Brassinosteroids control male fertility by regulating the expression of key genes involved in <i>Arabidopsis</i> anther and pollen development

The development of anther and pollen is important for male reproduction, and this process is coordinately regulated by many external and internal cues. In this study, we systematically examined the male reproductive phenotypes of a series of brassinosteroid biosynthetic and signaling mutants and found that, besides the expected cell-expansion defects, these mutants also showed reduced pollen number, viability, and release efficiency. These defects were related with abnormal tapetum and microspore development. Using both real-time quantitative RT-PCR and microarray experiments, we found that the expression of many key genes required for anther and pollen development was suppressed in these mutants. ChIP analysis demonstrated that BES1, an important transcription factor for brassinosteroid signaling, could directly bind to the promoter regions of genes encoding transcription factors essential for anther and pollen development, SPL/NZZ, TDF1, AMS, MS1, and MS2. Taken together, these data lead us to propose that brassinosteroids control male fertility at least in part via directly regulating key genes for anther and pollen development in Arabidopsis. Our work provides a unique mechanism to explain how a phytohormone regulates an essential genetic program for plant development.