About half of all biologically fixed nitrogen is produced by root-associated bacteria (rhizobia) in symbioses with legume plants. These symbioses form the basis for crop rotation and allow legumes to thrive without the application of nitrogen fertilizer. Establishment of the symbiosis between Sinorhizobium meliloti and its plant hosts requires the S. meliloti ExoS/ChvI genes, which encode an evolutionarily conserved signaling pathway. Orthologs of the ExoS/ChvI genes also play essential roles in host interactions of other alpha-proteobacteria, such as the plant pathogen Agrobacterium tumefaciens. To elucidate the roles of ExoS/ChvI signaling in both symbiotic and free-living S. meliloti, new transcriptional target genes of ExoS/ChvI will be characterized, and their contributions to ExoS/ChvI function will be analyzed using genetics, genomics, and microscopy. Further, the regulation of ExoS/ChvI signaling will be investigated by biochemical and structural analysis of a novel ExoS/ChvI inhibitor. These studies will provide crucial insight into the molecular mechanisms underlying a bacteria-plant symbiosis with agricultural and economic importance. The project will be accomplished at a Hispanic-serving, comprehensive university by undergraduate and master's students, including future high school biology teachers. These students will gain experience in molecular biology research while working collaboratively. The open-ended learning experiences presented by the project will allow students to build significantly on their classroom education and prepare them for careers in science.
