Pathogen Evolution


Evolution of Global Diversity and Dynamics of Plant Pathogen Proliferation

Thomas Wicker (IPMB), Beat Keller (IPMB), Lukas Keller (EBES)

The spread of newly evolved pathogens is an important selective force in evolution, and it poses major challenges to agriculture and medicine. In the proposed project, we want to address this topic using a plant pathogen system established in our laboratory. Our previous study in the framework of the URPP Evolution has revealed insights into the diversity of the gene pool of wheat powdery mildew Blumeria graminis forma specialis tritici (B.g. tritici). Most of the diversity in the mildew isolates studied comes from recombination of ancient haplotypes that evolved long before the onset of agriculture. Here, we propose genomic sequencing of at least 100 isolates of B.g. tritici from all over the world. This will allow a quantitative assessment of the global diversity of the B.g. tritici gene pool. Additionally, we will be able to analyze how recombination of existing haplotypes contributes to the rise of new mildew strains. Furthermore, we will be able to perform analyses on population genetics and comparative genomics to study how rapidly ancient and new haplotype combinations spread across the globe, especially across geographical barriers. In collaboration with Prof. Beat Keller's group, mildew samples will be collected and their genomes sequenced. The group of Prof. Lukas Keller will bring in the expertise necessary to perform population genetic analysis. This project will generate the broadest assessment of global diversity of a fungal plant pathogen available so far and will allow conclusions on the evolution of new mildews strains and the dynamics of their proliferation across the globe.

PhD-Student: Alexandros Sotiropoulos


Molecular Basis of Recent Host Expansion and Adaptation of the Wheat Powdery Mildew Pathogen

Beat Keller (IPMB), Thomas Wicker (IPMB), Kentaro Shimizu (EBES), Frank Rühli (IEM)

In the framework of the URPP “Evolution in action”, our previous project has revealed insight into the evolution in action of host expansion in cereal powdery mildews. We found that powdery mildews infecting polyploid triticale (a crop developed by plant breeders 50 years ago) or bread wheat (a crop developed by farmers about 10’000 years ago) most likely evolved by the hybridization of mildew forms that were specialized on the parental species of triticale and bread wheat, respectively. Here, we propose to study at the molecular level the functional aspects of host specialization. Host expansion of mildew from bread wheat to triticale, and from durum wheat to bread wheat will be studied. Crosses between the narrow vs. extended mildew forms will be made and the progeny will be analyzed for segregation of pathogen growth on the narrow vs. extended host. This will allow us to determine if host expansion is controlled by few genes, or if it is a quantitative trait. Genes will be mapped at high resolution and molecularly isolated in case of major genes. Validation of gene function will be done by backcrosses to the mildew with the narrower host range (B.g. tritici or B.g. duri) and selection for growth on the extended host to narrow down genetic segments involved in host expansion. In addition, based on the large dataset of genomic/transcriptomic data, which will be further developed in Thomas Wicker’s project, we want to identify avirulence genes responsible for intraspecific pathogen adaptation to bread wheat resistance genes using genomics in combination with genome-wide association studies. The project will contribute to a detailed molecular understanding of host specificity in an obligate biotrophic fungal pathogen.

PhD-Student: Marion Müller