Fungi are important plant pathogens. They invade plant tissues through natural openings, such as stomata on leaves or wounds on root surfaces. In order to avoid or suppress the plant's defences, fungal pathogens secrete a wide variety of small molecules known as effectors, which interfere with immune responses and promote further host invasion. Many of these secreted molecules are proteins. Until now, these secreted proteins have been studied in the context of molecular plant-pathogen interactions; however, accumulating evidence suggests that many of these proteins play an important role as antimicrobial effectors, antagonising other microorganisms in the host tissue. The aim of this project is to elucidate the antimicrobial properties of secreted proteins in four fungal plant pathogens. We hypothesise that interactions with the host microbiota may be crucial for the successful invasion of plant tissues. Furthermore, we hypothesise that the repertoire of antimicrobial effectors produced by a given pathogen evolves in response to the particular microbiota of the host. To test these hypotheses, we will integrate different types of 'omics' data, machine learning approaches, and experimental methods. We have established culture collections of bacteria and fungi from three plant species, wild relatives of wheat, barley and sugar beet, four plants which are host the four fungal pathogens under study. This enables us to test if effector proteins, produced by the fungal pathogens, can suppress the growth of certain plant-associated microorganisms. For effectors that can suppress bacterial growth, we aim to understand the underlying mechanisms. Moreover, we aim to understand why some plant-associated microorganisms are suppressed by the fungal pathogen. To this end, we use plant experiments in which we propagate plants with defined microbial communities and pathogen mutants lacking a given effector of interest. The project will deliver novel insights into the relevance and diversity of microbial interactions in plants. Furthermore, we will unravel how such microbial interactions shape the evolution and host specificity of fungal plant pathogens.
