Spore germination of Trichoderma atroviride is inhibited by its Lys M protein TAL6.

Lys M motifs are carbohydrate-binding modules found in prokaryotes and eukaryotes. They have general N-acetylglucosamine binding properties and therefore bind to chitin and related carbohydrates. In plants, plasma-membrane-bound proteins containing Lys M motifs are involved in plant defence responses, but also in symbiotic interactions between plants and microorganisms. Filamentous fungi secrete Lys M proteins that contain several Lys M motifs but no enzymatic modules. In plant pathogenic fungi, for Lys M proteins roles in dampening of plant defence responses and protection from plant chitinases were shown. In this study, the carbohydrate-binding specificities and biological function of the Lys M protein TAL6 from the plant-beneficial fungus Trichoderma atroviride were investigated. TAL6 contains seven Lys M motifs and the sequences of its Lys M motifs are very different from other fungal Lys M proteins investigated so far. The results showed that TAL6 bound to some forms of polymeric chitin, but not to chito-oligosaccharides. Further, no binding to fungal cell wall preparations was detected. Despite these rather weak carbohydrate-binding properties, a strong inhibitory effect of TAL6 on spore germination was found. TAL6 was shown to specifically inhibit germination of Trichoderma spp., but interestingly not of other fungi. Thus, this protein is involved in self-signalling processes during fungal growth rather than fungal-plant interactions. These data expand the functional repertoire of fungal Lys M proteins beyond effectors in plant defence responses and show that fungal Lys M proteins are also involved in the self-regulation of fungal growth and development. [ABSTRACT FROM AUTHOR]