The mechanisms that specify BZR1’s function in transcription activation and repression are not understood.īZR1 is a plant-specific transcription factor with a DNA-binding domain that recognizes BR response element (CGTG(T/C)G) 5. BZR1 activates and represses different target genes to programme genome expression and cell growth.
BRI1 signalling activates the members of the brassinazole resistant1 (BZR1) family of transcription factors through a phosphorylation-mediated signal transduction pathway 3, 4. Unlike animal steroid hormones, which directly bind to nuclear receptor transcription factors, the plant steroid hormone brassinosteroid (BR) binds to a transmembrane receptor kinase, brassinosteroid insensitive1 (BRI1) 1, which has a leucine-rich repeat extracellular domain similar to the Toll receptors in metazoans 2. Steroids are important hormones for regulation of gene expression and development in both animals and plants. Our study demonstrates key roles of the EAR motif and TPL in BR regulation of gene expression and plant growth. BR repression of gene expression also requires histone deacetylases that interact with TPL. A triple tpl mutant ( tpl tpr1 tpr4) shows reduced BR sensitivity and suppresses the gain-of-function bzr1-1D mutant phenotype. The EAR motif in BZR1 mediates recruitment of TPL to BZR1-repressed promoters. Specific deletion or mutation of an evolutionarily conserved ERF-associated amphiphilic repression (EAR) motif at the carboxy terminus abolishes BZR1’s abilities to regulate gene expression and cell elongation, but these defects are rescued by TPL fusion to the EAR motif-mutated BZR1. Here we show that BZR1 represses target genes by recruiting the Groucho/TUP1-like transcriptional corepressor TOPLESS (TPL). The mechanisms that determine BZR1’s transcriptional activities remain largely unknown. Brassinosteroid (BR) regulates plant development by activating the transcription factor brassinazole resistant 1 (BZR1), which activates and represses different target genes to switch cellular programmes.
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