CONICET | Buscador de Institutos y Recursos Humanos

Common bean (Phaseolus vulgaris) establishes a nitrogen fixing interaction with its symbiotic partner Rhizobium etli. In this interaction, plants from the Mesoamerican genetic diversification center showed a fined tuned functional compatibility with bacterial strains that have coevolved within their native habitats. Plant molecular determinants that govern such functional compatibility have remained largely elusive. Here, we found that a C subunit of the heterotrimeric nuclear factor NF-Y plays a key role in determining preference for rhizobial strains that fix nitrogen more efficiently. NF-YC is specifically induced by highly efficient strains of R. etli. Overexpresion of this gene has a positive impact in nodulation performance and selection of strains that are naturally less efficient and bad competitors. On the other hand, knock-down of NF-YC by RNA interference (RNAi) leads to reduced nodulation performance with either high or low efficient R. etli strains. NF-YC RNAi plants showed obvious symptoms of nitrogen deficiency such as leaf chlorosis and poor shoot development. Examination of infection events at early stages of the interactions using a GFP labeled R. etli strains showed that initiation and progression of infection threads were severely reduced in NF-YC RNAi roots. NF-YC regulates early induction of cell cycle genes, providing a link between strain perception in the epidermis and cortical cell divisions required for nodule organogenesis. Our findings show that coevolution between legumes and rhizobia gave origin to a molecular mechanism to ensure infection by strains that fix nitrogen more efficiently, which holds important implications for optimizing legume performance and soil fertility. Further characterization of genes involved in this molecular recognition will certainly help to elucidate the mechanisms that determine the functional compatibility observed between Mesoamerican beans and their cognate rhizobial strains.