A widespread plant defense compound disarms bacterial type III injectisome assembly.

Abstract

Numerous gram-negative bacterial pathogens employ the type III secretion system (T3SS), a multiprotein injectisome, to deliver virulence proteins into host cells and cause diseases. We uncover erucamide as a previously unknown phytoalexin of both dicots and monocots that blocks the T3SS function of multiple bacterial pathogens. Genetically impairing erucamide accumulation or exogenous application in <i>Arabidopsis</i> highlighted erucamide's role in antibacterial immunity. Erucamide binds Hypersensitive response and conserved C (HrcC), a key T3SS component, to block injectisome assembly. Analyses of erucamide analogs and HrcC mutants indicated that the erucamide-HrcC binding is required for inhibiting T3SS in vitro and antibacterial resistance in plants, suggesting an essential role of erucamide-HrcC binding in disease resistance. This work reveals a plant chemical defense that targets major virulence machinery in bacterial pathogens.