Genetic Biochemical Studies of Plant Steroid Signaling

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The long-term goal of this project is to understand the molecular networks through which hormones, environmental factors, and nutrients together control plant growth and development. Plants have evolved robust cellular signaling systems to regulate growth and metabolism according to internal status and environmental conditions. Dissecting these plant regulatory systems is important not only for food security and environmental sustainability, but also for understanding cellular regulation in general, as many mechanisms are highly conserved in animals and plants. This research program focuses on the cellular signaling and regulatory network impinged upon by the steroid hormone brassinosteroid (BR), a major growth-promoting hormone that impact a wide range of developmental and physiological processes. Using a combination of genetic, genomic, biochemical, and proteomic approaches in the Arabidopsis model system, we have elucidated molecular mechanisms by which BR binding to receptor kinase BRI1 leads to activation of transcription factor BZR1 through the evolutionarily conserved BSU1 family of phosphatases and GSK3-like kinases. Furthermore, we have revealed at molecular level how the BR signaling pathway is integrated with many other signaling pathways into regulatory networks that control gene transcription program driving cell elongation and various specific developmental programs. Our ongoing research has uncovered many posttranslational mechanisms by which BR signaling directly modulates cellular reorganization and metabolic programs through direct protein- protein interactions and posttranslational modifications. We proposed to focus on these mechanisms that link signaling pathways with major cellular activities such as membrane trafficking, cell division, and carbon metabolism. In addition, we will investigate how BR signaling cross talks with other signaling pathways to balance metabolism with growth demand and to program cellular differentiation in plant development. The research outlined in this proposal will continue to significantly advance our understanding of the molecular mechanisms of cellular signal integration and information processing.