Engineered elicitin protein enhances Phytophthora resistance in plants by dual immune induction and pathogen inhibition

Phytophthora pathogens are devastating agricultural threats that cannot synthesize sterols and must scavenge them from host plants. This study exploits their sterol auxotrophy by engineering a dual-function elicitin protein, SOJ5^V84F, for enhanced disease control. The V84F mutation in the sterol-binding pocket of the Phytophthora sojae elicitin SOJ5 abolishes sterol binding but retains interaction with the pathogen's sterol-sensing receptor kinase SSRK1. SOJ5^V84F acts as a dominant-negative inhibitor: it competitively disrupts SSRK1-mediated sterol signaling (calcium influx, MAPK activation) and significantly inhibits P. sojae growth in an SSRK1-dependent manner. Crucially, SOJ5^V84F retains its ability as a microbe-associated molecular pattern to robustly elicit reactive oxygen species burst in soybean, pepper, tomato, and potato plants. Consequently, pre-treatment with SOJ5^V84F provided superior protection compared to wild-type SOJ5 against P. sojae in soybean, and against Phytophthora capsici and Phytophthora infestans in pepper, tomato, and potato under greenhouse conditions. This work demonstrates that engineered SOJ5^V84F combines direct pathogen inhibition with host immune activation, establishing a novel dual-mechanism strategy for protein-based biocontrol against sterol-auxotrophic oomycetes.