Plant cells under siege: plant immune system versus pathogen effectors.

Pathogen-secreted effector proteins enable pathogens to manipulate plant immunity for successful infection. To penetrate host apoplastic space, pathogens reopen the stomata. Once the invasion into the apoplast occurs, pathogens deceive the host detection system by deploying apoplastic effectors. Pathogens also deliver an arsenal of cytosolic effectors into the host cells, which undermine host immunity such as salicylic acid (SA)-dependent immunity. Here we summarize recent findings that highlight the functions of the effectors from fungal, oomycete and bacterial pathogens in the key steps of infection at the stomata, in the apoplast, and inside the cell. We also discuss cell type-specific responses in the host during infection and the necessity of further investigation of plant-pathogen interactions at spatial and temporal resolution.