As an important plant hormone, auxin regulates nearly all
the developmental processes. The IAA functions as ‘molecular
glue’ to mediate the interaction between the auxin receptors
(F-box proteins encoded by the TIR1 gene family) and AUX/IAA
proteins. The interaction between TIR1 and AUX/IAAs leads to
ubiquitylation and degradation of AUX/IAA proteins, which
release the transcription activity of ARF proteins to activate/suppress
the expression of auxin-responsive genes. At least genes
within three gene families are induced by auxin: the AUX/IAA,
GH3, and the small auxin-up RNA (SAUR)