Genome wide insights into signal integration by the G-protein pathway for regulation of carbon- and secondary metabolism in Trichoderma reesei

Nutrient sensing is of utmost importance for gene regulation in fungi, with the heterotrimeric G-protein pathway as prototypical transmission machinery. Previously we could show an interrelationship between light response and cellulase gene regulation in the filamentous fungus Trichoderma reesei. Recently we found that also secondary metabolism is regulated in a light dependent manner in T. reesei. In both cases, G-protein coupled receptors (GPCRs) exemplified these connections: the glucose sensors CSG1 and CSG2, which are responsible for posttranscriptional regulation of cellulase expression as well as GPR8, a GPCR associated with the sorbicillin cluster. To gain further insight into the balance between carbon- and secondary metabolism along with its dependence on light, we performed functional, transcriptome analyses and network analysis. We used deletion mutants Δgna1, Δgna2 and Δgna3, Δgnb1 and Δgng1 as well as strains expressing constitutively activated versions of the G-alpha proteins, GNA1QL, GNA2QL and GNA3QL in T. reesei QM6a. We found characteristic alterations in biomass formation, enzyme production and growth as well as an influence on sexual and asexual development. Cellulase gene transcription was differentially regulated between the investigated G-protein mutant strains with important differences between light and darkness. Analysis of secondary metabolite production revealed an impact on regulation of several compounds hence substantiating the link between cellulase regulation and secondary metabolism. We conclude that the G-protein pathway integrates signals relevant for carbon- and secondary metabolism to optimally balance enzyme biosynthesis and growth with metabolite production