Understanding the Phylogeny, Evolution and Host Specificity of the Exobasidiales (Ustilaginomycotina)

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Plant parasites constitute one of the largest ecological groups of fungi. The two major lineages that radiated once land plants were covering the planet, harbour several groups, which are exclusively plant parasitic. Although the Ascomycota and Basidiomycota evolved in direct interaction with their hosts, present data suggest, that the plant parasitic life-style has emerged several times. This is especially true, if we consider host-specific parasites like powdery mildews, rust or smut fungi. These host specific plant parasites are not only relevant as important drivers of evolution, but they represent also the largest threat to our major crop plants. E.g. all cereals are threatened by these three host specific fungal lineages and these fungi are responsible for a large economic loss each year.Major contributions have been made to the general understanding of virulence factors of Ustilaginomycotina. Ustilago maydis was the first fungal parasite, of which the genome has been fully sequenced. And in contrast to many other fungal plant parasites it can be easily grown in axenic conditions and is available for many genetic tools. The Ustilaginomycotina in total comprise more than 1700 species, most of which are highly host specific and in the meanwhile a few species have been studied in more detail. Comparative genomics and revers genetics have revealed, that so-called core effectors are important virulence factors being essential for the infection of the plant. However, the analyses of more distantly related species failed to identify factors relevant for host specificity. Therefore, we propose to use the order of Exobasidiales (Ustilaginomycotina) as a study case to identify and study factors relevant for host specificity. In contrast to the relatives of Ustilago maydis, the species of Exobasidium are very common and easy to find and isolated. A complementary sampling in China and Europe would allow to compare two lineages of closely related species. Thus, comparative genomics will go beyond the identification of core effectors, as more detailed analyses like studies of synteny, selection analyses or even transcriptomics will allow much more informative approaches. Therefore, based on 40-50 additional genomes, we will provide a phylogeny of the Exobasidiales to analyse trait evolution among and within the respective lineages. We would pay special attention to the analysis of the secretome, but we will include all informative aspects of the genomes. Additionally, we plan to use electron microscopy to study the ultrastructure of the interaction apparatus, as this might be an additional trait for host specificity. By applying these various approaches we want to analyse 1) the nutrition mode of various lineages, 2) the evolution of the sex-loci and potential sex chromosomes, 3) the evolution of effector pools of respective lineages and species, 4) morphological traits to integrate these data in the genome evolution in Ustilaginomycotina.