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Joanne Chory - One of the best experts on this subject based on the ideXlab platform.

  • tyrosine phosphorylation controls Brassinosteroid receptor activation by triggering membrane release of its kinase inhibitor
    Genes & Development, 2011
    Co-Authors: Tsegaye Dabi, Youssef Belkhadir, Zachary L Nimchuk, Elliot M Meyerowitz, Michael Hothorn, Yvon Jaillais, Joanne Chory
    Abstract:

    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.

  • the epidermis both drives and restricts plant shoot growth
    Nature, 2007
    Co-Authors: Sigal Savaldigoldstein, Charles A Peto, Joanne Chory
    Abstract:

    Plant shoots are derived from three tissue types — the epidermal, sub-epidermal and inner cell tissue. One of them holds the key to determining the final size of the plant, but the question as to which one has remained controversial for more than a century. Now the targeted expression of Brassinosteroid biosynthesis genes in dwarf Arabidopsis plants has provided the answer: it is the epidermis that both drives and restricts shoot growth. Brassinosteroids are plant hormones that are chemically related to cortisol and have a broad spectrum of effects on plant growth. Plant shoots are derived from three tissue types, but which tissues drive or restrict growth has long been debated. A targeted expression of steroid genes in their corresponding dwarf mutant backgrounds is used to conclude that the epidermis both drives and restricts shoot growth. The size of an organism is genetically determined, yet how a plant or animal achieves its final size is largely unknown. The shoot of higher plants has a simple conserved body plan based on three major tissue systems: the epidermal (L1), sub-epidermal (L2) and inner ground and vascular (L3) tissues. Which tissue system drives or restricts growth has been a subject of debate for over a century1,2,3,4. Here, we use dwarf, Brassinosteroid biosynthesis and Brassinosteroid response mutants in conjunction with tissue-specific expression of these components as tools to examine the role of the epidermis in shoot growth. We show that expression of the Brassinosteroid receptor or a Brassinosteroid biosynthetic enzyme in the epidermis, but not in the vasculature, of null mutants is sufficient to rescue their dwarf phenotypes. Brassinosteroid signalling from the epidermis is not sufficient to establish normal vascular organization. Moreover, shoot growth is restricted when Brassinosteroids are depleted from the epidermis and Brassinosteroids act locally within a leaf. We conclude that the epidermis both promotes and restricts shoot growth by providing a non-autonomous signal to the ground tissues.

  • Brassinosteroids regulate dissociation of bki1 a negative regulator of bri1 signaling from the plasma membrane
    Science, 2006
    Co-Authors: Xuelu Wang, Joanne Chory
    Abstract:

    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.

  • a putative leucine rich repeat receptor kinase involved in Brassinosteroid signal transduction
    Cell, 1997
    Co-Authors: Joanne Chory
    Abstract:

    Brassinosteroids are a class of growth-promoting regulators that play a key role throughout plant development. Despite their importance, nothing is known of the mechanism of action of these steroid hormones. We describe the identification of 18 Arabidopsis dwarf mutants that are unable to respond to exogenously added Brassinosteroid, a phenotype that might be expected for Brassinosteroid signaling mutants. All 18 mutations define alleles of a single previously described gene, BRI1. We cloned BRI1 and examined its expression pattern. It encodes a ubiquitously expressed putative receptor kinase. The extracellular domain contains 25 tandem leucine-rich repeats that resemble repeats found in animal hormone receptors, plant disease resistance genes, and genes involved in unknown signaling pathways controlling plant development.

  • conservation of function between mammalian and plant steroid 5α reductases
    Proceedings of the National Academy of Sciences of the United States of America, 1997
    Co-Authors: Michael G Iswas, Ale Chao, David W Russell, Joanne Chory
    Abstract:

    Arabidopsis det2 mutants are small dark-green dwarfs displaying pleiotropic defects in light-regulated development during multiple stages of the plant life cycle. The DET2 gene encodes a protein that shares ≈40% sequence identity with mammalian steroid 5α-reductases and is implicated in the synthesis of a class of plant steroids, the Brassinosteroids. Here we show that the DET2 protein, when expressed in human embryonic kidney 293 cells, catalyzes the 5α-reduction of several animal steroid substrates and has similar kinetic properties to the mammalian steroid 5α-reductase enzymes. Moreover, human steroid 5α-reductases expressed in det2 mutant plants can substitute for DET2 in Brassinosteroid biosynthesis. These data indicate that DET2 is an ortholog of the mammalian steroid 5α-reductases and provide further evidence that Brassinosteroids play an essential role in light-regulated plant development. The structural and functional conservation between DET2 and human steroid 5α-reductases raise interesting issues concerning the evolutionary origin of the steroid hormone signaling system.

Shigeo Yoshida - One of the best experts on this subject based on the ideXlab platform.

  • erect leaves caused by Brassinosteroid deficiency increase biomass production and grain yield in rice
    Nature Biotechnology, 2006
    Co-Authors: Tomoaki Sakamoto, Shozo Fujioka, Suguru Takatsuto, Yoichi Morinaka, Toshiyuki Ohnishi, Hidehiko Sunohara, Miyako Ueguchitanaka, Masaharu Mizutani, Kanzo Sakata, Shigeo Yoshida
    Abstract:

    New cultivars with very erect leaves, which increase light capture for photosynthesis and nitrogen storage for grain filling, may have increased grain yields. Here we show that the erect leaf phenotype of a rice Brassinosteroid-deficient mutant, osdwarf4-1, is associated with enhanced grain yields under conditions of dense planting, even without extra fertilizer. Molecular and biochemical studies reveal that two different cytochrome P450s, CYP90B2/OsDWARF4 and CYP724B1/D11, function redundantly in C-22 hydroxylation, the rate-limiting step of Brassinosteroid biosynthesis. Therefore, despite the central role of Brassinosteroids in plant growth and development, mutation of OsDWARF4 alone causes only limited defects in Brassinosteroid biosynthesis and plant morphology. These results suggest that regulated genetic modulation of Brassinosteroid biosynthesis can improve crops without the negative environmental effects of fertilizers.

  • 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, 2005
    Co-Authors: Junko Terakado, Shigeo Yoshida, Shinsuke Fujihara, Shigeko Goto, Ryoko Kuratani, Yoshito Suzuki, Tadakatsu Yoneyama
    Abstract:

    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...

  • cyp72b1 inactivates Brassinosteroid hormones an intersection between photomorphogenesis and plant steroid signal transduction
    Plant Physiology, 2003
    Co-Authors: Edward M Turk, Shozo Fujioka, Hideharu Seto, Yukihisa Shimada, Suguru Takatsuto, Megan A Denzel, Quetzal I Torres, Shigeo Yoshida, Michael M. Neff
    Abstract:

    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.

  • organ specific expression of Brassinosteroid biosynthetic genes and distribution of endogenous Brassinosteroids in arabidopsis
    Plant Physiology, 2003
    Co-Authors: Yukihisa Shimada, Shozo Fujioka, Suguru Takatsuto, Hideki Goda, Ayako Nakamura, Shigeo Yoshida
    Abstract:

    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.

  • Brassinazole, an inhibitor of Brassinosteroid biosynthesis, inhibits development of secondary xylem in cress plants (Lepidium sativum).
    Plant & cell physiology, 2001
    Co-Authors: Noriko Nagata, Tadao Asami, Shigeo Yoshida
    Abstract:

    Brassinazole (Brz) is a specific Brassinosteroid biosynthesis inhibitor. Cress plants (Lepidium sativum) grown in medium containing Brz exhibited a slight predominance of phloem differentiation at the expense of xylem differentiation and remarkable inhibition of the development of secondary xylem. This result indicates that Brassinosteroids function in xylem development in vivo.

Xuelu Wang - One of the best experts on this subject based on the ideXlab platform.

  • Editorial : An update on Brassinosteroids : homeostasis, crosstalk, and adaptation to environmental stress
    'Frontiers Media SA', 2021
    Co-Authors: Gruszka Damian, Shamsul Hayat, Xuelu Wang, Bajguz Andrzej, Li Qian-feng, Mats Hansson, Li Jianming
    Abstract:

    Over the last three decades, there have been significant advances in the understanding of Brassinosteroid (BR) biosynthesis and signaling, particularly in the model plant species Arabidopsis thaliana. BRs regulate a variety of morphogenetic and physiological processes throughout plant life. Notably, BR biosynthesis and signaling are interconnected with the signaling pathways of other phytohormones and environmental stresses. Gathering knowledge about these aspects in monocot and dicot crops is of particular importance as it may allow modulation of these processes and enable the development cultivars better adapted to ongoing climate change. This Research Topic, providing An Update on Brassinosteroids: Homeostasis, Crosstalk, and Adaptation to Environmental Stress is aimed at introducing the latest findings in the regulation of BR metabolism, the interconnection of the BR signalosome with phytohormonal and stress signaling pathways, and the BR-mediated adaptation of plants to environmental conditions. The Research Topic includes five reviews and one original research article. [fragm. tekstu

  • Brassinosteroids regulate pavement cell growth by mediating bin2 induced microtubule stabilization
    Journal of Experimental Botany, 2018
    Co-Authors: Qin Yang, Xiaolei Liu, Yuan Wang, Linhai Wang, Xuelu Wang
    Abstract:

    Brassinosteroids (BRs), a group of plant steroid hormones, play important roles in regulating plant development. The cytoskeleton also affects key developmental processes and a deficiency in BR biosynthesis or signaling leads to abnormal phenotypes similar to those of microtubule-defective mutants. However, how BRs regulate microtubule and cell morphology remains unknown. Here, using liquid chromatography-tandem mass spectrometry, we identified tubulin proteins that interact with Arabidopsis Brassinosteroid INSENSITIVE2 (BIN2), a negative regulator of BR responses in plants. In vitro and in vivo pull-down assays confirmed that BIN2 interacts with tubulin proteins. High-speed co-sedimentation assays demonstrated that BIN2 also binds microtubules. The Arabidopsis genome also encodes two BIN2 homologs, BIN2-LIKE 1 (BIL1) and BIL2, which function redundantly with BIN2. In the bin2-3 bil1 bil2 triple mutant, cortical microtubules were more sensitive to treatment with the microtubule-disrupting drug oryzalin than in wild-type, whereas in the BIN2 gain-of-function mutant bin2-1, cortical microtubules were insensitive to oryzalin treatment. These results provide important insight into how BR regulates plant pavement cell and leaf growth by mediating the stabilization of microtubules by BIN2.

  • Brassinosteroids control root epidermal cell fate via direct regulation of a myb bhlh wd40 complex by gsk3 like kinases
    eLife, 2014
    Co-Authors: Yinwei Cheng, Tadao Asami, Xuelu Wang, Wenjiao Zhu, Yuxiao Chen, Shinsaku Ito
    Abstract:

    In Arabidopsis, root hair and non-hair cell fates are determined by a MYB-bHLH-WD40 transcriptional complex and are regulated by many internal and environmental cues. Brassinosteroids play important roles in regulating root hair specification by unknown mechanisms. Here, we systematically examined root hair phenotypes in Brassinosteroid-related mutants, and found that Brassinosteroid signaling inhibits root hair formation through GSK3-like kinases or upstream components. We found that with enhanced Brassinosteroid signaling, GL2, a cell fate marker for non-hair cells, is ectopically expressed in hair cells, while its expression in non-hair cells is suppressed when Brassinosteroid signaling is reduced. Genetic analysis demonstrated that Brassinosteroid-regulated root epidermal cell patterning is dependent on the WER-GL3/EGL3-TTG1 transcriptional complex. One of the GSK3-like kinases, BIN2, interacted with and phosphorylated EGL3, and EGL3s mutated at phosphorylation sites were retained in hair cell nuclei. BIN2 phosphorylated TTG1 to inhibit the activity of the WER-GL3/EGL3-TTG1 complex. Thus, our study provides insights into the mechanism of Brassinosteroid regulation of root hair patterning.

  • the mechanisms of Brassinosteroids action from signal transduction to plant development
    Molecular Plant, 2011
    Co-Authors: Cangjin Yang, Chi Zhang, Jiaqi Jin, Xuelu Wang
    Abstract:

    Brassinosteroids play diverse roles in plant growth and development. Plants deficient in Brassinosteroid (BR) biosynthesis or defective in signal transduction show many abnormal developmental phenotypes, indicating the importance of both BR biosynthesis and the signaling pathway in regulating these biological processes. Recently, using genetics, proteomics, genomics, cell biology, and many other approaches, more components involved in the BR signaling pathway were identified. Furthermore, the physiological, cellular, and molecular mechanisms by which BRs regulate various aspects of plant development, are being discovered. These include root development, anther and pollen development and formation, stem elongation, vasculature differentiation, and cellulose biosynthesis, suggesting that the biological functions of BRs are far beyond promoting cell elongation. This review will focus on the up-to-date progresses about regulatory mechanisms of the BR signaling pathway and the physiological and molecular mechanisms whereby BRs regulate plant growth and development.

  • Brassinosteroids control male fertility by regulating the expression of key genes involved in arabidopsis anther and pollen development
    Proceedings of the National Academy of Sciences of the United States of America, 2010
    Co-Authors: Wenjiao Zhu, Shanshan Zhang, Yanhai Yin, Xuelu Wang
    Abstract:

    The development of anther and pollen is important for male reproduction, and this process is coordinately regulated by many external and internal cues. In this study, we systematically examined the male reproductive phenotypes of a series of Brassinosteroid biosynthetic and signaling mutants and found that, besides the expected cell-expansion defects, these mutants also showed reduced pollen number, viability, and release efficiency. These defects were related with abnormal tapetum and microspore development. Using both real-time quantitative RT-PCR and microarray experiments, we found that the expression of many key genes required for anther and pollen development was suppressed in these mutants. ChIP analysis demonstrated that BES1, an important transcription factor for Brassinosteroid signaling, could directly bind to the promoter regions of genes encoding transcription factors essential for anther and pollen development, SPL/NZZ, TDF1, AMS, MS1, and MS2. Taken together, these data lead us to propose that Brassinosteroids control male fertility at least in part via directly regulating key genes for anther and pollen development in Arabidopsis. Our work provides a unique mechanism to explain how a phytohormone regulates an essential genetic program for plant development.

Hiroo Fukuda - One of the best experts on this subject based on the ideXlab platform.

  • transfer of phenylpropanoids via the medium between xylem cells in zinnia xylogenic culture
    Plant Biotechnology, 2004
    Co-Authors: Yasuko Ito, Naohito Tokunaga, Yasushi Sato, Hiroo Fukuda
    Abstract:

    In order to understand cell-cell interactions involved in xylem differentiation, we studied intercellular molecules in an in vitro Zinnia xylogenic culture system, where single mesophyll cells transdifferentiate into tracheary elements (TEs) and xylem parenchyma cells. We found that UV-absorbing substances accumulated predominantly in xylogenesis-inducing medium and kept increasing even after the TEs died. This accumulation was inhibited by L-α-aminooxy-β-phenylpropionic acid (AOPP), an inhibitor of phenylalanine ammonia-lyase, and also by brefeldin A, an inhibitor of vesicle transport. These results indicated that living non-TE cells, probably xylem parenchyma cells, secrete some kinds of phenylpropanoids via a vesicle transport system. Further experiment showed that inhibition of Brassinosteroid biosynthesis by uniconazole suppressed TE differentiation, but not the secretion of UV-absorbing substances into the medium, implying that differentiation of xylem parenchyma cells might not be strongly affected by the depletion of endogenous Brassinosteroids.

  • hd zip iii homeobox genes that include a novel member zehb 13 zinnia athb 15 arabidopsis are involved in procambium and xylem cell differentiation
    Plant and Cell Physiology, 2003
    Co-Authors: Kyoko Ohashiito, Hiroo Fukuda
    Abstract:

    HD-Zip III homeobox genes are known to be essential transcriptional factors for vascular development. To further understand the relation of HD-Zip III genes in vascular differentiation, we isolated a new member of the HD-Zip III genes, ZeHB-13, as a Zinnia homolog of ATHB-15, and then characterized the expression profile using a Zinnia xylogenic cell culture and Zinnia plants. We compared the accumulation pattern of transcripts for ZeHB-13 and other HD-Zip III genes and suggested that the expression of ZeHB-13 was restricted to the procambium and was not severely suppressed by brassinazole, an inhibitor of Brassinosteroid biosynthesis, unlike other HD-Zip III genes. We also characterized its Arabidopsis counterpart, ATHB-15. A histochemical promoter analysis using ATHB-15::GUS transgenic Arabidopsis plants indicated that ATHB-15 was active specifically in the procambium. These results strongly suggest that ZeHB-13/ATHB-15 is a pivotal transcriptional regulator responsible for early vascular development. Based on these results, we will discuss the regulation of xylem development in light of the functions of HD-Zip III members and Brassinosteroids.

  • promotion of transcript accumulation of novel zinnia immature xylem specific hd zip iii homeobox genes by Brassinosteroids
    Plant and Cell Physiology, 2002
    Co-Authors: Kyoko Ohashiito, Taku Demura, Hiroo Fukuda
    Abstract:

    We isolated three novel homeobox genes (ZeHB-10, -11 and -12) from Zinnia elegans to elucidate the molecular mechanism underlying vascular system formation. ZeHB-10, -11 and -12 encode for HD-Zip proteins of the class III to which Arabidopsis Athb-8, -9, -14, -15 and IFL1 belong. In situ hybridization analysis demonstrated that the ZeHB-10, -11 and -12 mRNAs accumulated preferentially in procambium and immature xylem cells in 14-day-old plants. Transcripts for the three genes also accumulated in cultured Zinnia cells in a xylogenesis-specific manner. The accumulation of transcripts for all of ZeHB-10, -11 and -12 in cultured Zinnia cells was suppressed strongly by uniconazole, an inhibitor of Brassinosteroid synthesis, and such suppression was reversed by the addition of brassinolide, a biologically active Brassinosteroid. Thus the expression of ZeHB-10, -11 and -12 may be regulated by endogenous levels of Brassinosteroids. Taken together with the fact that ZeHB-10, -11 and -12 proteins can bind to each other in yeast, the roles of HD-Zip III genes in vascular development are discussed.

  • Brassinosteroids induce entry into the final stage of tracheary element differentiation in cultured zinnia cells
    Plant and Cell Physiology, 1997
    Co-Authors: Ryo Yamamoto, Taku Demura, Hiroo Fukuda
    Abstract:

    To elucidate the involvement of Brassinosteroids in the progression of tracheary element differentiation in cultured Zinnia cells, we analyzed the effects of uniconazole, an inhibitor of Brassinosteroid synthesis, and brassinolide, a biologically active Brassinosteroid, on the accumulation of raRNAs for various genes that were expressed in different stages of differentiation. Uniconazole specifically suppressed the accumulation of transcripts for genes that were induced in the final stage of differentiation in association with secondary wall formation and cell death. This suppression was recovered with the addition of brassinolide. These results strongly suggest that endogenous Brassinosteroids induce entry into the final stage of differentiation.

Josep Vilarrasablasi - One of the best experts on this subject based on the ideXlab platform.

  • paracrine Brassinosteroid signaling at the stem cell niche controls cellular regeneration
    Journal of Cell Science, 2017
    Co-Authors: Fidel Lozanoelena, Josep Vilarrasablasi, Ainoa Planasriverola, Rebecca Schwab, Ana I Canodelgado
    Abstract:

    Stem cell regeneration is crucial for both cell turnover and tissue healing in multicellular organisms. In Arabidopsis roots, a reduced group of cells known as the quiescent center (QC) acts as a cell reservoir for surrounding stem cells during both normal growth and in response to external damage. Although cells of the QC have a very low mitotic activity, plant hormones such as Brassinosteroids (BR) can promote QC divisions. Here, we used a tissue-specific strategy to investigate the spatial signaling requirements of BR-mediated QC divisions. We generated stem cell niche-specific receptor knockout lines by placing an artificial microRNA against BRI1 (Brassinosteroid RESPONSE INSENSITIVE 1) under the control of the QC-specific promoter WOX5. Additionally, QC-specific knock-in lines for BRI1 and its downstream transcription factor BES1 (BRI1-EMS-SUPPRESOR1) were also created using the WOX5 promoter. By analyzing the roots of these lines, we uncover that BES1-mediated signaling cell-autonomously promotes QC divisions, that BRI1 is essential for sensing nearby inputs and triggering QC divisions, and that DNA damage promotes BR-dependent paracrine signaling in the stem cell niche as a prerequisite to stem cell replenishment.

  • regulation of plant stem cell quiescence by a Brassinosteroid signaling module
    Developmental Cell, 2014
    Co-Authors: Josep Vilarrasablasi, Marypaz Gonzalezgarcia, David Frigola, Norma Fabregas, Konstantinos G Alexiou, Susana Rivas, Nuria Lopezbigas, Alain Jauneau, Jan U Lohmann
    Abstract:

    Summary The quiescent center (QC) maintains the activity of the surrounding stem cells within the root stem cell niche, yet specific molecular players sustaining the low rate of QC cell division remain poorly understood. Here, we identified a R2R3-MYB transcription factor, BRAVO (BrassinosteroidS AT VASCULAR AND ORGANIZING CENTER), acting as a cell-specific repressor of QC divisions in the primary root of Arabidopsis . Ectopic BRAVO expression restricts overall root growth and ceases root regeneration upon damage of the stem cells, demonstrating the role of BRAVO in counteracting Brassinosteroid (BR)-mediated cell division in the QC cells. Interestingly, BR-regulated transcription factor BES1 (BRI1-EMS SUPRESSOR 1) directly represses and physically interacts with BRAVO in vivo, creating a switch that modulates QC divisions at the root stem cell niche. Together, our results define a mechanism for BR-mediated regulation of stem cell quiescence in plants.