Role of NPR1 in Systemic Acquired Stomatal Immunity

Stomatal immunity is the primary gate of the plant pathogen defense system. Non-expressor of Pathogenesis Related 1 (NPR1) is the salicylic acid (SA) receptor, which is critical for stomatal defense. SA induces stomatal closure, but the specific role of NPR1 in guard cells and its contribution to systemic acquired resistance (SAR) remain largely unknown. In this study, we compared the response to pathogen attack in wild-type Arabidopsis and the npr1-1 knockout mutant in terms of stomatal movement and proteomic changes. We found that NPR1 does not regulate stomatal density, but the npr1-1 mutant failed to close stomata when under pathogen attack, resulting in more pathogens entering the leaves. Moreover, the ROS levels in the npr1-1 mutant were higher than in the wild type, and several proteins involved in carbon fixation, oxidative phosphorylation, glycolysis, and glutathione metabolism were differentially changed in abundance. Our findings suggest that mobile SAR signals alter stomatal immune response possibly by initiating ROS burst, and the npr1-1 mutant has an alternative priming effect through translational regulation.