Effects of the vfm quorum-sensing system on the phenotypic features and virulence of Dickeya zeae WH1

mailto:Soft rot caused by <i>Dickeya zeae</i> is an important bacterial disease affecting rice and other plants around the world. Several studies found that the specific virulence factor-modulating quorum sensing (<i>vfm</i>-QS) system is present in bacteria. <i>vfmI</i> is the key member encoding a two-component system sensor histidine kinase. Therefore, to determine the effects of <i>vfm</i>-QS on phenotypic features and virulence, the system was inactivated through the construction of a <i>vfmI</i> mutant in the <i>D. zeae</i> WH1 strain. The results of the phenotypic features and pathogenicity assays revealed that the deletion of <i>vfmI</i> 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 <i>vfmI</i> 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 <i>Dickeya</i> strains. Finally, our findings indicated that the <i>vfm</i> 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 <i>D. zeae</i> strain.