Plasmopara viticola effector PvRXLR53 suppresses innate immunity in Nicotiana benthamiana.

Plasmopara viticola, the casual oomycete of grapevine downy mildew, could cause yield loss and compromise berry quantity. Previously, we have identified several PvRXLR effectors that could suppress plant immunity to promote infection and disease development. In this study, the role of effector, PvRXLR53, in plant-microbe interaction was investigated. PvRXLR53 has several orthologs in other oomycetes and contains a functional signal peptide. Expression level of PvRXLR53 was already detected upon inoculation, further induced in the early stage after P. viticola inoculation and decreased to low level in the late infection stage in grapevine (Vitis vinifera 'Cabernet Sauvignon'). PvRXLR53 is localized in both nucleus and cytoplasm. When transiently expressed in Nicotiana benthamiana, PvRXLR53 suppressed oomycete elicitor INF1-triggered programmed cell death and defense gene expression, and Phytophthora capsici-induced reactive oxygen species production (ROS) and eventually resistance to P. capsici. In summary, these findings suggest that P. viticola secretes PvRXLR53 to suppress host immunity from the very early stage of infection.