acid-pretreated corncob residue every 24 h. **b** Glucose released from saccharification of delignified corncob residue every 24 h. Data are the means of three independent experiments; error bars show standard deviations

In filamentous fungi *T. reesei* and *N. crassa*, Cre1/CRE-1 functions as a global transcription factor and affects gene expression directly or indirectly \[[@CR44], [@CR45]\]. The functions of enzymes encoded by the Cre1/CRE-1-regulated genes include lignocellulosic biomass-degrading, nitrogen-uptaking, developmental processes, chromatin remodeling, and so on \[[@CR46]\]. In this study, the CBH activity of the control strain SP4 was remarkably reduced compared to that of SDC11 (Fig. [2](#Fig2){ref-type="fig"}c). The reason might be that Cre1 could bind to two closely spaced 5′-CCCCAC-3′ motifs in the *cbh1* promoter region and then directly represses *cbh1* transcription in the *cre1* ^+^ strain but not in the Δ*cre1* strain \[[@CR46], [@CR47]\]. Moreover, *cbh2* is found to be not Cre1 regulation dependent as some evidences indicate that CCR is only conferred by double Cre1-binding sites and only a single putative Cre1-binding site exists in the *cbh2* promoter region in *T. reesei* \[[@CR39], [@CR48]--[@CR50]\]. However, Cre1 could indirectly suppress *cbh2* expression via regulating Xyr1, the major activator of the cellulase-encoding genes \[[@CR50]\]. Thus, the CBH activity in SDC11 could be speculated to be enhanced due to the absence of Cre1. The transcriptional regulation of *egl1* is shown to be strictly dependent on Xyr1 and repressed by Cre1 indirectly, like *cbh2* \[[@CR39], [@CR49]\]. Therefore, deletion of *cre1* also caused the significant enhancement of EG activity in SDC11 (Fig. [2](#Fig2){ref-type="fig"}b). Besides, studies have indicated that *bgl1* encoding the extracellular β-glucosidase BGL1 is also suppressed by Cre1 indirectly \[[@CR48], [@CR49], [@CR51]\]. Furthermore, the absence of *cre1* in the hypercellulolytic strain QM9414 resulted in a significant increa