Functional analysis of Stp1, a secreted effector of Ustilago maydis essential for host colonization
L. LIANG (1), K. Schipper (2), L. Lo Presti (1), N. Ludwig (1), B. Zechmann (3), T. Glatter (1), R. Kahmann (1) (1) Max Planck Institute for Terrestrial Microbiology, Germany; (2) Heinrich Heine University Düsseldorf, Dept. Microbiology, Germany; (3) Baylor University, Center for Microscopy and Imaging, U.S.A.

The biotrophic fungus Ustilago maydis trigger tumor formation on infected maize plants. The secreted U. maydis effector Stp1 is essential for host colonization. stp1 mutants are non-pathogenic and elicit strong plant defense reactions. The N- and C-terminal domains of Stp1 are essential for function while the large central region is dispensable. Additionally, separated N- and C-terminal domains (both fused to signal peptides) of Stp1 can complement a ?stp1 strain when co-expressed. Yeast two-hybrid screening yielded a large number of potentially interactors. Of these a secreted maize cysteine protease and a cytoplasmic serine/threonine-protein kinase could both be inhibited by Stp1. Whether these interactions have biological relevance is currently under investigation. In parallel, we have isolated interactors of Stp1 by performing Co-IP of tagged Stp1 from infected maize tissue followed by mass-spectroscopic analysis. We will contrast these results to results from the yeast two-hybrid screen. Stp1 localization studies by immuno-EM and a newly established uptake assay based on transgenic maize expressing cytoplasmic BirA biotin ligase yielded diverging results. We are now attempting to determine the localization of Stp1 via functional complementation of the ?stp1 strain by transgenic maize expressing Stp1 in the cytosol or apoplast, respectively. Results of these studies will be shown and explanations for the opposing behaviour of Stp1 in different assays will be attempted.

Abstract Number: P4-98
Session Type: Poster