Evolutionary and population genomic analyses of the Zymoseptoria species complex

Plant pathogenic fungi in agricultural environments have to adapt to rapidly changing environments. Comparative analyses of closely related pathogens adapted to natural or agricultural ecosystems allow gaining more profound knowledge about the evolutionary responses that play a role in the adaptation to these differing environments. The members of the Zymoseptoria species complex comprise an excellent model system for comparative analyses since they either are specialized on wheat (Z. tritici) or associated with wild plant species (Z. ardabiliae, Z. brevis, Z. pseudotritici). Using methods of comparative genomics and molecular genetics this thesis shows that the Zymoseptoria species have unusual genome plasticity, which is characterized by the occurrence of accessory chromosomes and by structural changes associated with repetitive elements. Further, the results of population genomic analyses show that genetic diversity is much higher in the wheat pathogen Z. tritici compared to the wild grass associated pathogens Z. ardabiliae and Z. brevis. The results of this thesis connect the observed differences in genetic diversity levels between the species with differences in demographic events during their evolution. Genome-wide analyses of signatures of selection reveal a much higher number of genes with signatures of positive selection in the wheat pathogen Z. tritici compared to Z. ardabiliae and Z. brevis. Further, an ABC transporter candidate shows signatures of positive directional and positive diversifying selection in Z. tritici. Previous already studies connected ABC transporters with virulence and drug resistance in this species making this ABC transporter candidate an interesting candidate for future analyses. In this thesis, the detection of effector candidates, a class of proteins that are known to be important for modulating the immune system of the host, indicates the importance of species-specific effectors on host adaptation.


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