Enhanced resistance in T heobroma cacao against oomycete and fungal pathogens by secretion of phosphatidylinositol‐3‐phosphate‐binding proteins

Summary The internalization of some oomycete and fungal pathogen effectors into host plant cells has been reported to be blocked by proteins that bind to the effectors' cell entry receptor, phosphatidylinositol‐3‐phosphate ( PI 3 P ). This finding suggested a novel strategy for disease control by engineering plants to secrete PI 3 P ‐binding proteins. In this study, we tested this strategy using the chocolate tree T heobroma cacao . Transient expression and secretion of four different PI 3 P ‐binding proteins in detached leaves of T . cacao greatly reduced infection by two oomycete pathogens, P hytophthora tropicalis and P hytophthora palmivora, which cause black pod disease. Lesion size and pathogen growth were reduced by up to 85%. Resistance was not conferred by proteins lacking a secretory leader, by proteins with mutations in their PI 3 P ‐binding site, or by a secreted PI 4 P ‐binding protein. Stably transformed, transgenic T . cacao plants expressing two different PI 3 P ‐binding proteins showed substantially enhanced resistance to both P . tropicalis and P . palmivora , as well as to the fungal pathogen C olletotrichum theobromicola . These results demonstrate that secretion of PI 3 P ‐binding proteins is an effective way to increase disease resistance in T . cacao , and potentially in other plants, against a broad spectrum of pathogens.