Av-Shalom, T. V.; Lai, Y.; Singh, R. A.; Gohmann, R.; Mackey, D.; Desveaux, D.; Guttman, D. S.

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 upon non-self recognition-driven closure of their stomata. 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 CAR1-mediated stomatal immunity against the conserved effector AvrE1 provides a broadly significant barrier to host accessibility by P. syringae.