The Methyltransferase HemK Regulates the Virulence and Nutrient Utilization of the Phytopathogenic Bacterium Xanthomonas citri Subsp. citri

Citrus canker, caused by the bacterium subsp. ( ), seriously affects fruit quality and yield, leading to significant economic losses around the world. Understanding the mechanism of virulence is important for the effective control of infection. In this report, we investigate the role of a protein named HemK in the regulation of the virulence traits of . The gene was deleted in the jx-6 background, and the Δ mutant phenotypically displayed significantly decreased motility, biofilm formation, extracellular enzymes, and polysaccharides production, as well as increased sensitivity to oxidative stress and high temperatures. In accordance with the role of HemK in the regulation of a variety of virulence-associated phenotypes, the deletion of resulted in reduced virulence on citrus plants as well as a compromised hypersensitive response on a non-host plant, . These results indicated that HemK is required for the virulence of . To characterize the regulatory effect of deletion on gene expression, RNA sequencing analysis was conducted using the wild-type jx-6 strain and its isogenic Δ mutant strain, grown in XVM2 medium. Comparative transcriptome analysis of these two strains revealed that deletion specifically changed the expression of several virulence-related genes associated with the bacterial secretion system, chemotaxis, and quorum sensing, and the expression of various genes related to nutrient utilization including amino acid metabolism, carbohydrate metabolism, and energy metabolism. In conclusion, our results indicate that HemK plays an essential role in virulence, the regulation of virulence factor synthesis, and the nutrient utilization of .