Final answer:
Auxin prevents Aux/IAA proteins from stopping gene expression by promoting their degradation through the ubiquitin-proteasome pathway.
Step-by-step explanation:
Auxin prevents Aux/IAA proteins from stopping gene expression by promoting their degradation through the ubiquitin-proteasome pathway. When auxin levels are high, auxin binds to a receptor protein called TIR1, which then recruits Aux/IAA proteins. This complex is targeted for degradation, allowing transcription factors called ARFs to activate gene expression.
For example, in the presence of auxin, Aux/IAA proteins are ubiquitinated, which marks them for degradation by the 26S proteasome. This degradation releases transcription factors called ARFs, which can then bind to target gene promoters and activate gene expression.