Nuclear factors NF-YC3 and NF-YBs positively regulate arbuscular mycorrhizal symbiosis in tomato

The involvement of nuclear factor Y (NF-Y) in transcriptional reprogramming during arbuscular mycorrhizal symbiosis has been demonstrated in several plant species. However, a comprehensive picture is lacking. We showed that the spatial expression of NF-YC3 was observed in cortical cells containing arbuscules via the cis-regulatory element GCC boxes. Moreover, NF-YC3 promoter was transactivated by the combination of CYCLOPS and autoactive CCaMK via GCC boxes. Knockdown of NF-YC3 significantly reduced the abundance of all intraradical fungal structures and affected arbuscules size. BCP1, SbtM1, and WRI5a, whose expression was correlated with NF-YC3 level, might be downstream of NF-YC3. NF-YC3 interacted with one of three NF-YBs, NF-YB3a, NF-YB5c, or NF-YB3b, in yeast and in planta, and interacted with NF-YA3a in yeast. Spatial expression of three NF-YBs was observed in all cell layers of roots under both mock and mycorrhizal conditions. Knockdown of three NF-YBs collectively, but not individually, reduced the fungal colonization level, suggesting that there might be functional redundancy of NF-YBs to regulate AM symbiosis. Collectively, our data suggest that NF-YC3 and NF-YBs positively regulate AM symbiosis in tomato, and arbuscule-related NF-YC3 may be important downstream gene of common symbiosis signaling pathway. Overall design: Comparative gene expression profiling analysis of RNA-seq data for tomato (Solanum lycopersicum cv. Micro-Tom) composite plants transformed with empty vector (EV, pK7GWIWG II-RedRoot) and nf-yc3 RNAi construct in the hairy roots and colonized without (mock) or with AM fungi Rhizophagus irregularis