The phytocytokine CAPE9 and its receptor CAPER1 function on plant systemic stomatal immunity

Stomata mediate gas flux for physiological events while they provide entries for pathogens. Plants evolve specific mechanisms to trigger stomatal closure to restrict further invasions. This response is found to be a systemic process, yet how plants activate and propagate the signal systemically is unclear. Here, we show the Arabidopsis CAPE9 peptide, derived from systemic acquired resistance marker protein PR1, triggers stomatal closure and reduces the bacterial entry by its perception through AtCAPE receptor 1 (AtCAPER1) in guard cells. CAPE9 is further validated as a mobile signal transferred from local sites to systemic tissues, contributing to whole plant stomatal immunity.