Identifizierung und Charakterisierung organspezifischer Ustilago maydis Effektoren

Ustilago maydis, the causative agent of corn smut disease, penetrates its host plant Zea mays over the epidermis and induces tumor formation in all areal parts of the plant after successful colonization. For efficient suppression of the plant immune system U. maydis depends on the secretion of several effector proteins. The infected plant organs differ in structure and physiology, suggesting organ-specific infection structures of U. maydis. This assumption was strengthened by transcriptional analysis of infected maize plants that showed organ specific transcriptional differences during tumor formation at pathogen and host. This thesis focused on the identification and functional characterization of organ-specific U. maydis effectors. 17 leave-specific and four tassel-specific induced candidates with a predicted signal peptide were selected. Deletion analyses revealed that seven of these U. maydis genes have an important influence in seedling infections, two of them in tassel infections and two are important for virulence in both tested organs. One of the identified organ-specific candidates is the U. maydis effector Um01829. The gene um01829 was strongly expressed during leave infections, but very weak during colonization of tassels. The U. maydis deletion mutant SG200Δum01829 showed a reduced virulence at seedling infections, whereas tassel infections were comparable with the wildtype SG200. Microscopic analyses confirmed the predicted secretion of the protein and revealed that it localizes at cell/cell-passages and in the apoplastic space. Additionally it was observed, that the deletion mutant has a significant defect at the cell/cell-passaging at infected maize leaves four and eight days post infection. In vitro assays with several 4-nitrophenyl labeled substrates showed that the protein encoded by um01829 is an α-L-arabinofuranosidase. Seedling infections with enzymatic inactive Um01829 showed a partial virulence-influence of the α-L-arabinofuranosidase function, and suggest additionally further virulence-relevant functions of this effector.