Pathogens secrete effector proteins that are transported into the cytoplasm of infected plant cells.
An exciting recent development in our understanding of plant-pathogen interactions has been the discovery that fungal and oomycete pathogens deliver small effector proteins into the cytoplasm of infected host cells (Catanzariti et al. 2006).
In resistant plants, the effectors are recognized by resistance proteins and a defence response in the form of hypersensitive cell death is triggered. In susceptible plants, the effectors are not recognized and function in the establishment of disease. As yet, the mechanism of delivery of effectors across the plant plasma membrane is not known.