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Joanne Chory - One of the best experts on this subject based on the ideXlab platform.
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Internalization and vacuolar targeting of the brassinosteroid hormone receptor BRI1 are regulated by ubiquitination
Nature Communications, 2015Co-Authors: Sara Martins, Joanne Chory, Yvon Jaillais, Esther M. N. Dohmann, Anne Cayrel, Alexander Johnson, Wolfgang Fischer, Florence Pojer, Béatrice Satiat-jeunemaître, Niko GeldnerAbstract:Brassinosteroids are plant steroid hormones that control many aspects of plant growth and development, and are perceived at the cell surface by the plasma membrane-localized receptor kinase BRI1. Here we show that BRI1 is post-translationally modified by K63 polyubiquitin chains in vivo. Using both artificial ubiquitination of BRI1 and generation of an ubiquitination-defective BRI1 mutant form, we demonstrate that ubiquitination promotes BRI1 internalization from the cell surface and is essential for its recognition at the trans-Golgi network/early endosomes (TGN/EE) for vacuolar targeting. Finally, we demonstrate that the control of BRI1 protein dynamics by ubiquitination is an important control mechanism for brassinosteroid responses in plants. Altogether, our results identify ubiquitination and K63-linked polyubiquitin chain formation as a dual targeting signal for BRI1 internalization and sorting along the endocytic pathway, and highlight its role in hormonally controlled plant development.
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tyrosine phosphorylation controls brassinosteroid receptor activation by triggering membrane release of its kinase inhibitor
Genes & Development, 2011Co-Authors: Tsegaye Dabi, Youssef Belkhadir, Zachary L Nimchuk, Elliot M Meyerowitz, Michael Hothorn, Yvon Jaillais, Joanne ChoryAbstract:Receptor tyrosine kinases control many critical processes in metazoans, but these enzymes appear to be absent in plants. Recently, two Arabidopsis receptor kinases—BRASSINOSTEROID INSENSITIVE 1 (BRI1) and BRI1-ASSOCIATED KINASE1 (BAK1), the receptor and coreceptor for Brassinosteroids—were shown to autophosphorylate on tyrosines. However, the cellular roles for tyrosine phosphorylation in plants remain poorly understood. Here, we report that the BRI1 KINASE INHIBITOR 1 (BKI1) is tyrosine phosphorylated in response to brassinosteroid perception. Phosphorylation occurs within a reiterated [KR][KR] membrane targeting motif, releasing BKI1 into the cytosol and enabling formation of an active signaling complex. Our work reveals that tyrosine phosphorylation is a conserved mechanism controlling protein localization in all higher organisms.
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Brassinosteroid signaling and auxin transport are required to establish the periodic pattern of Arabidopsis shoot vascular bundles.
Proceedings of the National Academy of Sciences of the United States of America, 2009Co-Authors: Marta Ibañes, Norma Fabregas, Joanne Chory, Ana I. Caño-delgadoAbstract:The plant vascular system provides transport and support capabilities that are essential for plant growth and development, yet the mechanisms directing the arrangement of vascular bundles within the shoot inflorescence stem remain unknown. We used computational and experimental biology to evaluate the role of auxin and brassinosteroid hormones in vascular patterning in Arabidopsis. We show that periodic auxin maxima controlled by polar transport and not overall auxin levels underlie vascular bundle spacing, whereas Brassinosteroids modulate bundle number by promoting early procambial divisions. Overall, this study demonstrates that auxin polar transport coupled to brassinosteroid signaling is required to determine the radial pattern of vascular bundles in shoots.
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Brassinosteroids regulate dissociation of bki1 a negative regulator of bri1 signaling from the plasma membrane
Science, 2006Co-Authors: Xuelu Wang, Joanne ChoryAbstract:Brassinosteroids, the steroid hormones of plants, are perceived at the plasma membrane by a leucine-rich repeat receptor serine/threonine kinase called BRI1. We report a BRI1-interacting protein, BKI1, which is a negative regulator of brassinosteroid signaling. Brassinosteroids cause the rapid dissociation of BKI1-yellow fluorescent protein from the plasma membrane in a process that is dependent on BRI1-kinase. BKI1 is a substrate of BRI1 kinase and limits the interaction of BRI1 with its proposed coreceptor, BAK1, suggesting that BKI1 prevents the activation of BRI1.
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Perception of Brassinosteroids by the Extracellular Domain of the Receptor Kinase BRI1
Science (New York N.Y.), 2000Co-Authors: Zhi-yong Wang, Qun Zhu, Christopher J. Lamb, Pamela C. Ronald, Joanne ChoryAbstract:An assay was developed to study plant receptor kinase activation and signaling mechanisms. The extracellular leucine-rich repeat (LRR) and transmembrane domains of the Arabidopsis receptor kinase BRI1, which is implicated in brassinosteroid signaling, were fused to the serine/threonine kinase domain of XA21, the rice disease resistance receptor. The chimeric receptor initiates plant defense responses in rice cells upon treatment with Brassinosteroids. These results, which indicate that the extracellular domain of BRI1 perceives Brassinosteroids, suggest a general signaling mechanism for the LRR receptor kinases of plants. This system should allow the discovery of ligands for the LRR kinases, the largest group of plant receptor kinases.
Vladimir A. Khripach - One of the best experts on this subject based on the ideXlab platform.
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Regio- and stereoselective C-H functionalization of Brassinosteroids.
Steroids, 2019Co-Authors: Alaksiej L. Hurski, Vladimir N Zhabinskii, Aliaksandr G. Kukel, Aliaksandra I. Liubina, Aliona G. Baradzenka, Darya Straltsova, Vadim Demidchik, Pavel Drašar, Vladimir A. KhripachAbstract:Late stage CH functionalization is a powerful tool for modification of natural compounds. Herein we report that the rhodium-catalyzed reaction of Brassinosteroids with aryloxysulfonamides proceeds regio- and stereoselectively at C15 position. The derivative obtained from 24-epibrassinolide was easily transformed to the conjugate with a BODIPY dye bearing unaffected functional groups of the native brassinosteroid.
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A new ELISA for quantification of Brassinosteroids in plants.
Steroids, 2014Co-Authors: Andrey G. Pradko, Vladimir N Zhabinskii, Raisa P. Litvinovskaya, A. L. Sauchuk, S. V. Drach, Alexander V. Baranovsky, Tatyana V. Mirantsova, Vladimir A. KhripachAbstract:Starting from (22R,23R)-2α,3α,22,23,26-pentahydroxy-5α-cholestan-6-one 26-hemisuccinate, conjugates of 28-norcastasterone with horse radish peroxidase and bovine serum albumin were prepared. The latter conjugate was injected into rabbits; produced polyclonal antibodies were used to quantitate 6-keto-Brassinosteroids. The newly developed analytical system was used in combination with two other immunoenzymatic assays for Brassinosteroids to determine individual compounds of this series. In addition, a direct method of brassinosteroid analysis was proposed. It has the advantage of requiring no sample pretreatment steps such as extraction with organic solvents and chromatography.
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Brassinosteroids: A New Role of Steroids as Bio-Signaling Molecules
Chemical Probes in Biology Science at the Interface of Chemistry Biology and Medicine, 2003Co-Authors: Vladimir A. Khripach, Vladimir N Zhabinskii, Raisa KarnachukAbstract:A current status of research in brassinosteroid area and recent results on Brassinosteroids’ involvement in light and hormone signal transduction cross talk are presented.
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Synthesis of [26-2H3]Brassinosteroids
Steroids, 2002Co-Authors: Vladimir A. Khripach, Vladimir N Zhabinskii, Olga V. Konstantinova, Andrey P. Antonchick, Bernd SchneiderAbstract:A number of [26-2H(3)]Brassinosteroids were prepared for biochemical studies. The parent, nondeuterated compounds were considered to be biosynthetic intermediates in brassinosteroid biosynthesis. Claisen rearrangement was used to construct the steroidal side chain. Deuterium was introduced by reducing the corresponding intermediates with lithium aluminium deuteride.
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twenty years of Brassinosteroids steroidal plant hormones warrant better crops for the xxi century
Annals of Botany, 2000Co-Authors: Vladimir A. Khripach, Vladimir N Zhabinskii, Aede De GrootAbstract:The discovery of Brassinosteroids (BS) just over 20 years ago opened a new era in studies of bio-regulation in living organisms. Previously, the only known role of steroids as hormones was in animals and fungi; now a steroidal hormone in plants had been added. Progress in brassinosteroid research has been very rapid. Only 20 years passed between the discovery of brassinolide, the first member of the series, and the application of Brassinosteroids in agriculture. Although the other plant hormones have been studied for a much longer period, there has not been similar development. Within the last couple of years two books on Brassinosteroids (Khripach VA, Zhabinskii VN, de Groot A. 1999. Brassinosteroids—a new class of plant hormones. San Diego: Academic Press; Sakurai A, Yokota T, Clouse SD, eds. 1999. Brassinosteroids: steroidal plant hormones. Tokyo: Springer Verlag) have been published, but many new data have appeared since that time. Many of the more recent data is devoted to molecular biological aspects of BS and has helped to create a vision of their role in plants and their mechanisms of action. New discoveries of the physiological properties of BS allow us to consider them as highly promising, environmentally-friendly, natural substances suitable for wide application in plant protection and yield promotion in agriculture. This aspect of BS is the main subject of this Botanical Briefing.
Shigeo Yoshida - One of the best experts on this subject based on the ideXlab platform.
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systemic effect of a brassinosteroid on root nodule formation in soybean as revealed by the application of brassinolide and brassinazole
Soil Science and Plant Nutrition, 2005Co-Authors: Junko Terakado, Shigeo Yoshida, Shinsuke Fujihara, Shigeko Goto, Ryoko Kuratani, Yoshito Suzuki, Tadakatsu YoneyamaAbstract:Leguminous plants form nitrogen-fixing root nodules and the number of nodules is controlled by a self-regulating mechanism called autoregulation. However, signaling substances involved in nodule regulation have not been identified. In the present study, we used brassinolide, a most effective molecular species of plant hormone Brassinosteroids, and brassinazole, an effective inhibitor of brassinosteroid biosynthesis to determine whether brassinolide played a role in systemic regulation of noduel formation in wild type soybean and its super-nodulating mutant. Foliar application or direct injection of brassinolide into the root base inhibited nodule formation and root development in the super-nodulating mutant (En6500), but not in the parent line (cv. Enrei). The internodes in the plants subjected to foliar application were significantly longer than those in the untreated plants. In contrast, the application of brassinazole on mature leaves or into the culture media resulted in the increase of the nodule num...
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cyp72b1 inactivates brassinosteroid hormones an intersection between photomorphogenesis and plant steroid signal transduction
Plant Physiology, 2003Co-Authors: Edward M Turk, Shozo Fujioka, Hideharu Seto, Yukihisa Shimada, Suguru Takatsuto, Megan A Denzel, Quetzal I Torres, Shigeo Yoshida, Michael M. NeffAbstract:Active Brassinosteroids, such as brassinolide (BL) and castasterone, are growth promoting plant hormones. An Arabidopsis cytochrome P450 monooxygenase encoded by CYP72B1 has been implicated in brassinosteroid catabolism as well as photomorphogenesis. We expressed CYP72B1 in yeast, coupled with brassinosteroid feeding, and established the biochemical function to be the hydroxylation of BL and castasterone, to give 26-hydroxybrassinolide and 26-hydroxycastasterone, respectively. Brassinosteroid feeding experiments with wild-type Arabidopsis, a CYP72B1 null mutant, and a CYP72B1 overexpression line demonstrated that carbon 26 hydroxylation of active Brassinosteroids is an endogenous function of CYP72B1. Seedling growth assays demonstrated that 26-hydroxybrassinolide is an inactive brassinosteroid. Genetic and physiological analysis of the hypocotyl response to exogenous BL and varying intensities of white and monochromatic light suggested that CYP72B1 modulates photomorphogenesis primarily through far-red light and to a lesser extent through blue- and red-light pathways. CYP72B1 transcript accumulation in dark-grown seedlings was organ specific and down-regulated after 1 h of illumination in dim white, red, and blue light, but not far-red light. CYP72B1 translational fusions with the β-glucuronidase reporter gene demonstrated that protein levels increased in the hypocotyl elongation zone when shifted from the dark to far-red light, but not blue or red light. We propose a model in which Arabidopsis seedling development switches from dark-grown development (skotomorphogenesis) to light-grown development (photomorphogenesis) in part by rapid modulation of brassinosteroid sensitivity and levels. CYP72B1 provides an intersection between the light and brassinosteroid pathways mainly by far-red-light-dependent modulation of brassinosteroid levels.
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organ specific expression of brassinosteroid biosynthetic genes and distribution of endogenous Brassinosteroids in arabidopsis
Plant Physiology, 2003Co-Authors: Yukihisa Shimada, Shozo Fujioka, Suguru Takatsuto, Hideki Goda, Ayako Nakamura, Shigeo YoshidaAbstract:Brassinosteroids (BRs) are steroidal plant hormones that are essential for growth and development. There is only limited information on where BRs are synthesized and used. We studied the organ specificity of BR biosynthesis in Arabidopsis, using two different approaches: We analyzed the expression of BR-related genes using real-time quantitative reverse transcriptase-polymerase chain reaction, and analyzed endogenous BRs using gas chromatography-mass spectrometry. Before starting this study, we cloned the second BR-6-oxidase ( BR6ox2 ) gene from Arabidopsis and found that the encoded enzyme has the same substrate specificity as the enzyme encoded by the previously isolated 6-oxidase gene ( BR6ox1 ) of Arabidopsis. Endogenous BRs and the expression of BR-related genes were detected in all organs tested. The highest level of endogenous BRs and the highest expression of the BR6ox1 , BR6ox2 , and DWF4 genes were observed in apical shoots, which contain actively developing tissues. These genes are important in BR biosynthesis because they encode the rate-limiting or farthest downstream enzyme in the BR biosynthesis pathway. The second highest level of endogenous BRs and expression of BR6ox1 and DWF4 were observed in siliques, which contains actively developing embryos and seeds. These findings indicate that BRs are synthesized in all organs tested, but are most actively synthesized in young, actively developing organs. In contrast, synthesis was limited in mature organs. Our observations are consistent with the idea that BRs function as the growth-promoting hormone in plants.
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BAS1: A gene regulating brassinosteroid levels and light responsiveness in Arabidopsis.
Proceedings of the National Academy of Sciences of the United States of America, 1999Co-Authors: Michael M. Neff, Shozo Fujioka, Hideharu Seto, Suguru Takatsuto, Takahiro Noguchi, Serena M. Nguyen, Elizabeth J. Malancharuvil, Masayoshi Tsubuki, Toshio Honda, Shigeo YoshidaAbstract:The Arabidopsis bas1-D mutation suppresses the long hypocotyl phenotype caused by mutations in the photoreceptor phytochrome B (phyB). The adult phenotype of bas1-D phyB-4 double mutants mimics that of brassinosteroid biosynthetic and response mutants. bas1-D phyB-4 has reduced levels of Brassinosteroids and accumulates 26-hydroxybrassinolide in feeding experiments. The basis for the mutant phenotype is the enhanced expression of a cytochrome P450 (CYP72B1). bas1-D suppresses a phyB-null allele, but not a phyA-null mutation, and partially suppresses a cryptochrome-null mutation. Seedlings with reduced BAS1 expression are hyperresponsive to Brassinosteroids in a light-dependent manner and display reduced sensitivity to light under a variety of conditions. Thus, BAS1 represents one of the control points between multiple photoreceptor systems and brassinosteroid signal transduction.
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brassinosteroid insensitive dwarf mutants of arabidopsis accumulate Brassinosteroids
Plant Physiology, 1999Co-Authors: Takahiro Noguchi, Shozo Fujioka, Suguru Takatsuto, Shigeo Yoshida, Sunghwa Choe, Heng Yuan, Kenneth A Feldmann, Frans E. TaxAbstract:Seven dwarf mutants resembling brassinosteroid (BR)-biosynthetic dwarfs were isolated that did not respond significantly to the application of exogenous BRs. Genetic and molecular analyses revealed that these were novel alleles of BRI1 (Brassinosteroid-Insensitive 1), which encodes a receptor kinase that may act as a receptor for BRs or be involved in downstream signaling. The results of morphological and molecular analyses indicated that these represent a range of alleles from weak to null. The endogenous BRs were examined from 5-week-old plants of a null allele ( bri1-4 ) and two weak alleles ( bri1-5 and bri1-6 ). Previous analysis of endogenous BRs in several BR-biosynthetic dwarf mutants revealed that active BRs are deficient in these mutants. However, bri1-4 plants accumulated very high levels of brassinolide, castasterone, and typhasterol (57-, 128-, and 33-fold higher, respectively, than those of wild-type plants). Weaker alleles ( bri1-5 and bri1-6 ) also accumulated considerable levels of brassinolide, castasterone, and typhasterol, but less than the null allele ( bri1-4 ). The levels of 6-deoxoBRs in bri1 mutants were comparable to that of wild type. The accumulation of biologically active BRs may result from the inability to utilize these active BRs, the inability to regulate BR biosynthesis in bri1 mutants, or both. Therefore, BRI1 is required for the homeostasis of endogenous BR levels.
Steven D. Clouse - One of the best experts on this subject based on the ideXlab platform.
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Brassinosteroids steroidal plant hormones
1999Co-Authors: A Sakurai, 孝雄 横田, Steven D. ClouseAbstract:History Natural occurrence in the plant kingdom Biochemical analysis of natural Brassinosteroids Chemical synthesis of Brassinosteroids Biosynthesis of Brassinosteroids Metabolism of Brassinosteroids Physiological actions of Brassinosteroids Molecular genetics of Brassinosteroids Structure-activity relationship Practical application of brassionosteroids in agricultural fields.
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Brassinolide affects the rate of cell division in isolated leaf protoplasts of Petunia hybrida.
Plant cell reports, 1998Co-Authors: Steven D. ClouseAbstract:Brassinosteroids are known to promote cell elongation in a wide range of plant species but their effect on cell division has not been as extensively studied. We examined the effect of brassinolide on the kinetics and final division frequencies of regenerating leaf mesophyll protoplasts of Petunia hybrida Vilm v. Comanche. Under optimal auxin and cytokinin conditions, 10-100 nM brassinolide accelerated the time of first cell division by 12 h but had little effect on the final division frequencies after 72-120 h of culture. One micromolar brassinolide showed the same acceleration of first cell division but inhibited the final division frequency by approximately 20%. Under sub-optimal auxin conditions, 10-100 nM brassinolide both accelerated the time of first cell division and dramatically increased the 72- to 120-h final division frequencies. Isolated protoplasts may provide a useful model system to investigate the molecular mechanisms of brassinosteroid action on cell proliferation.
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Molecular genetic analysis of brassinosteroid action
Physiologia Plantarum, 1997Co-Authors: Steven D. ClouseAbstract:Recent applications of molecular techniques to the study of brassinosteroid action have enhanced our understanding of these unique plant growth regulators. The cloning of genes regulated by Brassinosteroids has revealed novel information on the control of gene expression by plant steroids and has extended our knowledge of brassinosteroid-promoted cell expansion. The analysis of brassinosteroid-deficient and brassinosteroid-insensitive mutants has implicated these growth regulators in a number of essential developmental programs including organ elongation, leaf development, photomorphogenesis, fertility, apical dominance and vascular differentiation.
Shozo Fujioka - One of the best experts on this subject based on the ideXlab platform.
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Auxins increase expression of the brassinosteroid receptor and brassinosteroid-responsive genes in Arabidopsis
Plant signaling & behavior, 2013Co-Authors: Tomoaki Sakamoto, Shozo FujiokaAbstract:Auxins and Brassinosteroids are essential phytohormones that synergistically regulate physiological and developmental processes in plants. Previously, we demonstrated that auxins stimulate brassinosteroid perception by regulating the level of brassinosteroid receptor in rice. Here we showed that auxin treatment increased expression of the Arabidopsis brassinosteroid receptor gene BRI1. The promoter of BRI1 has an auxin-response element that is targeted by auxin-response factor transcription factors. Auxin pretreatment increased the sensitivity to Brassinosteroids of brassinosteroid-responsive genes. Although multilevel interactions between auxins and Brassinosteroids have previously been reported, our findings suggest a possibility that auxins control the degree of brassinosteroid perception by regulating the expression of gene for brassinosteroid receptor, and this phenomenon is conserved between monocots (rice) and dicots (Arabidopsis).
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Auxin signal transcription factor regulates expression of the brassinosteroid receptor gene in rice.
The Plant journal : for cell and molecular biology, 2013Co-Authors: Tomoaki Sakamoto, Yoichi Morinaka, Yoshiaki Inukai, Hidemi Kitano, Shozo FujiokaAbstract:Summary The phytohormones auxins and Brassinosteroids are both essential regulators of physiological and developmental processes, and it has been suggested that they act inter-dependently and synergistically. In rice (Oryza sativa), auxin co-application improves the brassinosteroid response in the rice lamina inclination bioassay. Here, we showed that auxins stimulate brassinosteroid perception by regulating the level of brassinosteroid receptor. Auxin treatment increased expression of the rice brassinosteroid receptor gene OsBRI1. The promoter of OsBRI1 contains an auxin-response element (AuxRE) that is targeted by auxin-response factor (ARF) transcription factors. An AuxRE mutation abolished the induction of OsBRI1 expression by auxins, and OsBRI1 expression was down-regulated in an arf mutant. The AuxRE motif in the OsBRI1 promoter, and thus the transient up-regulation of OsBRI1 expression caused by treatment with indole-3-acetic acid, is essential for the indole-3-acetic acid-induced increase in sensitivity to Brassinosteroids. These findings demonstrate that some ARFs control the degree of brassinosteroid perception required for normal growth and development in rice. Although multi-level interactions between auxins and Brassinosteroids have previously been reported, our findings suggest a mechanism by which auxins control cellular sensitivity to Brassinosteroids, and further support the notion that interactions between auxins and Brassinosteroids are extensive and complex.
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Rice CYP734As function as multisubstrate and multifunctional enzymes in brassinosteroid catabolism
The Plant journal : for cell and molecular biology, 2011Co-Authors: Tomoaki Sakamoto, Shozo Fujioka, Yukihisa Shimada, Suguru Takatsuto, Ayami Kawabe, Asako Tokida‐segawa, Bun-ichi Shimizu, Masaharu MizutaniAbstract:*† SUMMARY Catabolism of Brassinosteroids regulates the endogenous level of bioactive Brassinosteroids. In Arabidopsis thaliana, bioactive Brassinosteroids such as castasterone (CS) and brassinolide (BL) are inactivated mainly by two cytochrome P450 monooxygenases, CYP734A1/BAS1 and CYP72C1/SOB7/CHI2/SHK1; CYP734A1/BAS1 inactivates CS and BL by means of C-26 hydroxylation. Here, we characterized CYP734A orthologs from Oryza sativa (rice). Overexpression of rice CYP734As in transgenic rice gave typical brassinosteroid-deficient phenotypes. These transformants were deficient in both the bioactive CS and its precursors downstream of the C-22 hydroxylation step. Consistent with this result, recombinant rice CYP734As utilized a range of C-22 hydroxylated brassinosteroid intermediates as substrates. In addition, rice CYP734As can catalyze hydroxylation and the second and third oxidations to produce aldehyde and carboxylate groups at C-26 in vitro. These results indicate that rice CYP734As are multifunctional, multisubstrate enzymes that control the endogenous bioactive brassinosteroid content both by direct inactivation of CS and by the suppression of CS biosynthesis by decreasing the levels of brassinosteroid precursors.
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cyp72b1 inactivates brassinosteroid hormones an intersection between photomorphogenesis and plant steroid signal transduction
Plant Physiology, 2003Co-Authors: Edward M Turk, Shozo Fujioka, Hideharu Seto, Yukihisa Shimada, Suguru Takatsuto, Megan A Denzel, Quetzal I Torres, Shigeo Yoshida, Michael M. NeffAbstract:Active Brassinosteroids, such as brassinolide (BL) and castasterone, are growth promoting plant hormones. An Arabidopsis cytochrome P450 monooxygenase encoded by CYP72B1 has been implicated in brassinosteroid catabolism as well as photomorphogenesis. We expressed CYP72B1 in yeast, coupled with brassinosteroid feeding, and established the biochemical function to be the hydroxylation of BL and castasterone, to give 26-hydroxybrassinolide and 26-hydroxycastasterone, respectively. Brassinosteroid feeding experiments with wild-type Arabidopsis, a CYP72B1 null mutant, and a CYP72B1 overexpression line demonstrated that carbon 26 hydroxylation of active Brassinosteroids is an endogenous function of CYP72B1. Seedling growth assays demonstrated that 26-hydroxybrassinolide is an inactive brassinosteroid. Genetic and physiological analysis of the hypocotyl response to exogenous BL and varying intensities of white and monochromatic light suggested that CYP72B1 modulates photomorphogenesis primarily through far-red light and to a lesser extent through blue- and red-light pathways. CYP72B1 transcript accumulation in dark-grown seedlings was organ specific and down-regulated after 1 h of illumination in dim white, red, and blue light, but not far-red light. CYP72B1 translational fusions with the β-glucuronidase reporter gene demonstrated that protein levels increased in the hypocotyl elongation zone when shifted from the dark to far-red light, but not blue or red light. We propose a model in which Arabidopsis seedling development switches from dark-grown development (skotomorphogenesis) to light-grown development (photomorphogenesis) in part by rapid modulation of brassinosteroid sensitivity and levels. CYP72B1 provides an intersection between the light and brassinosteroid pathways mainly by far-red-light-dependent modulation of brassinosteroid levels.
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organ specific expression of brassinosteroid biosynthetic genes and distribution of endogenous Brassinosteroids in arabidopsis
Plant Physiology, 2003Co-Authors: Yukihisa Shimada, Shozo Fujioka, Suguru Takatsuto, Hideki Goda, Ayako Nakamura, Shigeo YoshidaAbstract:Brassinosteroids (BRs) are steroidal plant hormones that are essential for growth and development. There is only limited information on where BRs are synthesized and used. We studied the organ specificity of BR biosynthesis in Arabidopsis, using two different approaches: We analyzed the expression of BR-related genes using real-time quantitative reverse transcriptase-polymerase chain reaction, and analyzed endogenous BRs using gas chromatography-mass spectrometry. Before starting this study, we cloned the second BR-6-oxidase ( BR6ox2 ) gene from Arabidopsis and found that the encoded enzyme has the same substrate specificity as the enzyme encoded by the previously isolated 6-oxidase gene ( BR6ox1 ) of Arabidopsis. Endogenous BRs and the expression of BR-related genes were detected in all organs tested. The highest level of endogenous BRs and the highest expression of the BR6ox1 , BR6ox2 , and DWF4 genes were observed in apical shoots, which contain actively developing tissues. These genes are important in BR biosynthesis because they encode the rate-limiting or farthest downstream enzyme in the BR biosynthesis pathway. The second highest level of endogenous BRs and expression of BR6ox1 and DWF4 were observed in siliques, which contains actively developing embryos and seeds. These findings indicate that BRs are synthesized in all organs tested, but are most actively synthesized in young, actively developing organs. In contrast, synthesis was limited in mature organs. Our observations are consistent with the idea that BRs function as the growth-promoting hormone in plants.