Abstract
mailto:Soft rot caused by Dickeya zeae is an important bacterial disease affecting rice and other plants around the world. Several studies found that the specific virulence factor-modulating quorum sensing (vfm-QS) system is present in bacteria. vfmI is the key member encoding a two-component system sensor histidine kinase. Therefore, to determine the effects of vfm-QS on phenotypic features and virulence, the system was inactivated through the construction of a vfmI mutant in the D. zeae WH1 strain. The results of the phenotypic features and pathogenicity assays revealed that the deletion of vfmI abolished motility and reduced biofilm-forming capacity. Moreover, the mutation had a limited role in regulating the activity of plant cell wall-degrading enzymes (PCWDEs) and decreased the maceration of potato tubers in the tested dicotyledonous plants. Importantly, the vfmI mutant became avirulent to the rice plants, although the gene mutation slightly increased rice seed germination. These features are considerably different from those that have been shown for other Dickeya strains. Finally, our findings indicated that the vfm system controls the motility of WH1 by regulating flagellar biosynthesis and biofilm formation, which is achieved by regulating the intracellular c-di-GMP level. Taken together, these findings highlight the complexity and plasticity of QS regulatory circuits in the D. zeae strain.