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

Abstract

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_Xcc ). To gain insight into the role of HprK_Xcc and other PTS-related components in Xcc we individually mutated and phenotypically assessed the resulting strains. Deletion of hprK _Xcc 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_Xcc had a broad regulatory role in Xcc. Additionally, through overexpression, double gene deletion and transcriptome analysis we demonstrated that hprK _Xcc shares an epistatic relationship with ptsH. Furthermore, we demonstrate that HprK_Xcc 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_Xcc and previously uncharacterized PTS components that control virulence in this pathogen.