Genetic control of alfalfa infection by the nitrogen fixing symbiotic bacterium Sinorhizobium meliloti

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Nitrogen fixing nodules form on alfalfa roots as a result of infection by Sinorhizobium meliloti bacteria. This plant-microbe interaction is a complex developmental process that is a model system for study of symbiotic nitrogen fixation. Our research program uses bacterial genetic tools to study the control of infection by the ExoS-ChvI transcriptional regulatory system that coordinates the expression of a large number of genes both directly and indirectly. We are carrying out a detailed characterization of this regulatory system in an effort to determine its role in controlling infection. DNA binding screens are used to determine exactly which genes are directly turned off and on by this system, and we will improve the screen by incorporating Illumina DNA sequencing technology. We will try to determine the inducing signal, and we will also compare the pleiotropic phenotype of mutants of the regulatory system with the phenotypes of mutants of the individual target genes. Our work has the potential to greatly improve our understanding of the infection process, and this will impact not only on agricultural symbiotic nitrogen fixation improvements, but will also contribute to our overall research program by further developing the fundamentals of bacterial molecular genetics. The work will be carried out by graduate students, in an intellectually stimulating, active research environment.