Identification and functional characterization of conserved sebacinoid effector candidates

Microbes are suspected to be strongly subjected to an evolutionary "arms race" with their host. Thus, due to adaptation and evolution, effector proteins are expected to be under positive selection and to accumulate mutations. Prediction of homologies between different species is therefore quite difficult when based solely on computational pipelines. Here careful manual examination and validation must follow as well as structure-based homology search methods which may provide additional information. A manually curated search for potential effectors (with predicted signal peptide) smaller than 300 aa and with no known functional domain resulted in 249 putative effector candidates in P. indica and 337 in S. vermifera. An additional search among Pfam domain-containing effector candidates longer than 300 aa identified about 30 additional proteins with signal peptide but putative intracellular regulatory functions, suggesting translocation into the host cell. Comparative analyses between P. indica and S. vermifera effector candidates induced in planta identified a small core of effector-like proteins conserved in these related sebacinoid isolates which seems to be absent in more distantly related symbionts and saprotrophic fungi. As we expect a conservation of effector actions in these two species a list of 20 top in planta-induced effector candidates from S. vermifera and P. indica orthologs was compiled and functions as a priority list for functional analyses using different tools established in our group. We recently succeeded in establishing a transformation system also for S. vermifera which will provide a crucial tool for functional analysis of effectors.