Plant transcription factors and nodule development

Legumes have an intimate relationship with nitrogen-fixing gram-negative soil bacteria called rhizobia. Rhizobia convert the atmospheric inert nitrogen (N2) into ammonia inside the nodules, which plants directly assimilate, and in return, rhizobia get photosynthate carbon from plants for survival. This intimate interaction is costly for the plant, and hence it is tightly regulated. Several transcription factors (TF) such as calcium-calmodulin-dependent protein kinase (CCaMK), CYCLOPS, CCaMK/CYCLOPS, Ethylene Response Factor Required for Nodulation 1 (ERN1) and ERN2, members of GRAS family Nodulation Signaling Pathway 1 (NSP1) and NSP2, NODULE INCEPTION (NIN), Nuclear Factor-Y (NF-Y), Nodulation Pectate Lyase (NPL), LOB-domain protein gene (LBD16), Rhizobium-Directed Polar Growth (RPG) and SHORT INTERNODES/STYLISH (STY), and others have been shown to play a significant role in the tight regulation of root nodule symbiosis (RNS). Here, we present comprehensive and recent advances in identification, evolution, structure, and functions of all the major TFs, their crosstalk and further discuss their potential application to maximize RNS to increase nitrogen fixation and decrease the dependency on nitrogen fertilizers.