Brassinosteroids (BRs) play important roles in plant growth, development and responses to environmental cues. BRs signal through plasma membrane-localized receptors to control BES1/BZR1 family transcription factors, which mediate the expression of thousands of genes. BRs activate and repress approximately equal numbers of genes. BES1/BZR1 interact with other transcription factors, histone-modifying enzymes, and transcription elongation factors to activate BR-induced genes. However, the mechanisms by which BES1/BZR1 mediate the BR-repressed gene expression are not well understood. Recent studies revealed that 2 BR-repressed transcription factors, MYBL2 and HAT1, cooperate with BES1 to downregulate BR-repressed genes expression. Moreover, BIN2 kinase, a well-established negative regulator in the BR signaling pathway, phosphorylates MYBL2 and HAT1. While BIN2 phosphorylates and destabilizes BES1/BZR1, BIN2 phosphorylated MYBL2 and HAT1 appear to be stabilized. These results not only extended our understanding of BR-repressed gene expression, but also revealed multiple inputs of BR signaling into BR transcriptional networks.
Keywords: Arabidopsis thaliana; BES1; BIN2; Brassinosteroids; HAT1; MYBL2; phosphorylation; protein stability; signaling.