B3 Comparative analysis of cross kingdom RNA transfer in smut/plant pathosystems

Extracellular vesicles (EVs) are potent vehicles for RNA delivery mediating for example the intensive communication between microbes and their host plants. We will study this novel RNA trafficking process from the perspective of two smut fungi with distinct host specificities. Ustilago maydis causes smut disease in corn and serves as an established and amenable model for intracellular RNA transport. Thecaphora thlaspeos infects Brassicaceae species including the model plant Arabidopsis thaliana, which facilitates in-depth examination of the interaction from the plant side. Interestingly, U. maydis has lost its RNAi machinery, while it is still present in T. thlaspeos. By following a comparative approach, we will benefit from the relative strengths of both pathosystems. Thus, we are in a unique position for a detailed analysis of EV-delivered RNA from related fungi to identify common themes. Differences will give insights into host specialisation and the employment of the RNAi machinery in the infection process. We will examine both the sRNA and mRNA cargos of fungal EVs to determine their relative biological significance. In order to reach our goals, we will (i) generate a detailed inventory of the RNA and protein content of smut EVs, (ii) study the functional relevance of the EV-mediated RNA transfer as well as (iii) investigate the underlying mechanism of selection and loading of RNAs in EVs. This strategy will clarify the question of how RNA contributes to smut-host communication. The comparative analysis of related smuts with the diverse pathogens and symbionts studied in our research unit will uncover both highly conserved core components as well as life-style or host-specific adaptations. Gained insights will guide novel approaches to target pathogens by RNA-mediated defence strategies.