Transcription Factor Atf1 Regulates Expression of Cellulase and Xylanase Genes during Solid-State Fermentation of Ascomycetes

Abstract

Transcriptional regulation of cellulolytic and xylolytic genes in ascomycete fungi is controlled by specific carbon sources in different external environments. Here, comparative transcriptomic analyses of Penicillium oxalicum grown on wheat bran (WB), WB plus rice straw (WR), or WB plus Avicel (WA) as the sole carbon source under solid-state fermentation (SSF) revealed that most of the differentially expressed genes (DEGs) were involved in metabolism, specifically, carbohydrate metabolism. Of the DEGs, the basic core carbohydrate-active enzyme-encoding genes which responded to the plant biomass resources were identified in P. oxalicum, and their transcriptional levels changed to various extents depending on the different carbon sources. Moreover, this study found that three deletion mutants of genes encoding putative transcription factors showed significant alterations in filter paper cellulase production compared with that of a parental P. oxalicum strain with a deletion of Ku70 (ΔPoxKu70 strain) when grown on WR under SSF. Importantly, the ΔPoxAtf1 mutant (with a deletion of P. oxalicum Atf1, also called POX03016) displayed 46.1 to 183.2% more cellulase and xylanase production than a ΔPoxKu70 mutant after 2 days of growth on WR. RNA sequencing and quantitative reverse transcription-PCR revealed that PoxAtf1 dynamically regulated the expression of major cellulase and xylanase genes under SSF. PoxAtf1 bound to the promoter regions of the key cellulase and xylanase genes in vitro. This study provides novel insights into the regulatory mechanism of fungal cellulase and xylanase gene expression under SSF. IMPORTANCE The transition to a more environmentally friendly economy encourages studies involving the high-value-added utilization of lignocellulosic biomass. Solid-state fermentation (SSF), that simulates the natural habitat of soil microorganisms, is used for a variety of applications such as biomass biorefinery. Prior to the current study, our understanding of genome-wide gene expression and of the regulation of gene expression of lignocellulose-degrading enzymes in ascomycete fungi during SSF was limited. Here, we employed RNA sequencing and genetic analyses to investigate transcriptomes of Penicillium oxalicum strain EU2101 cultured on medium containing different carbon sources and to identify and characterize transcription factors for regulating the expression of cellulase and xylanase genes during SSF. The results generated will provide novel insights into genetic engineering of filamentous fungi to further increase enzyme production.

Filamentous fungi for sustainable remediation of pharmaceutical compounds, heavy metal and oil hydrocarbons

“…Combination of Fusarium sp. ZH-H2 and starch offers a suitable alternative for bioremediation of aged polycyclic aromatic hydrocarbon (PAH)-contaminated soil in coal mining areas ( Zhao et al, 2019 ).…”

“…Overexpression of mutated AraR in Penicillium oxalicum lead to constitutive production of α-L-arabinofuranosidase ( Gao et al, 2019 ). Deletion of the regulatory gene Atf1 increased cellulase and xylanase production in P. oxalicum ( Zhao et al, 2019 ). Deletion of repressors SxlR and Rce1 in Trichoderma reesei significantly stimulated xylanase ( Liu et al, 2017 ) and cellulase ( Cao et al, 2017 ) activities, respectively.…”

miR-589-3p promoted osteogenic differentiation of periodontal ligament stem cells through targeting ATF1

“…ATF1 has been shown to play an important role in cell proliferation, differentiation and apoptosis [ 27 ]. ATF1, as a regulator, also promoting sexual differentiation and entry into the stationary phase in S. pombe [ 28 ]. AtfA and Atf1 are quite highly conserved and that they are involved in multiple cellular processes [ 28 ].…”

“…ATF1, as a regulator, also promoting sexual differentiation and entry into the stationary phase in S. pombe [ 28 ]. AtfA and Atf1 are quite highly conserved and that they are involved in multiple cellular processes [ 28 ]. In this study, we found that overexpression of ATF1 partially reversed the promotion effects of miR-589-3p on osteogenic differentiation of PDLSCs.…”

Tailoring in fungi for next generation cellulase production with special reference to CRISPR/CAS system

“…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 ] …”