Histidine kinase two-component response regulators Ssk1, Skn7 and Rim15 differentially control growth, developmental and volatile organic compounds emissions as stress responses in Trichoderma atroviride.

The Skn7, Ssk1 and Rim15 proteins are response regulators involved in osmotic, oxidative and nutritional stress in fungi. In order to verify the involvement of these genes in IMI206040's growth, conidiation, direct antagonism against plant pathogens ( and ), production of volatile organic compounds (VOCs) with fungistatic effect, and interaction with plants (growth promotion), single mutants were generated, and the phenotypic patterns were analysed in comparison to the wild-type () strain. The mutants were submitted to osmotic, oxidative, membrane and cell wall stress conditions in vitro. The Δ and Δ mutants did not show either significant differences at morphological level, or marked decreases in mycelial growth and conidiation in relation to , whereas Δ had altered phenotypes in most conditions tested. The plant-growth promotion of seedlings induced by VOCs was not quantitatively modified by any of the mutants in relation to the strain, although possible differences in secondary root hairs was noticed for Δ. The fungistatic activity was significantly altered for Δ and Δ. Overall, the Δ strain showed remarkable morphological differences, with decrease in mycelial growth and conidiation, being also affected in the antagonistic capacity against plant pathogens. The impacts demonstrated by the deletion of suggest this gene has a relevant participation in the signalling response to different stresses in and in the interactive metabolism with phytopathogens and plants. On the other hand, unlike other fungal models, Skn7 did not appear to have a critical participation in the above-mentioned processes; Rim15 seemed to confirm its involvement in modulating cellular responses to nutritional status, although with a possible cross-talk with other cellular processes. Our results suggest that Ssk1 likely plays a key regulatory role, not only in basic metabolisms of , but also in biocontrol-related characteristics.