Auxin signaling and regulated protein degradation.

Auxin regulates many aspects of plant growth and development. Auxin is known to regulate gene expression through degradation of the AUX/IAA proteins, short-lived nuclear proteins that regulate gene transcription. The AUX/IAA proteins are degraded through the action of a ubiquitin protein ligase called SCF. Auxin promotes the interaction between AUX/IAA proteins and SCF in a soluble extract, suggesting that the auxin receptor is a soluble factor. These studies also indicate that the auxin-induced AUX/IAA–SCF interaction does not depend on phosphorylation or hydroxylation of AUX/IAA proteins. Although the mechanism of auxin-induced AUX/IAA– SCF interaction is not yet clear, auxin might induce a modification in TIR1, AUX/IAA proteins or an adaptor protein that is required for the interaction.