The role of regulated protein degradation in auxin response

Auxin-regulated gene expression is mediated by two families of transcription factors. The ARF proteins bind to a conserved DNA sequence called the AuxRE and activate transcription. The Aux/IAA proteins repress ARF function, presumably by forming dimers with ARF proteins. Recent genetic studies in Arabidopsis indicate that auxin regulates this system by promoting the ubiquitin-mediated degradation of the Aux/IAA proteins, thus permitting ARF function. Mutations in components of SCFTIR1, a ubiquitin protein ligase (E3) result in stabilization of Aux/IAA proteins and decreased auxin response. Further, recent biochemical experiments indicate that the Aux/IAA proteins bind SCFTIR1 in an auxin-dependent manner.