The Role of Brassinosteroid Inactivation in Plant Development

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Brassinosteroids are growth-promoting hormones involved in modulating plant development in response to changes in the environment. Most brassinosteroid investigations using the model plant Arabidopsis have concentrated on either the biosynthesis of these hormones or on the receptor-mediated signaling pathways. Previous research undertaken by the PI has focused on the brassinosteroid-inactivating enzymes, CYP734A1 and CYP72C1 and demonstrated that an important mode of regulating the level of these hormones is achieved through inactivation. Genetic analysis demonstrates that these enzymes act together to regulate many aspects of plant development. Biochemical analysis demonstrates that these two enzymes inactivate brassinosteroids, doing so via different mechanisms. In this project, a biochemical approach will be taken to test the hypothesis that CYP734A1 binds multiple active brassinosteroids, doing so with different affinities. Similar approaches will be used to test the hypothesis that CYP72C1 inactivates brassinosteroids via a different biochemical mechanism than CYP734A1. Molecular-genetic analysis will be used to test the hypothesis that CYP734A1 and CYP72C1 have overlapping as well unique roles in plant development. Similar approaches will be used to test the hypothesis that the CYP734A1- and CYP72C1-mediated brassinosteroid-inactivation pathway interacts with another brassinosteroid-inactivating enzyme, UCG73C5. These studies will help reveal the mechanisms regulating brassinosteroid inactivation and how this process affects many aspects of plant development. Findings from this project will impact multiple areas of research including studies of: plant development, brassinosteroids and other plant hormones, enzyme function, and synergistic/redundant genetic interactions. These studies will contribute directly to the education of a Ph.D. student, a postdoc, undergraduates and high school students.