The phytohormone auxin, is implicated in gynoecium development. Auxin response mainly depends on two protein families: ARFs (Auxin Response Factors) and Aux/IAAs. ARFs are transcription factors that regulate the transcription of auxin responsive genes, whereas Aux/IAAs inhibit the ARFs transcriptional activity by dimerization. In the presence of auxin, Aux/IAAs are degraded and consequently, ARFs are released. During my thesis, I focused on two close paralogs ETTIN/ARF3 and ARF4 involved in gynoecium development in Arabidopsis thaliana. Among the direct targets of ETT identified in the team, two categories held attention: genes involved in auxin signaling and genes encoding enzymes involved in cell wall remodeling. The aim of my project was to understand the implication of these transcriptional regulations in gynoecium development. In a first part, I analyzed auxin signaling during gynoecium development, as well as the implication of ETT in this pathway. In a second part, I confirmed the repression of the target genes by ETT. Interestingly, we showed that ETT activates the pectins demethylation by inhibiting the inhibitors of pectin methylesterase. Furthermore, I showed that ETT and ARF4 act in a redundant manner to positively control gynoecium growth. In a third part, I initiated the analysis of the functional domains of CRABS CLAW, a transcription factor also involved in gynoecium development. In conclusion, these results bring new information on the role of auxin signaling during gynoecium development and highlight the importance of cell wall remodeling in morphogenesis.
