The Different Roles of Penicillium oxalicum LaeA in the Production of Extracellular Cellulase and β-xylosidase

Abstract

Cellulolytic enzyme hydrolysis of lignocellulose biomass to release fermentable sugars is one of the key steps in biofuel refining. Gene expression of fungal cellulolytic enzymes is tightly controlled at the transcriptional level. Key transcription factors such as activator ClrB/CLR2 and XlnR/XYR1, as well as repressor CreA/CRE1 play crucial roles in this process. The putative protein methyltransferase LaeA/LAE1 has also been reported to regulate the gene expression of the cellulolytic enzyme. The formation and gene expression of the cellulolytic enzyme was compared among Penicillium oxalicum wild type (WT) and seven mutants, including ΔlaeA (deletion of laeA), OEclrB (clrB overexpression), OEclrBΔlaeA (clrB overexpression with deletion of laeA), OExlnR (xlnR overexpression), OExlnRΔlaeA (xlnR overexpression with deletion of laeA), ΔcreA (deletion of creA), and ΔcreAΔlaeA (double deletion of creA and laeA). Results revealed that LaeA extensively affected the expression of glycoside hydrolase genes. The expression of genes that encoded the top 10 glycoside hydrolases assayed in secretome was remarkably downregulated especially in later phases of prolonged batch cultures by the deletion of laeA. Cellulase synthesis of four mutants ΔlaeA, OEclrBΔlaeA, OExlnRΔlaeA, and ΔcreAΔlaeA was repressed remarkably compared with their parent strains WT, OEclrB, OExlnR, and ΔcreA, respectively. The overexpression of clrB or xlnR could not rescue the impairment of cellulolytic enzyme gene expression and cellulase synthesis when LaeA was absent, suggesting that LaeA was necessary for the expression of cellulolytic enzyme gene activated by ClrB or XlnR. In contrast to LaeA positive roles in regulating prominent cellulase and hemicellulase, the extracellular β-xylosidase formation was negatively regulated by LaeA. The extracellular β-xylosidase activities improved over 5-fold in the OExlnRΔlaeA mutant compared with that of WT, and the expression of prominent β-xylosidase gene xyl3A was activated remarkably. The cumulative effect of LaeA and transcription factor XlnR has potential applications in the production of more β-xylosidase.

Gene Regulatory Networks of Penicillium echinulatum 2HH and Penicillium oxalicum 114-2 Inferred by a Computational Biology Approach

“…This was confirmed by OExlnR laeA mutant, which induced a remarkable 28.5 fold increase in the expression of xyl3A in relation to the wild-type. This result also showed that the regulation of xyl3A is not LaeAdependent as the regulatory system of most of the cellulases or hemicellulases (Li et al, 2016).…”

Transcription Factor NsdD Regulates the Expression of Genes Involved in Plant Biomass-Degrading Enzymes, Conidiation, and Pigment Biosynthesis in Penicillium oxalicum

“…Studies on the regulatory mechanism for amylase genes in fungi are minimal. In P. oxalicum, the major amylase gene, Amy15A, is positively regulated by the G protein PGA3 (38), the casein kinase CK2 (39), the heterochromatin protein Hep1 (40), and the TFs LaeA (16), PrtT for activating the expression of genes encoding extracellular proteinases (41) and AmyR (13). However, it is unknown whether these regulators, except for AmyR, directly or indirectly regulate amylase genes.…”

“…Most studies on the identification of such TFs and the exploration of their regulatory mechanisms have focused mainly on cellulolytic filamentous fungi, such as Trichoderma, Aspergillus, and Penicillium (9)(10)(11). Studies on such TFs mainly include the transcription activators CLR-2/ClrB of Aspergillus nidulans FGSC A4 (12) and Penicillium oxalicum 114-2 (13) and HP7-1 (14), XYR1/XLR-1/XlnR of Trichoderma reesei QM9136 (15) and P. oxalicum 114-2 (13), AmyR of P. oxalicum 114-2 (13) and Aspergillus niger CICC2462 (11), and LaeA of P. oxalicum 114-2 (16) and T. reesei QM9414 (17) and the carbon catabolite repressor CreA/CRE1/CRE-1 of A. nidulans FGSC A4 (18) and T. reesei QM9414 (19). Interestingly, expression of genes encoding plant biomass-degrading enzymes and genes involved in asexual reproduction is coregulated by some TFs, such as BrlA (10), ClrC (20), and FlbC (21) of P. oxalicum 114-2.…”

Modulating Transcriptional Regulation of Plant Biomass Degrading Enzyme Networks for Rational Design of Industrial Fungal Strains

“…Apart from the approaches described above in the previous paragraphs, modulating chromatin accessibility is yet an under-utilized approach to increase the expression of CAZyme encoding genes in filamentous fungi. Chromatin remodeling of the promoters of CAZyme encoding genes through the actions of the histone acetyltransferase Gcn5, the CCAAT-binding complex, and possibly the putative protein methyltransferase Lae1 is required for the full expression of these CAZymes in T. reesei (Zeilinger et al, 1998 ; Xin et al, 2013 ; Aghcheh and Kubicek, 2015 ; Li et al, 2016 ). Overexpression of a putative GCN5-related N-acetyltransferase (gene ID 123668) via the A. nidulans gpdA promoter or lae1 via the tef1 promoter resulted in an increased expression of cellulase encoding genes under inducing conditions (on lactose) (Seiboth et al, 2012b ; Häkkinen et al, 2014 ).…”