show Abstracthide AbstractFilamentous fungi are one of the primary degraders of plant biomass because of their ability to produce enzymes that break down complex polysaccharides. The production of cellulolytic enzymes in fungi is dependent on transcription factors. In this article, we identified a N. crassa Zn2Cys6 transcription factor Clr5 that regulates the expression of cellulase on cellulose. N. crassa ?clr5 exhibited a significant decrease in secreted proteins (~46%), endo-glucanase (~55%), xylanase (~33%), ß-glucosidase (~38%), and exocellulase (~40%) compared with the WT, while transcriptomic analysis revealed that clr5 was essential in cellulase expression. We also determined that clr5 is crucial in amino acid- Leucine and Histidine metabolism. When using Leucine or Histidine as solo nitrogen source, ?clr5 strain cannot grow as normally as WT, and the expression of most CAZyme genes were reduced obviously, which indicated nitrogen metabolism played an important role in cellulose degradation. Moreover, the function of Clr5 is conservative in M. thermophila, the other fungi with a capacity for biomass degradation. Overall design: mRNA profiles of Neurospora crassa exposed to Avicel.