Endo-β-1,3-glucanase (GH16 Family) from Trichoderma harzianum Participates in Cell Wall Biogenesis but Is Not Essential for Antagonism Against Plant Pathogens

Abstract

<i>Trichoderma</i> species are known for their ability to produce lytic enzymes, such as exoglucanases, endoglucanases, chitinases, and proteases, which play important roles in cell wall degradation of phytopathogens. β-glucanases play crucial roles in the morphogenetic-morphological process during the development and differentiation processes in <i>Trichoderma</i> species, which have β-glucans as the primary components of their cell walls. Despite the importance of glucanases in the mycoparasitism of <i>Trichoderma</i> spp., only a few functional analysis studies have been conducted on glucanases. In the present study, we used a functional genomics approach to investigate the functional role of the <i>gluc31</i> gene, which encodes an endo-β-1,3-glucanase belonging to the GH16 family in <i>Trichoderma harzianum</i> ALL42. We demonstrated that the absence of the <i>gluc31</i> gene did not affect the in vivo mycoparasitism ability of mutant <i>T. harzianum</i> ALL42; however, <i>gluc31</i> evidently influenced cell wall organization. Polymer measurements and fluorescence microscopy analyses indicated that the lack of the <i>gluc31</i> gene induced a compensatory response by increasing the production of chitin and glucan polymers on the cell walls of the mutant hyphae. The mutant strain became more resistant to the fungicide benomyl compared to the parental strain. Furthermore, qRT-PCR analysis showed that the absence of <i>gluc31</i> in <i>T. harzianum</i> resulted in the differential expression of other glycosyl hydrolases belonging to the GH16 family, because of functional redundancy among the glucanases.