A new regulator of cellulase and xylanase in the thermophilic fungus Myceliophthora thermophila strain ATCC 42464.

Myceliophthora thermophila (ATCC 42464) is a thermophilic fungus that produces cellulolytic enzymes with high thermal stability. Unlike its mesophile counterparts, study on gene expression regulation of cellulolytic enzymes in M. thermophila is inadequate. This work identified the function of MHR1, a putative transcription regulator of cellulolytic enzymes in M. thermophila that was found through RNA-Seq based gene expression profile analysis. RNA interference was used to study the role of MHR1. A recombinant plasmid, pUC19-Ppdc-mhr1-Tpdc, which contained the RNAi sequence for mhr1 was constructed and transformed into M. thermophila. One of the transformants, MtR5, in which the RNA interference efficiency was the highest, was used for the following studies. In the mhr1-silenced strain MtR5, the filter paper hydrolyzing activity was 1.33-fold; β-1, 4-endoglucanase activity was 1.65-fold; and xylanase activity was 1.48-fold higher than those of the parental strain after induction, respectively, by wheat straw powder. qRT-PCR showed that gene expression of cbh1, cbh2, egl3 and xyr1 were 9.56-, 37.36-, 56.14- and 28.30-fold higher in MtR5 than in wild type, respectively. Our findings suggest that the transcription factor MHR1 of M. thermophila can repress cellulase and xylanase activities. Silenced mhr1 results in increased expression not only of the main cellulase genes, but also of the positive regulatory gene xyr1. This work is relevant to the development of M. thermophila as an industrial production host for cellulolytic and hemicellulolytic enzymes, which could be used to degrade a wide range of different biomass, converting lignocellulosic feedstock into sugar precursors for biofuels.