Crp-like protein (Clp) plays both positive and negative roles in regulating the pathogenicity of bacterial pustule pathogen Xanthomonas axonopodis pv. glycines.

The global regulator Clp (Crp-like protein) is positively involved in the production of virulence factors in some of the Xanthomonas spp.. However, the functional importance of Clp in Xanthomonas axonopodis pv. glycines (Xag) has not been investigated previously. Here, we showed that deletion of clp led to significant reduction in the virulence of Xag in soybean, which was highly correlated with the drastically reductions in carbohydrates utilization, extracellular polysaccharide (EPS) production, biofilm formation, cell motility, and synthesis of cell-wall degrading enzymes (CWDEs). These significantly impaired properties in the clp mutant were completely rescued by a single-copy integration of the wild-type clp into the mutant chromosome via homologous recombination. Interestingly, overexpression of clp in the wild-type strain resulted in significant increases in cell motility and synthesis of the CWDEs. To our surprise, significant reductions in carbohydrates utilization, EPS production, biofilm formation and the protease activity were observed in the wild-type strain overexpressing clp, suggesting that Clp also plays a negative role in these properties. Furthermore, qRT-PCR analysis suggested that clp was positively regulated by the DSF-mediated quorum-sensing system and the HrpG/HrpX cascade. Taken together, our results reveal that Clp functions as both activator and repressor in multiple biological processes in Xag that are essential for its full virulence.