KSEF RDE: Host genetic control of strain-specific nitrogen fixation in Medicago truncatula

Legumes represent the second most important family of crop plants, accounting for ~27% of the world’s crop production. A hallmark trait of legumes is their unique ability to establish a root nodule symbiosis with nitrogenfixing soil bacteria, known as rhizobia. However, the beneficial function of the legume-rhizobia mutualism varies tremendously with different plant-rhizobial combinations and environmental conditions. Even though many legumes can nodulate with indigenous soil bacteria, the nitrogen fixation efficiency of the resulting nodules is frequently low, which is insufficient to provide the plant with all its demand for organic nitrogen. Thus, there exists a great potential to improve the effectiveness of symbiotic nitrogen fixation and consequently enhance the benefit of the legume-rhizobia symbiosis to sustainable agriculture. Unfortunately, nitrogen fixation efficiency is a complex trait involving multi-level interactions between host and bacterial signal molecules. Despite recent advances in our understanding of the signaling pathways leading to root nodule development, the molecular mechanisms underlying natural variation in nitrogen fixation efficiency/specificity are largely unknown. The overall goal of this proposal is twofold: 1) to explore genomic signatures of efficient nitrogen fixation in the legumerhizobia symbiosis using the Medicago-Sinorhizobium model, and 2) to clone and characterize a host gene that regulates strain-specific nitrogen fixation in Medicago truncatula. This research will provide novel insights into the genetic mechanisms that regulate host specificity in the legume-rhizobial symbiosis