Effector-triggered stomatal immunity prevents leaf invasion by bacterial pathogens

The phytopathogen Pseudomonas syringae must enter the leaf interior through natural openings such as stomata to cause disease. Plants restrict pathogen entry into the leaf through non–self-recognition–driven stomatal closure. P. syringae counters this stomatal immunity by deploying a range of toxins and effectors. Here, we show that stomatal immunity in Arabidopsis thaliana is reinforced upon recognition of the ubiquitous P. syringae type III effector AvrE1 by the resistance protein CAR1. CAR1 expression is enriched in guard cells, and its activation prolongs the effective duration of stomatal immunity. We also show that CAR1 prevents the invasion of leaf tissue by natural isolates of P. syringae , demonstrating that stomatal immunity provides a broadly significant barrier to host accessibility by P. syringae that carry the conserved effector AvrE1.