The PhoPQ two-component system is the major regulator of cell surface properties, stress responses and plant-derived substrate utilisation during development ofPectobacterium versatile-host plant pathosystem

Abstract

The PhoPQ two-component system, originally described in pectobacteria as PehRS, was previously shown to regulate a single gene, pehA. Using an insertional phoP mutant of Pectobacterium versatile, we demonstrate that PhoP controls a regulon of at least 116 genes with a large fraction of regulon members specific for pectobacteria. The functions performed by the PhoP controlled genes include transport and metabolism of plant-derived carbon sources (polygalacturonate, arabinose and citrate), modification of bacterial cell envelope and stress resistance. High concentrations of calcium and magnesium ions were found to abolish the PhoPQdependent transcription activation. Reduced PhoP expression and minimisation of PhoP dependence of regulon members' expression in the cells isolated from rotten potato tuber tissues suggest that PhoPQ system may adjust expression levels of multiple virulence-related genes during the course of P. versatile-host plant pathosystem development.PehR was originally described as a transcriptional activator of the pehA gene encoding endopolygalacturonase, a major virulence factor in soft rot bacteria (16). PehR is a response regulator that forms a two-component sensory system (TCS) with the membrane histidine kinase PehS. In the SCC3193 strain, which is currently classified as Pectobacterium parmentieri, inactivation of either pehR or pehS resulted in reduced virulence and Ca 2+ was reported as the ligand detected by the PehS sensor (16,17). It was also suggested that the PehRS system is responsible for the decrease of the polygalacturonase and increase of the pectate lyase activities in response to Ca 2+ released from the degraded cell walls (17).The pectobacterial PehRS two-component system received very little attention since its discovery two decades ago. However, much information has been accumulated about the orthologous system called PhoPQ in other bacteria from the order Enterobacetrales. In Dickeya dadantii, which belongs to the Pectobacteriaceae family together with Pve, PhoPQ TCS was shown to control pellicle formation, motility, resistance to cationic antimicrobial peptides and expression of pectate lyases in response to Mg 2+ concentration (18,19). The PhoPQ system has been thoroughly characterised in Salmonella and to a lesser extent in few more Enterobacteriaceae species including Escherichia coli and Yersinia spp. (see (20) for a review). The PhoQ sensor histidine kinase activates PhoP by phosphorylation in response to several stimuli, including low Mg 2+ concentration (21), cationic peptides (22), acidity (23) and high osmolarity (24). PhoP binds to direct repeats with a consensus gGTTTA which seems to be well conserved in enterobacteria (25,26). The regulon composition nevertheless varies widely even between closely related bacteria. In Salmonella enterica, over a hundred genes are regulated by PhoP, but only three of them (phoP, phoQ and slyB) are always under PhoP control in other enterobacteria. Some regulon members are shared by several species, but most PhoP controlled gene...

The PhoPQ Two-Component System Is the Major Regulator of Cell Surface Properties, Stress Responses and Plant-Derived Substrate Utilisation During Development of Pectobacterium versatile-Host Plant Pathosystems

“…We thank Dr. Alexander Ageichik for critical reading of the manuscript. A preprint of this paper was published ( Kravchenko et al, 2020 ).…”