The cysteine protease RD19C suppresses plant immunity to Phytophthora by modulating copper chaperone ATX1 stability

SUMMARY Papain‐like cysteine proteases (PLCPs) are pivotal in plant development and immunity, though their specific regulatory mechanisms in immune responses remain largely unexplored. In this study, we identify AtRD19C, a vacuole‐localized PLCP, and demonstrate its role in negatively regulating plant immunity to Phytophthora parasitica . We show that AtRD19C suppresses the ethylene (ET) signaling pathway by destabilizing the copper chaperone AtATX1, which is essential for activating ET signaling through the ethylene receptor ETR1. Genetic and biochemical analyses reveal that AtATX1 and the ET signaling pathway positively regulate immunity against Phytophthora . Given the conserved roles of RD19C and ATX1 in Solanum tuberosum , our findings suggest a conserved mechanism by which RD19C and ATX1 regulate resistance to Phytophthora across plant species.