"Our existence as human beings is based on plants and their products. Worldwide, crops are threatened by pests including biotrophic fungi. Therefore, it is of vital interest to develop new strategies to reduce crop losses and to improve crop plants for the growing world population. Biotrophic plant pathogens employ small secreted molecules, so-called effectors, to overcome plant defence systems and to establish biotrophy. The rapid increase in available genome sequences of biotrophic pathogens and in transcriptomic datasets of their biotrophic stages allow us to identify putative secreted proteinaceous effectors by bioinformatic means. However, our insight into the functions of these effectors is still very limited. In this proposal, the PI´s extensive experience on both the plant host side and the fungal pathogen side of the biotrophic interaction is exploited to develop a workflow for functional, partially robotic-based screens to fill this gap. The combination of screen-deduced functional information with the analysis of effector localisation and specific host interactors will provide the basis for formulating starting hypotheses of effector function. These will then be tested in individual case studies, employing the well established Ustilago maydis-Zea mays as well as the new Ustilago bromivora-Brachypodium distachyon model systems. The project will be conducted at the Max Planck Institute (MPI) for Terrestrial Microbiology in a highly stimulating scientific environment. Linking the dramatic morphological changes and underlying molecular events during biotrophy on the host side to the action of subsets or even single effector proteins will allow the creation of a synthetic effectome. The deep functional understanding of the manipulative toolbox of biotrophs has the potential to facilitate transgenic crop development and will open a new era in the development of sustainable antifungal plant protection strategies."