The genomic basis of host specificity as tool for species recognition and delimitations in Ustilaginales - a parasite group with high gene flow

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During the first funding period of the SPP 1991 we were focusing on questions of hybridization and species delimitation in Ustilaginales. Previous work has shown that species within the Ustilaginales that have been separated for millions of years are able to initiate sexual reproduction. Based on several newly genome sequenced species, we could now show that hybridization is a common feature in this lineage of host specific plant parasites and most probably was an important feature during the evolution of the whole lineage. This makes species concepts, such as the biological species concept (mating population of compatible individuals producing viable offspring) or the phylogenetic species concept (coalescent based approaches) and species recognition based on these concepts difficult to apply in this lineage. Thus we would like to study and test the relevance of host specificity for species recognition and delimitation in this follow-up proposal. We will compare members of two closely related families namely the Ustilaginaceae and Anthracoideaceae to analyze different different aspects relevant for taxonomy of plant parasites. We plan to study the following aspects: (1) We will study the contribution of genes linked to the infection process (such as genes coding for effectors) with respect to host specificity and their fate during hybridization events. (2) We will use information of full genomes, host specificity and co-phylogeny to understand lineage sorting of relevant genes in different evolutionary strata in the Ustilaginaceae. (3) Based on a target-enrichment approach will study recent speciation in populations of four sibling species of Anthracoideaceae. Thereby we will contribute to the discussion of species concepts and species delimitation in plant parasites, where traditional species concepts like the morphological, biological or phylogenetic species concepts fail to provide a satisfying taxonomic concept so far.