Molecular mechanisms of glucose repression in the filamentous fungus Trichoderma reesei

The filamentous fungus Trichoderma reesei is one of the best studied cellulolytic organisms. It is also an industrially important producer of cellulolytic and hemicellulolytic enzymes. In this work carbon source dependent regulation of cellulase and hemicellulase gene expression was studied at the transcriptional level. Expression of cellulase genes was found to be controlled by separate induction and repression controls in T. reesei. Functional analysis of the cellulase promoter cbh1 was carried out using the Eschericia coli lacZ gene as a reporter. Sequences mediating carbon source dependent regulation of the cbh1 promoter activity were identified. The cre1 gene coding for the glucose repressor was isolated from T. reesei and Trichoderma harzianum. The CREI protein is a DNA-binding protein, which is similar to the glucose repressors CREA of Aspergillus nidulans and Aspergillus niger, and the MIG1 and MIG2 of Saccharomyces cerevisiae. The T. reesei strain Rut-C30 expressed a mutated form of the cre1 gene and was defective in glucose repression of cellulase and hemicellulase gene expression. Introduction of the native cre1 gene into the Rut-C30 strain conferred glucose repression of these genes, demonstrating that glucose repression is mediated by the cre1 gene in T. reesei.