N -hydroxy-pipecolic acid is a mobile metabolite that induces systemic disease resistance in Arabidopsis

Significance Plants lack circulating immune cells and instead rely on small molecule chemistry for local and long-distance defense signaling. Following pathogen attack, plants activate innate immune pathways at the site of infection to limit pathogen growth. Plants also possess the ability to prime similar immune responses in uninfected tissues to prevent the spread of pathogens or protect against new infections. Despite the importance of systemic immunity, the mechanism for signaling is not clear. In this study, we show that N -hydroxy-pipecolic acid metabolites are mobile defense signals produced at the site of bacterial infection and establish and amplify defense in uninfected, distal tissues. Our study illuminates the chemical nature of a mobile bioactive metabolite that confers pathogen resistance throughout the plant.