The putative methyltransferase LaeA regulates mycelium growth and cellulase production in Myceliophthora thermophila

BackgroundFilamentous fungi with the ability to use complex carbon sources has been developed as platforms for biochemicals production. Myceliophthora thermophila has been developed as the cell factory to produce lignocellulolytic enzymes and plant biomass-based biofuels and biochemicals in biorefinery. However, low fungal growth rate and cellulose utilization efficiency are significant barriers to the satisfactory yield and productivity of target products, which needs our further exploration and improvement.ResultsIn this study, we comprehensively explored the roles of the putative methyltransferase LaeA in regulating mycelium growth, sugar consumption, and cellulases expression. Deletion of laeA in thermophile fungus Myceliophthora thermophila enhanced mycelium growth and glucose consumption significantly. Further exploration of LaeA regulatory network indicated that multiple growth regulatory factors (GRF) Cre-1, Grf-1, Grf-2, and Grf-3, which act as negative repressors of carbon metabolism, were regulated by LaeA in this fungus. We also determined that phosphoenolpyruvate carboxykinase (PCK) is the core node of the metabolic network related to fungal vegetative growth, of which enhancement partially contributed to the elevated sugar consumption and fungal growth of mutant Delta laeA. Noteworthily, LaeA participated in regulating the expression of cellulase genes and their transcription regulator. Delta laeA exhibited 30.6% and 5.5% increases in the peak values of extracellular protein and endo-glucanase activity, respectively, as compared to the WT strain. Furthermore, the global histone methylation assays indicated that LaeA is associated with modulating H3K9 methylation levels. The normal function of LaeA on regulating fungal physiology is dependent on methyltransferase activity.ConclusionsThe research presented in this study clarified the function and elucidated the regulatory network of LaeA in the regulation of fungal growth and cellulase production, which will significantly deepen our understanding about the regulation mechanism of LaeA in filamentous fungi and provides the new strategy for improvement the fermentation properties of industrial fungal strain by metabolic engineering.

Automated summary

This study investigated the role of the putative methyltransferase LaeA in regulating fungal growth and cellulase production. Deletion of laeA in Myceliophthora thermophila resulted in enhanced mycelium growth and glucose consumption. LaeA was found to regulate multiple growth regulatory factors (GRF) and the expression of cellulase genes. Overall, this research deepens our understanding of the regulatory mechanism of LaeA in filamentous fungi and provides new strategies for improving fermentation properties of industrial fungal strains through metabolic engineering.