**10. Regulation of cell-wall degrading enzymes production in fungi**

The production of CWDEs by fungi is an energy-consuming process. The fine-tuned regula‐ tion of genes encoding CWDEs ensures that these enzymes will be produced only under conditions in which the fungus requires plant polymers as carbon source. Readily metabo‐ lizable carbohydrates repress the synthesis of enzymes related to catabolism of alternative carbon sources such as plant cell wall polysaccharides. In this way, preferential utilization of the most favored carbon source prevails, and one of the regulatory mechanisms involved in this adaptation is carbon catabolite repression (CCR). The CCR is activated by many carbon sources, depending on the lifestyle of the microorganism, but usually glucose is the most re‐ pressive molecule [75]. Nowadays, the search for microorganisms able to efficiently degrade lignocellulosic biomass is pivotal for the establishment of sustainable production of bio‐ mass-derived ethanol and other biocompounds. In this context, CCR appears as a major challenge to overcome, once this mechanism is responsible for enzymatic exclusion of less preferred carbon source such as lignocellulose-derived sugars. Hence, the comprehension of molecular mechanisms behind CCR, as well as the transcriptional control of cell wall de‐ rived enzymes are prerequisite in order to develop new microbial strains for lignocellulose degradation. In this section, the induction of expression of cellulases and hemicellulases, the transcriptional control of genes encoding CWDEs and the overall mechanism behind CCR will be discussed.
