Heterotrimeric G-Protein Signaling Is Required for Cellulose Degradation in Neurospora crassa.

The filamentous fungus decomposes lignocellulosic biomass to generate soluble sugars as carbon sources. In this study, we investigated a role for heterotrimeric G-protein signaling in cellulose degradation. Loss of the Gα subunit genes and , the Gβ subunit genes and , the Gγ gene , or the gene for downstream effector adenylyl cyclase () resulted in loss of detectable cellulase activity. This defect was also observed in strains expressing a constitutively active version of - ( ). We found that GNA-1 levels are greatly reduced in Δ-, Δ, and Δ strains, likely contributing to cellulase defects in these genetic backgrounds. The observation that Δ strains exhibit cellulase activity, despite greatly reduced levels of GNA-1 protein, is consistent with positive control of cellulase production by GNA-3 that is manifested in the absence of Expression patterns for five cellulase genes showed that Δ, Δ, and Δ mutants produce less cellulase mRNA than the wild type, consistent with transcriptional regulation. Δ mutants had wild-type levels of cellulase transcripts, suggesting posttranscriptional control. In contrast, results for Δ mutants support both transcriptional and posttranscriptional control of cellulase activity by cAMP signaling. Cellulase activity defects in Δ mutants were fully remediated by cAMP supplementation, consistent with GNA-3 operating upstream of cAMP signaling. In contrast, cAMP addition only partially corrected cellulase activity defects in Δ and Δ mutants, suggesting participation of GNA-1 and GNB-1 in additional cAMP-independent pathways that control cellulase activity. Filamentous fungi are critical for the recycling of plant litter in the biosphere by degrading lignocellulosic biomass into simpler compounds for metabolism. Both saprophytic and pathogenic fungi utilize plant cell wall-degrading enzymes to liberate carbon for metabolism. Several studies have demonstrated a role for cellulase enzymes during infection of economically relevant crops by fungal pathogens. Especially in developing countries, severe plant disease means loss of entire crops, sometimes leading to starvation. In this study, we demonstrate that G-protein signaling is a key component of cellulase production. Therefore, understanding the role of G-protein signaling in the regulation of the unique metabolism of cellulose by these organisms can inform innovations in strain engineering of industrially relevant species for biofuel production and in combatting food shortages caused by plant pathogens.