Auxin-induced degradation dynamics and plant development

Development requires cells to send and receive information, often in the form of small molecules or peptides. An emerging theme in biology is that information can be encoded in the dynamics of signaling, not just in the relative abundance of signaling molecules. In plants, response to the hormone auxin is a useful tool for studying the role that signal dynamics play in development. Auxin triggers degradation of an Aux/IAA repressor protein, which activates transcription of a large number of genes. Auxin facilitates Aux/IAA degradation by mediating interaction between Aux/IAAs and auxin receptors called TIR1/AFBs. Each component in the auxin signaling pathway belongs to a gene family, and different family members play distinct roles throughout development. Our work building a synthetic auxin response system in yeast revealed that Aux/IAAs exhibit a range of degradation rates. I hypothesized that these IAA degradation rates act as biological pacemakers to coordinate developmental processes. To test this, I characterized the effect of altered rates of Aux/IAA degradation on lateral root initiation. These studies demonstrate that Aux/IAA degradation dynamics determine the rate of progression through lateral root development in Arabidopsis. This work has revealed a molecular connection between the dynamics of auxin signaling and the dynamics of organogenesis, supporting the hypothesis that the Aux/IAAs act as auxin-induced pacemakers in plant development.