Plasmopara viticola effector PvRxLR24 (a potential phosphatase) interferes grapevine stomatal immunity by targeting VvOST1.

Numerous pathogens invade plants through stomata, and plants, on the other hands, could close the stomata after sensing the pathogens PAMPs. Subsequently, pathogens could overcome this plant immune response with their phytotoxins and effectors. A previous study showed that Plasmopara viticola, a strictly obligate biotrophic oomycete, could inhibit the Vitis vinifera stomatal closure to promote infection. However, the underlying mechanism stimulating the stomata movement is still poorly understood. Here we demonstrate that PvRxLR24, an effector from P. viticola, functions analogously to a phosphatase by directly inhibiting the kinase activity of OPEN STOMATA 1 (OST1), a central regulator of ABA signaling and stomatal closure. This inhibition subsequently abolishes the activation of the slow-type anion channel SLAC1, resulting in a "stomatal lock" open state. Our study demonstrated that OST1 is the direct target of pathogen effectors, shedding light on a new mechanism by which pathogens could manipulate the plant ABA signaling pathways to influence stomatal movement for successful invasion.