Transcriptomic analysis reveals opposing roles of CEL1B in sophorose and lactose induced cellulase expression in Trichoderma reesei Rut C30
The beta-glucosidase CEL1B has been linked to regulating cellulase expression in Trichoderma reesei, yet its inducer-specific functions and broader regulatory roles remain poorly characterized. In this study, CRISPR-Cas9-mediated gene knockout was applied in the industrial high-producing T. reesei Rut C30 to investigate CEL1B function without the confounding effects of KU70 deletion. Unlike previous studies focused solely on cellulose or lactose induction, transcriptomic analysis of the CEL1B knockout strain revealed its regulatory roles under both lactose and sophorose-rich conditions, with sophorose representing the most potent natural inducer of cellulase expression. Under lactose induction, CEL1B deletion resulted in a 52.4% increase in cellulase activity (p < 0.05), accompanied by transcriptome-wide upregulation of beta-glucosidase genes (CEL3A: 729%, CEL D: 666.8%, CEL C: 110.9%), cellulose-sensing receptors (CRT1: 203%, CRT2: 105.8%), and key transcription factors (XYR1: 2.65-fold, ACE3: 2.79-fold, VIB1: 2.12-fold). Expression of ER proteostasis genes was significantly upregulated (BIP1: 3.33-fold, HSP70: 6.16-fold), contributing to enhanced enzyme secretion. Conversely, under sophorose induction, CEL1B deletion reduced cellulase activity by 25.7% (p < 0.05), which was associated with transcriptome profiling showing significant downregulation of beta-glucosidase CEL3H (66.6%) and cellodextrin transporters (TrireC30_91594: 79.3%, TrireC30_127980: 76.3%), leading to reduced cellobiohydrolase expression (CEL7A: 57.8%, CEL6A: 67.8%). This first transcriptomic characterization of the CEL1B knockout strain reveals its dual opposing roles in modulating cellulase expression in response to lactose versus sophorose, providing new strategies for optimizing inducer-specific enzyme production in T. reesei.