CreA-independent carbon catabolite repression of cellulase genes by trimeric G-protein and protein kinase A in Aspergillus nidulans

Cellulase production in filamentous fungi is repressed by various carbon sources. In our preliminary survey in Aspergillus nidulans , degree of de-repression differed depending on carbon sources in a mutant of creA , encoding the transcriptional repressor for carbon catabolite repression (CCR). To further understand mechanisms of CCR of cellulase production, we compared the effects of creA deletion with deletion of protein kinase A ( pkaA ) and G ( ganB ) genes, which constitute a nutrient sensing and signaling pathway. In plate culture with carboxymethyl cellulose and d -glucose, deletion of pkaA and ganB , but not creA , led to significant de-repression of cellulase production. In submerged culture with cellobiose and d -glucose or 2-deoxyglucose, both creA or pkaA single deletion led to partial de-repression of cellulase genes with the highest level by their double deletion, while ganB deletion caused de-repression comparable to that of the creA / pkaA double deletion. With ball-milled cellulose and d -glucose, partial de-repression was detected by deletion of creA but not of pkaA or ganB . The creA / pkaA or creA / ganB double deletion led to earlier expression than the creA deletion. Furthermore, the effect of each deletion with d -xylose or L-arabinose as the repressing carbon source was significantly different from that with d -glucose, d -fructose, and d -mannose. Consequently, this study revealed that PkaA and GanB participate in CreA-independent CCR and that contribution of CreA, PkaA, and GanB in CCR differs depending on the inducers, repressing carbon sources, and culture conditions (plate or submerged). Further study of CreA-independent mechanisms is needed to fully understand CCR in filamentous fungi.