Spore germination of Trichoderma atroviride is inhibited by its LysM protein TAL6

Abstract

LysM 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 LysM motifs are involved in plant defence responses, but also in symbiotic interactions between plants and microorganisms. Filamentous fungi secrete LysM proteins that contain several LysM motifs but no enzymatic modules. In plant pathogenic fungi, for LysM proteins roles in dampening of plant defence responses and protection from plant chitinases were shown. In this study, the carbohydratebinding specificities and biological function of the LysM protein TAL6 from the plant-beneficial fungus Trichoderma atroviride were investigated. TAL6 contains seven LysM motifs and the sequences of its LysM motifs are very different from other fungal LysM 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 selfsignalling processes during fungal growth rather than fungal-plant interactions. These data expand the functional repertoire of fungal LysM proteins beyond effectors in plant defence responses and show that fungal LysM proteins are also involved in the self-regulation of fungal growth and development.

Verticillium dahliaeLysM effectors differentially contribute to virulence on plant hosts

“…Interestingly, the second clade solely contains the LysMs of the V. dahliae core effectors and the Trichoderma atroviride LysM effector TAL6 that was previously shown to specifically inhibit germination of conidia of Trichoderma spp. and that was proposed to act in fungal development rather than in host interactions (Seidl-Seiboth et al, 2013) (Fig. 6B).…”

The Genomes of Three Uneven Siblings: Footprints of the Lifestyles of Three Trichoderma Species

“…S32 in the supplemental material). Interestingly, it was reported recently that TAL6 (TA_297859) is implicated in the inhibition of conidial germination in T. atroviride (1306). However, this finding does not exclude a role of these molecules in plant or fungi interactions and needs to be tested.…”

LysM Effectors: Secreted Proteins Supporting Fungal Life

“…Fungi secrete lytic enzymes that break chitin polymers and in this manner maintain cell wall flexibility to allow hyphal growth, branching, morphogenesis, and spore germination. Recently, a Trichoderma atroviride LysM effector was found to be coexpressed with an adjacent chitinase gene [26]. Since addition of the purified LysM effector to T. atroviride inhibited spore germination in vitro , a role in hyphal growth was proposed for this LysM effector.…”