Table 2.
Transcription factors involved in cellulase expression
| Transcription factors | Function | References |
|---|---|---|
| Tmk1, Tmk2, and Tmk3 | In T. reesei, it causes phosphorylation and activation of TFs liable for cellulase (cbh1, cbh2, egl1, egl2, and bgl1) production. Removal of tmk3 down regulated the transcription level expression of cbh1, cbh2, egl1, egl2, and bgl1 | [97] |
| XlnR/ Xyr1 | XlnR (xylanase regulator), primarily in Aspergillus sp., and Xyr1 (xylanase regulator 1), primarily in T. reesei are the prime transcriptional activators of the genes encoding cellulase (cbh1, cbh2, egl1, and bgl1) enzymes | [98] |
| RXE1 | It (RXE1 orthologs in Aspergillus chrysogenum, Beauveria bassiana, and Fusarium oxysporum are designated BRLA) regulate cellulase gene expression, exhibits intense binding activity to the xyr1 promoter | [99] |
| Rce1 | It acts as a transcriptional repressor for cellulase gene expression by binding at the cbh1 promoter region, antagonized Xyr1 from binding to the cbh1 promoter | [100] |
| BglR | It positively regulates the expression of genes encoding BGL in T. reesei. Its activation causes repression of the CBH and EG genes | [101] |
| ClbR | In A. aculeatus it regulates cellulase-encoding genes induced by cellulose and cellobiose | [102] |
| Ace3 | In T. reesei, its overexpression led to increase cellulase gene expression, while its removal causes a remarkable reduction in cellulase activity | [103] |
| CreA/Cre1 | They regulates CCR (carbon catabolite repression) where, in the existence of simple sugars such as glucose, fructose, mannose or xylose, it suppresses the transcription of genes encoding enzymes involved in the metabolism of more complex polysaccharides | [104] |
| Crz1 | Through the conduction of Ca2+/Mn2+ mediated signalling, it affects the promoter region of xyr1 and cbh1, and induced cellulase production | [105], [135] |
| Ctf1 | In T. reesei, it downregulate RCE1 gene, thus it upregulate genes of the transcription factors XYR1 and ACE3, resulting in the activation of cellulolytic genes | [106] |
| Clr-1/Clr-2/Clr-3 | Activation of the Clr-1 requires the presence of an inducer such as cellobiose, prompts expressions of bgl, but Clr-2 does not require any inducer for its activation. Abolition of them in N. crassa may prevent cellulose utilization as a carbon source | [107] |
| Clr-3 | Clr-3 prevent the activity of Clr-1, removal of it led to the Clr-1 mediated gene expression in the absence of inducer | [108] |
| HAP complexes | HAP complexes are recognized in Aspergillus spp. (HapB/C/E), T. reesei (Hap2/3/5), and N. crassa (Hap2/3/5). They allow moderate expression of cellulase and xylanase genes in T. reesei (cbh2 and xyn2) | [109] |
| Lae1 and VELVET complex | In T. reesei (LaeA orthologue in A. nidulans), it act as a methyltransferase induces cellulase expression and forming the VELVET complex, which in turn regulates the transcription of major cellulase genes | [110] |
| PacC/Pac1 | In A. nidulans and T. reesei, it respond to pH variance in the external environment, stimulate or prevent cellulase production. At neutral pH, the abolition of the pac1 gene increases Xyr1 activity | [5, 55] |
| PoxMBF1 | In Penicillium oxalicum, it binds directly to the promoter regions of principal cellulase and xylanase genes to induce cellulase production | [111] |
| PoxFlbC | In Penicillium oxalicum (FlbC orthologue in Aspergillus), it upregulates most of the cellulase genes | [112] |
| PoxAtf1 | In filamentous fungi, it controls the expression of cellulase and xylanase genes during the solid-state fermentation | [113] |
| Blr1, Blr2, and Env1 | Photoreceptor proteins (Blr1, Blr2, and Env1) in both light and dark regulate the cellulase gene from T. reesei. The photoreceptor regulative mechanism of carbon metabolism in T. reesei is dependent on Blr1 and Blr2 controlled by the Env1 photoreceptor | [114] |
| Seb1 | In Talaromyces pinophilus EMU, Seb1 transcription factor binds to the stress response element (STRE) and CRISPR-Cas9 mediated degradation of seb1 gene led to the 20–40% increment in FPase activity | [123] |
| TrAZF1 | In T. reesei and A. nidulans positively regulates the activity of BGL and CBH by interacting with the cel7a, cel45a, and sow promoter region | [115] |
| PoSet1/PoSet2 | In Penicillium oxalicum, PoSet1 and PoSet2 are responsible for methylation of histone (H3) lysine 4 and lysine 36, respectively. They are involved in the upregulation (PoSet1) or down regulation (PoSet2) of cellulase production | [116] |
| MAT1-2-1 | It is a mating-type locus protein of T. reesei modulates cellulase gene expression in daylight by interacting with the Xyr1 and binds to the cbh1 promoter | [117] |