Response regulator, VemR, positively regulates the virulence and adaptation of Xanthomonas campestris pv. campestris

Xanthomonas campestris pv. campestris (Xcc) is the causal agent of black rot disease in cruciferous plants. The synthesis of known virulence factors in this organism, such as extracellular enzymes and biofilm, is strictly regulated in response to environmental stimuli. Two-component signal transduction systems sense environmental signals and alter bacterial behavior by regulating gene expression. Here, we identified a response regulator, VemR, that regulates Xcc pathogenesis. The vemR gene encodes an atypical response regulator that only contains a receiver domain. Deletion of vemR resulted in decreased virulence, exopolysaccharide production and motility of Xcc. The vemR gene is located in an operon flanked by genes fleQ and rpoN2. Genetic analysis indicated that deletion of fleQ does not affect motility significantly. However, a double mutant Delta vemR/Delta fleQ reversed the phenotype of Delta vemR, indicating that fleQ is epistatic to vemR in the regulation of virulence and adaptation.