Towards understanding the diversity, evolutionary origins, and host spectrum of the overlooked oomycete genus Lagena

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The genus Lagena, long thought to contain just a single species, has recently been revealed by environmental sequencing to encompass much more diversity. Gaining insights into the diversity of the group, the hosts they parasitise and the genomic features underlying pathogenicity is crucial for understanding the evolution of pythiaceeous oomycetes and the acquisition of obligate biotrophy in this group. In our previous work we could already show that the holocarpic genus Lagena not only contains parasites of plants, but also parasitoids of diatoms. It is the aim of this project to explore the diversity and evolution of Lagena and Lagena-like species still placed in other genera further, testing the hypotheses that 1) Lagena species have diversified in diatom hosts and the parasites of diatoms assigned to Lagenidium belong to Lagena instead, 2) Lagena is a widespread but overlooked root parasite, and there are lineages specialised to certain host groups, 3) There are hosts other than diatoms and angiosperms infected by the genus Lagena, e.g. filamentous cyanobacteria and oomycetes. 4) Holocarpic spore production in Lagena is a derived state, resulting from the reduction of a larger vegetative mycelium into a holocarpic thallus. 5) There are genomic features that correlate with the hosts infected and physiology (obligate vs. facultative biotrophy). The testing of these hypotheses will yield fundamental insights into an apparently widespread and diverse, yet mostly overlooked group of small holocarpic oomycetes closely related to Pythium. Overall, the knowledge gained with respect to the phylogeny, pathogenic versatility, genomic features, and evolutionary processes of these little-studied parasites will be a vital step towards understanding the evolution of pythiacaeous oomycetes. It will also constitute the basis for future studies, e.g. into the reduction of mycelia to holocarpic thalli and the parallel evolution of obligate biotrophy in different oomycete groups.