Plants in the legume family form symbioses with nitrogen-fixing soil bacteria or rhizobia that provide a sustainable nitrogen source to improve soil fertility in agricultural settings. Symbiotic nitrogen fixation is central to any plan for energy-sustainable production of food or fuel. Crop plants for food, oil, and green manure are able to produce high-protein seeds and leaves because of the fixed nitrogen provided by the bacteria. A major challenge for transforming future agriculture is to gain a detailed understanding of the bidirectional interplay between crop plants and nitrogen-assimilating bacteria. Genetic approaches in plants and bacteria have led to discovering some of the molecular components required for symbiosis processes including root nodule development and nitrogen fixation. However, many steps in symbiosis remain uncharacterized. Using the symbiosis model system between Sinorhizobium meliloti and its host plant, researchers expect to conducted a systems-genetic analysis of the S. meliloti genome and identify the entire set of genetic instructions required for free-living growth and establishment of nitrogen-assimilating symbiosis with the forage crop Medicago truncatula. This approach is expected to establish a functional map of the genome of the nitrogen-fixing soil bacterium S. meliloti and identify a near-complete set of genetic instructions required for successful establishment of symbiosis with agricultural crop plants.
PI: Lucy Shapiro, Stanford University