Microbe effector proteins have been well studied in bacteria but are relatively unexplored in fungi such as the powdery mildews. Sequence analysis of the barley powdery mildew genome suggested this species encoded ~400 candidate effectors. K. Scheibel has initiated a screen of Golovinomyces cichoracearum powdery mildew effectors for those that reduce pathogen success on its host Arabidopsis when the effector gene is silenced by host-induced gene silencing. Effectors that are important for pathogen success is this screen will be characterized in detail to determine how the effectors impact host biology. In a separate screen, G. Yu will screen for effectors that modify the host gene expression (e.g., various defense response genes or various genes implicated in susceptibility) in transient assays to expand the range of tests for effectors.