Plant steroid hormones, Brassinosteroids (BRs), play important roles in plant growth, development and response to environmental stresses. BRs act through several signaling components to regulate BES1/BZR1 and other families of transcription factors (TFs), which in turn control the expression of about 4000 genes required for various BR responses. How BR-regulated TFs control the expression of the large number of target genes and various BR responses is not well defined and will be the main focus of the proposal. The functions and mechanisms of several BR-regulated transcription factors (proteins responsible for activating or inactivating genes) will be studied by reverse genetic and genomic approaches and their regulation by BR signaling will be investigated by biochemical experiments. The results will reveal how each of the BR-regulated TFs controls a subset of BR target genes and a portion of BR responses. The studies will also provide important insight into how BR signal is integrated into the complex transcriptional network to control various BR-regulated processes. The knowledge obtained can be used to design strategies to improve the crop yield and tolerance to environmental stresses. Both mutants and transgenic lines generated from the project will be made available through the Arabidopsis Information Resource. In addition, the large-scale gene expression data will be deposited into NASC Arrays or GEO Datasets for wide dissemination. The proposed research will generate new knowledge that is essential for agriculture and bioenergy, especially under the constant environmental changes. In addition, a graduate student, research assistant and high school teacher will be trained to carry out the proposed experiments as a coordinated and cohesive team. The high school biology teacher will also be trained to bring some of the BR mutants to high school biology classes. The proposal, therefore, has a great potential in training future scientists and educators.
Intellectual merit: Plant steroid hormone called brassinosteroid (BR) can increase plant growth and help plants deal with environmental stresses and various plant pathogens. Understanding how BR functions thus has important application in increasing crop yield, especially under adverse environmental conditions. BR acts through several signaling components including receptor BRI1 and a negatively-acting kinase BIN2 to control BES1/BZR1 family transcription factors, which regulate thousands of genes responsible for plant growth and plant responses to stress conditions. BR is known to regulate about 5,000 genes (activates and represses about 2,500 each) in model plant Arabdopsis thaliana, but the mechanisms by which BES1/BZR1 regulates the large number of genes are not well defined. The goal of this proposal is to define the mechanisms of BR-regulated gene expression, especially on how BES1 represses gene expression in the model plant. It has been found that BES1 cooperates with other BR-regulated transcription factors such as MYBL2 and HAT1 to inhibit the expression of BR-repressed genes and facilitate optimal plant growth. In addition, MYBL2 and HAT1 are both phosphorylated by BIN2 kinase and phosphorylated MYBL2 and HAT1 are stabilized, which is in contrast with BES1 that is destabilized by BIN2 phosphorylation. These results not only revealed new mechanisms of BR-regulated gene expression, but also provided new insight into the integration of BR signaling and BRtranscriptional network. Since both MYBL2 and HAT1 are also implicated in responses to stress and light conditions, the knowledge from these studies can be used to manipulate specific sets of genes required for optimal plant growth under certain environmental conditions. Broader impact: The NSF award provided excellent opportunities to train next generation plant scientists. The experiments were carried out by graduate and undergraduate students under the supervision of the principal investigator and staff scientist. The undergraduate student worked in the laboratory was coauthor for scientific publications and is now in graduate school to pursue Ph.D. degree in plant biology. In addition, a high school teacher worked in the summer in the laboratory to learn the modern genetic and genomic approaches, which enriches high school science education. The research results were also widely dissimilated to scientific community through peer-reviewed scientific publications and both oral and poster presentations at science conferences.
