The putative cellodextrin transporter-like protein CLP1 is involved in cellulase induction in Neurospora crassa

Neurospora crassa recently has become a novel system to investigate cellulase induction. Here, we discovered a novel membrane protein, CLP1 (NCU05853), a putative cellodextrin transporter-like protein, that is a critical component of the cellulase induction pathway in N. crassa. Although CLP1 protein cannot transport cellodextrin, the suppression of cellulase induction by this protein was discovered on both cellobiose and Avicel. The co-disruption of the cellodextrin transporters cdt2 and clp1 in strain Δ3βG formed strain CPL7. With induction by cellobiose, cellulase production was enhanced 6.9-fold in CPL7 compared with Δ3βG. We also showed that the suppression of cellulase expression by CLP1 occurred by repressing the expression of cellodextrin transporters, particularly cdt1 expression. Transcriptome analysis of the hypercellulase-producing strain CPL7 showed that the cellulase expression machinery was dramatically stimulated, as were the cellulase enzyme genes including the inducer transporters and the major transcriptional regulators. These data deepen the understanding of cellulase induction pathway and provide a new strategy to improve cellulase production in N.crassa. Because homologs of CLP1 can be found in many other fungi, the strategy that we used to show cellulase induction regulation in N. crassa might also work in other cellulase-producing organisms such as T. reesei.