VIB1, a Link between Glucose Signaling and Carbon Catabolite Repression, Is Essential for Plant Cell Wall Degradation by Neurospora crassa
CCR is decreased in absence of glucose, allowing scouting enzymes to liberate cellobiose from cellulose. Cellobiose (or a derivative) results in activation of the transcription factor CLR1, which induces expression of transporters for cellodextrins, β-glucosidases, and clr-2. Production of the transcription factor CLR2 drives cellulase gene expression. Both intracellular and extracellular β-glucosidase enzymes catalyze conversion of cellobiose to glucose, which can trigger carbon catabolite repression via glucose sensing mechanisms and transcriptional repression by CRE1.