Auxin Receptors and Plant Development: A New Signaling Paradigm

The plant hormone auxin, in particular indole-3-acetic acid (IAA), is a key regulator of virtually every aspect of plant growth and development. Auxin regulates transcription by rapidly modulating levels of Aux/IAA proteins throughout development. Recent studies demonstrate that auxin perception occurs through a novel mechanism. Auxin binds TIR1, the F-box subunit of the ubiquitin ligase complex SCFTIRI, and stabilizes the interaction between TIR1 and Aux/IAA substrates. This interaction results in Aux/IAA ubiquitination and subsequent degradation. Regulation of the Aux/IAA protein family by TIR1 and TIR1-like Auxin receptors (AFBs) links auxin action to transcriptional regulation and provides model by which the vast array of auxin influences on development. May be understood. Moreover, auxin receptor function is the first example of small molecule regulation of an SCF uibiquitin ligase and may have important implications for studies of regulated protein degradation in other species, including animals.