Brassinosteroids (BRs) are a group of steroid hormones regulating plant growth and development. Since BRs do not undergo transport among plant tissues, their metabolism is tightly regulated by transcription factors (TFs) and feedback loops. BAS1 (CYP734A1, formerly CYP72B1) and SOB7 (CYP72C1) are two BR-inactivating cytochrome P450s identified in Arabidopsis thaliana. We previously found that a TF ATAF2 (ANAC081) suppresses BAS1 and SOB7 expression by binding to the Evening Element (EE) and CIRCADIAN CLOCK ASSOCIATED 1 (CCA1)-binding site (CBS) on their promoters. Both the EE and CBS are known binding targets of the circadian regulatory protein CCA1. Here, we confirm that CCA1 binds the EE and CBS motifs on BAS1 and SOB7 promoters, respectively. Elevated accumulations of BAS1 and SOB7 transcripts in the CCA1 null mutant cca1-1 indicate that CCA1 is a repressor of their expression. When compared with either cca1-1 or the ATAF2 null mutant ataf2-2, the cca1-1 ataf2-2 double mutant shows higher SOB7 transcript accumulations and a stronger BR-insensitive phenotype of hypocotyl elongation in white light. CCA1 interacts with ATAF2 at both DNA-protein and protein-protein levels. ATAF2, BAS1, and SOB7 are all circadian regulated with distinct expression patterns. These results demonstrate that CCA1 and ATAF2 differentially suppress BAS1- and SOB7-mediated BR inactivation.

中文翻译：

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CIRCADIAN CLOCK关联1和ATAF2差异抑制细胞色素P450介导的油菜素甾体失活。

油菜素类固醇（BRs）是一组类固醇激素，可调节植物的生长和发育。由于BR不会在植物组织之间进行运输，因此它们的代谢受到转录因子（TF）和反馈环的严格调控。BAS1（CYP734A1，以前为CYP72B1）和SOB7（CYP72C1）是在拟南芥中鉴定的两种BR失活细胞色素P450。我们之前发现，TF ATAF2（ANAC081）通过与启动子上的晚元素（EE）和CIRCADIAN CLOCK ASSOCIATED 1（CCA1）结合位点（CBS）结合来抑制BAS1和SOB7的表达。EE和CBS都是昼夜节律调节蛋白CCA1的已知结合靶标。在这里，我们确认CCA1分别绑定BAS1和SOB7启动子上的EE和CBS基序。在CCA1空突变体cca1-1中BAS1和SOB7转录本的累积积累表明，CCA1是其表达的阻遏物。当与cca1-1或ATAF2空突变体ataf2-2比较时，cca1-1 ataf2-2双突变体在白光下显示出更高的SOB7转录物积累和下胚轴伸长的更强的BR不敏感表型。CCA1在DNA-蛋白质和蛋白质-蛋白质水平上均与ATAF2相互作用。ATAF2，BAS1和SOB7均由昼夜节律调节，并具有不同的表达模式。这些结果表明，CCA1和ATAF2差异性抑制BAS1和SOB7介导的BR失活。cca1-1 ataf2-2双突变体在白光下显示出更高的SOB7转录物积累和下胚轴伸长的更强的BR不敏感表型。CCA1在DNA-蛋白质和蛋白质-蛋白质水平上均与ATAF2相互作用。ATAF2，BAS1和SOB7均由昼夜节律调节，并具有不同的表达模式。这些结果表明，CCA1和ATAF2差异性抑制BAS1和SOB7介导的BR失活。cca1-1 ataf2-2双突变体在白光下显示出更高的SOB7转录物积累和下胚轴伸长的更强的BR不敏感表型。CCA1在DNA-蛋白质和蛋白质-蛋白质水平上均与ATAF2相互作用。ATAF2，BAS1和SOB7均由昼夜节律调节，并具有不同的表达模式。这些结果表明，CCA1和ATAF2差异性抑制BAS1和SOB7介导的BR失活。