The plant hormone auxin is a key regulator of multiple cellular and developmental responses in plants including cell division, expansion, and differentiation; patterning of embryos, vasculature and other tissues; and distribution of growth between primary and lateral root and shoot meristems. This multiplicity of regulatory activities has spurred considerable interest in mechanisms of auxin signaling and response. We use techniques of genetics, molecular biology, microscopy, physiology, and biochemistry to study signal transduction pathways by which auxin regulates plant development. For these studies we use the model plant Arabidopsis thaliana, which has numerous technical advantages (including a completely sequenced genome) that allow rapid experimental progress.

Auxin acts largely by regulating gene expression. A family of proteins called ARFs bind to promoters of auxin-responsive genes and regulate their expression, and proteins of a second family called Aux/IAA can dimerize with ARFs and also thereby affect gene expression. To reveal the roles of these proteins in development, we are characterizing phenotypes of plants with mutations in genes encoding ARF and Aux/IAA proteins. We are also using these mutants in global gene expression studies to identify regulatory targets of ARF and Aux/IAA proteins, and studying functions of these target genes by reverse genetic methods. To understand how auxin signaling pathways might regulate Aux/IAA or ARF protein function, we are studying interactions among these proteins, and their modification and stability in plant extracts under different conditions. We are exploring how environmental light signals modulate auxin signaling pathways using similar methods. A particular focus is whether auxin or light regulates turnover or some other activity of Aux/IAA proteins, and whether these proteins are modified (for example by phosphorylation) after perception of one of these signals.