The cellulase and xylanase genes of filamentous Trichoderma fungi exist under carbon catabolite repression mediated by the regulator carbon catabolite repressor (CREI). Our objective was to find the role of CREI in a cellulase-hyperproducing mutant of Trichoderma koningii, and address whether enzyme production can be further improved by silencing the crel gene. crel partially silenced strains were constructed to improve enzyme production in T. koningii YC01, a cellulase-hyperproducing mutant. Silencing of crel resulted in derepression of cellulase gene expression in glucose-based cultivation. The cre1 interference strain C313 produced 2.1-, 1.4-, 0.8-, and 0.8-fold higher amounts of filter paper activity, beta-1,4-exoglucanase activity (rho-nitropheny1-beta-D-cellobioside as substrate), 8-1,4-endoglucanase activity (sodium carboxymethyl cellulose as substrate), and xylanase activity, respectively, than the control strain, suggesting that silencing of crel resulted in enhanced enzyme production capability. In addition, downregulation of crel resulted in elevated expression of another regulator of xylanase and cellulase expression, xyrl, indicating that CREI also acted as a repressor of xyrl transcription in T. koningii under inducing conditions. These results show that RNAi is a feasible method for analyzing the regulatory mechanisms of gene expression and improving xylanase and cellulase productivity in T. koningii. (C) 2013 Elsevier Inc. All rights reserved.