BRASSINAZOLE RESISTANT Research Articles

WOX1 controls leaf serration development via temporally restricting BZR1 and CUC3 expression in Arabidopsis.

Leaves evolve shape diversity ranging from simple leaves with smooth margin to complicated shape with toothed/serrated, lobed and dissected leaves with leaflets. In the model plant Arabidopsis thaliana with simple leaves producing serrated margin, boundary regulatory factors CUP SHAPED COTYLEDON 2 (CUC2) and CUC3 play important roles in promoting leaf serration initiation and maintenance. Stem cell related WUSCHEL-RELATED HOMEOBOX1 (WOX1) and PRESSED FLOWER/WOX3 are also essential for leaf margin morphogenesis, but the role of WOX1 and PRS as well as the relationships between CUCs and WOXs on tooth development was unclear. In this study, we found that WOX1, but not PRS, prevents overproduction of tooth number and excessive tooth size by limiting CUC3 expression to a moderate level in a temporally regulated manner. We also revealed that BRASSINAZOLE RESISTANT 1 (BZR1), a known regulator for plant development including boundary regions, is involved in WOX1 negative regulation of tooth development by repressing CUC3 expression during the initiation/early stage of tooth development. WOX1 parallelly limits BZR1 and CUC3 expression from the late stage of the first 2 teeth, while restricts CUC3 activity in a BZR1 dependent manner from the initiation/early stage of subsequently developed teeth. This study uncovers a new mechanism for WOX1 in fine-tuning the leaf margin geometry.

Identification of the BZR Family in Garlic (Allium sativum L.) and Verification of the AsBZR11 under Salt Stress

Brassinazole-Resistant (BZR) is an important transcription factor (TF) in the brassinosteroid (BR) signaling pathway, which plays a crucial role in plant growth, development and stress resistance. In this study, we performed a genome-wide analysis of BZRs in garlic (Allium sativum L.) and identified a total of 11 members of the AsBZR gene family. By comparing the expression patterns of AsBZR genes under salt stress, the candidate gene AsBZR11 with salt tolerance function was identified. Subcellular localization results showed that AsBZR11 was localized in the nucleus. The salt tolerance of overexpression lines improved, and the germination rate and root length of overexpression lines increased as compared with wild type. The content of reactive oxygen species (ROS) decreased, and the activity of antioxidant enzymes increased in AsBZR11-OE, suggesting that AsBZR11 has the function of improving plant salt tolerance. Our results enriched the knowledge of plant BZR family and laid a foundation for the molecular mechanism of salt tolerance of garlic, which will provide a theoretical basis for the subsequent creation of salt-tolerant germplasm resources.

Transcription factors BZR1 and PAP1 cooperate to promote anthocyanin biosynthesis in Arabidopsis shoots.

Anthocyanins play critical roles in protecting plant tissues against diverse stresses. The complicated regulatory networks induced by various environmental factors modulate the homeostatic level of anthocyanins. Here, we show that anthocyanin accumulation is induced by brassinosteroids (BRs) in Arabidopsis (Arabidopsis thaliana) shoots and shed light on the underlying regulatory mechanism. We observed that anthocyanin levels are altered considerably in BR-related mutants, and BRs induce anthocyanin accumulation by upregulating the expression of anthocyanin biosynthetic genes. Our genetic analysis indicated that BRASSINAZOLE RESISTANT 1 (BZR1) and PRODUCTION OF ANTHOCYANIN PIGMENT 1 (PAP1) are essential for BR-induced anthocyanin accumulation. The BR-responsive transcription factor BZR1 directly binds to the PAP1 promoter, regulating its expression. In addition, we found that intense anthocyanin accumulation caused by the pap1-D-dominant mutation is significantly reduced in BR mutants, implying that BR activity is required for PAP1 function after PAP1 transcription. Moreover, we demonstrated that BZR1 physically interacts with PAP1 to cooperatively regulate the expression of PAP1-target genes, such as TRANSPARENT TESTA 8, DIHYDROFLAVONOL 4-REDUCTASE, and LEUKOANTHOCYANIDIN DIOXYGENASE. Our findings indicate that BZR1 functions as an integral component of the PAP1-containing transcription factor complex, contributing to increased anthocyanin biosynthesis. Notably, we also show that functional interaction of BZR1 with PAP1 is required for anthocyanin accumulation induced by low nitrogen stress. Taken together, our results demonstrate that BR-regulated BZR1 promotes anthocyanin biosynthesis through cooperative interaction with PAP1 of the MBW complex.

Genome-wide identification and expression analysis of the BZR gene family in Zanthoxylum armatum DC and functional analysis of ZaBZR1 in drought tolerance.

In this study, six ZaBZRs were identified in Zanthoxylum armatum DC, and all the ZaBZRs were upregulated by abscisic acid (ABA) and drought. Overexpression of ZaBZR1 enhanced the drought tolerance of transgenic Nicotiana benthamian. Brassinosteroids (BRs) are a pivotal class of sterol hormones in plants that play a crucial role in plant growth and development. BZR (brassinazole resistant) is a crucial transcription factor in the signal transduction pathway of BRs. However, the BZR gene family members have not yet been identified in Zanthoxylum armatum DC. In this study, six members of the ZaBZR family were identified by bioinformatic methods. All six ZaBZRs exhibited multiple phosphorylation sites. Phylogenetic and collinearity analyses revealed a closest relationship between ZaBZRs and ZbBZRs located on the B subgenomes. Expression analysis revealed tissue-specific expression patterns of ZaBZRs in Z. armatum, and their promoter regions contained cis-acting elements associated with hormone response and stress induction. Additionally, all six ZaBZRs showed upregulation upon treatment after abscisic acid (ABA) and polyethylene glycol (PEG), indicating their participation in drought response. Subsequently, we conducted an extensive investigation of ZaBZR1. ZaBZR1 showed the highest expression in the root, followed by the stem and terminal bud. Subcellular localization analysis revealed that ZaBZR1 is present in the cytoplasm and nucleus. Overexpression of ZaBZR1 in transgenic Nicotiana benthamiana improved seed germination rate and root growth under drought conditions, reducing water loss rates compared to wild-type plants. Furthermore, ZaBZR1 increased proline content (PRO) and decreased malondialdehyde content (MDA), indicating improved tolerance to drought-induced oxidative stress. The transgenic plants also showed a reduced accumulation of reactive oxygen species. Importantly, ZaBZR1 up-regulated the expression of drought-related genes such as NbP5CS1, NbDREB2A, and NbWRKY44. These findings highlight the potential of ZaBZR1 as a candidate gene for enhancing drought resistance in transgenic N. benthamiana and provide insight into the function of ZaBZRs in Z. armatum.

Jasmonate mimic modulates cell elongation by regulating antagonistic bHLH transcription factors via brassinosteroid signaling.

Lodging restricts growth, development, and yield formation in maize (Zea mays L.). Shorter internode length is beneficial for lodging tolerance. However, although brassinosteroids (BRs) and jasmonic acid (JA) are known to antagonistically regulate internode growth, the underlying molecular mechanism is still unclear. In this study, application of the JA mimic coronatine (COR) inhibited basal internode elongation at the jointing stage and repressed expression of the cell wall-related gene XYLOGLUCAN ENDOTRANSGLUCOSYLASE/HYDROLASE 1 (ZmXTH1), whose overexpression in maize plants promoted internode elongation. We demonstrated that the basic helix-loop-helix (bHLH) transcription factor ZmbHLH154 directly binds to the ZmXTH1 promoter and induces its expression, whereas the bHLH transcription factor ILI1 BINDING BHLH 1 (ZmIBH1) inhibits this transcriptional activation by forming a heterodimer with ZmbHLH154. Overexpressing ZmbHLH154 led to longer internodes, whereas zmbhlh154 mutants had shorter internodes than the wild type. The core JA-dependent transcription factors ZmMYC2-4 and ZmMYC2-6 interacted with BRASSINAZOLE RESISTANT 1 (ZmBZR1), a key factor in BR signaling, and these interactions eliminated the inhibitory effect of ZmBZR1 on its downstream gene ZmIBH1. Collectively, these results reveal a signaling module in which JA regulates a bHLH network by attenuating BR signaling to inhibit ZmXTH1 expression, thereby regulating cell elongation in maize.

BcBZR1 Regulates Leaf Inclination Angle in Non-Heading Chinese Cabbage (Brassica campestris ssp. chinensis Makino)

Brassinosteroids (BRs) play critical roles in plant growth by promoting cell elongation and division, leading to increased leaf inclination angles. BRASSINAZOLE RESISTANT 1 (BZR1) and BRI1-EMS-SUPPRESSOR 1 (BES1) act as transcription factors in the brassinosteroid signaling pathway and are involved in several physiological activities regulated by BRs. In this study, we identified and cloned BcBZR1 from the heitacai non-heading Chinese cabbage (NHCC) cultivar. The sequence analysis showed that the coding sequence length of BcBZR1 is 996 bp, encoding 331 amino acid residues. Subcellular localization assays showed that BcBZR1 is localized in the nucleus and cytoplasm and that BcBZR1 protein is transported to the nucleus after receiving BR signals. Compared with Col-0, the leaf inclination angle was smaller in BcBZR1-OX. The EBR treatment experiment indicated that BRs regulate the differential expression of paclobutrazol resistance1 (PRE1) and ILI1 binding bHLH1 (IBH1) in the adaxial and abaxial cells of the petiole through BZR1, thus regulating the leaf inclination angle. The bimolecular fluorescence complementation (BiFC) assay indicated that BcBZR1 interacts with C-repeat Binding Factor2 (BcCBF2) and CBF3. Taken together, our findings not only validate the function of BcBZR1 in leaf inclination angle distribution in non-heading Chinese cabbage, but also contribute to the mechanism of leaf inclination angle regulation in this species under cold stress.

Comprehensive investigation of BZR gene family in four dicots and the function of PtBZR9 and PtBZR12 under drought stress

Brassinazole-resistant (BZR) transcription factor plays an important role in plant growth and stress resistance through brassinosteroid (BR) signal transduction. However, systematic analysis of the BZR family in dicots remains limited. In this study, we conducted a genome-wide study of four typical dicots: Arabidopsis thaliana, Carica papaya, Vitis vinifera and Populus trichocarpa. Thirty-four BZR gene family members were identified and classified them into three subfamilies. Analysis of promoter and expression patterns revealed crucial role of a pair of homologous BZR genes, PtBZR9 and PtBZR12, in poplar may play a critical role under abiotic stress. PtBZR9 and PtBZR12 were localised in the nucleus and exhibited mutual interactions. Moreover, transient overexpression (OE) of PtBZR9 and PtBZR12 in poplar enhanced tolerance to drought stress. The phenotypic and physiological characteristics of PtBZR9 and PtBZR12 OE in Arabidopsis mirrored those of transient OE in the poplar. Additionally, PtBZR9 and PtBZR12 can bind to the E-box element. Under exogenous BR treatment, transgenic lines displayed a greater decrease in root length than the wild type. Thus, these findings provide a solid foundation for future research on the complex regulatory mechanisms of BZR genes.

HvGSK1.1 Controls Salt Tolerance and Yield through the Brassinosteroid Signaling Pathway in Barley.

Brassinosteroids (BRs) are a class of plant steroid hormones that are essential for plant growth and development. BRs control important agronomic traits and responses to abiotic stresses. Through the signaling pathway, BRs control the expression of thousands of genes, resulting in a variety of biological responses. The key effectors of the BR pathway are two transcription factors (TFs): BRASSINAZOLE RESISTANT 1 (BZR1) and BRI1-EMSSUPPRESSOR 1 (BES1). Both TFs are phosphorylated and inactivated by the Glycogen synthase kinase 3 BRASSINOSTEROID INSENSITIVE2 (BIN2), which acts as a negative regulator of the BR pathway. In our study, we describe the functional characteristics of HvGSK1.1, which is one of the GSK3/SHAGGY-like orthologs in barley. We generated mutant lines of HvGSK1.1 using CRISPR/Cas9 genome editing technology. Next Generation Sequencing (NGS) of the edited region of the HvGSK1.1 showed a wide variety of mutations. Most of the changes (frameshift, premature stop codon, and translation termination) resulted in the knock-out of the target gene. The molecular and phenotypic characteristics of the mutant lines showed that the knock-out mutation of HvGSK1.1 improved plant growth performance under salt stress conditions and increased the thousand kernel weight of the plants grown under normal conditions. The inactivation of HvGSK1.1 enhanced BR-dependent signaling, as indicated by the results of the leaf inclination assay in the edited lines. The plant traits under investigation are consistent with those known to be regulated by BRs. These results, together with studies of other GSK3 gene members in other plant species, suggest that targeted editing of these genes may be useful in creating plants with improved agricultural traits.

Genome-Wide Identification of BrassinaZole Resistant (BZR) Gene Family in Brassica rapa ssp. pekinensis and Its Expression Pattern During Flowering Process

The BrassinaZole Resistant (BZR) gene family mediates the signal transduction of brassinolide, which is vital in regulating vegetative and reproductive growth of plants. In this research, a comprehensive analysis of all candidate BrBZR genes in Chinese cabbage (Brassica rapa ssp. pekinensis) was conducted using bioinformatics methods, including protein physicochemical properties, evolutionary relationship, gene structure, and conserved domains. Additionally, these candidate genes’ expression patterns during flowering development were analyzed utilizing transcriptome data, and key genes that regulate flowering of Chinese cabbage were screened. In the results, 14 BrBZR genes were identified, with coding sequence (CDS) lengths of 460–1162 bp, and encoding proteins of 152–386 amino acids. The majority of BrBZRs had a highly conserved motif 1 as well as numerous regulatory elements associated with hormone and abiotic stress responses. Transcriptome sequencing showed that 12 BrBZRs were expressed during the flowering development, among which BrBES1.1 and BrBES1.2 were highly expressed, with FPKM ranges of 61.78–99.91 and 43.71–76.69, respectively. Their expression was upregulated during vernalization and flower bud differentiation, suggesting that they may play a key role in regulating the flowering process of Chinese cabbage. Overall, our study provides comprehensive insights into the BrBZR gene family, and has important implications for the further elucidation of the mechanisms that regulate flower development in Chinese cabbage and potentially other related Brassica species.

Transcription factors BZR2/MYC2 modulate brassinosteroid and jasmonic acid crosstalk during pear dormancy.

Bud dormancy is an important physiological process during winter. Its release requires a certain period of chilling. In pear (Pyrus pyrifolia), the abscisic acid (ABA)-induced expression of DORMANCY-ASSOCIATED MADS-box (DAM) genes represses bud break, whereas exogenous gibberellin (GA) promotes dormancy release. However, with the exception of ABA and GA, the regulatory effects of phytohormones on dormancy remain largely uncharacterized. In this study, we confirmed brassinosteroids (BRs) and jasmonic acid (JA) contribute to pear bud dormancy release. If chilling accumulation is insufficient, both 24-epibrassinolide (EBR) and methyl jasmonic acid (MeJA) can promote pear bud break, implying that they positively regulate dormancy release. BRASSINAZOLE RESISTANT 2 (BZR2), which is a BR-responsive transcription factor, inhibited PpyDAM3 expression and accelerated pear bud break. The transient overexpression of PpyBZR2 increased endogenous GA, JA, and JA-Ile levels. In addition, the direct interaction between PpyBZR2 and MYELOCYTOMATOSIS 2 (PpyMYC2) enhanced the PpyMYC2-mediated activation of Gibberellin 20-oxidase genes PpyGA20OX1L1 and PpyGA20OX2L2 transcription, thereby increasing GA3 contents and accelerating pear bud dormancy release. Interestingly, treatment with 5 μm MeJA increased the bud break rate, while also enhancing PpyMYC2-activated PpyGA20OX expression and increasing GA3,4 contents. The 100 μm MeJA treatment decreased the PpyMYC2-mediated activation of the PpyGA20OX1L1 and PpyGA20OX2L2 promoters and suppressed the inhibitory effect of PpyBZR2 on PpyDAM3 transcription, ultimately inhibiting pear bud break. In summary, our data provide insights into the crosstalk between the BR and JA signaling pathways that regulate the BZR2/MYC2-mediated pathway in the pear dormancy release process.

Vacuolar H+-ATPase and BZR1 form a feedback loop to regulate the homeostasis of BR signaling in Arabidopsis

Brassinosteroid (BR) is a vital plant hormone that regulates plant growth and development. BRASSINAZOLE RESISTANT 1 (BZR1) is a key transcription factor in BR signaling, and its nucleocytoplasmic localization is crucial for BR signaling. However, the mechanisms that regulate BZR1 nucleocytoplasmic distribution and thus the homeostasis of BR signaling remain largely unclear. The vacuole is the largest organelle in mature plant cells and plays a key role in maintenance of cellular pH, storage of intracellular substances, and transport of ions. In this study, we uncovered a novel mechanism of BR signaling homeostasis regulated by the vacuolar H+-ATPase (V-ATPase) and BZR1 feedback loop. Our results revealed that the vha-a2 vha-a3 mutant (vha2, lacking V-ATPase activity) exhibits enhanced BR signaling with increased total amount of BZR1, nuclear-localized BZR1, and the ratio of BZR1/phosphorylated BZR1 in the nucleus. Further biochemical assays revealed that VHA-a2 and VHA-a3 of V-ATPase interact with the BZR1 protein through a domain that is conserved across multiple species. VHA-a2 and VHA-a3 negatively regulate BR signaling by interacting with BZR1 and promoting its retention in the tonoplast. Interestingly, a series of molecular analyses demonstrated that nuclear-localized BZR1 could bind directly to specific motifs in the promoters of VHA-a2 and VHA-a3 to promote their expression. Taken together, these results suggest that V-ATPase and BZR1 may form a feedback regulatory loop to maintain the homeostasis of BR signaling in Arabidopsis, providing new insights into vacuole-mediated regulation of hormone signaling.

Genome-Wide Identification Reveals That BZR1 Family Transcription Factors Involved in Hormones and Abiotic Stresses Response of Lotus (Nelumbo)

The brassinazole-resistant (BZR) transcription factors (TFs) are key components of brassinosteroid (BR) signaling, which play an important role in regulating plant growth and development as well as responding to abiotic stress. However, a functional study of BZR transcription factors in lotuses has not been reported. A total 10 BZR1 genes (four NnBZR1 and six NlBZR1) were identified from the genomes of two lotus species (Nelumbo nucifera and Nelumbo lutea). The construction of the phylogenetic tree showed that the 10 BZR1 genes of the lotus were divided into four groups; the NnBZR1s and NlBZR1s were unevenly distributed on three and four chromosomes, respectively. Gene structure analysis showed that motif 1 and motif 9 are highly conserved in the lotus BZR1 protein, which might be related to the conserved domain BES_N of BZR1. The analysis of promoter cis-acting elements showed that the promoters of most of the BZR1 genes in the lotus contained elements related to light-responsive, ABA-responsive and abiotic stress-responsive factors, indicating that the BZR1 gene of the lotus played an important role in its response to abiotic stress. The responses of BZR1 genes to BR, ABA and four abiotic stresses (Cold, PEG6000, Cd and NaCl) were analyzed by qRT-PCR. The qRT-PCR results further verified that the lotus BZR1 genes play an important role in responding to hormone signals and resisting abiotic stress. This study laid the foundation for further research on the function of lotus BZR1 genes and provided a theoretical basis for future breeding and horticultural applications.

Genome-wide identification and functional characterization of wheat Brassinazole-resistant transcription factors in response to abiotic stresses and stripe rust infection.

Brassinazole-resistant (BZR) transcription factors (TFs) are key players in brassinolides (BRs) signaling pathway, which is widely involved in regulating plant growth and development, as well as in plant responding to a variety stresses. Despite their critical roles, little is known about BZR TFs in wheat. In this study, we performed genome-wide analysis of BZR gene family from wheat genome, and 20 TaBZRs were identified. Based on the phylogenetic relationships of TaBZR and BZRs from rice and Arabidopsis, all BZR genes were clustered into four groups. The intron-exon structural patterns and conserved protein motifs of TaBZRs showed high group specificity. TaBZR5, 7, and 9 were significantly induced after salt, drought treatment, and stripe rust infection. However, TaBZR16, which was significantly upregulated under NaCl application, was not expressed during wheat-stripe rust fungus interaction. These results indicated that BZR genes in wheat play different roles in response to various stresses. The results of this study will lay a foundation for further in-depth functional studies of TaBZRs and will provide information for the breeding and genetic improvement of wheat against drought and salt stresses.

The APETALA2a/DWARF/BRASSINAZOLE-RESISTANT 1 module contributes to carotenoid synthesis in tomato fruits.

Ethylene (ET) signaling plays a critical role in the ripening of climacteric fruits such as tomato. Brassinosteroids (BRs) were found to promote the ripening of both climacteric and non-climacteric fruits. However, the mechanism of interaction between ET and BRs during fruit ripening is unclear. Here, we found that BR synthesis and signaling increased after the onset of fruit ripening. Overexpression of the BR synthesis gene DWARF (DWF) promotedfruit softening, lycopene synthesis and ET production, whereas defect of DWF inhibited them. BRASSINAZOLE RESISTANT 1 (BZR1) as a key component of BR signaling, enhanced fruit lycopene content by directly activating the transcription of PSY1 gene. Interestingly, the increases in BR synthesis and BZR1 protein levels were dependent on ET signaling. Knocking out the ET-induced APETALA2a (AP2a) suppressed the expression of DWF and BR accumulation. Molecular assays demonstrated that AP2a was a positive regulator of DWF expression. Furthermore, 28-homobrassinolide, a bioactive BR, partially compensated the defects of lycopene accumulation and expression of PSY1 in ap2a mutant fruits. The results demonstrated that AP2a mediated ET signaling to regulate BR synthesis and signaling. BRs played critical roles in lycopene synthesis after onset of fruit ripening.

BZR proteins: identification, evolutionary and expression analysis under various exogenous growth regulators in plants.

The BRASSINAZOLE-RESISTANT (BZR) family of transcription factors affects a variety of developmental and physiological processes and plays a key role in multiple stress-resistance functions in plants. However, the evolutionary relationship and individual expression patterns of the BZR genes are unknown in various crop plants. In this study, we performed a genome-wide analysis of the BZR genes family in wheat and rice. Here, we found a total of 16 and 6 proteins containing the BZR domain in wheat and rice respectively. The phylogenetic analysis divided the identified BZR proteins from several plants into five subfamilies. The intron/exon structural patterns and conserved motifs distribution revealed that BZR proteins exhibite high specificities in each subfamily. Moreover, the co-expression and protein-protein interaction analysis suggested that BZR proteins may interact/co-expressed with several other proteins to perform various functions in plants. The presence of different stresses, hormones and light-responsive cis-elements in promoter regions of BZR genes imply its diverse functions in plants. The expression patterns indicated that many BZR genes regulate organ development and differentiation. BZR genes significantly respond to exogenous application of brassinosteroids, melatonin and abiotic stresses, demonstrating its key role in various developmental and physiological processes. The present study establishes the foundation for future functional genomics studies of BZR genes through reverse genetics and to further explore the potential of BZR genes in mitigating the stress tolerance in crop plants.

GhBZR3 suppresses cotton fiber elongation by inhibiting very-long-chain fatty acid biosynthesis.

SUMMARYThe BRASSINAZOLE‐RESISTANT (BZR) transcription factor is a core component of brassinosteroid (BR) signaling and is involved in the development of many plant species. BR is essential for the initiation and elongation of cotton fibers. However, the mechanism of BR‐regulating fiber development and the function of BZR is poorly understood in Gossypium hirsutum L. (cotton). Here, we identified a BZR family transcription factor protein referred to as GhBZR3 in cotton. Overexpression of GhBZR3 in Arabidopsis caused shorter root hair length, hypocotyl length, and hypocotyl cell length, indicating that GhBZR3 negatively regulates cell elongation. Pathway enrichment analysis from VIGS‐GhBZR3 cotton plants found that fatty acid metabolism and degradation might be the regulatory pathway that is primarily controlled by GhBZR3. Silencing GhBZR3 expression in cotton resulted in taller plant height as well as longer fibers. The very‐long‐chain fatty acid (VLCFA) content was also significantly increased in silenced GhBZR3 plants compared with the wild type. The GhKCS13 promoter, a key gene for VLCFA biosynthesis, contains two GhBZR3 binding sites. The results of yeast one‐hybrid, electrophoretic mobility shift, and luciferase assays revealed that GhBZR3 directly interacted with the GhKCS13 promoter to suppress gene expression. Taken together, these results indicate that GhBZR3 negatively regulates cotton fiber development by reducing VLCFA biosynthesis. This study not only deepens our understanding of GhBZR3 function in cotton fiber development, but also highlights the potential of improving cotton fiber length and plant growth using GhBZR3 and its related genes in future cotton breeding programs.

Behavior and possible function of Arabidopsis BES1/BZR1 homolog 2 in brassinosteroid signaling

ABSTRACT Two key transcription factors (TFs) in brassinosteroid (BR) signaling BRASSINOSTEROID INSENSITIVE 1-EMS-SUPPRESSOR 1 (BES1) and BRASSINAZOLE RESISTANT 1 (BZR1), belong to a small family with four BES1/BZR1 homologs (BEH1–4). To date, in contrast to the wealth of knowledge regarding BES1 and BZR1, little is known about BEH1–4. Here, we show that BEH2 was expressed preferentially in the roots and leaf margins including serrations, which was quite different from another member BEH4, and that BRs downregulated BEH2 through a module containing GSK3-like kinases and BES1/BZR1 TFs, among which BES1, rather than BZR1, contributed to this process. In addition, BEH2 consistently existed in the nucleus, suggesting that its subcellular localization is not under BR-dependent nuclear-cytoplasmic shuttling control. Furthermore, gene ontology analysis on RNA-seq data indicated that BEH2 may be implicated in stress response and photosynthesis. These findings might assist in the future elucidation of the molecular mechanisms underlying BR signaling.

Citrus FRIGIDA cooperates with its interaction partner dehydrin to regulate drought tolerance.

Drought is a major environmental stress that severely affects plant growth and crop productivity. FRIGIDA (FRI) is a key regulator of flowering time and drought tolerance in model plants. However, little is known regarding its functions in woody plants, including citrus. Thus, we explored the functional role of the citrus FRI ortholog (CiFRI) under drought. Drought treatment induced CiFRI expression. CiFRI overexpression enhanced drought tolerance in transgenic Arabidopsis and citrus, while CiFRI suppression increased drought susceptibility in citrus. Moreover, transcriptomic profiling under drought conditions suggested that CiFRI overexpression altered the expression of numerous genes involved in the stress response, hormone biosynthesis, and signal transduction. Mechanistic studies revealed that citrus dehydrin likely protects CiFRI from stress-induced degradation, thereby enhancing plant drought tolerance. In addition, a citrus brassinazole-resistant (BZR) transcription factor family member (CiBZR1) directly binds to the CiFRI promoter to activate its expression under drought conditions. CiBZR1 also enhanced drought tolerance in transgenic Arabidopsis and citrus. These findings further our understanding of the molecular mechanisms underlying the CiFRI-mediated drought stress response in citrus.

The CCCH zinc finger protein C3H15 negatively regulates cell elongation by inhibiting brassinosteroid signaling.

Plant CCCH proteins participate in the control of multiple developmental and adaptive processes, but the regulatory mechanisms underlying these processes are not well known. In this study, we showed that the Arabidopsis (Arabidopsis thaliana) CCCH protein C3H15 negatively regulates cell elongation by inhibiting brassinosteroid (BR) signaling. Genetic and biochemical evidence showed that C3H15 functions downstream of the receptor BR INSENSITIVE 1 (BRI1) as a negative regulator in the BR pathway. C3H15 is phosphorylated by the GLYCOGEN SYNTHASE KINASE 3 -like kinase BR-INSENSITIVE 2 (BIN2) at Ser111 in the cytoplasm in the absence of BRs. Upon BR perception, C3H15 transcription is enhanced, and the phosphorylation of C3H15 by BIN2 is reduced. The dephosphorylated C3H15 protein accumulates in the nucleus, where C3H15 regulates transcription via G-rich elements (typically GGGAGA). C3H15 and BRASSINAZOLE RESISTANT 1 (BZR1)/BRI1-EMS-SUPPRESSOR 1 (BES1), two central transcriptional regulators of BR signaling, directly suppress each other and share a number of BR-responsive target genes. Moreover, C3H15 antagonizes BZR1 and BES1 to regulate the expression of their shared cell elongation-associated target gene, SMALL AUXIN-UP RNA 15 (SAUR15). This study demonstrates that C3H15-mediated BR signaling may be parallel to, or even attenuate, the dominant BZR1 and BES1 signaling pathways to control cell elongation. This finding expands our understanding of the regulatory mechanisms underlying BR-induced cell elongation in plants.

Genome-Wide Prediction, Functional Divergence, and Characterization of Stress-Responsive BZR Transcription Factors in B. napus.

BRASSINAZOLE RESISTANT (BZR) are transcriptional factors that bind to the DNA of targeted genes to regulate several plant growth and physiological processes in response to abiotic and biotic stresses. However, information on such genes in Brassica napus is minimal. Furthermore, the new reference Brassica napus genome offers an excellent opportunity to systematically characterize this gene family in B. napus. In our study, 21 BnaBZR genes were distributed across 19 chromosomes of B. napus and clustered into four subgroups based on Arabidopsis thaliana orthologs. Functional divergence analysis among these groups evident the shifting of evolutionary rate after the duplication events. In terms of structural analysis, the BnaBZR genes within each subgroup are highly conserved but are distinctive within groups. Organ-specific expression analyses of BnaBZR genes using RNA-seq data and quantitative real-time polymerase chain reaction (qRT-PCR) revealed complex expression patterns in plant tissues during stress conditions. In which genes belonging to subgroups III and IV were identified to play central roles in plant tolerance to salt, drought, and Sclerotinia sclerotiorum stress. The insights from this study enrich our understanding of the B. napus BZR gene family and lay a foundation for future research in improving rape seed environmental adaptability.