The mechanism and network of BES1 mediated transcriptional regulation in Brassinosteroids (BR) pathway in Arabidopsis

Brassinosteroids (BRs) are a family of steroid hormones present ubiquitously in plant kingdoms and play important roles throughout plant growth and development. BRs signal to regulate BES1 and BZR1 family transcription factors, which regulate target genes for various BR responses. However, our knowledge about the transcriptional network and mechanisms through which BES1 regulates gene expression is still limited. Background information about BR signaling and transcriptional regulation is presented in Chapter 1.;The goal of my research is to understand the mechanism and network for BES1 mediated transcription regulation using both forward and reverse genetics, as well as genomic approaches. Specifically, my thesis includes three main projects I have worked on. Chapter 2 is about the transcription factor AtMYB30 that was identified as BR-induced transcription factor. I found that AtMYB30 is a BES1 direct target and meanwhile its protein helps BES1 to activate downstream target genes. Chapter 3 describes the discovery of a novel transcription elongation factor AtIWS1 required for BES1-regulated gene expression, which was identified by a forward genetics screen. In chapter 4, I describe a collaborative project in which we used chromatin immunoprecipitation coupled with tiling arrays (ChIP-chip), global gene profiling, as well as computational modeling to construct and validate a BR-transcriptional network. Finally, conclusions and future directions are summarized in chapter 5.