DSSS - The role of microbial interactions in fungal pathogenicity

Zymoseptoria tritici is an ascomycete pathogen that infects wild and domesticated species of wheat causing the disease Septoria Leaf Blotch. This fungus is one of the most devastating pathogens of wheat in temperate areas. In spite of its agricultural importance, the infection biology of Z. tritici is poorly understood. We have integrated evolutionary genomics, comparative transcriptomics, proteomics and experimental approaches to decipher the mechanisms that determine host specificity and allow successful plant invasion by Z. tritici. Notably, we focused on the early invasion and the extended “biotrophic” phase of Z. tritici considering these to be critical stages for the pathogen to overcome plant defenses. Comparative transcriptome analyses and proteome analyses of apoplastic fluid samples allowed us to identify candidate proteins that are produced by the fungus and by the plant in response to pathogen invasion. We focused our analyses on a set of fungal-produced proteins and further investigated their function using targeted gene deletion and heterologous gene expression. Hereby, we show that Z. tritici produces effector proteins that specifically interact with Pathogenicity Related (PR) proteins in wheat and thereby interfere with basic immune response pathways. Intriguingly, some effector proteins share a structural homology with proteins predicted to be antimicrobial. We further tested the ability of Z. tritici effectors to inhibit the growth of wheat-associated microbes. We show that a large number of effector candidates indeed can inhibit bacterial growth. In summary, our research demonstrates a close structural relatedness of effector proteins produced to interfere with plant defense and plant-associated microbes. Our findings underline the importance of considering ecological interactions in efforts to understand pathogen evolution and virulence.