Auxin is an important plant hormone involved in virtually all aspects of plant development. In the canonical auxin signalling pathway, auxin response factors (ARFs) that mediate gene expression are repressed through interactions with a corepressor complex when auxin is absent.
The binding of auxin to its receptor leads to the sequestration and degradation of the corepressor complex, thus freeing the ARFs from repression.
ETTIN (ETT), also known as ARF3, is an atypical ARF that lacks the domain required for interaction with the corepressor complex, thus excluding it from participating in the canonical pathway.
Nonetheless, the Ostergaard lab has shown that ETT itself can bind auxin and participates in a non-canonical auxin signalling mechanism. This novel signalling pathway has been shown to be important for the development of the gynoecium in the model plant Arabidopsis thaliana.
Phylogenetic analyses suggests that ETT-like ARFs have existed since the divergence of ferns and seed plants from the bryophytes, and further diversified within the seed plants to acquire domains and motifs thought to be important for its biochemical function.
Part of Aaron’s research focuses on elucidating the molecular mechanism behind the ETT-mediated auxin signalling pathway, e.g. protein-protein interactions and target genes regulated by ETT in an auxin-dependent manner.
Another aspect of his research aims to uncover the evolutionary origin of ETT and its role in leaf and gynoecium development, by studying ETT-like orthologues in species from key phylogenetic lineages, such as the bryophyte Marchantia polymorpha, the fern Ceratopteris richardii, and the basal angiosperm Nymphaea thermarum.