Abstract
Phytopathogenic fungi are a severe threat for agricultural crop yields. With the domestication of plants as food sources for the human society new pathogens emerged and spread together with their host plants. Since host-pathogen interactions underlie a strong force by natural selection, they constantly co-evolve. Pathogens need to adapt to their hosts, for instance their repertoires of virulence factors that are required to establish compatible infections. Virulence factors include pathogen effectors that are small secreted molecules that interfere with host plant immunity and can confer host specialisation. Fungi that lack host-specific adaptations are unable to infect and their interactions with the host plant are incompatible. However, host infections by adapted pathogens can facilitate co-infections of non-adapted species and thereby might provide a possible route for host shifts and the emergence of new host adapted pathogens.
We conducted wheat infection experiments using Zymoseptoria tritici and the two closely related sister species Zymoseptoria ardabiliae and Zymoseptoria pseudotritici. Our goal was to study the ability of co-infections of Zymoseptoria spp. in local leaf tissue or in adjacent leaf areas. Z. tritici is a globally distributed fungus and is highly virulent on wheat (Triticum aestivum). The sister species were isolated from wild grasses in the Middle East and are non-adapted to wheat. By analysing their infection success in the different experiments, we found that co-infection did not occur locally in the same leaf tissue while a co-infection in adjacent leaf areas was likely facilitated. This indicates that an infection by Z. tritici suppresses the immune response in adjacent leaf areas of the plant and enables further infections.
As effectors are key molecules for host specialisation, their identification and characterisation are essential to understand their interference with the host immunity. In this study, we engineered a Z. tritici deletion mutant lacking a candidate effector gene. This mutant will facilitate future functional studies that will help to understand the role of this putative effector for host specialisation of Z. tritici.
