Proteomic analysis of the regulatory function of DSF-dependent quorum sensing in Xanthomonas oryzae pv. oryzicola

Xanthomonas oryzae pv. oryzicola (Xoc), which caused bacterial leaf streak in rice, is a bacterial pathogen limited to the apoplast of the mesophyll tissue. The rpfF that encodes diffusible signal factor (DSF) synthase, played a key role in the virulence of many plant pathogenic bacteria. In this study, the rpf gene cluster was cloned, and the rpfF was deleted in Xoc. It was observed that the rpfF mutant lost the ability to produce DSF molecular, and exhibited a significant reduction of virulence in rice compared to the wild-type strain. Furthermore, the mutation of rpfF impaired EPS production, and led to Xoc cell aggregation. To analyze the differences of proteome expression between Xoc wild type and rpfF mutant, a comparative proteome analysis was performed by two-dimensional gel electrophoresis (2-DE). The results clearly revealed that 48 protein spots were differentially expressed above the threshold ratio of 1.5. Among them, 18 proteins were identified by MS, which were involved in nitrogen transfer, protein folding, elimination of superoxide radicals and flagellar formation. Our results indicated that DSF might play an important role in virulence and growth of Xoc by mediating expression of proteins.