Abstract
Research on regulation of cellulases and hemicellulases gene expression may be very useful for increasing the production of these enzymes in their native producers. Mechanisms of gene regulation of cellulase and hemicellulase expression in filamentous fungi have been studied, mainly in Aspergillus and Trichoderma. The production of these extracellular enzymes is an energy-consuming process, so the enzymes are produced only under conditions in which the fungus needs to use plant polymers as an energy and carbon source. Moreover, production of many of these enzymes is coordinately regulated, and induced in the presence of the substrate polymers. In addition to induction by mono- and oligo-saccharides, genes encoding hydrolytic enzymes involved in plant cell wall deconstruction in filamentous fungi can be repressed during growth in the presence of easily metabolizable carbon sources, such as glucose. Carbon catabolite repression is an important mechanism to repress the production of plant cell wall degrading enzymes during growth on preferred carbon sources. This manuscript reviews the recent advancements in elucidation of molecular mechanisms responsible for regulation of expression of cellulase and hemicellulase genes in fungi.
Highlights
In order to enhance energy security and mitigate climate change, interest in finding renewable fuels to replace petroleum-based ones is enormously increasing
In support of this mechanism, it was shown that antibodies against CBHI, CBHII, EGI and EGII blocked the expression of cbh1/cel7a gene in the presence of cellulose but not the soluble inducer sophorose [50]
The results demonstrated that the expression of this antisense RNA produced marked effects on the induction of the cbh1 transcript using cellulose but not sophorose as an inducer
Summary
In order to enhance energy security and mitigate climate change, interest in finding renewable fuels to replace petroleum-based ones is enormously increasing. The enzymes so far identified and characterized as responsible for the cellulolytic activity of T. reesei include five endoglucanases -EGI/Cel7B, EGII/Cel5A, EGIII/Cel12A [28, 29], EGIV/Cel61A [30], and EGV/Cel45A [31] and two exoglucanases -the cellobiohydrolases CBHI/Cel7A and CBHII/Cel6A [32] These enzymes act synergistically to convert cellulose into cellobiose [28-33], whose hydrolysis into glucose involves two glucosidases -BGLI/Cel3A [34] and BGLII/Cel1A [35]. One of the proposed mechanisms is that the fungus produces basal levels of cellulase (mainly CEL7A and CEL6A) and that the activity of these extracellular enzymes on cellulose produces a soluble inducer, which can enter the cell and affect induction [50, 51] In support of this mechanism, it was shown that antibodies against CBHI, CBHII, EGI and EGII blocked the expression of cbh1/cel7a gene in the presence of cellulose but not the soluble inducer sophorose [50]. 232 Current Genomics, 2013, Vol 14, No 4
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