description
- Nitrogen is an essential element of biological molecules and life on earth. Lack of usable nitrogen limits growth of microbes, plants, and animals. Lack of nitrogen in agricultural soils limits plant production of food, feed, fiber and fuel. Nature solved the nitrogen limitation problem via evolution of biological nitrogen fixation in diazotrophic bacteria that reduce atmospheric N2 to NH3, which is readily assimilated into biological molecules. Biological nitrogen fixation is catalyzed by a complex metalloenzyme called nitrogenase whose oxygen-sensitivity may explain its restricted distribution amongst prokaryotes. Some plants, including most legumes and a few non-legumes form intimate, nitrogen-fixing symbioses with diazotrophs that provide the plants with ammonia. As a consequence, legumes have been an integral part of sustainable agricultural systems for thousands of years. Unfortunately, many important food species, including the grasses maize/corn, rice, and wheat cannot establish effective nitrogen-fixing symbioses with diazotrophs, which means that they are dependent on nitrogenous fertilizers for high yield. Large-scale use of industrially-produced N-fertilizer has doubled the influx of N into the terrestrial biogeochemical N-cycle, with serious negative consequences for human health and the natural environment. Therefore, the long-term sustainability of massive N-fertilizer inputs in agriculture has come into question. A team of six investigators has come together to solve the dual nitrogen problems of N-fertilizer over-use in developed countries and soil N-paucity in developing countries by developing effective endophytic and associative nitrogen-fixing symbioses in a model and a crop plant species. The team brings together expertise in bacterial and plant genetics, genomics, biochemistry, molecular and cell biology, physiology and synthetic biology with a deep knowledge of biological nitrogen fixation. The overarching goal of the project proposed here is to develop effective N2-fixing symbioses between the model C4-grass, Setaria viridis, or the related crop species, Zea mays, and the endophytic bacterium, Rhizobium sp. IRBG74, or the associative bacterium, Pseudomonas fluorescenes Pf5. Successful deployment of biological nitrogen fixation in model or crop grass species will pave the way for a second Green Revolution that will increase crop yields for resource-poor farmers and decrease the use and environmental-impact of industrial N-fertilizers by wealthier farmers.