Role of <i>Trichoderma reesei</i> Heterotrimeric G Protein Signaling in Growth and Cellulose Degradation

Trichoderma reesei decomposes renewable cellulose into soluble sugars by secreting cellulase and hemicellulase. Heterotrimeric G protein signaling regulates cellulase production. Here, we assessed the effects of G protein subunit deletion on cellulase production in T. reesei. The results revealed that G proteins bidirectionally regulate cellulase production, activation, and repression; GNA1, GNA3, TGB1, and GBG1 downregulate cellulase synthesis, whereas GNA2 upregulates it. To understand the role of the ACY1-cAMP-PKA pathway and G protein signaling in cellulase expression, we overexpressed/knocked out acy1 in G protein subunit-knockout strains. GNA1 orchestrates the G protein signaling pathway, with its core function being the transmission of glucose repression signals. GNA3 serves as a complement to GNA1. GNA2 is the only Gα subunit that transduces cellulose-induced signals. The ACY1-cAMP-PKA pathway can act as an activator, a repressor, or an inactive regulator in G protein signal transduction. Our study highlights avenues for constructing cellulase-hyperproducing strains.