Auxin is a phytohormone involved in almost every aspect of plant growth and development, and there is a well established model for how auxin signalling occurs within a cell.
This “canonical” pathway functions because transcription factors, known as auxin response factors (ARFs) are bound by AUX/IAA repressor proteins via a C-terminal protein:protein interaction domain in the absense of auxin, preventing them from altering gene expression.
In the presence of auxin, these repressors are degraded, and the transcription of auxin responsive genes is activated.
An atypical auxin response factor called ETTIN lacks the C-terminal domain required to interact with AUX/IAA proteins and has been shown to respond to auxin independently of the canonical pathway.
ETTIN binds to transcription factors from many different families in an auxin sensitive manner, with auxin inhibiting these interactions. It also interacts with the co-repressor topless and other chromatin remodelling proteins to regulate gene expression in response to auxin.
The main focus of Heather’s PhD project is to understand how these two auxin signalling pathways work together during development, particularly in the gynoecium (the female reproductive structure of flowering plants), whose patterning is dependent on proper auxin mediated signalling.