KSEF R&D Excellence: Protein secretion by fungal pathogens: delivery into the host cell cytoplasm

When phytopathogenic microbes colonize host plants, they secrete a large number of proteins that function in pathogenicity. Sometimes, the plant can detect the presence of a "non-self' molecule and mounts a defense response, which prevents infection. Studies of bacterial proteins that elicit plant defenses reveal that these molecules are delivered directly into the plant cell c)10plasm by a specialized secretion system. In susceptible plant varieties that are unable to detect the elicitor(s), the proteins act as pathogenicity factors by suppressing the cell's basal defenses. Magnaporthe oryzae is the major fungal pathogen of rice, making it one of the most important plant pathogens worldwide. It is also a model organism for studies of fungal phytopathogenesis. Recent studies of elicitor proteins produced by M oryzae have provided indirect evidence that fungi also deliver proteins into the host cell cy1oplasm, though the mechanisms by which they accomplish this, and the functions of the transferred proteins, are unknown. The goal of this project is to develop a sensitive reporter system to detect when fungal proteins are delivered into the cytoplasm of a plant cell. Initially, the system will be employed to obtain direct evidence that the Magnaporthe oryzae elicitor proteins A VR-PIT A and A VR l-C039 enter the rice cell cytoplasm. It will then be used in large-scale screens to identify other M. oryzae proteins that enter host cells, potentially leading to the identification of novel pathogenicity factors. With this project, we will be exploring a new area of fungal pathogen biology. If successful, our findings will likely prompt new avenues of research in many different fungal pathogens, including ones that infect humans and other animals. The ability to identify and characterize large suites of proteins that fungi deljver into their hosts will also provide unprecedented insights into the mechanisms by which fungi cause disease. Keywords: rice blast, avirulence, effector, plant pathology