It is known that the filamentous Ascomycete Trichoderma atroviride is an effective mycoparasite to control a large number of phytopathogenic fungi. The ability to invade host organisms during parasitism requires adaptive remodeling of the cell wall polysaccharides to prevent host recognition and defensive responses. Strategies by which chitin evades the host's immune system are common to all plant and human pathogens, but have not been studied in mycoparasites so far.

Recently we have shown that chitin and chitosan act as key elements in the remodeling of cell walls during mycoparasitism. We believe that converting chitin to chitosan could serve as a disguise strategy and as a scavenger for oxidative stress from phytopathogens. Accordingly, we found an enriched number of chitin and chitosan metabolic enzymes with essential roles in cell wall turnover. In addition, not only chitin but also glucan, the main component of the polysaccharide core, could play a fundamental role in the restructuring of the functional cell walls and thus in mycoparasitism.

We will analyze the synergistic behavior and spatial relationship of chitin and glucan remodeling enzymes during mycoparasitism and hyphal development. Advanced microscopic studies include the single and co-localization of chitin synthases, chitin deacetylases, glucan synthase, and transglycosylases using multiple labeling strategies. Expression studies and phenotypic characterization of selected knockout lines provide additional information about their function and possible synergies. In addition, we will develop a highly specific probe that enables the visualization of surface exposed chitosan in vivo during the fungal interaction and growth. The analysis of the biochemical cell wall composition and the chitin synthase assays of the most important chitin synthases will complement our analysis. The differential proteome of chitin deacetylases and chitosanases during mycoparasitism will provide further insights into the invasive strategies during mycoparasitsm. Level of originality / innovation. With our approach, we will be able to draw the first, holistic picture of the spatial and interdependent processes of cell wall remodeling in T. atroviride as model organism for mycoparasitism. The developed chitosan affinity probe will be a versatile, reliable tool for this project and future studies to illuminate the chitosan layer in vivo and in situ. The novel insights could also be transferred to pathogenic fungi for humans, animals and plants. Thus, our research could provide anchor points for the development of new drugs to combat such organisms. For this reason, we also consider the information obtained from this project as an accelerator of research beyond the scope of this proposal.

Working group: WG Gruber

Primary researchers involved:

Sabine Gruber

Lisa Kappel

Harald Kühnel

Vincent Bulone