Auxin receptors: a new role for F-box proteins

The plant hormone auxin regulates transcription by promoting the degradation of a family of transcriptional repressors called Aux/IAA proteins. Genetic and biochemical studies have shown that this degradation is dependent on a ubiquitin protein ligase called SCFTIR1. In the presence of auxin, the F-box protein TIR1 binds to the Aux/IAA proteins, resulting in their ubiquitination and degradation. Recent attention has focused on the nature of the auxin receptor and upstream signaling events involved in this process. Now, two recent papers demonstrate that auxin binds directly to TIR1 and promotes the interaction with the Aux/IAA proteins. Furthermore, TIR1 functions together with at least three other related F-box protein/receptors to mediate the auxin response throughout plant growth and development.