Tvbgn3, a β-1,6-Glucanase from the Biocontrol Fungus Trichoderma virens , Is Involved in Mycoparasitism and Control of Pythium ultimum

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Abstract
Even though beta-1,6-glucanases have been purified from several filamentous fungi, the physiological function has not been conclusively established for any species. In the present study, the role of Tvbgn3, a beta-1,6-glucanase from Trichoderma virens, was examined by comparison of wild-type (WT) and transformant strains in which Tvbgn3 was disrupted (GKO) or constitutively overexpressed (GOE). Gene expression analysis revealed induction of Tvbgn3 in the presence of host fungal cell walls, indicating regulation during mycoparasitism. Indeed, while deletion or overexpression of Tvbgn3 had no evident effect on growth and development, GOE and GKO strains showed an enhanced or reduced ability, respectively, to inhibit the growth of the plant pathogen Pythium ultimum compared to results with the WT. The relevance of this activity in the biocontrol ability of T. virens was confirmed in plant bioassays. Deletion of the gene resulted in levels of disease protection that were significantly reduced from WT levels, while GOE strains showed a significantly increased biocontrol capability. These results demonstrate the involvement of beta-1,6-glucanase in mycoparasitism and its relevance in the biocontrol activity of T. virens, opening a new avenue for biotechnological applications.