Grant: Discovery Grants Program - Individual

The biological fixation of atmospheric nitrogen is a critical component to the global nitrogen cycle and is particularly valuable to worldwide agriculture. Globally, nitrogen fixation symbioses between rhizobia and legumes are the major source of nitrogen input to agricultural systems, and many legume species, such as peas, lentils, soybeans and chickpeas are important food crops. Rhizobial-legume interactions have been studied extensively, but the process is complex and further fundamental research is required to appreciate this complexity fully. Rhizobia induce the formation of root nodules on legume plants, and within these nodules, the bacteria convert atmospheric nitrogen to a form that is useable by the plants.  The dramatic transformation that occurs when rhizobia differentiate into symbiont cells (bacteroids) has been clearly documented by recent microarray gene expression and proteomic studies. However, the mechanisms that regulate bacteroid differentiation, particularly the down-regulation of gene expression during nodulation, are largely unknown. The long-term objectives of my research program are to use genetics based methodologies to discover unknown regulatory pathways that control bacteroid development in rhizobia and to identify novel genes required for bacteroid development. More specifically, the proposed research will identify regulators and signals that control the down-regulation of genes related to cellular division, motility and outer membrane proteins during bacteroid development. The role of proteases as regulators of bacteroid development will also be studied in this proposal. Results from this research may be applied to other bacterial-host relationships, particularly pathogenic interactions within the alpha-proteobacteria class, possibly to identify novel mechanisms that regulate the pathogenic process.