Increasing legume nodulation for improved symbiotic nitrogen fixation
CSANR Project 166
We have identified a gene from Sinorhizobium medicae that substantially increases nodulation of Sinorhizobium meliloti on barrel medic and Rhizobium leguminosarum on pea and increases biomass of nodulated barrel medic by ~40%. The glx gene appears to work by overcoming plant-mediated inhibition of nodule formation and is the first gene we know of with this activity. We hypothesize that glx will form more nodules on additional legumes and may improve yield. We will test this with diverse legumes, including forage and pulse crops grown in Washington State, by transferring glx into the corresponding symbiotic rhizobia and carrying out nodulation and growth experiments in growth chambers and greenhouses. We will also determine whether glx can promote nodulation under inhibitory conditions that affect local cropping, like low pH, high salt or the presence of nitrate. These inhibitions are mediated by a circuit that is genetically similar to the one that mediates autoinhibition of nodulation. glx is homologous to genes involved in small molecule degradation. We propose to investigate its metabolic activity by looking for changes in metabolites and the effect of added metabolites on gene expression. The research will contribute to basic understanding of legume nodulation and may contribute to increased nitrogen fixation and yield by legume crops, which are key sources of nitrogen in many types of organic and sustainable agriculture. The data will be useful in defining the generality and mechanism of the glx gene and will strengthen proposals to external agencies and commodity groups.