Comparative genomics ofPseudomonas syringaepathovartomatoreveals novel chemotaxis pathways associated with motility and plant pathogenicity

Abstract

The majority of bacterial foliar plant pathogens must invade the apoplast of host plants through points of ingress, such as stomata or wounds, to replicate to high population density and cause disease. How pathogens navigate plant surfaces to locate invasion sites remains poorly understood. Many bacteria use chemical-directed regulation of flagellar rotation, a process known as chemotaxis, to move towards favorable environmental conditions. Chemotactic sensing of the plant surface is a potential mechanism through which foliar plant pathogens home in on wounds or stomata, but chemotactic systems in foliar plant pathogens are not well characterized. Comparative genomics of the plant pathogenPseudomonas syringaepathovartomato(Pto) implicated annotated chemotaxis genes in the recent adaptations of one Pto lineage. We therefore characterized the chemosensory system of Pto. The Pto genome contains two primary chemotaxis gene clusters,che1andche2. Theche2cluster is flanked by flagellar biosynthesis genes and similar to the canonical chemotaxis gene clusters of other bacteria based on sequence and synteny. Disruption of the primary phosphorelay kinase gene of theche2cluster,cheA2, eliminated all swimming and surface motility at 21  °C but not 28  °C for Pto. Theche1cluster is located next to Type IV pili biosynthesis genes but disruption ofcheA1has no observable effect on twitching motility for Pto. Disruption ofcheA2also altersin plantafitness of the pathogen with strains lacking functionalcheA2being less fit in host plants but more fit in a non-host interaction.