Investigating the roles of Lon and DegP proteases in Rhizobia

Rhizobial species are well-known for their ability to form symbiotic relationships with legumes. The two species investigated in this study, Rhizobium leguminosarum and Sinorhizobium meliloti, are able to nodulate legumes in the tribes Vicieae and Trifolieae respectively. In this study, two proteases were investigated to better understand the Rhizobium-legume relationship, especially in the context of bacteroid development.;The degP gene family in R. leguminosarum and S. meliloti was investigated. Unlike other prokaryotes which carry only one copy of the gene, sequence analysis of R. leguminosarum and S. meliloti found five and four paralogs of degP respectively. degP4 was selected for further study. This gene was not expressed in R. leguminosarum in various conditions tested. Additionally mutagenesis of the degP4 gene did not reveal any phenotypic changes in R. leguminosarum. This suggests possible functional redundancy in this gene family. Conversely the S. meliloti degP4 was expressed in free-living cells and down-regulated in bacteroid cells. Therefore, although the degP4 s are structurally If similar they are regulated differently in these two closely related rhizobial species, this implies that they may be involved in different functions in the cell.;The R. leguminosarum lon gene was studied using mutational approaches. Gene expression analysis revealed that this gene is expressed in both free-living and bacteroid cells, which implies that the lon gene plays a role in the normal growth and bacteroid development in R. leguminosarum. Lon is a heat shock protein in many organisms however expression was not induced by heat shock in R. leguminosarum. Multiple attempts to inactivate lon were unsuccessful, suggesting that this gene may be an essential gene necessary for the viability of R. leguminosarum under normal growth conditions.