HprK is a serine kinase that regulates virulence in the Gram-negative phytopathogen Xanthomonas campestris.

The HprK serine kinase is a component of the phosphoenolpyruvate phosphotransferase system (PTS) of bacteria that generally regulates catabolite repression through phosphorylation/dephosphorylation of the PTS protein PtsH at a conserved serine residue. However, many bacteria do not encode a complete PTS or even have an HprK homologue. Xanthomonas campestris pv. campestris (Xcc) is a pathogen that cause black rot disease in crucifer plants and one of the few Gram-negative bacteria that encodes a homologue of HprK protein (herein HprK ). To gain insight into the role of HprK and other PTS-related components in Xcc we individually mutated and phenotypically assessed the resulting strains. Deletion of hprK demonstrated its requirement for virulence and other diverse cellular processes associated including extracellular enzyme activity, extracellular-polysaccharide production and cell motility. Global transcriptome analyses revealed the HprK had a broad regulatory role in Xcc. Additionally, through overexpression, double gene deletion and transcriptome analysis we demonstrated that hprK shares an epistatic relationship with ptsH. Furthermore, we demonstrate that HprK is a functional serine kinase, which has the ability to phosphorylate PtsH. Taken together, the data illustrates the previously unappreciated global regulatory role of HprK and previously uncharacterized PTS components that control virulence in this pathogen.