The small molecule Zaractin activates ZAR1-mediated immunity in Arabidopsis

Significance Pathogenic microbes inject virulence proteins, termed effectors, into the cells of their hosts where they sabotage the cellular machinery and promote the infection process. However, plant and animal cells have evolved the ability to sense the molecular activities of these pathogenic proteins and mount an immune response to protect against infection. Here we have identified a chemical that mimics the immune eliciting activity of a pathogenic effector protein and importantly, it also activates immune responses in plants. We showcase how the intricate molecular dialog of the host–pathogen interface can be used to uncover chemical immunogens that specifically activate the eukaryotic immune system to prevent disease.