Seminars

Plants are captives of their environment and as a consequence, must adapt to changing environmental conditions. We are interested in identifying and characterizing the role the ubiquitin modification system plays in plant adaptation to their environment.  Ubiquitin is a protein modifier of other proteins. We are also interested in understanding the specificity and regulation of the ubiquitin attachment in plants.  We use the higher plant model organism, Arabidopsis thaliana for these studies.  The ubiquitin pathway plays key roles in regulating the abundance of transcription factors in all eukaryotes. In plants, this includes transcription factors important for sensing the environment and in responding to developmental changes.  We focused on the degradation of transcription factors important in the response to the stress hormone ABA (ABFs and ABI5) and the Aux/IAA proteins that function in auxin signaling.  ABFs/ABI5 are positive regulators of the ABA response, while Aux/IAA proteins function to repress auxin responses.  Using proteins fusions or epitope-tagged proteins in transgenic plants, we demonstrated that Aux/IAA proteins are very short-lived and their degradation is accelerated with increasing auxin.  In contrast, ABFs have moderate stabilities, and their degradation is slowed by exogenous ABA.

We are also studying members of the RING family of ubiquitin ligases.  These are large gene families in all organisms, and the function of many specific E3s is unknown.  We are characterizing RING-type E3s using reverse genetics, cell biology and in vitro biochemistry.  We are studying a small family responsible for regulating amino acid homeostasis, a ligase important for ABA responses and a heteromeric E3 ligase that is required for seed germination. All together, these studies will aid in our understanding of how the ubiquitin pathway regulates plant responses to their environment.