Showing papers on "Brassinosteroid published in 2009"
TL;DR: Results strongly suggest that elevated H2O2 levels resulting from enhanced NADPH oxidase activity are involved in the BR-induced stress tolerance.
Abstract: Brassinosteroids (BRs) induce plant tolerance to a wide spectrum of stresses. To study how BR induces stress tolerance, we manipulated the BR levels in cucumber (Cucumis sativus) through a chemical genetics approach and found that BR levels were positively correlated with the tolerance to photo-oxidative and cold stresses and resistance to Cucumber mosaic virus. We also showed that BR treatment enhanced NADPH oxidase activity and elevated H2O2 levels in apoplast. H2O2 levels were elevated as early as 3 h and returned to basal levels 3 d after BR treatment. BR-induced H2O2 accumulation was accompanied by increased tolerance to oxidative stress. Inhibition of NADPH oxidase and chemical scavenging of H2O2 reduced BR-induced oxidative and cold tolerance and defense gene expression. BR treatment induced expression of both regulatory genes, such as RBOH, MAPK1, and MAPK3, and genes involved in defense and antioxidant responses. These results strongly suggest that elevated H2O2 levels resulting from enhanced NADPH oxidase activity are involved in the BR-induced stress tolerance.
603 citations
TL;DR: A complete BR signalling pathway is described by elucidating key missing steps and new insights are provided into the mechanism of GSK3 regulation.
Abstract: Brassinosteroid (BR) regulates gene expression and plant development through a receptor kinase-mediated signal transduction pathway. Despite the identification of many components of this pathway, it remains unclear how the BR signal is transduced from the cell surface to the nucleus. Here we describe a complete BR signalling pathway by elucidating key missing steps. We show that phosphorylation of BSK1 (BR-signalling kinase 1) by the BR receptor kinase BRI1 (BR-insensitive 1) promotes BSK1 binding to the BSU1 (BRI1 suppressor 1) phosphatase, and BSU1 inactivates the GSK3-like kinase BIN2 (BR-insensitive 2) by dephosphorylating a conserved phospho-tyrosine residue (pTyr 200). Mutations that affect phosphorylation/dephosphorylation of BIN2 pTyr200 (bin2-1, bin2-Y200F and quadruple loss-of-function of BSU1-related phosphatases) support an essential role for BSU1-mediated BIN2 dephosphorylation in BR-dependent plant growth. These results demonstrate direct sequential BR activation of BRI1, BSK1 and BSU1, and inactivation of BIN2, leading to accumulation of unphosphorylated BZR (brassinazole resistant) transcription factors in the nucleus. This study establishes a fully connected BR signalling pathway and provides new insights into the mechanism of GSK3 regulation.
574 citations
TL;DR: Genetic manipulation of BR activity has indeed led to increases in crop yield by 20-60%, confirming the value of further research on BRs to improve productivity.
348 citations
TL;DR: The results identify a previously unknown pathway that functions cooperatively with, but largely independent of the BR pathway to regulate cell elongation and establishes a platform to identify other signaling components in this important pathway for plant growth and provides a paradigm to study the coordination of independent pathways in the regulation of a common biological process.
Abstract: Cell elongation in plants is controlled by environmental cues such as light and internal growth regulators including plant steroid hormones, brassinosteroids (BRs). In this study, we found that 3 related receptor-like kinases (RLKs), HERCULES1, THESEUS1, and FERONIA, are transcriptionally induced by BRs and are down-regulated in the loss-of-function BR mutant bri1 and up-regulated in the constitutive BR-response mutant bes1-D. These RLKs belong to the CrRLK family that has 17 members in Arabidopsis. We hypothesize that these RLKs are involved in BR-regulated processes. Although 2 of the RLKs were recently found to mediate male-female interaction during pollen tube reception (FERONIA) and to sense cell wall integrity (THESEUS1), our genetic studies demonstrated that they are required for cell elongation during vegetative growth as herk1 the1 double and fer RNAi mutants displayed striking dwarf phenotypes. The herk1 the1 double mutant enhances the dwarf phenotype of bri1 and partially suppresses bes1-D phenotype, supporting a role of HERK1/THE1 in BR-mediated cell elongation. Microarray experiments demonstrated that these RLKs control the expression of a unique set of genes including those implicated in cell elongation and 16% of the genes affected in herk1 the1 are regulated by BRs. Our results, therefore, identify a previously unknown pathway that functions cooperatively with, but largely independent of the BR pathway to regulate cell elongation. The work establishes a platform to identify other signaling components in this important pathway for plant growth and provides a paradigm to study the coordination of independent pathways in the regulation of a common biological process.
318 citations
TL;DR: A rice dwarf and low-tillering mutant and cloned the corresponding gene via map-based cloning identified a new signaling component that is involved in several specific BR responses in rice that encodes a new member of the plant-specific GRAS family.
Abstract: Rapid progress has been made regarding the understanding of brassinosteroid (BR) signaling in Arabidopsis. However, little is known about BR signaling in monotyledons. Here, we characterized a rice dwarf and low-tillering (dlt) mutant and cloned the corresponding gene via map-based cloning. DLT encodes a new member of the plant-specific GRAS family. The dwarf phenotype of dlt is similar to BR-deficient or signaling mutants in rice. In addition, both lamina bending and coleoptile elongation assays show that dlt is insensitive or much less responsive to brassinolide (BL), the most active BR, suggesting that DLT is involved in BR signaling. Consistent with this conclusion, the accumulation of transcripts of BR biosynthesis genes in the dlt mutant indicated that DLT is involved in feedback inhibition of BR biosynthesis genes. In addition, transcription of several other BR-regulated genes is altered in the dlt mutant. Finally, consistent with the fact that DLT is also negatively feedback-regulated by BR treatment, a gel mobility shift assay showed that OsBZR1 can bind to the DLT promoter through the BR-response element. Taken together, these studies have enabled us to identify a new signaling component that is involved in several specific BR responses in rice.
291 citations
TL;DR: Current knowledge of the functional repertoire of BAK1 is summarized and it is discussed how its multiple functions could be integrated, how receptor complexes are potentially formed and how specificity might be determined.
279 citations
TL;DR: The data suggest that GSK3 inhibition is the sole activation mode of BR signaling and argues against GSK2-independent BR responses in Arabidopsis, and bikinin represents a useful tool to further unravel regulatory mechanisms.
241 citations
TL;DR: A new mechanism is established by which AtMYB30, a direct target of BES1, functions to amplify BR signaling by helping BES 1 activate downstream target genes.
Abstract: A paradox of plant hormone biology is how a single small molecule can affect a diverse array of growth and developmental processes. For instance, brassinosteroids (BRs) regulate cell elongation, vascular differentiation, senescence and stress responses. BRs signal through the BES1/BZR1 (bri1-EMS-suppressor 1/Brassinazole-Resistant 1) family of transcription factors, which regulate hundreds of target genes involved in this pathway; yet little is known of this transcriptional network. By microarray and chromatin immunoprecipitation (ChIP) experiments, we identified a direct target gene of BES1, AtMYB30, which encodes a MYB family transcription factor. AtMYB30 null mutants display decreased BR responses and can enhance the dwarf phenotype of a weak allele of the BR receptor mutant bri1. Many BR-regulated genes have reduced expression and/or hormone-induction in AtMYB30 mutants, indicating that AtMYB30 functions to promote the expression of a subset of BR-target genes. AtMYB30 and BES1 bind to a conserved MYB-binding site and E-box sequences, respectively, in the promoters of genes that are regulated by both BRs and AtMYB30. Finally, AtMYB30 and BES1 interact with each other both in vitro and in vivo. These results demonstrated that BES1 and AtMYB30 function cooperatively to promote BR target gene expression. Our results therefore establish a new mechanism by which AtMYB30, a direct target of BES1, functions to amplify BR signaling by helping BES1 activate downstream target genes.
225 citations
TL;DR: Overexpression of AtRALF23 impairs BL-induced hypocotyl elongation in seedlings, and mature overexpressing plants are shorter and bushier, presumably relieving the growth-retarding effect of a peptide growth factor, which is processed from a larger precursor protein by AtS1P.
Abstract: Arabidopsis has 34 genes encoding proteins related to rapid alkalinization factor (RALF), a peptide growth factor. One of those genes (AtRALF23) is significantly downregulated by brassinolide (BL) treatment of Arabidopsis seedlings or in mutant seedlings expressing a constitutively active form of BES1, a transcriptional effector of the brassinosteroid signaling pathway. Overexpression of AtRALF23 impairs BL-induced hypocotyl elongation in seedlings, and mature overexpressing plants are shorter and bushier. Overexpression of AtRALF23 produces slower growing seedlings, with roots that have reduced capacity to acidify the rhizosphere. AtRALF23 encodes a 138-aa protein, and when an epitope-tagged form (AtRALF23-myc) was expressed in transgenic plants, the protein was processed to release a C-terminal peptide. The presumed junction between the precursor and the processed peptide contains a recognition site for site-1 protease (AtS1P), a plant subtilisin-like serine protease (subtilase). When AtRALF23-myc was expressed in the background of a site-1 protease mutant (s1p-3), or when the AtS1P recognition site (RRIL) was mutated (RR --> GG) and expressed in a wild-type background, the precursor was not cleaved, and the bushy phenotype was not produced. A fluorogenic peptide representing the presumed subtilase recognition site in AtRALF23 was cleaved in vitro by AtS1P. Thus, BL downregulates AtRALF23 expression, presumably relieving the growth-retarding effect of a peptide growth factor, which is processed from a larger precursor protein by AtS1P.
190 citations
TL;DR: Results indicate that BU1 protein is a positive regulator of BR response: it controls bending of the lamina joint in rice and it is a novel primary response gene that participates in two BR signaling pathways through OsBRI1 and RGA1.
Abstract: Brassinosteroids (BRs) are involved in many developmental processes and regulate many subsets of downstream genes throughout the plant kingdom. However, little is known about the BR signal transduction and response network in monocots. To identify novel BR-related genes in rice (Oryza sativa), we monitored the transcriptomic response of the brassinosteroid deficient1 (brd1) mutant, with a defective BR biosynthetic gene, to brassinolide treatment. Here, we describe a novel BR-induced rice gene BRASSINOSTEROID UPREGULATED1 (BU1), encoding a helix-loop-helix protein. Rice plants overexpressing BU1 (BU1:OX) showed enhanced bending of the lamina joint, increased grain size, and resistance to brassinazole, an inhibitor of BR biosynthesis. In contrast to BU1:OX, RNAi plants designed to repress both BU1 and its homologs displayed erect leaves. In addition, compared to the wild type, the induction of BU1 by exogenous brassinolide did not require de novo protein synthesis and it was weaker in a BR receptor mutant OsbriI (Oryza sativa brassinosteroid insensitive1, d61) and a rice G protein alpha subunit (RGA1) mutant d1. These results indicate that BU1 protein is a positive regulator of BR response: it controls bending of the lamina joint in rice and it is a novel primary response gene that participates in two BR signaling pathways through OsBRI1 and RGA1. Furthermore, expression analyses showed that BU1 is expressed in several organs including lamina joint, phloem, and epithelial cells in embryos. These results indicate that BU1 may participate in some other unknown processes modulated by BR in rice.
188 citations
TL;DR: The authors' genetic, biochemical, and physiological assays revealed that despite functional redundancy, BIN2 plays a dominant role among the three group II members in regulating BR signaling, and lithium chloride treatment was able to suppress the gain-of-function bin2-1 mutation but had a much weaker effect on a strong BR receptor mutant, suggesting the presence of a BIN1-independent regulatory step downstream of BR receptor activation.
Abstract: GLYCOGEN SYNTHASE KINASE3 (GSK3) is a highly conserved serine/threonine kinase involved in a variety of developmental signaling processes. The Arabidopsis (Arabidopsis thaliana) genome encodes 10 GSK3-like kinases that are clustered into four groups. Forward genetic screens have so far uncovered eight mutants, all of which carry gain-of-function mutations in BRASSINOSTEROID-INSENSITIVE2 (BIN2), one of the three members in group II. Genetic and biochemical studies have implicated a negative regulatory role for BIN2 in brassinosteroid (BR) signaling. Here, we report the identification of eight ethyl methanesulfonate-mutagenized loss-of-function bin2 alleles and one T-DNA insertional mutation each for BIN2 and its two closest homologs, BIN2-Like1 and BIN2-Like2. Our genetic, biochemical, and physiological assays revealed that despite functional redundancy, BIN2 plays a dominant role among the three group II members in regulating BR signaling. Surprisingly, the bin2bil1bil2 triple T-DNA insertional mutant still responds to BR and accumulates a more phosphorylated form of a BIN2 substrate than the wild-type plant. Using the specific GSK3 inhibitor lithium chloride, we have provided strong circumstantial evidence for the involvement of other Arabidopsis GSK3-like kinases in BR signaling. Interestingly, lithium chloride treatment was able to suppress the gain-of-function bin2-1 mutation but had a much weaker effect on a strong BR receptor mutant, suggesting the presence of a BIN2-independent regulatory step downstream of BR receptor activation.
TL;DR: The data suggest that ACS is regulated by phytohormones through regulatory inputs that probably act together to continuously adjust ethylene biosynthesis in various tissues and in response to various environmental conditions.
Abstract: A major question in plant biology is how phytohormone pathways interact. Here, we explore the mechanism by which cytokinins and brassinosteroids affect ethylene biosynthesis. Ethylene biosynthesis is regulated in response to a wide variety of endogenous and exogenous signals, including the levels of other phytohormones. Cytokinins act by increasing the stability of a subset of ACC synthases, which catalyze the generally rate-limiting step in ethylene biosynthesis. The induction of ethylene by cytokinin requires the canonical cytokinin two-component response pathway, including histidine kinases, histidine phosphotransfer proteins and response regulators. The cytokinin-induced myc-ACS5 stabilization occurs rapidly (<60 min), consistent with a primary output of this two-component signaling pathway. We examined the mechanism by which another phytohormone, brassinosteroid, elevates ethylene biosynthesis in etiolated seedlings. Similar to cytokinin, brassinosteroid acts post-transcriptionally by increasing the stability of ACS5 protein, and its effects on ACS5 were additive with those of cytokinin. These data suggest that ACS is regulated by phytohormones through regulatory inputs that probably act together to continuously adjust ethylene biosynthesis in various tissues and in response to various environmental conditions.
TL;DR: Overall, this study demonstrates that auxin polar transport coupled to brassinosteroid signaling is required to determine the radial pattern of vascular bundles in shoots.
Abstract: 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.
TL;DR: The study underscores the importance of hormonal interactions on relevant agricultural traits and raises a novel biological mechanism in tomato that may differ from the BR and JA interaction already suggested for Arabidopsis.
Abstract: Given the susceptibility of tomato plants to pests, the aim of the present study was to understand how hormones are involved in the formation of tomato natural defences against insect herbivory Tomato hormone mutants, previously introgressed into the same genetic background of reference, were screened for alterations in trichome densities and allelochemical content Ethylene, gibberellin, and auxin mutants indirectly showed alteration in trichome density, through effects on epidermal cell area However, brassinosteroids (BRs) and jasmonates (JAs) directly affected trichome density and allelochemical content, and in an opposite fashion The BR-deficient mutant dpy showed enhanced pubescence, zingiberene biosynthesis, and proteinase inhibitor expression; the opposite was observed for the JA-insensitive jai1-1 mutant The dpy x jai1-1 double mutant showed that jai1-1 is epistatic to dpy, indicating that BR acts upstream of the JA signalling pathway Herbivory tests with the poliphagous insect Spodoptera frugiperda and the tomato pest Tuta absoluta clearly confirmed the importance of the JA-BR interaction in defence against herbivory The study underscores the importance of hormonal interactions on relevant agricultural traits and raises a novel biological mechanism in tomato that may differ from the BR and JA interaction already suggested for Arabidopsis
TL;DR: The results suggested that OsIAA1 may play important roles in the cross-talk of auxin and brassinosteroid signaling pathways and plant morphogenesis.
Abstract: Aux/IAA and auxin response factor (ARF) are two important families that have been well recognized for their roles in auxin-mediated responses. Aux/IAA proteins are short-lived transcriptional regulators that mediate the auxin responses through interaction with ARF transcription factors. Although quite a few members of the Aux/IAA family have been functionally characterized in dicotyledonous plants such as Arabidopsis, but relatively limited information is available in important crops such as rice. This work focused on isolation and characterization of a member of Aux/IAA family in rice named OsIAA1. The results indicated that OsIAA1 was constitutively expressed in all the tissues and organs investigated. The expression of this gene was induced by various phytohormones including IAA, 2,4-D, kinetin, 24-epibrassinolide, and jasmonic acid. Over-expression of OsIAA1 in rice resulted in reduced inhibition of root elongation to auxin treatment, but increased sensitivity to 24-epiBL treatment. In addition, the OsIAA1-overexpression transgenic plants showed distinctive morphological changes such as decreased plant height and loose plant architecture. Protein interaction analysis suggested that OsIAA1 may act through interaction with OsARF1. T-DNA insertion mutant of OsARF1 showed reduced sensitivity to BR treatment, resembling the phenotype of OsIAA1-overexpression plants. In addition, expression patterns of some genes responsive to brassinosteroid and auxin were changed in the OsIAA1-overexpression plants. These data suggested that OsIAA1 may play important roles in the cross-talk of auxin and brassinosteroid signaling pathways and plant morphogenesis.
TL;DR: This study reported ebs2 (EMS-mutagenized bri1 suppressor 2) as an allele-specific suppressor of bri1–9, a dwarf Arabidopsis mutant caused by retention of a defective brassinosteroid receptor in the ER.
Abstract: Mammalian calreticulin (CRT) is a multifunctional Ca2+-binding protein involved in more than 40 cellular processes in various subcellular compartments, such as Ca2+ storage and protein folding in the endoplasmic reticulum (ER). CRT homologues were discovered in plants almost 15 years ago, and recent studies revealed that many plant species contain 2 or more CRTs that are members of 2 distinct families, the CRT1/2 family and the plant-specific CRT3 family. However, little is known about their physiological functions. Here we report ebs2 (EMS-mutagenized bri1 suppressor 2) as an allele-specific suppressor of bri1–9, a dwarf Arabidopsis mutant caused by retention of a defective brassinosteroid receptor in the ER. EBS2 encodes the Arabidopsis CRT3 that interacts with ER-localized bri1–9 in a glycan-dependent manner. Loss-of-function ebs2 mutations compromise ER retention of bri1–9 and suppress its dwarfism, whereas EBS2 over-expression enhances its dwarf phenotype. In contrast, mutations of 2 other CRTs or their membrane-localized homologues calnexins had little effect on bri1–9. A domain-swapping experiment revealed that the positively charged C-terminal tail of CRT3 is crucial for its “bri1–9-retainer” function. Our study revealed not only a functional role for a plant-specific CRT, but also functional diversity among the 3 Arabidopsis CRT paralogues.
TL;DR: Results indicate that (1) BR is involved in JA signaling and negatively regulates JA inhibition of root growth, and (2) the DWF4 is down-regulated by JA and is located downstream of COI1 in the JA-signaling pathway.
Abstract: The F-box protein CORONATINE INSENSITIVE1 (COI1) plays a central role in jasmonate (JA) signaling and is required for all JA responses in Arabidopsis (Arabidopsis thaliana). To dissect JA signal transduction, we isolated the partially suppressing coi1 (psc1) mutant, which partially suppressed coi1 insensitivity to JA inhibition of root growth. The psc1 mutant partially restored JA sensitivity in coi1-2 background and displayed JA hypersensitivity in wild-type COI1 background. Genetic mapping, sequence analysis, and complementation tests revealed that psc1 is a leaky mutation of DWARF4 (DWF4) that encodes a key enzyme in brassinosteroid (BR) biosynthesis. Physiological analysis showed that an application of exogenous BR eliminated the partial restoration of JA sensitivity by psc1 in coi1-2 background and the JA hypersensitivity of psc1 in wild-type COI1 background. Exogenous BR also attenuated JA inhibition of root growth in the wild type. In addition, the expression of DWF4 was inhibited by JA, and this inhibition was dependent on COI1. These results indicate that (1) BR is involved in JA signaling and negatively regulates JA inhibition of root growth, and (2) the DWF4 is down-regulated by JA and is located downstream of COI1 in the JA-signaling pathway.
TL;DR: Gene expression patterns and growth assays suggest that EXO mediates BR-induced leaf growth, however, EXO does not control BR-levels or BR-sensitivity in the shoot.
Abstract: The EXO (EXORDIUM) gene was identified as a potential mediator of brassinosteroid (BR)-promoted growth. It is part of a gene family with eight members in Arabidopsis. EXO gene expression is under control of BR, and EXO overexpression promotes shoot and root growth. In this study, the consequences of loss of EXO function are described. The exo loss of function mutant showed diminished leaf and root growth and reduced biomass production. Light and scanning electron microscopy analyses revealed that impaired leaf growth is due to reduced cell expansion. Epidermis, palisade, and spongy parenchyma cells were smaller in comparison to the wild-type. The exo mutant showed reduced brassinolide-induced cotyledon and hypocotyl growth. In contrast, exo roots were significantly more sensitive to the inhibitory effect of synthetic brassinolide. Apart from reduced growth, exo did not show severe morphological abnormalities. Gene expression analyses of leaf material identified genes that showed robust EXO-dependent expression. Growth-related genes such as WAK1, EXP5, and KCS1, and genes involved in primary and secondary metabolism showed weaker expression in exo than in wild-type plants. However, the vast majority of BR-regulated genes were normally expressed in exo. HA- and GFP-tagged EXO proteins were targeted to the apoplast. The EXO gene is essential for cell expansion in leaves. Gene expression patterns and growth assays suggest that EXO mediates BR-induced leaf growth. However, EXO does not control BR-levels or BR-sensitivity in the shoot. EXO presumably is involved in a signalling process which coordinates BR-responses with environmental or developmental signals. The hypersensitivity of exo roots to BR suggests that EXO plays a diverse role in the control of BR responses in the root.
01 Jan 2009
TL;DR: Based on the observations that pretreatment with 24-epibrassinolide caused a decrease in MDA together with an increase in antioxidant enzymes, it is likely that BR mitigated damage caused by water stress.
Abstract: Drought stress is considered as a restricting factor for plant products. Therefore, many compounds have been applied to minimize the harmful effects of stress. Brassinosteroid is one of the compounds with antioxidative characteristics. In this experiment, when the fourth leaf of tomato plants appeared, 24-epibrassinolide was sprayed to the leaves at 0.01 and 1 μM concentrations for 3 days with one day interval. Then three levels of drought stress (control, 3 and 5 days withholding water) were applied. Thereafter, the interaction effects of 24-brassinosteroid (BR27) and water stress on some biochemical and antioxidative parameters of tomato plants were investigated. Peroxidation of lipids and H2O2 content were reduced in the plants which were treated with BR27. The intensity of some bands of stress enzymes (GPOD and APX) in the electrophoretic pattern was different in stressed plants treated with 24-epibrassinolide when compared with the plants under drought stress. An increase in the activity of antioxidant enzymes (POD, SOD, CAT, APX) and antioxidative compounds content including ascorbate, carotenoids and proline was observed in drought stress plants after pretreatment with BR. Based on our observations that pretreatment with 24-epibrassinolide caused a decrease in MDA together with an increase in antioxidant enzymes, it is likely that BR mitigated damage caused by water stress.
TL;DR: The results suggest that the rice Galpha affects the BR signaling cascade but the Galpha may not be a signaling molecule in BRI1-meditated perception/transduction.
Abstract: The α subunit of plant heterotrimeric G proteins (Gα) plays pivotal roles in multiple aspects of development and responses to plant hormones. Recently, several lines of evidence have shown that Gα participates in brassinosteroid (BR) responses in Arabidopsis and rice plants. In this study, we conducted a comprehensive analysis of the roles of the rice Gα in the responses to BR using a defective mutant of the Gα gene, T65d1. Decreased sensitivity to 24-epi-brassinolide (24-epiBL) in the T65d1 mutant was observed in many processes examined, e.g. in the inhibition of root growth and the promotion of coleoptile elongation. The T65d1 mutant also showed similar phenotypes to those of BR-deficient mutants, such as the specifically shortened second internode and the constitutive photomorphogenic growth phenotype under dark conditions. However, a negative feedback effect by 24-epiBL on the expression of BR biosynthetic genes was observed in the T65d1 mutant, and the levels of BR intermediates did not fluctuate in this mutant. To determine the epistatic relationship between the T65d1 mutant and d61-7, a weak allele of a rice BR receptor mutant, the two mutants were crossed. The T65d1/d61-7 double mutant showed no epistasis in the elongation inhibition of the internodes, the internode elongation pattern, the leaf angle and the morphological abnormality of leaf, except for the vertical length of seed and the seed weight. Our results suggest that the rice Gα affects the BR signaling cascade but the Gα may not be a signaling molecule in BRI1-meditated perception/transduction.
TL;DR: This review will survey the oxidative reactions by P450s involved in BR biosynthesis and catabolism and provide insights into the evolution of the steroid-biosynthetic P450 genes in the plant kingdom.
TL;DR: The results reveal an interaction between BRs, auxin, and ABA in the control of root growth and indicate that altered sensitivity to ABA is partly responsible for the brx short-root phenotype.
Abstract: To gain further insight into abscisic acid (ABA) signaling and its role in growth regulation, we have screened for Arabidopsis (Arabidopsis thaliana) mutants hypersensitive to ABA-mediated root growth inhibition. As a result, we have identified a loss-of-function allele of BREVIS RADIX (BRX) in the Columbia background, named brx-2, which shows enhanced response to ABA-mediated inhibition of root growth. BRX encodes a key regulator of cell proliferation and elongation in the root, which has been implicated in the brassinosteroid (BR) pathway as well as in the regulation of auxin-responsive gene expression. Mutants affected in BR signaling that are not impaired in root growth, such as bes1-D, bzr1-D, and bsu1-D, also showed enhanced sensitivity to ABA-mediated inhibition of root growth. Triple loss-of-function mutants affected in PP2Cs, which act as negative regulators of ABA signaling, showed impaired root growth in the absence of exogenous ABA, indicating that disturbed regulation of ABA sensitivity impairs root growth. In agreement with this result, diminishing ABA sensitivity of brx-2 by crossing it with a 35S:HAB1 ABA-insensitive line allowed significantly higher recovery of root growth after brassinolide treatment. Finally, transcriptomic analysis revealed that ABA treatment negatively affects auxin signaling in wild-type and brx-2 roots and that ABA response is globally altered in brx-2. Taken together, our results reveal an interaction between BRs, auxin, and ABA in the control of root growth and indicate that altered sensitivity to ABA is partly responsible for the brx short-root phenotype.
TL;DR: Genome-wide analyses carried out through examining the gene expressions of the dark-grown WT or BR biosynthesis-defective mutant det2 seedlings showed that BR deficiency stimulates, while BL treatment suppresses, the expressions of light-responsive genes andPhotomorphogenesis, confirming the negative effects of BR in photomorphogenesis.
TL;DR: This review focuses on the recent advances of the signaling cross-talk between brassinosteroid and other hormones, including abscisic acid, auxin, gibberellins, ethylene, and jasmonate.
Abstract: Various environmental and internal cues play essential roles in regulating diverse aspects of plant growth and development. Phytohormones usually coordinate multiple stimuli to directly regulate multiple developmental programs. Recent studies have provided progresses into the complexity of their cross-talk. Particularly, the signaling pathways of various phytohormones have been being revealed, leading to the discovery of the mechanisms of the interplay among different hormone signaling pathways. This review focuses on the recent advances of the signaling cross-talk between brassinosteroid and other hormones, including abscisic acid, auxin, gibberellins, ethylene, and jasmonate.
TL;DR: The data suggest that BRI1 can function as a systemin binding protein, but that binding of the ligand does not transduce the signal into the cell.
Abstract: The tomato wound signal systemin is perceived by a specific high-affinity, saturable, and reversible cell surface receptor. This receptor was identified as the receptor-like kinase SR160, which turned out to be identical to the brassinosteroid receptor BRI1. Recently, it has been shown that the tomato bri1 null mutant cu3 is as sensitive to systemin as wild type plants. Here we explored these contradictory findings by studying the responses of tobacco plants (Nicotiana tabacum) to systemin. A fluorescently-labeled systemin analog bound specifically to plasma membranes of tobacco suspension-cultured cells that expressed the tomato BRI1-FLAG transgene, but not to wild type tobacco cells. On the other hand, signaling responses to systemin, such as activation of mitogen-activated protein kinases and medium alkalinization, were neither increased in BRI1-FLAG-overexpressing tobacco cells nor decreased in BRI1-silenced cells as compared to levels in untransformed control cells. Furthermore, in transgenic tobacco plants BRI1-FLAG became phosphorylated on threonine residues in response to brassinolide application, but not in response to systemin. When BRI1 transcript levels were reduced by virus-induced gene silencing in tomato plants, the silenced plants displayed a phenotype characteristic of bri1 mutants. However, their response to overexpression of the Prosystemin transgene was the same as in control plants. Taken together, our data suggest that BRI1 can function as a systemin binding protein, but that binding of the ligand does not transduce the signal into the cell. This unusual behavior and the nature of the elusive systemin receptor will be discussed.
TL;DR: The results suggest that early and late C6 oxidation pathways are operating in Chlorella vulgaris, the first isolation of BRs from C. vulgaris cultures.
TL;DR: It is shown that enhanced MSBP1 expression reduces the interaction between BRI1 and BAK1 in vivo, demonstrating that MS BP1 acts as a negative factor at an early step of the BR signaling pathway.
Abstract: Membrane steroid-binding protein 1 (MSBP1) negatively regulates brassinosteroid signaling by enhancing the endocytosis of BAK1
Journal Article•
TL;DR: Increase in activity of antioxidant enzymes (POD, CAT, APX, GR, and SOD) and change in isoenzymes pattern with higher intensity as well as increases in proline and protein content in drought stressed plants treated with BR will probably show the role of brassinosteroids in increased tolerance of plants to water stress.
Abstract: Drought stress is considered a restricting factor for plant products; therefore many compounds were applied to minimise the harmful effects of stress. One type of these compounds that have antioxidative characteristics is brassinosteroids. In this experiment, when 4 fully expanded leaves of tomato plants appeared, 24-epibrassinolide (24-EBL) was sprayed onto the leaves at 0.01 and 1 μM concentrations for 3 days with a 1-day interval. Three levels of drought stress (0, 3, and 5 days withholding water) were applied. Thereafter, the effects of brassinosteroids and water stress were investigated on some biochemical and antioxidative parameters of tomato plants. Lipid peroxidation, peroxide hydrogen, and proline content increased in plants subjected to drought stress. Reduction in protein content in drought conditions showed that drought stress affected protein synthesis and degradation. Decline in the activity of antioxidant enzymes (POD and APX) and increases in the SOD, GR, and CAT activities were observed in drought stressed plants. Reduction in peroxidation of lipids and H2O2 content in the plants treated with both 24-EBL and drought stress was observed. Based on our results it seems that brassinosteroids considerably alleviated oxidative damage that occurred under drought stress. Increase in activity of antioxidant enzymes (POD, CAT, APX, GR, and SOD) and change in isoenzymes pattern with higher intensity as well as increases in proline and protein content in drought stressed plants treated with BR will probably show the role of brassinosteroids in increased tolerance of plants to water stress. Therefore, 24-epibrassinolide may have a role in the mitigation of damage caused by water stress.
TL;DR: It is proposed that C-22-hydroxylated BRs participate in auxin signaling via a novel OsBRI1-independent signaling pathway in lamina joint bending.
Abstract: The rice lamina joint is ideal material for investigating the activity of brassinosteroids (BRs) and auxin because of its high sensitivity to these compounds. Using a series of rice BR biosynthetic and receptor mutants, we conducted lamina joint tests to elucidate the mechanism of cross-talk between BR and auxin signaling in lamina joint bending. In BR biosynthetic mutants d2 and brd1, which are defective in C-23 hydroxylase and C-6 oxidase, respectively, the lamina joint response to auxin was significantly higher than that of wild-type plants. The other BR-biosynthetic mutants, brd2, osdwarf4 and d11, which are defective in C-22-hydroxylated BRs, showed less or no response to auxin. These results suggest that C-22-hydroxylated BRs are involved in auxin-induced lamina joint bending. The results were supported by the observation that inhibition of the hyper-response to auxin in d2 was reduced by treatment with brassinazole, which inhibits the function of DWARF4, the C-22 hydroxylase. In d61, which is defective in OsBRI1, a possible BR receptor in rice, the bending angle of the lamina joint in response to auxin and C-22-hydroxylated 6-deoxoBRs was nearly the same as that in wild-type plants. This implies that C-22-hydroxylated BRs function in auxin signaling independently of OsBRI1. From these observations, we propose that C-22-hydroxylated BRs participate in auxin signaling via a novel OsBRI1-independent signaling pathway.
TL;DR: Functional validation of these somatic embryogenesis receptor-like kinase genes may help in elucidating their precise functions in regulating various facets of plant development.
Abstract: Somatic embryogenesis (SE) is the developmental restructuring of somatic cells towards the embryogenic pathway and forms the basis of cellular totipotency in angiosperms. With the availability of full-length cDNA sequences from Knowledge-based Oryza Molecular Biological Encylopedia (KOME), we identified the leucine-rich repeat receptor-like kinase (LRR-RLK) genes from rice (Oryza sativa), which also encompasses genes involved in regulating somatic embryogenesis. Eight out of eleven of the rice SERK and SERL (SERK-like) genes have the TIGR annotation as (putative) brassinosteroid insensitive 1-associated receptor kinase (precursor). Real-time polymerase chain reaction analysis was undertaken to quantify transcript levels of these 11 genes. Most of these genes were upregulated by brassinosteroids although only a few of these displayed auxin induction. The expression profile of these genes is nearly uniform in the zygotic embryogenic tissue, but the expression pattern is more complex in the somatic embryogenic tissue. It is likely that OsSERKs and OsSERLs may be involved in somatic embryogenesis and also perform a role in morphogenesis and various other plant developmental processes. Functional validation of these somatic embryogenesis receptor-like kinase genes may help in elucidating their precise functions in regulating various facets of plant development.