P-430 - Uncovering SMAX1-dependent regulation of transcription factors during arbuscular mycorrhizal symbiosis in rice

Arbuscular mycorrhizal symbiosis (AMS) is one of the most ancient and widespread forms of plant symbiosis and is established between most land plants and Glomeromycotina fungi. In rice, AMS development is tightly regulated by the host and requires the α/β-fold hydrolase Dwarf14-Like (D14L). D14L forms a complex with the F-box protein Dwarf3 (D3), triggering the degradation of Suppressor of MAX2-1 (SMAX1), a known negative regulator of AMS. SMAX1 degradation lifts repression on the symbiotic genetic program, likely by affecting the activity or expression of specific transcription factors (TFs). This study investigates candidate TFs regulated by SMAX1 using both untargeted and targeted approaches. In the untargeted approach, SMAX1 pull-down assays identified several potential interactors, including the transcriptional corepressor TOPLESS-Related 3 (TPR3). These candidates will be further validated through additional protein–protein interaction assays. In the targeted approach, two APETALA2 (AP2) TFs, were found to be upregulated in smax1 rice mutants, and identified as potential targets downstream of SMAX1-mediated regulation in AMS. Future work focusing on protein-protein interaction and genetic engineering will be used to confirm these findings and offer further insights on the genetic regulation of AMS downstream of SMAX1.