On the front lines: How bacterial effectors at the host-pathogen interface govern host specificity

Bacterial pathogens pose a serious threat to global food security and human health. One critical virulence apparatus that pathogens deploy is the type III secretion system. The effectors that are delivered by this system mediate the outcomes of host-pathogen interactions because they can either promote pathogenesis on susceptible hosts or activate an effector triggered immune response on resistant hosts. Using the pangenome from nearly 500 strains of the agricultural pathogen Pseudomonas syringae, we conducted evolutionary genomic analyses to identify more than 14,000 effectors from 70 gene families. We then used a diverse representative collection of effectors to probe the effector triggered immunity landscape between P. syringae and the model plant Arabidopsis. We find that a shocking number of effectors elicit an immune response in Arabidopsis that reverses the outcome of the interaction from disease to resistance. These results illustrate that despite their widespread importance for pathogenesis, effectors may ultimately limit the host range of bacterial pathogens. My lab is now extending this pangenome approach to other bacterial phytopathogens, where we hope to identify host resistance genes that can provide stable resistance against a range of bacterial species.