Nodule Number Control 1, a member of the AP2 family of transcription factors, functions as a negative regulator of bacterial infection and nodule organogenesis in the model legume Medicago truncatula

MILAGROS YACULLO, SOLEDAD TRAUBENIK, MAURICIO REYNOSO , MAUREEN HUMMEL, JULIA BAILEY-SERRES , FLAVIO BLANCO, MARÍA EUGENIA ZANETTI

Rosario

Congreso; XXXIV Argentinian Meeting of Plant Physiology; 2023

Sociedad Argentina de Fisiolog{ia Vegetal

Legumes and rhizobia establish a nitrogen-fixing symbiosis results in the formation of a postembryonic lateral root organ, the nodule and requires the suppression of the plant immune response to allow intracellular bacterial infection. Nodule formation and bacterial infection are timely and spatially coordinated through the reprogramming of gene expression which occurs at both transcriptional and post-transcriptional levels. A previous study identified. A transcript encoding the Subunit 3 of the Superkiller Complex (SKI), designated as MtSKI3, as differentially up regulated at the translational level at early stages of the nitrogen foxing symbiosis between Medicago truncatula and Sinorhizobium meliloti. The SKI complex acts along with the exosome in the 3´-5´ degradation of mRNAs. We have found that MtSKI3 is required for nodule formation, bacterial survival, and induction of early nodulation genes such as ENOD40. A recent degradome analysis showed that MtSKI3 affected the miR172-directed endonucleolytic cleavage of the mRNA encoding the APETALA 2 member of transcription factors Nodule Number Control 1 (referred to as MtNNC1). Expression analysis revealed that MtNNC1 is expressed at high levels in roots as compared with aerial tissues, but repressed during nodulation, along with genes involved in defense mechanisms against pathogens. Post-transcriptional silencing of MtNNC1 produced a significant increase in the density of infection events and the number of nodules . These data suggest that MtNNC1 would function as a negative modulator of the formation of nitrogen-fixing nodules. As an alternative approach to elucidate the biological function of MtNNC1, we are currently using overexpression MtNNC1in M. truncatula transgenic roots.. The results will allow a better understanding of the mechanisms by which MtNNC1 exerts its activity during an agronomically relevant biotic interaction such as the nitrogen-fixing symbiosis.