phototropism using spotlight irradiation with etiolated Arabidopsis seedlings. The results demonstrated that the topmost part of about 1.1 mm of the hypocotyl constituted the light-responsive region in which both light perception and actual bending occurred. In addition, cotyledons and the shoot apex were dispensable for the response. Hence, the response was more region autonomous in dicots than in monocots. We next examined the elongation rates, the levels of phot1 and the auxin-reporter gene expression along the hypocotyl during the phototropic response. The light-responsive region was more active than the non-responsive region with respect to all of those parameters.

    DOI: 10.1093/pcp/pct184

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  • Yucasin is a potent inhibitor of YUCCA, a key enzyme in auxin biosynthesis Reviewed

    Takeshi Nishimura, Ken-ichiro Hayashi, Hiromi Suzuki, Atsuko Gyohda, Chihiro Takaoka, Yusuke Sakaguchi, Sachiko Matsumoto, Hiroyuki Kasahara, Tatsuya Sakai, Jun-ichi Kato, Yuji Kamiya, Tomokazu Koshiba

    PLANT JOURNAL   77 ( 3 )   352 - 366   2014.2

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    Language:English   Publishing type:Research paper (scientific journal)   Publisher:WILEY-BLACKWELL  

    Indole-3-acetic acid (IAA), an auxin plant hormone, is biosynthesized from tryptophan. The indole-3-pyruvic acid (IPyA) pathway, involving the tryptophan aminotransferase TAA1 and YUCCA (YUC) enzymes, was recently found to be a major IAA biosynthetic pathway in Arabidopsis. TAA1 catalyzes the conversion of tryptophan to IPyA, and YUC produces IAA from IPyA. Using a chemical biology approach with maize coleoptiles, we identified 5-(4-chlorophenyl)-4H-1,2,4-triazole-3-thiol (yucasin) as a potent inhibitor of IAA biosynthesis in YUC-expressing coleoptile tips. Enzymatic analysis of recombinant AtYUC1-His suggested that yucasin strongly inhibited YUC1-His activity against the substrate IPyA in a competitive manner. Phenotypic analysis of Arabidopsis YUC1 over-expression lines (35S::YUC1) demonstrated that yucasin acts in IAA biosynthesis catalyzed by YUC. In addition, 35S::YUC1 seedlings showed resistance to yucasin in terms of root growth. A loss-of-function mutant of TAA1, sav3-2, was hypersensitive to yucasin in terms of root growth and hypocotyl elongation of etiolated seedlings. Yucasin combined with the TAA1 inhibitor l-kynurenine acted additively in Arabidopsis seedlings, producing a phenotype similar to yucasin-treated sav3-2 seedlings, indicating the importance of IAA biosynthesis via the IPyA pathway in root growth and leaf vascular development. The present study showed that yucasin is a potent inhibitor of YUC enzymes that offers an effective tool for analyzing the contribution of IAA biosynthesis via the IPyA pathway to plant development and physiological processes.

    DOI: 10.1111/tpj.12399

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  • Mycorrhizal infection is controlled by the light quality and quantity in higher plants

    SUZUKI Akihiro, NAGATA Maki, YAMAMOTO Naoya, SHIGEYAMA Tamaki, ANAI Toyoaki, ARIMA Susumu, SAKAI Tatsuya, HIRSCH Ann M

    82   236 - 237   2013.3

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  • Differential roles of auxin efflux carrier PIN proteins in hypocotyl phototropism of etiolated Arabidopsis seedlings depend on the direction of light stimulus Reviewed

    Ken Haga, Tatsuya Sakai

    Plant Signaling and Behavior   8 ( 1 )   50 - 52   2013.1

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    In a recent study, we demonstrated that although the auxin efflux carrier PIN-FORMED (PIN) proteins, such as PIN3 and PIN7, are required for the pulse-induced first positive phototropism in etiolated Arabidopsis hypocotyls, they are not necessary for the continuous-light-induced second positive phototropism when the seedlings are grown on the surface of agar medium, which causes the hypocotyls to separate from the agar surface. Previous reports have shown that hypocotyl phototropism is slightly impaired in pin3 single mutants when they are grown along the surface of agar medium, where the hypocotyls always contact the agar, producing some friction. To clarify the possible involvement of PIN3 and PIN7 in continuous-light-induced phototropism, we investigated hypocotyl phototropism in the pin3 pin7 double mutant grown along the surface of agar medium. Intriguingly, the phototropic curvature was slightly impaired in the double mutant when the phototropic stimulus was presented on the adaxial side of the hook, but was not impaired when the phototropic stimulus was presented on the abaxial side of the hook. These results indicate that PIN proteins are required for continuous-light-induced second positive phototropism, depending on the direction of the light stimulus, when the seedlings are in contact with agar medium. © 2013 Landes Bioscience.

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  • Role of RPT2 in Leaf Positioning and Flattening and a Possible Inhibition of phot2 Signaling by phot1 Reviewed

    Akiko Harada, Atsushi Takemiya, Shin-ichiro Inoue, Tatsuya Sakai, Ken-ichiro Shimazaki

    PLANT AND CELL PHYSIOLOGY   54 ( 1 )   36 - 47   2013.1

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    We investigated the roles of the blue light receptors phototropins (phot1 and phot2) and ROOT PHOTOTROPISM 2 (RPT2) in leaf positioning and flattening, and plant growth under weak, moderate and strong white light (10, 25 and 70 mu molm(-2) s(-1)). RPT2 mediated leaf positioning and flattening, and enhanced plant growth in a phot1-dependent manner. Under weak light, phot1 alone controls these responses. Under moderate and strong light, both phot1 and phot2 affect the responses. These results indicate that plants utilize a wide range of light intensities through phot1 and phot2 to optimize plant growth. The rpt2 single mutant generally exhibited phenotypes that resembled those of the phot1 phot2 double mutant. To our surprise, when the PHOT1 gene was disrupted in the rpt2 mutant, the resulting phot1 rpt2 double mutant showed the morphology of the wild-type plant under strong light, and additional disruption of PHOT2 in the double mutant abolished this recovery. This suggested that phot2 may function in the absence of phot1 and bypass RPT2 to transmit the signal to downstream elements. Expression and light-induced autophosphorylation of phot2 were not affected in the rpt2 mutant. We conclude that RPT2 mediates leaf flattening and positioning in a phot1-dependent manner, and that phot1 may inhibit the phot2 signaling pathways. We discuss the functional role of RPT2 in phototropin signaling.

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  • PIN Auxin Efflux Carriers Are Necessary for Pulse-Induced But Not Continuous Light-Induced Phototropism in Arabidopsis Reviewed

    Ken Haga, Tatsuya Sakai

    PLANT PHYSIOLOGY   160 ( 2 )   763 - 776   2012.10

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    Auxin efflux carrier PIN-FORMED (PIN) proteins are thought to have central roles in regulating asymmetrical auxin translocation during tropic responses, including gravitropism and phototropism, in plants. Although PIN3 is known to be involved in phototropism in Arabidopsis (Arabidopsis thaliana), no severe defects of phototropism in any of the pin mutants have been reported. We show here that the pulse-induced, first positive phototropism is impaired partially in pin1, pin3, and pin7 single mutants, and severely in triple mutants. In contrast, such impairment was not observed in continuous-light-induced second positive phototropism. Analysis with an auxin-reporter gene demonstrated that PIN3-mediated auxin gradients participate in pulse-induced phototropism but not in continuous-light-induced phototropism. Similar functional separation was also applicable to PINOID, a regulator of PIN localization. Our results strongly suggest the existence of functionally distinct mechanisms i.e. a PIN-dependent mechanism in which transient stimulation is sufficient to induce phototropism, and a PIN-independent mechanism that requires continuous stimulation and does not operate in the former phototropism process. Although a previous study has proposed that blue-light photoreceptors, the phototropins, control PIN localization through the transcriptional down-regulation of PINOID, we could not detect this blue-light-dependent down-regulation event, suggesting that other as yet unknown mechanisms are involved in phototropin-mediated phototropic responses.

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  • Molecular Genetic Analysis of Phototropism in Arabidopsis Reviewed

    Tatsuya Sakai, Ken Haga

    PLANT AND CELL PHYSIOLOGY   53 ( 9 )   1517 - 1534   2012.9

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    Plant life is strongly dependent on the environment, and plants regulate their growth and development in response to many different environmental stimuli. One of the regulatory mechanisms involved in these responses is phototropism, which allows plants to change their growth direction in response to the location of the light source. Since the study of phototropism by Darwin, many physiological studies of this phenomenon have been published. Recently, molecular genetic analyses of Arabidopsis have begun to shed light on the molecular mechanisms underlying this response system, including phototropin blue light photoreceptors, phototropin signaling components, auxin transporters, auxin action mechanisms and others. This review highlights some of the recent progress that has been made in further elucidating the phototropic response, with particular emphasis on mutant phenotypes.

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  • Additional cause for reduced JA-Ile in the root of a Lotus japonicus phyB mutant Reviewed

    Tamaki Shigeyama, Akiyoshi Tominaga, Susumu Arima, Tatsuya Sakai, Sayaka Inada, Yusuke Jikumaru, Yuji Kamiya, Toshiki Uchiumi, Mikiko Abe, Masatsugu Hashiguchi, Ryo Akashi, Ann M. Hirsch, Akihiro Suzuki

    Plant Signaling and Behavior   7 ( 7 )   1 - 3   2012.7

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    Light is critical for supplying carbon for use in the energetically expensive process of nitrogen-fixing symbiosis between legumes and rhizobia. We recently showed that root nodule formation in phyB mutants [which have a constitutive shade avoidance syndrome (SAS) phenotype] was suppressed in white light, and that nodulation in wild-type is controlled by sensing the R/FR ratio through jasmonic acid (JA) signaling. We concluded that the cause of reduced root nodule formation in phyB mutants was the inhibition of JA-Ile production in root. Here we show that the shoot JA-Ile level of phyB mutants is higher than that of the wild-type strain MG20, suggesting that translocation of JA-Ile from shoot to root is impeded in the mutant. These results indicate that root nodule formation in phyB mutants is suppressed both by decreased JA-Ile production, caused by reduced JAR1 activity in root, and by reduced JA-Ile translocation from shoot to root. © 2012 Landes Bioscience.

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  • The WAVY GROWTH 3 E3 ligase family controls the gravitropic response in Arabidopsis roots Reviewed

    Tatsuya Sakai, Susumu Mochizuki, Ken Haga, Yukiko Uehara, Akane Suzuki, Akiko Harada, Takuji Wada, Sumie Ishiguro, Kiyotaka Okada

    PLANT JOURNAL   70 ( 2 )   303 - 314   2012.4

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    Regulation of the root growth pattern is an important control mechanism during plant growth and propagation. To better understand alterations in root growth direction in response to environmental stimuli, we have characterized an Arabidopsis thaliana mutant, wavy growth 3 (wav3), whose roots show a short-pitch pattern of wavy growth on inclined agar medium. The wav3 mutant shows a greater curvature of root bending in response to gravity, but a smaller curvature in response to light, suggesting that it is a root gravitropism-enhancing mutation. This wav3 phenotype also suggests that enhancement of the gravitropic response in roots strengthens root tip impedance after contact with the agar surface and/or causes an increase in subsequent root bending in response to obstacle-touching stimulus in these mutants. WAV3 encodes a protein with a RING finger domain, and is mainly expressed in root tips. RING-containing proteins often function as an E3 ubiquitin ligase, and the WAV3 protein shows such activity in vitro. There are three genes homologous to WAV3 in the Arabidopsis genome [EMBRYO SAC DEVELOPMENT ARREST 40 (EDA40), WAVH1 and WAVH2?], and wav3 wavh1 wavh2 triple mutants show marked root gravitropism abnormalities. This genetic study indicates that WAV3 functions positively rather than negatively in root gravitropism, and that enhancement of the gravitropic response in wav3 roots is dependent upon the function of WAVH2 in the absence of WAV3. Hence, our results demonstrate that the WAV3 family of proteins are E3 ligases that are required for root gravitropism in Arabidopsis.

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  • Control of auxin transport in the phototropic response(<Feature Article>New development in auxin studies)

    Sakai Tatsuya, Haga Ken

    Regulation of Plant Growth & Development   47 ( 2 )   85 - 92   2012

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    Phototropism allows plants to change their growth direction in response to the location of the light source. Asymmetric distribution of the phytohormone auxin occurs in response to a phototropic stimulus, and causes differential growth on the two sides of the plant organ and consequent organ bending. Recently, molecular genetic analyses of Arabidopsis have begun to shed light on the molecular mechanisms underlying this response system, including phototropin blue light photoreceptors, phototropin signaling components, auxin transporters and others. This review highlights some of the recent progress on the control of auxin transport in the phototropic response.

    DOI: 10.18978/jscrp.47.2_85

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  • The main auxin biosynthesis pathway in Arabidopsis Reviewed

    Kiyoshi Mashiguchi, Keita Tanaka, Tatsuya Sakai, Satoko Sugawara, Hiroshi Kawaide, Masahiro Natsume, Atsushi Hanada, Takashi Yaeno, Ken Shirasu, Hong Yao, Paula McSteen, Yunde Zhao, Ken-ichiro Hayashi, Yuji Kamiya, Hiroyuki Kasahara

    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA   108 ( 45 )   18512 - 18517   2011.11

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    The phytohormone auxin plays critical roles in the regulation of plant growth and development. Indole-3-acetic acid (IAA) has been recognized as the major auxin for more than 70 y. Although several pathways have been proposed, how auxin is synthesized in plants is still unclear. Previous genetic and enzymatic studies demonstrated that both TRYPTOPHAN AMINOTRANSFERASE OF ARABIDOPSIS (TAA) and YUCCA (YUC) flavin monooxygenase-like proteins are required for biosynthesis of IAA during plant development, but these enzymes were placed in two independent pathways. In this article, we demonstrate that the TAA family produces indole-3-pyruvic acid (IPA) and the YUC family functions in the conversion of IPA to IAA in Arabidopsis (Arabidopsis thaliana) by a quantification method of IPA using liquid chromatography-electrospray ionization-tandem MS. We further show that YUC protein expressed in Escherichia coli directly converts IPA to IAA. Indole-3-acetaldehyde is probably not a precursor of IAA in the IPA pathway. Our results indicate that YUC proteins catalyze a rate-limiting step of the IPA pathway, which is the main IAA biosynthesis pathway in Arabidopsis.

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  • Lotus japonicus nodulation is photomorphogenetically controlled by sensing the red/far red (R/FR) ratio through jasmonic acid (JA) signaling Reviewed

    Akihiro Suzuki, Lalith Suriyagoda, Tamaki Shigeyama, Akiyoshi Tominaga, Masayo Sasaki, Yoshimi Hiratsuka, Aya Yoshinaga, Susumu Arima, Sakae Agarie, Tatsuya Sakai, Sayaka Inada, Yusuke Jikumaru, Yuji Kamiya, Toshiki Uchiumi, Mikiko Abe, Masatsugu Hashiguchi, Ryo Akashi, Shusei Sato, Takakazu Kaneko, Satoshi Tabata, Ann M. Hirsch

    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA   108 ( 40 )   16837 - 16842   2011.10

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    Light is critical for supplying carbon to the energetically expensive, nitrogen-fixing symbiosis between legumes and rhizobia. Here, we show that phytochrome B (phyB) is part of the monitoring system to detect suboptimal light conditions, which normally suppress Lotus japonicus nodule development after Mesorhizobium loti inoculation. We found that the number of nodules produced by L. japonicus phyB mutants is significantly reduced compared with the number produced of WT Miyakojima MG20. To explore causes other than photoassimilate production, the possibility that local control by the root genotype occurred was investigated by grafting experiments. The results showed that the shoot and not the root genotype is responsible for root nodule formation. To explore systemic control mechanisms exclusive of photoassimilation, we moved WT MG20 plants from white light to conditions that differed in their ratios of low or high red/far red (R/FR) light. In low R/FR light, the number of MG20 root nodules dramatically decreased compared with plants grown in high R/FR, although photoassimilate content was higher for plants grown under low R/FR. Also, the expression of jasmonic acid (JA) -responsive genes decreased in both low R/FR light-grown WT and white light-grown phyB mutant plants, and it correlated with decreased jasmonoyl-isoleucine content in the phyB mutant. Moreover, both infection thread formation and root nodule formation were positively influenced by JA treatment of WT plants grown in low R/FR light and white light-grown phyB mutants. Together, these results indicate that root nodule formation is photomorphogenetically controlled by sensing the R/FR ratio through JA signaling.

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  • NIMA-related kinases 6, 4, and 5 interact with each other to regulate microtubule organization during epidermal cell expansion in Arabidopsis thaliana Reviewed

    Hiroyasu Motose, Takahiro Hamada, Kaori Yoshimoto, Takashi Murata, Mitsuyasu Hasebe, Yuichiro Watanabe, Takashi Hashimoto, Tatsuya Sakai, Taku Takahashi

    PLANT JOURNAL   67 ( 6 )   993 - 1005   2011.9

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    NimA-related kinase 6 (NEK6) has been implicated in microtubule regulation to suppress the ectopic outgrowth of epidermal cells; however, its molecular functions remain to be elucidated. Here, we analyze the function of NEK6 and other members of the NEK family with regard to epidermal cell expansion and cortical microtubule organization. The functional NEK6-green fluorescent protein fusion localizes to cortical microtubules, predominantly in particles that exhibit dynamic movement along microtubules. The kinase-dead mutant of NEK6 (ibo1-1) exhibits a disturbance of the cortical microtubule array at the site of ectopic protrusions in epidermal cells. Pharmacological studies with microtubule inhibitors and quantitative analysis of microtubule dynamics indicate excessive stabilization of cortical microtubules in ibo1/nek6 mutants. In addition, NEK6 directly binds to microtubules in vitro and phosphorylates beta-tubulin. NEK6 interacts and co-localizes with NEK4 and NEK5 in a transient expression assay. The ibo1-3 mutation markedly reduces the interaction between NEK6 and NEK4 and increases the interaction between NEK6 and NEK5. NEK4 and NEK5 are required for the ibo1/nek6 ectopic outgrowth phenotype in epidermal cells. These results demonstrate that NEK6 homodimerizes and forms heterodimers with NEK4 and NEK5 to regulate cortical microtubule organization possibly through the phosphorylation of beta-tubulins.

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  • Alkoxy-auxins Are Selective Inhibitors of Auxin Transport Mediated by PIN, ABCB, and AUX1 Transporters Reviewed

    Etsuko Tsuda, Haibing Yang, Takeshi Nishimura, Yukiko Uehara, Tatsuya Sakai, Masahiko Furutani, Tomokazu Koshiba, Masakazu Hirose, Hiroshi Nozaki, Angus S. Murphy, Ken-ichiro Hayashi

    JOURNAL OF BIOLOGICAL CHEMISTRY   286 ( 3 )   2354 - 2364   2011.1

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    Polar auxin movement is a primary regulator of programmed and plastic plant development. Auxin transport is highly regulated at the cellular level and is mediated by coordinated transport activity of plasma membrane-localized PIN, ABCB, and AUX1/LAX transporters. The activity of these transporters has been extensively analyzed using a combination of pharmacological inhibitors, synthetic auxins, and knock-out mutants in Arabidopsis. However, efforts to analyze auxin-dependent growth in other species that are less tractable to genetic manipulation require more selective inhibitors than are currently available. In this report, we characterize the inhibitory activity of 5-alkoxy derivatives of indole 3-acetic acid and 7-alkoxy derivatives of naphthalene 1-acetic acid, finding that the hexyloxy and benzyloxy derivatives act as potent inhibitors of auxin action in plants. These alkoxy-auxin analogs inhibit polar auxin transport and tropic responses associated with asymmetric auxin distribution in Arabidopsis and maize. The alkoxy-auxin analogs inhibit auxin transport mediated by AUX1, PIN, and ABCB proteins expressed in yeast. However, these analogs did not inhibit or activate SCF(TIR1) auxin signaling and had no effect on the subcellular trafficking of PIN proteins. Together these results indicate that alkoxy-auxins are inactive auxin analogs for auxin signaling, but are recognized by PIN, ABCB, and AUX1 auxin transport proteins. Alkoxy-auxins are powerful new tools for analyses of auxin-dependent development.

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  • Role of the phytochrome and cryptochrome signaling pathways in hypocotyl phototropism Reviewed

    Tomoko Tsuchida-Mayama, Tatsuya Sakai, Atsushi Hanada, Yukiko Uehara, Tadao Asami, Shinjiro Yamaguchi

    PLANT JOURNAL   62 ( 4 )   653 - 662   2010.5

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    P&gt;Unilateral blue-light irradiation activates phototropin (phot) photoreceptors, resulting in asymmetric distribution of the phytohormone auxin and induction of a phototropic response in higher plants. Other photoreceptors, including phytochrome (phy) and cryptochrome (cry), have been proposed as modulators of phototropic responses. We show here that either phy or cry is required for hypocotyl phototropism in Arabidopsis thaliana under high fluence rates of blue light, and that constitutive expression of ROOT PHOTOTROPISM 2 (RPT2) and treatment with the phytohormone gibberellin (GA) biosynthesis inhibitor paclobutrazol partially and independently complement the non-phototropic hypocotyl phenotype of the phyA cry1 cry2 mutant under high fluence rates of blue light. Our results indicate that induction of RPT2 and reduction in the GA are crucial for hypocotyl phototropic regulation by phy and cry. We also show that GA suppresses hypocotyl bending via destabilization of DELLA transcriptional regulators under darkness, but does not suppress the phototropic response in the presence of either phyA or cryptochromes, suggesting that these photoreceptors control not only the GA content but also the GA sensing and/or signaling that affects hypocotyl phototropism. The metabolic and signaling regulation of not only auxin but also GA by photoreceptors therefore appears to determine the hypocotyl growth pattern, including phototropic and gravitropic responses and inhibition of hypocotyl elongation, for adaptation to various light environments.

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  • ABCB19/PGP19 stabilises PIN1 in membrane microdomains in Arabidopsis Reviewed

    Boosaree Titapiwatanakun, Joshua J. Blakeslee, Anindita Bandyopadhyay, Haibing Yang, Jozef Mravec, Michael Sauer, Yan Cheng, Jiri Adamec, Akitomo Nagashima, Markus Geisler, Tatsuya Sakai, Jiri Friml, Wendy Ann Peer, Angus S. Murphy

    PLANT JOURNAL   57 ( 1 )   27 - 44   2009.1

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    Auxin transport is mediated at the cellular level by three independent mechanisms that are characterised by the PIN-formed (PIN), P-glycoprotein (ABCB/PGP) and AUX/LAX transport proteins. The PIN and ABCB transport proteins, best represented by PIN1 and ABCB19 (PGP19), have been shown to coordinately regulate auxin efflux. When PIN1 and ABCB19 coincide on the plasma membrane, their interaction enhances the rate and specificity of auxin efflux and the dynamic cycling of PIN1 is reduced. However, ABCB19 function is not regulated by the dynamic cellular trafficking mechanisms that regulate PIN1 in apical tissues, as localisation of ABCB19 on the plasma membrane was not inhibited by short-term treatments with latrunculin B, oryzalin, brefeldin A (BFA) or wortmannin - all of which have been shown to alter PIN1 and/or PIN2 plasma membrane localisation. When taken up by endocytosis, the styryl dye FM4-64 labels diffuse rather than punctuate intracellular bodies in abcb19 (pgp19), and some aggregations of PIN1 induced by short-term BFA treatment did not disperse after BFA washout in abcb19. Although the subcellular localisations of ABCB19 and PIN1 in the reciprocal mutant backgrounds were like those in wild type, PIN1 plasma membrane localisation in abcb19 roots was more easily perturbed by the detergent Triton X-100, but not other non-ionic detergents. ABCB19 is stably associated with sterol/sphingolipid-enriched membrane fractions containing BIG/TIR3 and partitions into Triton X-100 detergent-resistant membrane (DRM) fractions. In the wild type, PIN1 was also present in DRMs, but was less abundant in abcb19 DRMs. These observations suggested a rationale for the observed lack of auxin transport activity when PIN1 is expressed in a non-plant heterologous system. PIN1 was therefore expressed in Schizosaccharomyces pombe, which has plant-like sterol-enriched microdomains, and catalysed auxin transport in these cells. These data suggest that ABCB19 stabilises PIN1 localisation at the plasma membrane in discrete cellular subdomains where PIN1 and ABCB19 expression overlaps.

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  • The ABC subfamily B auxin transporter AtABCB19 is involved in the inhibitory effects of N-1-Naphthyphthalamic acid on the phototropic and gravitropic responses of Arabidopsis hypocotyls Reviewed

    Akitomo Nagashima, Yukiko Uehara, Tatsuya Sakai

    PLANT AND CELL PHYSIOLOGY   49 ( 8 )   1250 - 1255   2008.8

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    N-1-Naphthylphthalamic acid (NPA) causes the abnormal growth and development of plants by suppressing polar auxin transport. The mechanisms underlying this inhibition, however, have remained elusive. In Arabidopsis, we show that a defect in the ABC subfamily B auxin transporter AtABCB19 suppresses the inhibitory effects of NPA on hypocotyl phototropism and gravitropism, but not on hypocotyl elongation. Expression analysis using the auxin reporter gene DR5:GUS further suggests that NPA partially inhibits the asymmetric distribution of auxin in an AtABCB19-dependent manner. These data thus suggest that AtABCB19 plays an important role in the inhibitory effects of NPA on hypocotyl tropism induced by auxin.

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  • Mapping of the phosphorylation sites on the phototropic signal transducer, NPH3 Reviewed

    Tomoko Tsuchida-Mayama, Michiharu Nakano, Yukiko Uehara, Miho Sano, Noriko Fujisawa, Kiyotaka Okada, Tatsuya Sakai

    PLANT SCIENCE   174 ( 6 )   626 - 633   2008.6

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    The phototropic response in Arabidopsis thaliana is initiated by the blue-light photoreceptors, phototropin (phot)1 and phot2. A recent study has shown that one of the phototropic signal transducers, NPH3, is phosphorylated under dark conditions and dephosphorylated by blue-light irradiation. To further understand the function of phosphorylation and dephosphorylation of NPH3 during this phototropic response, we have mapped the phosphorylation sites of NPH3 in our current study. The NPH3 protein has at least three phosphorylation sites at serine residues, Ser212, Ser222, and Ser236, and these sites are dephosphorylated by blue-light irradiation. By immunoblotting analysis, these phosphorylation sites in phot1 mutants are not dephosphorylated following blue-light irradiation at both low and high fluence rates, even though such irradiations induce the phot2-dependent phototropic response in phot1. These results suggest that the dephosphorylated NPH3 is involved in the phot1-dependent phototropic response and is not essential for the phot2-dependent phototropic response. We generated two types of transgenic nph3 plants expressing a NPH3(S212A/S222A/S232A/S236A) protein and a NPH3(Delta 212-238) protein in which the phosphorylation region is deleted, and assessed the phototropic phenotype of these. Based upon our present findings, we discuss the role of dephosphorylated and phosphorylated NPH3 in mediating the phototropic response. (C) 2008 Elsevier Ireland Ltd. All rights reserved.

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  • Phytochromes and cryptochromes regulate the differential growth of Arabidopsis hypocotyls in both a PGP19-dependent and a PGP19-independent manner Reviewed

    Akitomo Nagashima, Genki Suzuki, Yukiko Uehara, Kensuke Saji, Toshiko Furukawa, Tomokazu Koshiba, Masayo Sekimoto, Shozo Fujioka, Takeshi Kuroha, Mikiko Kojima, Hitoshi Sakakibara, Noriko Fujisawa, Kiyotaka Okada, Tatsuya Sakai

    PLANT JOURNAL   53 ( 3 )   516 - 529   2008.2

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    Photoreceptors, phytochromes and cryptochromes regulate hypocotyl growth under specific conditions, by suppressing negative gravitropism, modulating phototropism and inhibiting elongation. Although these effects seem to be partially caused via the regulation of the phytohormone auxin, the molecular mechanisms underlying this process are still poorly understood. In our present study, we demonstrate that the flabby mutation enhances both phytochrome- and cryptochrome-inducible hypocotyl bending in Arabidopsis. The FLABBY gene encodes the ABC-type auxin transporter, PGP19, and its expression is suppressed by the activation of phytochromes and cryptochromes. Our current results therefore indicate that the phytochromes and cryptochromes have at least two effects upon the tropic responses of the hypocotyls in Arabidopsis: the enhancement of hypocotyl bending through the suppression of PGP19, and a PGP19-independent mechanism that induces hypocotyl bending. By the using an auxin polar transport assay and DR5:GUS expression analysis, we further find that the phytochromes inhibit basipetal auxin transport, and induce the asymmetric distribution of auxin in the hypocotyls. These data suggest that the control of auxin transport by phytochromes and cryptochromes is a critical regulatory component of hypocotyl growth in response to light.

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  • Armadillo repeat-containing kinesins and a NIMA-related kinase are required for epidermal-cell morphogenesis in Arabidopsis Reviewed

    Tatsuya Sakai, Hannie van der Honing, Miki Nishioka, Yukiko Uehara, Mihoko Takahashi, Noriko Fujisawa, Kensuke Saji, Motoaki Seki, Kazuo Shinozaki, Mark A. Jones, Nicholas Smirnoff, Kiyotaka Okada, Geoffrey O. Wasteneys

    PLANT JOURNAL   53 ( 1 )   157 - 171   2008.1

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    The involvement of kinesin motor proteins in both cell-tip growth and cell-shape determination has been well characterized in various organisms. However, the functions of kinesins during cell morphogenesis in higher plants remain largely unknown. In the current study, we demonstrate that an armadillo repeat-containing kinesin-related protein, ARMADILLO REPEAT KINESIN1 (ARK1), is involved in root-hair morphogenesis. Microtubule polymers are more abundant in ark1 null allele root hairs, but analysis shows that these extra microtubules are concentrated in the endoplasm, and not in the cortical array, suggesting that ARK1 regulates tip growth by limiting the assembly and distribution of endoplasmic microtubules. The ARK1 gene has two homologues in the Arabidopsis genome, ARK2 and ARK3, and our results show that ARK2 is involved in root-cell morphogenesis. We further reveal that a NIMA-related protein kinase, NEK6, binds to the ARK family proteins and has pleiotropic effects on epidermal-cell morphogenesis, suggesting that NEK6 is involved in cell morphogenesis in Arabidopsis via microtubule functions associated with these armadillo repeat-containing kinesins. We discuss the function of NIMA-related protein kinases and armadillo repeat-containing kinesins in the cell morphogenesis of eukaryotes.

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  • Distinct leaf developmental and gene expression responses to light quantity depend on blue-photoreceptor or plastid-derived signals, and can occur in the absence of phototropins Reviewed

    Enrique Lopez-Juez, John R. Bowyer, Tatsuya Sakai

    PLANTA   227 ( 1 )   113 - 123   2007.12

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    Leaf palisade cell development and the composition of chloroplasts respond to the fluence rate of light to maximise photosynthetic light capture while minimising photodamage. The underlying light sensory mechanisms are, probably multiple and remain only partially understood. Phototropins (PHOT1 and PHOT2) are blue light receptors regulating responses which are light quantity-dependent and which include the control of leaf expansion. Here we show that genes for proteins in the reaction centres show long-term responses in wild type plants, and single blue photoreceptor mutants, to light fluence rate consistent with regulation by photosynthetic redox signals. Using contrasting intensities of white or broad-band red or blue light, we observe that increased fluence rate results in thicker leaves and greater number of palisade cells, but the anticlinal elongation of those cells is specifically responsive to the fluence rate of blue light. This palisade cell elongation response is still quantitatively normal in fully light-exposed regions of phot1 phot2 double mutants under increased fluence rate of white light. Plants grown at high light display elevated expression of RBCS (for the Rubisco small subunit) which, together with expected down-regulation of LHCB1 (for the photosynthetic antenna primarily of photosystem II), is also observed in phot double mutants. We conclude that an unknown blue light photoreceptor, or combination thereof, controls the development of a typical palisade cell morphology, but phototropins are not essential for either this response or acclimation-related gene expression changes. Together with previous evidence, our data further demonstrate that photosynthetic (chloroplast-derived) signals play a central role in the majority of acclimation responses.

    DOI: 10.1007/s00425-007-0599-7

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  • Blue light-dependent nuclear positioning in Arabidopsis thaliana leaf cells. Reviewed

    Kosei Iwabuchi, Tatsuya Sakai, Shingo Takagi

    Plant & cell physiology   48 ( 9 )   1291 - 8   2007.9

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    The plant nucleus changes its intracellular position not only upon cell division and cell growth but also in response to environmental stimuli such as light. We found that the nucleus takes different intracellular positions depending on blue light in Arabidopsis thaliana leaf cells. Under dark conditions, nuclei in mesophyll cells were positioned at the center of the bottom of cells (dark position). Under blue light at 100 mumol m(-2) s(-1), in contrast, nuclei were located along the anticlinal walls (light position). The nuclear positioning from the dark position to the light position was fully induced within a few hours of blue light illumination, and it was a reversible response. The response was also observed in epidermal cells, which have no chloroplasts, suggesting that the nucleus has the potential actively to change its position without chloroplasts. Light-dependent nuclear positioning was induced specifically by blue light at >50 mumol m(-2) s(-1). Furthermore, the response to blue light was induced in phot1 but not in phot2 and phot1phot2 mutants. Unexpectedly, we also found that nuclei as well as chloroplasts in phot2 and phot1phot2 mutants took unusual intracellular positions under both dark and light conditions. The lack of the response and the unusual positioning of nuclei and chloroplasts in the phot2 mutant were recovered by externally introducing the PHOT2 gene into the mutant. These results indicate that phot2 mediates the blue light-dependent nuclear positioning and the proper positioning of nuclei and chloroplasts. This is the first characterization of light-dependent nuclear positioning in spermatophytes.

    DOI: 10.1093/pcp/pcm095

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  • Interactions among PIN-FORMED and P-glycoprotein auxin transporters in Arabidopsis Reviewed

    Joshua J. Blakeslee, Anindita Bandyopadhyay, Ok Ran Lee, Jozef Mravec, Boosaree Titapiwatanakun, Michael Sauer, Srinivas N. Makam, Yan Cheng, Rodolphe Bouchard, Jiri Adamec, Markus Geisler, Akitomo Nagashima, Tatsuya Sakai, Enrico Martinoia, Jiri Friml, Wendy Ann Peer, Angus S. Murphy

    PLANT CELL   19 ( 1 )   131 - 147   2007.1

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    Directional transport of the phytohormone auxin is established primarily at the point of cellular efflux and is required for the establishment and maintenance of plant polarity. Studies in whole plants and heterologous systems indicate that PIN-FORMED ( PIN) and P-glycoprotein (PGP) transport proteins mediate the cellular efflux of natural and synthetic auxins. However, aromatic anion transport resulting from PGP and PIN expression in nonplant systems was also found to lack the high level of substrate specificity seen in planta. Furthermore, previous reports that PGP19 stabilizes PIN1 on the plasma membrane suggested that PIN-PGP interactions might regulate polar auxin efflux. Here, we show that PGP1 and PGP19 colocalized with PIN1 in the shoot apex in Arabidopsis thaliana and with PIN1 and PIN2 in root tissues. Specific PGP-PIN interactions were seen in yeast two-hybrid and coimmunoprecipitation assays. PIN-PGP interactions appeared to enhance transport activity and, to a greater extent, substrate/inhibitor specificities when coexpressed in heterologous systems. By contrast, no interactions between PGPs and the AUXIN1 influx carrier were observed. Phenotypes of pin and pgp mutants suggest discrete functional roles in auxin transport, but pin pgp mutants exhibited phenotypes that are both additive and synergistic. These results suggest that PINs and PGPs characterize coordinated, independent auxin transport mechanisms but also function interactively in a tissue-specific manner.

    DOI: 10.1105/tpc.106.040782

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  • Ca2+ transient induced by extracellular changes in osmotic pressure in Arabidopsis leaves: differential involvement of cell wall-plasma membrane adhesion Reviewed

    T Hayashi, A Harada, T Sakai, S Takagi

    PLANT CELL AND ENVIRONMENT   29 ( 4 )   661 - 672   2006.4

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    We investigated the mechanism underlying the perception of extracellular changes in osmotic pressure in Vallisneria gigantea Graebner and transgenic Arabidopsis thaliana (L.) Heynh. expressing cytoplasmic aequorin. Hypertonic and hypotonic treatments of A. thaliana leaves each rapidly induced a Ca2+ transient. Both responses were essentially dependent on the presence of extracellular Ca2+ and were sensitive to Gd3+, a potential blocker of stretch-activated Ca2+ channels. Immediately after plasmolysis caused by hypertonic treatment and subsequent deplasmolysis caused by hypotonic treatment, the cells did not respond to a second hypertonic treatment and exhibited an impaired adhesion of the plasma membrane (PM) to the cell wall (CW). Recovery of the responsiveness required about 6 h. By contrast, no refractory phenomenon was observed in response to hypotonic treatment. Pretreatment with cellulase completely inhibited the Ca2+ transient induced by hypertonic treatment, but it did not affect the response to hypotonic treatment. V. gigantea mesophyll cells pretreated with cellulase exhibited an impaired adhesion of the PM to the CW. The leaf cells of multicellular plants can respond to both hypertonic and hypotonic treatments through the stretch-activated Ca2+ channels, whereas cellulase-sensitive adhesion of the PM to the CW is involved only in the response to hypertonic treatment.

    DOI: 10.1111/j.1365-3040.2005.01447.x

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  • The Arabidopsis WAVY GROWTH 2 protein modulates root bending in response to environmental stimuli Reviewed

    S Mochizuki, A Harada, S Inada, K Sugimoto-Shirasu, N Stacey, T Wada, S Ishiguro, K Okada, T Sakai

    PLANT CELL   17 ( 2 )   537 - 547   2005.2

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    To understand how the direction of root growth changes in response to obstacles, light, and gravity, we characterized an Arabidopsis thaliana mutant, wavy growth 2 (wav2), whose roots show a short-pitch pattern of wavy growth on inclined agar medium. The roots of the wav2 mutant bent with larger curvature than those of the wild-type seedlings in wavy growth and in gravitropic and phototropic responses. The cell file rotations of the root epidermis of wav2-1 in the wavy growth pattern were enhanced in both right-handed and left-handed rotations. WAV2 encodes a protein belonging to the BUD EMERGENCE 46 family with a transmembrane domain at the N terminus and an alpha/beta-hydrolase domain at the C terminus. Expression analyses showed that mRNA of WAV2 was expressed strongly in adult plant roots and seedlings, especially in the root tip, the cell elongation zone, and the stele. Our results suggest that WAV2 is not involved in sensing environmental stimuli but that it negatively regulates stimulus-induced root bending through inhibition of root tip rotation.

    DOI: 10.1105/tpc.104.028530

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  • The different growth responses of the Arabidopsis thaliana leaf blade and the petiole during shade avoidance are regulated by Photoreceptors and sugar Reviewed

    T Kozuka, G Horiguchi, GT Kim, M Ohgishi, T Sakai, H Tsukaya

    PLANT AND CELL PHYSIOLOGY   46 ( 1 )   213 - 223   2005.1

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    During the shade-avoidance response, leaf blade expansion is inhibited and petiole elongation is enhanced. In this study, we examined the roles of photoreceptors and sugar on the differential growth of the leaf blade and petiole in shade conditions. Under the conditions examined, cell expansion, not cell division, played a major role in the differential leaf growth. The enhanced cell expansion in the leaf blade is associated with an increase in the ploidy level, whereas cell elongation was stimulated in the petiole in dark conditions without an increase in the ploidy level. Analysis of phytochrome, cryptochrome and phototropin mutants revealed that phytochromes and cryptochromes specifically regulate the contrasting growth patterns of the leaf blade and petiole in shade. Examination of the effects of photo-assimilated sucrose on the growth of the leaf blade and petiole revealed growth-pro motional effects of sucrose that are highly dependent on the light conditions. The leaf blades of abscisic acid-deficient and sugar-insensitive mutants did not expand in blue light, but expanded normally in red light. These results suggest that both the regulation of light signals and the modulation of responses to sugar are important in the control of the differential photomorphogenesis of the leaf blade and petiole.

    DOI: 10.1093/pcp/pci016

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  • RPT2 is a signal transducer involved in phototropic response and stomatal opening by association with phototropin 1 in Arabidopsis thaliana Reviewed

    S Inada, M Ohgishi, T Mayama, K Okada, T Sakai

    PLANT CELL   16 ( 4 )   887 - 896   2004.4

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    Phototropin 1 (phot1) and phot2, which are blue light receptor kinases, function in blue light-induced hypocotyl phototropism, chloroplast relocation, and stomatal opening in Arabidopsis (Arabidopsis thaliana). Previous studies have shown that the proteins RPT2 (for ROOT PHOTOTROPISM2) and NPH3 (for NONPHOTOTROPIC HYPOCOTYL3) transduce signals downstream of phototropins to induce the phototropic response. However, the involvement of RPT2 and NPH3 in stomatal opening and in chloroplast relocation mediated by phot1 and phot2 was unknown. Genetic analysis of the rpt2 mutant and of a series of double mutants indicates that RPT2 is involved in the phot1-induced phototropic response and stomatal opening but not in chloroplast relocation or phot2-induced movements. Biochemical analyses indicate that RPT2 is purified in the crude microsomal fraction, as well as phot1 and NPH3, and that RPT2 makes a complex with phot1 in vivo. On the other hand, NPH3 is not necessary for stomatal opening or chloroplast relocation. Thus, these results suggest that phot1 and phot2 choose different signal transducers to induce three responses: phototropic response of hypocotyl, stomatal opening, and chloroplast relocation.

    DOI: 10.1105/tpc.019901

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  • Functional analysis of each blue light receptor, cry1, cry2, phot1, and phot2, by using combinatorial multiple mutants in Arabidopsis Reviewed

    M Ohgishi, K Saji, K Okada, T Sakai

    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA   101 ( 8 )   2223 - 2228   2004.2

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    Blue light receptors in Arabidopsis include two types of proteins, cryptochromes and phototropins. Previous studies have suggested that the cryptochromes cry1 and cry2 function mainly in photomorphogenic responses and that the phototropins phot1 and phot2 mainly regulate photo-induced movements. Receptors in the same family have redundant functions, although their responses to the fluence rate of blue light differ. To uncover functions of blue light receptors that may be concealed by their functional redundancy, we conducted analyses of combinatorial multiple mutants of blue light receptors. Comparison of the responses of the quadruple mutant cry1 cry2 phot1 phot2 to blue light with those of related triple mutants revealed that cryptochromes function in blue light-dependent, random hypocotyl-bending and that phototropins function in one photomorphogenic response, cotyledon expansion. Microarray analysis suggested that cry1 and cry2 independently function as key regulators of early blue light-induced genes, whereas phot1 and phot2 play subsidiary roles in transcriptional regulation by blue light.

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  • phot1 and phot2 mediate blue light-induced transient increases in cytosolic Ca2+ differently in Arabidopsis leaves Reviewed

    A Harada, T Sakai, K Okada

    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA   100 ( 14 )   8583 - 8588   2003.7

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    Phototropins (phot1 and phot2) are blue light (BL) receptors that mediate phototropism, chloroplast movements, and stomatal opening in Arabidopsis thaliana. Physiological studies have suggested that Ca2+ in the cytoplasm plays a pivotal role in these BL-induced responses. A phot1-mediated increase in cytosolic Ca2+ was reported in deetiolated seedlings of A. thaliana; however, the contribution of phot2 remains unknown. We examined a BL-induced transient increase in cytosolic free Ca2+ in leaves of transgenic A. thaliana of WT plants, phot1 and phot2 mutants, and phot1 phot2 double mutants expressing the Ca2+-sensitive luminescent protein aequorin. phot1 and phot2 had different photosensitivities: phot1 increased cytosolic Ca2+ at lower fluence rates (0.1-50 mumol(.)m(-2.)s(-1)) and phot2 increased it at higher fluence rates (1-250 mumol(.)m(-2.)s(-1)). By using Ca2+ channel blockers, Ca2+ chelating agents, and inhibitors of phospholipase C, we further demonstrated that both phot1 and phot2 could induce Ca2+ influx from the apoplast through the Ca2+ channel in the plasma membrane, whereas phot2 alone induced phospholipase C-mediated phosphoinositide signaling, which might result in Ca2+ release from internal Ca2+ stores. These results suggest that phot1 and phot2 mediate the BL-induced increase in cytosolic free Ca2+ differently.

    DOI: 10.1073/pnas.1336802100

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  • Arabidopsis nph1 and npl1: Blue light receptors that mediate both phototropism and chloroplast relocation Reviewed

    T Sakai, T Kagawa, M Kasahara, TE Swartz, JM Christie, WR Briggs, M Wada, K Okada

    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA   98 ( 12 )   6969 - 6974   2001.6

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    UV-A/blue light acts to regulate a number of physiological processes in higher plants. These include light-driven chloroplast movement and phototropism. The NPH1 gene of Arabidopsis encodes an autophosphorylating protein kinase that functions as a photoreceptor for phototropism in response to low-intensity blue light. However, nph1 mutants have been reported to exhibit normal phototropic curvature under high-intensity blue light, indicating the presence of an additional phototropic receptor. A likely candidate is the nph1 homologue, npl1, which has recently been shown to mediate the avoidance response of chloroplasts to high-intensity blue light in Arabidopsis, Here we demonstrate that npl1, like nph1, noncovalently binds the chromophore flavin mononucleotide (FMN) within two specialized PAS domains, termed LOV domains. Furthermore, when expressed in insect cells, npl1. like nph1, undergoes light-dependent autophosphorylation, indicating that npl1 also functions as a light receptor kinase, Consistent with this conclusion, we show that a nph1 npl1 double mutant exhibits an impaired phototropic response under both low- and high-intensity blue light. Hence, npl1 functions as a second phototropic receptor under high fluence rate conditions and is, in part, functionally redundant to nph1. We also demonstrate that both chloroplast accumulation in response to low-intensity light and chloroplast avoidance movement in response to high-intensity light are lacking in the nph1 npl1 double mutant. Our findings therefore indicate that nph1 and npl1 show partially overlapping functions in two different responses, phototropism and chloroplast relocation, in a fluence rate-dependent manner.

    DOI: 10.1073/pnas.101137598

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  • The phototropin family of photoreceptors Reviewed

    WR Briggs, CF Beck, AR Cashmore, JM Christie, J Hughes, JA Jarillo, T Kagawa, H Kanegae, E Liscum, A Nagatani, K Okada, M Salomon, W Rudiger, T Sakai, M Takano, M Wada, JC Watson

    PLANT CELL   13 ( 5 )   993 - 997   2001.5

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    DOI: 10.1105/tpc.13.5.993

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  • Arabidopsis NPL1: A phototropin homolog controlling the chloroplast high-light avoidance response Reviewed

    T Kagawa, T Sakai, N Suetsugu, K Oikawa, S Ishiguro, T Kato, S Tabata, K Okada, M Wada

    SCIENCE   291 ( 5511 )   2138 - 2141   2001.3

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    Chloroplasts relocate their positions in a cell in response to the intensity of incident Light, moving to the side wall of the cell to avoid strong Light, but gathering at the front face under weak Light to maximize Light interception. Here, Arabidopsis thaliana mutants defective in the avoidance response were isolated, and the mutated gene was identified as NPL1 (NPH-Like 1), a homolog of NPH1 (nonphototropic hypocotyl 1), a blue Light receptor used in phototropism. Hence, NPL1 is Likely a blue Light receptor regulating the avoidance response under strong light.

    DOI: 10.1126/science.291.5511.2138

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  • REPRESSION OFSHOOT GROWTH, a bZIP transcriptional activator, regulates cell elongation by controlling the level of gibberellins Reviewed

    J Fukazawa, T Sakai, S Ishida, Yamaguchi, I, Y Kamiya, Y Takahashi

    PLANT CELL   12 ( 6 )   901 - 915   2000.6

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    Cell expansion, a developmental process regulated by both endogenous programs and environmental stimuli, is critically important for plant growth, Here, we report the isolation and characterization of RSG (for repression of shoot growth), a transcriptional activator with a basic leucine zipper (bZIP) domain. To examine the role of RSG in plant development, we generated transgenic tobacco plants expressing a dominant-negative form of RSG, which repressed the activity of full-length RSG, In transgenic plants, this expression severely inhibited stem internode growth, specifically cell elongation. These plants also had less endogenous amounts of the major active gibberellin (GA) in tobacco, GA,. Applying GAs restored the dwarf phenotypes of transgenic tobacco plants that expressed the dominant-negative form of RSG, To investigate the function of RSG in the regulation of the endogenous amounts of GAs, we identified a target for RSG, RSG bound and activated the promoter of Arabidopsis GA3, one of the genes encoding enzymes involved in GA biosynthesis. Moreover, the dominant-negative form of RSG decreased expression of the GA3 homolog in transgenic tobacco plants. Our results show that RSG, a bZIP transcriptional activator, regulates the morphology of plants by controlling the endogenous amounts of GAs.

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  • RPT2: A signal transducer of the phototropic response in arabidopsis Reviewed

    T Sakai, T Wada, S Ishiguro, K Okada

    PLANT CELL   12 ( 2 )   225 - 236   2000.2

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    The blue light receptor NPH1 (for nonphototropic hypocotyl) has been considered to be the only UV-A/blue light receptor that induces a phototropic response by the hypocotyl and root of Arabidopsis. By analysis of roof phototropism (rpt) mutants, we show, however, the involvement of another blue light receptor as well as the existence of two separate signaling pathways working downstream of these receptors in the phototropic response. A newly isolated gene, RPT2, controls one of these pathways. The RPT2 gene is light inducible; encodes a novel protein with putative phosphorylation sites, a nuclear localization signal, a BTB/POZ domain, and a coiled-coil domain; and belongs to a large gene family that includes the recently isolated NPH3 gene. From genetic, physiological, and biochemical evidence, we propose a genetic model of the signaling pathways that induce the phototropic response in Arabidopsis.

    DOI: 10.1105/tpc.12.2.225

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  • The identification of DNA binding factors specific for as-1-like sequences in auxin-responsive regions of parA, parB and parC Reviewed

    T Sakai, Y Takahashi, T Nagata

    PLANT AND CELL PHYSIOLOGY   39 ( 7 )   731 - 739   1998.7

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    We have identified the auxin-responsive region (Aux-RR) of the parA promoter; it is derived from a gene that is induced by auxin in tobacco mesophyll protoplasts, By analyses of gain-of-function and point mutations in transgenic tobacco plants, we showed that an as-1-like sequence was required, but not alone sufficient, for auxin responsiveness of the parA promoter, as has been also shown for the parC promoter in a recent study. A gel mobility shift assay revealed that the as-1-like sequence of the parA promoter bound specifically to the as-1 binding nuclear factor, ASF-1, while the as-1-like sequence of the parC promoter bound specifically to a novel nuclear factor named ALF-1 (as-1-like sequence binding factor-1). Since these bindings were correlated with auxin-induced activation of transcription, those results suggest that ALF-1 is a new nuclear factor involved in auxin responsiveness and that it is distinct from ASF-1, Furthermore, we found that an as-1-like sequence in the AuxRR of parB bound specifically to a tobacco nuclear factor, named ALF-2, which differed from ASF-1 and ALF-1. These results suggest that the auxin responsiveness of the auxin-inducible genes parA, parB and parC are regulated by different mechanisms, even though the cis-acting elements look similar.

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  • Analysis of the promoter of the auxin-inducible gene, parC, of tobacco Reviewed

    T Sakai, Y Takahashi, T Nagata

    PLANT AND CELL PHYSIOLOGY   37 ( 7 )   906 - 913   1996.10

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    The auxin-responsive region (AuxRR) in the promoter of the parC gene was analyzed in transgenic tobacco plants in which the 5' flanking region of the parC promoter was placed upstream of the gene for beta-glucuronidase (GUS). The AuxRR was located between nucleotides (nt) -226 and -54. Detailed dissection of this segment revealed that the presence of the non-contiguous sequences from nt -226 to -151 and from nt -84 to -54 was required for the expression of the auxin responsiveness of the parC promoter. The sequence from nt -226 to -151 was found to contain a sequence which resembles the as-1 element in the 35S promoter of cauliflower mosaic virus (CaMV). Although it has been reported that the as-1 element is involved in auxin responsiveness [Liu and Lam (1994) J. Biol. Chem. 269: 668], we showed that introduction of a point mutation into the as-1-like sequence completely eliminated auxin responsiveness, a result that suggests that the sequence is indispensable for auxin responsiveness. However, the presence of the as-1-like sequence alone was not sufficient for auxin responsiveness, since the segment (nt -226 to -84) that included the as-1-like sequence failed to confer auxin responsiveness on the core promoter. It is possible that the two separately located sequences play specific roles in interactions with trans-factors that are required for the expression of the auxin responsiveness of the parC promoter.

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  • IDENTIFICATION OF AUXIN-RESPONSIVE ELEMENTS OF PARB AND THEIR EXPRESSION IN APICES OF SHOOT AND ROOT Reviewed

    Y TAKAHASHI, T SAKAI, S ISHIDA, T NAGATA

    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA   92 ( 14 )   6359 - 6363   1995.7

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    Detailed analysis of transgenic tobaccos containing a series of chimeric parB promoter/beta-glucuronidase (GUS) gene constructs allowed us to define two auxin-responsive elements (AREs) of 48 bp and 95 bp (positions -210 to -163 and -374 to -280) in the parB promoter. The two AREs responded independently to physiological concentrations of auxin. Gel retardation assays revealed binding of nuclear protein(s) to the sequence conserved between ARE I and ARE II. The auxin responsiveness of the parB promoter did not mediate the pathway through the as-1 element and transcription factor ASF-1. AREs I and II were responsive to auxin at physiological concentrations, whereas as-1 responded only to higher concentrations of auxin which may be interpreted as stress, though as-1 had been reported to be a minimal ARE [Liu, X. and Lam, E. (1994) J. Biol. Chem. 269, 668-675]. Histochemical staining of transgenic tobacco that contained a parB promoter/GUS construct demonstrated the expression of GUS activity in the shoot apex as well as in the root tips, suggesting the involvement of parB expression in meristematic activity or differentiation. The drastic change in auxin responsiveness in the transgenic plants between the 6th and 10th day after imbibition of seeds implies the development or the activation of auxin signal transduction systems during plant development.

    DOI: 10.1073/pnas.92.14.6359

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  • The Role of Dephosphorylation of NPH3 in The Hypocotyl Phototropism of Arabidopsis

    木村太郎, 芳賀健, 野村有子, 檜垣匠, 中神弘史, 酒井達也

    日本植物生理学会年会(Web)   62nd   2021

  • S01 Action mechanism of phenylacetic acid as a natural auxin in Arabidopsis

    Sugawara Satoko, Mashiguchi Kiyoshi, Tanaka Keita, Hishiyama Shojiro, Sakai Tatsuya, Hanada Kousuke, Kinoshita-Tsujimura Kaori, Yu Hong, Dai Xinhua, Takebayashi Yumiko, Takeda Noriko, Kakimoto Tatsuo, Kawaide Hiroshi, Natsume Masahiro, Estelle Mark, Zhao Yunde, Hayashi Ken-ichiro, Kamiya Yuji, Kasahara Hiroyuki

    50   23 - 23   2015.10

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  • 7. Analysis of auxin function and its action mechanism in Arabidopsis root phototropism

    Kimura Taro, Haga Ken, Hayashi Ken-ichiro, Yunde Zhao, Takebayashi Yumiko, Kasahara Hiroyuki, Sakai Tatsuya

    48   22 - 22   2013.10

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  • 4. Structure-activity relationships of IAA biosynthesis inhibitor targeting to YUCCA enzyme

    Tsugafune Shinichi, Nishimura Takeshi, Kasahara Hiroyuki, Sakai Tatsuya, Kamiya Yuji, Nozaki Hiroshi, Koshiba Tomokazu, Hayashi Ken-ichiro

    47   21 - 21   2012.10

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  • 2. Analysis of a novel non-polar transport-type auxin in plants

    Sugawara Satoko, Mashiguchi Kiyoshi, Tanaka Keita, Hishiyama Shojiro, Sakai Tatsuya, Hanada Kousuke, Kinoshita(Tsujimura) Kaori, Kakimoto Tatsuo, Kawaide Hiroshi, Natsume Masahiro, Zhao Yunde, Hayashi Ken-ichiro, Kamiya Yuji, Kasahara Hiroyuki

    47   19 - 19   2012.10

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  • TAAとYUCによるインドール‐3‐酢酸の生合成

    増口潔, 田中慧太, 酒井達也, 菅原聡子, 夏目雅裕, 川出洋, 花田篤志, 八丈野孝, 白須賢, YAO Hong, MCSTEEN Paula, ZHAO Yunde, 林謙一郎, 神谷勇治, 笠原博幸

    日本植物生理学会年会要旨集   53rd   157   2012.3

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  • 34. Dissection of the main indole-3-acetic acid biosynthesis pathway in Arabidopsis

    Mashiguchi Kiyoshi, Tanaka Keita, Sakai Tatsuya, Sugawara Satoko, Natsume Masahiro, Kawaide Hiroshi, Hanada Atsushi, Hayashi Ken-ichiro, Kamiya Yuji, Kasahara Hiroyuki

    ( 46 )   50 - 50   2011.10

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    Language:Japanese   Publisher:The Japanese Society for Chemical Regulation of Plants  

    The phytohormone auxin plays a fundamental role in various aspects of plant growth and development. Indole-3-acetic acid (IAA) has been known as a major naturally occurring auxin in plants, but its biosynthesis has not been fully understood. Previous studies demonstrated that the YUCCA (YUC) family encodes a plant-specific flavin monooxygenase that catalyzes a rate-limiting step in IAA biosynthesis. More recent studies demonstrated that the Tryptophan Aminotransferase of Arabidopsis 1 (TAA1) converts Trp to indole-3-pyruvic acid (IPA). Both the TAA and YUC families play critical roles throughout plant development, but they are proposed to function in two independent pathways. In this study, we provide evidences that the YUC family acts in the IPA-dependent IAA biosynthesis in Arabidopsis. We found that co-overexpression of TAA and YUC genes dramatically increases IAA production and results in hyper-auxin phenotypes, suggesting a synergistic interaction between TAA and YUC genes in IAA biosynthesis. The LC-ESI-MS/MS analysis of IPA levels in TAA and YUC-related mutants indicates that TAA produces IPA from Trp and YUC converts IPA to IAA. We further showed that recombinant YUC proteins catalyze the direct conversion of IPA to IAA in an NADPH-dependent manner. From these results, we conclude that the IPA pathway is the main IAA biosynthesis pathway in Arabidopsis.

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  • PHYBシグナリングを介した光の質と量による根粒形成制御機構

    重山 珠紀, 佐々木 雅代, SURIYAGODA Lalith, 富永 晃好, 平塚 芳美, 内海 俊樹, 阿部 美紀子, 橋口 正嗣, 明石 良, 酒井 達也, 稲田 さやか, 佐藤 修正, 金子 貴一, 田畑 哲之, 東江 栄, 有馬 進, 鈴木 章弘

    根の研究 = Root research   20 ( 2 )   79 - 79   2011.6

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  • 4. Metabolic regulation of IAA in auxin biosynthesis mutants

    Tanaka Keita, Sugawara Satoko, Mashiguchi Kiyoshi, Jikumaru Yusuke, Natsume Masahiro, Kawaide Hiroshi, Sakai Tatsuya, Hayashi Ken-ichiro, Kamiya Yuji, Kasahara Hiroyuki

    ( 45 )   21 - 21   2010.10

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    Language:Japanese   Publisher:The Japanese Society for Chemical Regulation of Plants  

    Auxins have critical roles in plant growth and development. Arabidopsis has multiple pathways for biosynthesis of a naturally occurring auxin, indole-3-acetic acid (IAA): the YUCCA (YUC) pathway, the CYP79B pathway, the indole-3-pyruvic acid (IPA) pathway and the indole-3-acetamide pathway. The YUC and IPA pathways widely exist in plant kingdom. Recently, we found that the CYP79B pathway operates in the crucifer plants producing indole glucosinolates like Arabidopsis, but may not in non-crucifers. It has been demonstrated that cyp79b2 cyp79b3 mutants show IAA-deficient phenotype, but IAA levels are not greatly reduced in these mutants under the normal growth condition. yuc1D mutants show IAA-overproduction phenotype, but IAA levels are slightly increased in yuc1D. To address this question, we analyzed IAA metabolites in Arabidopsis IAA biosynthesis mutants. We found that IAA-amino acid conjugates were significantly decreased in the CYP79B-deficient mutants. In contrast, the levels of IAA-amino acid conjugates were dramatically increased in the YUC-overexpression lines. These results indicate that the IAA-amino acid conjugates may have important roles to maintain IAA levels in IAA biosynthesis-deficient mutants.

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  • Phot1 controls the de-phosphorylation of NPH3 in response to blue light.

    Tomoko Mayama-Tsuchida, Michiharu Nakano, Noriko Fujisawa, Kiyotaka Okada, Tatsuya Sakai

    PLANT AND CELL PHYSIOLOGY   48   S232 - S232   2007

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  • Differential growth of hypocotyls regulated by phytochromes and cryptochromes in Arabidopsis

    Akitomo Nmashim, Genki Suzuki, Kensuke Saji, Takeshi Kuroha, Noriko Fujisawa, Yukiko Uchara, Kiyotaka Okada, Tatsuya Sakai

    PLANT AND CELL PHYSIOLOGY   48   S199 - S199   2007

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  • Kinesin-related proteins containing armadillo repeats, antlers1 and antler2, and a NIMA-related kinase, AtNek6, regulate the epidermal cell morphogenesis in Arabidopsis.

    Tatsuya Sakai, Miki Nishioka, Yakiko Uehara, Mihoko Takahashi, Noriko Fujisawa, Kensuke Saji, Motoaki Seki, Kazuo Shinozaki, Kiyotaka Okada

    PLANT AND CELL PHYSIOLOGY   48   S83 - S83   2007

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  • Phytochromes and cryptochromes regulate hypocotyl-bending through the action of PGP19 in Arabidopsis

    A Nagashima, G Suzuki, K Saji, K Okada, T Sakai

    PLANT AND CELL PHYSIOLOGY   47   S124 - S124   2006

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  • phot1 controls the post-transcriptional regulations of RPT2 and NPH3

    T Mayama, M Nakano, N Fujisawa, K Okada, T Sakai

    PLANT AND CELL PHYSIOLOGY   47   S160 - S160   2006

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  • Analysis of the laziness mutant showing a defect in blue-light induced leaf movement

    S Inada, M Nakano, K Okada, T Sakai

    PLANT AND CELL PHYSIOLOGY   46   S165 - S165   2005

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  • Phototropic signal transducer NPH3 is de-modificated by blue light in manner dependent on light intensity

    T Mayama, M Nakano, N Fujisawa, K Okada, T Sakai

    PLANT AND CELL PHYSIOLOGY   46   S168 - S168   2005

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  • Analysis of regulations of root bending in respose to environmental stimuli using wav2 and wav3 mutants

    S Mochizuki, A Harada, A Suzuki, S Inada, K Sugimoto-Shirasu, N Stacey, S Ishiguro, T Wada, K Okada, T Sakai

    PLANT AND CELL PHYSIOLOGY   46   S77 - S77   2005

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  • Functional analysis of each blue light receptor, cry1, cry2, phot1, and phot2, by using combinatorial multiple mutants in Arabidopsis (vol 101, pg 2223, 2004)

    M Ohgishi, K Saji, K Okada, T Sakai

    PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA   101 ( 15 )   5696 - 5696   2004.4

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    DOI: 10.1073/pnas.0401218101

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  • Analysis of the stipule-less mutants in Lotus japonicus

    N Ishikawa, T Sakai, S Inada, H Tsukaya

    PLANT AND CELL PHYSIOLOGY   45   S163 - S163   2004

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  • Comprehensive preparation of mutants in the model plant of legume, Lotus japonicus.

    M Nakano, R Yamamoto, N Fujisawa, S Inada, K Okada, T Sakai

    PLANT AND CELL PHYSIOLOGY   45   S206 - S206   2004

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  • RPT2 is a signal transducer involved in stomatal opening mediated by phot1

    S Inada, M Ohgishi, T Mayama, K Okada, T Sakai

    PLANT AND CELL PHYSIOLOGY   45   S85 - S85   2004

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  • Functional analysis of each blue light receptor, cry1, cry2, phot1, phot2 using combinatorial multiple mutant in Arabidopsis

    M Ohgishi, K Saji, K Okada, T Sakai

    PLANT AND CELL PHYSIOLOGY   45   S86 - S86   2004

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  • Function of AtMDR1 for red-light dependent response against pathogen hypocotyl bending

    G Suzuki, K Saji, K Okada, T Sakai

    PLANT AND CELL PHYSIOLOGY   45   S1 - S1   2004

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  • Genetic analysis of green light induced phototropism

    T Mayama, T Sakai, K Okada

    PLANT AND CELL PHYSIOLOGY   45   S227 - S227   2004

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  • Analysis of the wav2 mutant exhibiting the strong wavy growth pattern of roots

    S Mochizuki, A Harada, K Okada, T Sakai

    PLANT AND CELL PHYSIOLOGY   45   S150 - S150   2004

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  • phot1 and phot2 mediate blue light-induced transient increase in cytosolic Ca2+ in Arabidopsis leaves

    A Harada, T Sakai, K Okada

    PLANT AND CELL PHYSIOLOGY   44   S195 - S195   2003

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  • Analysis of wav2 mutant of Arabidopsis thaliana exhibiting the strong wavy growth pattern of roots

    S Mochizuki, A Harada, K Okada, T Sakai

    PLANT AND CELL PHYSIOLOGY   44   S37 - S37   2003

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  • Analysis of Arabidopsis mutant exhibiting red-light dependent seedling curvature

    G Suzuki, T Sakai, K Okada

    PLANT AND CELL PHYSIOLOGY   44   S160 - S160   2003

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  • Molecular genetic analysis of leaf movement induced by blue light in Lotus japonicus

    S Inada, M Takahashi, K Okada, T Sakai

    PLANT AND CELL PHYSIOLOGY   44   S195 - S195   2003

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  • ANALYSIS OF ROOT PHOTOTROPISM MUTANT, rpt2, OF ARABIDOPSIS.

    SAKAI Tatsuya, WADA Takuji, ISHIGURO Sumie, OKADA Kiyotaka

    40   s87 - s87   1999.3

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Research Projects

  • 光屈性におけるシグナル伝達因子レベルの光順応機構の解明

    Grant number:21K06211

    2021.4 - 2024.3

    System name:科学研究費助成事業

    Research category:基盤研究(C)

    Awarding organization:日本学術振興会

    酒井 達也

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    Grant amount:\4160000 ( Direct Cost: \3200000 、 Indirect Cost:\960000 )

    植物の芽生えは地上部を光源方向に向かって成長させる光屈性を示す。シロイヌナズナ黄化芽生え胚軸の場合、ヒトの視覚と同程度の光感受性を示し、9桁に及ぶ光強度の異る環境下であっても同じように光屈性応答が誘導される。このような光環境応答においては、光が弱いときには光感受性を高め、逆に光が強いときには光感受性を下げる、高度な光順応機構が必要と考えられる。我々は、光屈性に必須の働きを示すシグナル伝達因子 NPH3 のリン酸化修飾調節が、シグナル伝達因子レベルの光順応機構を生み出すことを発見した。2021年度、本研究成果をまとめ、Plant Physiology誌及びPlant Signaling Behavior 誌で発表することができた。
    実験計画に沿い、NPH3 脂質修飾変異体発現体、NPH3天然変性ドメイン欠失変異体を作出し、その表現型を観察中である。またYFP融合変異体も同時に作成し、表現型を観察中である。少なくとも NPH3 天然変性ドメインのほとんどが NPH3 機能に必須ではないことが示唆される結果を得た。NPH3リン酸化調節に働く新奇因子同定のための phot1 エンハンサー変異体選抜は、候補株は複数単離したものの、リン酸化修飾異常の変異体は単離できなかった。phot1自己リン酸化がNPH3細胞内局在調節に与える影響を調べるため、PHOT1自己リン酸化修飾ができない変異体を作成した。現在その表現型を観察中である。

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  • Molecular genetic analysis on the asymmetric auxin distribution-independent phototropism

    Grant number:18K19329

    2018.6 - 2021.3

    System name:Grants-in-Aid for Scientific Research

    Research category:Grant-in-Aid for Challenging Research (Exploratory)

    Awarding organization:Japan Society for the Promotion of Science

    Sakai Tatsuya

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    Grant amount:\6370000 ( Direct Cost: \4900000 、 Indirect Cost:\1470000 )

    Etiolated hypocotyls of Arabidopsis seedlings show the phototropic responses in the asymmetric auxin distribution-dependent and -independent manners. We have identified the PP2C gene subfamily, which is probably involved in the asymmetric auxin distribution-independent phototropism. One of them is regulated by light irradiation transcriptionally, and another is phosphorylated in a phototropin-dependent manner. Our phosphoproteome analysis suggests that they function in the phosphorylation modification of many proteins in the etiolated seedlings.

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  • Analysis of regulatory mechanisms of phototropism through protein phosphorylations

    Grant number:17H03694

    2017.4 - 2020.3

    System name:Grants-in-Aid for Scientific Research

    Research category:Grant-in-Aid for Scientific Research (B)

    Awarding organization:Japan Society for the Promotion of Science

    Sakai Tatsuya

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    Grant amount:\17940000 ( Direct Cost: \13800000 、 Indirect Cost:\4140000 )

    Plant life is strongly dependent on light and Arabidopsis thaliana phototropin1 (phot1) is a blue-light photoreceptor, i.e. a blue-light-activated Ser/Thr-protein kinase that mediates various light responses including phototropism. Our research goal is an understanding of the phototropin signaling system. In this research, we were focusing on the protein phosphorylation of signaling factors in the phot1 signaling. Our study has revealed that RPT2 suppresses the phot1 autophosphorylation activity and that the phosphorylation status of NPH3 is involved in the photoadaptation mechanism of phototropism as an effector adaptation mechanism.

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  • オーキシン不均等分布に依存しない偏差成長誘導機構の解析

    Grant number:16H01231

    2016.4 - 2018.3

    System name:科学研究費助成事業

    Research category:新学術領域研究(研究領域提案型)

    Awarding organization:日本学術振興会

    酒井 達也

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    Grant amount:\10400000 ( Direct Cost: \8000000 、 Indirect Cost:\2400000 )

    我々はシロイヌナズナの根の光屈性がオーキシン不均等勾配非依存的に誘導されることを明らかにしたが、一方でオーキシン応答転写因子 ARF7 が根の光屈性に働くことが既に報告されていた。そこでオーキシンシグナル伝達因子の根の光屈性への関与についてさらに遺伝学的解析を行った。その結果、ARF7・ARF19転写因子に加え、AXR3/IAA17 転写調節因子及び TIR1 オーキシン受容体が根の光屈性に正に働くことを明らかにした。本研究成果をまとめ、論文発表した(Kimura et al. [2018] PCP, in press)。
    pin3 pin4 pin7 多重変異体及び d6pk 多重変異体は連続光照射誘導の胚軸二次正光屈性をほとんど示さないという報告がある。我々は独自に開発したチューブ法を用いて、pin3 pin4 pin7 及び d6pk0123多重変異体の表現型観察を行った。その結果、我々の観察方法においては、どちらも屈曲の抑制が観察されるものの、未だ連続光照射の胚軸二次正光屈性の反応を示すことを明らかにした。すなわち、胚軸においてもオーキシン不均等勾配非依存的な光屈性誘導機構の存在が示唆された。本研究成果をまとめ、論文発表した(Haga et al. [2018] PCP, in press)。
    オーキシン不均等勾配非依存的な光屈性誘導機構を明らかにすべく、pin/d6pk の表現型を促進するエンハンサー突然変異体 6 株を選抜し、その原因遺伝子探索を進めた。その結果、3株が同じPP2C 遺伝子の変異を示した。PP2C遺伝子にT-DNAが挿入された突然変異体を収集し、シングル突然変異体における表現型解析を行った。その結果、pp2cシングル突然変異体においては、赤色光前照射の胚軸光屈性促進効果に異常が観察された。

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  • Functional analysis of auxin transcriptional regulators in the phototropic responses

    Grant number:26440134

    2014.4 - 2017.3

    System name:Grants-in-Aid for Scientific Research

    Research category:Grant-in-Aid for Scientific Research (C)

    Awarding organization:Japan Society for the Promotion of Science

    Sakai Tatsuya, KIMURA Taro

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    Grant amount:\4940000 ( Direct Cost: \3800000 、 Indirect Cost:\1140000 )

    Function of Auxin transcriptional regulators were analyzed in the root phototropic response, which is induced independently of asymmetric auxin distribution. Auxin trascriptional facotr ARF7, transcriptional regulator IAA19 and auxin receptor TIR1 were involved in the phototropic response of roots. However, our results suggested that their function are not controlled by the phototropin signaling pathways.

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  • 光屈性を誘導するフォトトロピンシグナル伝達経路の解析

    Grant number:25120710

    2013.4 - 2015.3

    System name:科学研究費助成事業

    Research category:新学術領域研究(研究領域提案型)

    Awarding organization:日本学術振興会

    酒井 達也

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    Grant amount:\16380000 ( Direct Cost: \12600000 、 Indirect Cost:\3780000 )

    rpt2 の詳細な表現型解析と NPH3 リン酸化調節、及びNPH3細胞内局在の解析がつながり、一次正光屈性と二次正光屈性を分ける分子機構が明らかになった。RPT2 は phot1 の光感受性を下げる働きをしており、光によって発現が誘導されると、phot1の光感受性を下げて光寛容を与えている。NPH3は暗所でリン酸化されていると phot1 と結合し、細胞膜に局在してシグナルを流すことを可能にしているが、phot1が活性化してNPH3の脱リン酸化が誘導されるとNPH3がphot1及び細胞膜から解離して不活化することが明らかになった。RPT2によるphot1活性化抑制がNPH3脱リン酸化を抑制し、NPH3のリン酸化状態のゆるやかな回復、NPH3-phot1複合体の回復を誘導し、二次光屈性が誘導されることを明らかにした。この発見は、古典植物生理学で謎とされていた一次正光屈性の仕組みや赤色光照射による光屈性促進機構の解明として高く評価される。またphot1の光感受性変換機構の存在を明らかにしたことにより、phot1分子スイッチの調節技術の開発につながる可能性をひめた研究成果となった。

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  • Study of molecular mechanisms underlying phototropic responses independent of auxin lateral distribution

    Grant number:24657027

    2012.4 - 2014.3

    System name:Grants-in-Aid for Scientific Research

    Research category:Grant-in-Aid for Challenging Exploratory Research

    Awarding organization:Japan Society for the Promotion of Science

    HAGA Ken, SAKAI Tatsuya

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    Grant amount:\4160000 ( Direct Cost: \3200000 、 Indirect Cost:\960000 )

    Plants are growing to or away from light direction to adapt to their light environments. The responses, so-called phototropism, have been well-studied for a long time. Auxin, one of plant hormones, is known to stimulate plant growth and thought to be involved in phototropism by changing its endogenous distribution in responses to light irradiation. The present study analyzed phototropic responses of Arabidopsis seedling roots, and demonstrated existence of molecular mechanisms underlying phototropic responses independent of auxin asymmetrical lateral distribution. Our investigations strongly suggested that light stimulation directly controls regulatory components involved in auxin-mediated responses, such as auxin receptors and/or auxin responsive transcription factors. The present results contribute to establishment of a new model responsible for phototropic responses.

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  • 光屈性におけるオーキシン調節機構の解析

    Grant number:23120510

    2011.4 - 2013.3

    System name:科学研究費助成事業

    Research category:新学術領域研究(研究領域提案型)

    Awarding organization:日本学術振興会

    酒井 達也

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    Grant amount:\15080000 ( Direct Cost: \11600000 、 Indirect Cost:\3480000 )

    光屈性は、光環境に応答して植物ホルモン・オーキシン不等分布を誘導し、細胞の伸長の差から偏差成長を生じさせる現象と考えられており、オーキシン調節による植物の成長制御機構のモデルの一つとして研究されている。本研究は光屈性におけるオーキシン調節の分子機構を、シロイヌナズナの分子遺伝学的手法を用いて明らかにすることを目的として行った。昨年度、PIN オーキシン輸送体の網羅的な遺伝学的解析を行い、PIN1, PIN3, PIN7 が光屈性に関与すること、またこれらのPINに依存しない経路が存在することを示唆する結果を得た。
    本年度、PINの細胞内局在を制御すると考えられている PINOIDタンパク質キナーゼの光屈性における機能を解析し、PINOID ファミリーは phy 赤色光受容体の活性化によって遺伝子発現が抑制され、これが光屈性の促進に働くこと、光屈性を直接誘導するのに働く phot光受容体シグナリングの下流では働いていないことを明らかにした。さらに、AGC1 キナーゼファミリーが光屈性に関与することが明らかになった。また、新たに光屈性に関与する遺伝子を探索するため、完全長cDNA過剰発現株からの光屈性異常突然変異体選抜を進めた。その結果、小胞輸送調節に働く因子、微小管機能制御因子、タンパク質分解制御因子をコードする3つの遺伝子については、その過剰発現が光屈性異常をひきおこすことを明らかにした。
    今後、光屈性誘導機構における AGC タンパク質キナーゼの機能解析、及びPINに依存しない光屈性誘導機構の新たな突然変異体選抜を含む詳細な解析を行うことにより、植物の光環境に適応した成長パターンの調節の分子機構の理解に新しい研究領域を創造することが期待された。

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  • Analysis of the phototropin signaling pathways controlling the phototropic responses.

    Grant number:22570058

    2010 - 2012

    System name:Grants-in-Aid for Scientific Research

    Research category:Grant-in-Aid for Scientific Research (C)

    Awarding organization:Japan Society for the Promotion of Science

    SAKAI Tatsuya

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    Grant amount:\4680000 ( Direct Cost: \3600000 、 Indirect Cost:\1080000 )

    We have studied about the molecular mechanisms controlling the phototropic responses in plants. Our analyses have indicated that the blue-light photoreceptor phototropin stabilizes the signaling transducer RPT2 proteins, which are required for phototropism and degraded under the dark condition. Furthermore, we have revealed that PIN auxin efflux carriers are necessary for pulse-induced but not continuous light-induced phototropism in Arabidopsis.

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  • 光環境に適応した植物の成長制御機構の解析

    Grant number:18770043

    2006 - 2007

    System name:科学研究費助成事業

    Research category:若手研究(B)

    Awarding organization:日本学術振興会

    酒井 達也

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    Grant amount:\3700000 ( Direct Cost: \3700000 )

    本研究は植物の光環境応答に適応した成長制御機構を解明することを目的に、主にシロイヌナズナ芽生えの光屈性に着目し、研究を行った。光屈性を誘導する光受容体フォトトロピンのシグナル伝達機構を解明するために、そのシグナル伝達因子NPH3のphot1による脱リン酸化メカニズムを解析し、NPH3のリン酸化部位を3カ所同定し、それらのリン酸化部位が光屈性に必須でないことを明らかにした。もう一つのシグナル伝達因子RPT2は光屈性反応を修飾する他の光受容体フィトクロム、クリプトクロムによって転写誘導されること、この転写誘導機構が、フィトクロム、クリプトクロムによる光屈性反応修飾機構の一部であることを明らかにした。これらの結果は、フォトトロピンシグナル伝達因子が、光受容体の活性化によって発現やタンパク質修飾が調節され、光屈性反応を誘導することを示した。
    昨年度の研究によって、オーキシン輸送阻害剤NPAは光屈性を負に制御するオーキシン輸送体PGP19に依存して光屈性を阻害し、光屈性を誘導するオーキシン輸送体そのものはその活性が阻害されないこと、PGPl9とNPAが共存したときにのみその活性が阻害されることが明らかになっている。光屈性を誘導するオーキシン輸送体はPIN3が知られているが、pgp19との多重変異体解析を行った結果、NPA非感受性の光屈性誘導に関与するオーキシン輸送体はPIN3以外に存在することを明らかにした。この分子を同定すべく、現在pgp19のサプレッサー変異体選抜および、他のオーキシン輸送体との多重変異体解析を行っている。これらの研究成果をさらに発展させることによって、光シグナリングが具体的にどのオーキシン輸送体の活性を調節し、光屈性を誘導して、植物の生長方向を決定しているのか、近い将来明らかにできるものと考えられる。

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Teaching Experience

  • 生物学実習III

    2023
    Institution name:新潟大学

  • 生物学実習I

    2022
    Institution name:新潟大学

  • 理学基礎演習

    2022
    Institution name:新潟大学

  • 生物学特論 V

    2022
    Institution name:新潟大学

  • 植物生理学実習

    2021
    Institution name:新潟大学

  • 専門力アクティブ・ラーニング

    2021
    Institution name:新潟大学

  • 植物分子遺伝学特論II

    2021
    Institution name:新潟大学

  • 理学スタディ・スキルズ

    2021
    Institution name:新潟大学

  • 日本事情自然系A

    2020
    Institution name:新潟大学

  • 課題研究II(生物学)

    2018
    Institution name:新潟大学

  • 自然科学基礎実験

    2018
    Institution name:新潟大学

  • 自然科学総論Ⅳ

    2018
    Institution name:新潟大学

  • 課題研究I(生物学)

    2017
    Institution name:新潟大学

  • 生物学総合演習

    2017
    Institution name:新潟大学

  • 生物学基礎実習a

    2017
    Institution name:新潟大学

  • 理学スタディ・スキルズ

    2017
    -
    2021
    Institution name:新潟大学

  • 生物学基礎演習

    2017
    Institution name:新潟大学

  • 生物学実習

    2017
    Institution name:新潟大学

  • 植物生理学実習

    2016
    -
    2019
    Institution name:新潟大学

  • 生物学-植物A-

    2015
    Institution name:新潟大学

  • 外国語論文解説・討論Ⅰ

    2015
    Institution name:新潟大学

  • 生命・食料科学博士セミナーⅠ

    2015
    Institution name:新潟大学

  • 生物学特論Ⅰ

    2015
    Institution name:新潟大学

  • 生命・食料科学博士特定研究Ⅰ

    2015
    Institution name:新潟大学

  • 植物生理学演習

    2014
    Institution name:新潟大学

  • 基礎植物学

    2014
    Institution name:新潟大学

  • 発生生物学I

    2014
    Institution name:新潟大学

  • 生物英語II

    2014
    Institution name:新潟大学

  • 生物学-植物A-

    2014
    Institution name:新潟大学

  • 生物学実験 I

    2014
    -
    2018
    Institution name:新潟大学

  • 基礎生物科学実習I

    2014
    -
    2017
    Institution name:新潟大学

  • 課題研究I(生物学科)

    2014
    -
    2016
    Institution name:新潟大学

  • 課題研究II

    2014
    -
    2016
    Institution name:新潟大学

  • 生命・食料科学セミナーBⅡ

    2014
    -
    2015
    Institution name:新潟大学

  • 植物形態発生学実習

    2014
    -
    2015
    Institution name:新潟大学

  • 生命・食料科学特定研究BⅡ

    2014
    -
    2015
    Institution name:新潟大学

  • 文献詳読Ⅱ

    2014
    -
    2015
    Institution name:新潟大学

  • 研究発表

    2014
    Institution name:新潟大学

  • 研究発表演習(中間発表)

    2014
    Institution name:新潟大学

  • 植物分子遺伝学特論Ⅱ

    2013
    -
    2017
    Institution name:新潟大学

  • 生命・食料科学セミナーBⅠ

    2013
    -
    2014
    Institution name:新潟大学

  • 文献詳読Ⅰ

    2013
    -
    2014
    Institution name:新潟大学

  • 生命・食料科学特定研究BⅠ

    2013
    -
    2014
    Institution name:新潟大学

  • 植物分子遺伝学特論Ⅰ

    2012
    -
    2022
    Institution name:新潟大学

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