Effect of LAE1 gene deletion on gene expression in Trichoderma. Trichoderma reesei

The mitosporic fungus Trichoderma reesei is an industrial producer of enzymes for degradation of lignocellulosic polysaccharides to soluble monomers that can be fermented to biofuels. The genes encoding these enzymes in T. reesei have recently been shown to be clustered in the genome. Here we will show that the expression of these genes is epigenetically controlled at the heterochromatin level by the protein methyltransferase LAE1. Deletion of lae1 led to a loss of expression of the major cellulase and hemicellulase encoding genes, and resulted in an inability to grow on cellulose. The cellulase null phenotype was also seen with known soluble inducers of enzymes active on cellulose. In contrast, introduction of a second copy of lae1 or its enhanced expression under a strong constitutive promoter resulted in increased levels of cellulases. Thus, our data provides an experiment-based explanation for the advantage for clustering of cellulases in the genome of T. reesei, and imply that the heterochromatin structure is a major determinant of cellulase gene expression and hence an attractive target for strain improvement. Overall design: We used two biological replicas of four T. reesei strains growing on lactose, the parent strain (QM9414), a delta-lae1, and two overexpressing strains (tef1:lae1 mutant 1 and mutant 2).