The plant hormone auxin has been implicated in virtually every stage of plant growth and development from embryogenesis to senescence. My laboratory is using the genetically tractable plant Arabidopsis thaliana to identify and characterize auxin response pathways. Our work has shown that auxin promotes the rapid degradation of a family of transcriptional repressors called the Aux/IAA proteins via the ubiquitin proteasome pathway. Auxin interacts directly with a ubiquitin protein ligase called SCFTIR1, and promotes an interaction between the E3 and the Aux/IAAs. We are now studying the mechanism SCFTIR1 action and the role of the complex in various aspects of plant growth. In addition, we are turning our attention to the complex transcriptional networks that mediate auxin growth responses. Our ultimate goal is to understand the systems that mediate auxin-dependent development at the level of the cell and organism.