Abstract
BackgroundSolid-state fermentation (SSF) mimics the natural decay environment of soil fungi and can be employed to investigate the production of plant biomass-degrading enzymes. However, knowledge on the transcriptional regulation of fungal genes during SSF remains limited. Herein, transcriptional profiling was performed on the filamentous fungus Penicillium oxalicum strain HP7-1 cultivated in medium containing wheat bran plus rice straw (WR) under SSF (WR_SSF) and submerged fermentation (WR_SmF; control) conditions. Novel key transcription factors (TFs) regulating fungal cellulase and xylanase gene expression during SSF were identified via comparative transcriptomic and genetic analyses.ResultsExpression of major cellulase genes was higher under WR_SSF condition than that under WR_SmF, but the expression of genes involved in the citric acid cycle was repressed under WR_SSF condition. Fifty-six candidate regulatory genes for cellulase production were screened out from transcriptomic profiling of P. oxalicum HP7-1 for knockout experiments in the parental strain ∆PoxKu70, resulting in 43 deletion mutants including 18 constructed in the previous studies. Enzyme activity assays revealed 14 novel regulatory genes involved in cellulase production in P. oxalicum during SSF. Remarkably, deletion of the essential regulatory gene PoxMBF1, encoding Multiprotein Bridging Factor 1, resulted in doubled cellulase and xylanase production at 2 days after induction during both SSF and SmF. PoxMBF1 dynamically and differentially regulated transcription of a subset of cellulase and xylanase genes during SSF and SmF, and conferred stress resistance. Importantly, PoxMBF1 bound specifically to the putative promoters of major cellulase and xylanase genes in vitro.ConclusionsWe revealed differential transcriptional regulation of P. oxalicum during SSF and SmF, and identified PoxMBF1, a novel TF that directly regulates cellulase and xylanase gene expression during SSF and SmF. These findings expand our understanding of regulatory mechanisms of cellulase and xylanase gene expression during fungal fermentation.
Highlights
Solid-state fermentation (SSF) mimics the natural decay environment of soil fungi and can be employed to investigate the production of plant biomass-degrading enzymes
Comparative transcriptomic analysis of P. oxalicum strain HP7‐1 during SSF and submerged fermentation (SmF) The P. oxalicum wild-type strain HP7-1 was, respectively, cultivated in solid and liquid media containing wheat bran plus rice straw (WR) as the carbon source for 24 h, and total RNA was extracted and subjected to RNA sequencing (RNA-Seq) on an Illumina HiSeq 2000 system
Transcripts of POX05571/Cel7B, POX06783/Xyn11A and POX06835/Bgl1 were decreased by 19.6–42.1% at 48 h (Fig. 5a). Expression of these cellulase and xylanase genes was observed in ∆PoxMBF1 and ∆PoxKu70 during SmF using either WR or Avicel as the carbon source. These results indicate that the expression of most of the tested cellulase and xylanase genes was significantly increased in ∆PoxMBF1 compared with ∆PoxKu70 at certain induction periods, the extent varied with different carbon sources used for induction
Summary
Solid-state fermentation (SSF) mimics the natural decay environment of soil fungi and can be employed to investigate the production of plant biomass-degrading enzymes. Transcriptional profiling was performed on the filamentous fungus Penicillium oxalicum strain HP7-1 cultivated in medium containing wheat bran plus rice straw (WR) under SSF (WR_SSF) and submerged fermentation (WR_SmF; control) conditions. Solid-state fermentation (SSF) mimics the natural decay environment of soil fungi, and can be used to investigate production of plant biomass-degrading enzymes, the global carbon cycle, and commercial production of high value-added bioproducts including ancient Chinese liquor, soy sauce, vinegar, penicillin and other antibiotics, pigments, and environmentally friendly sources of alternative energy [1, 2]. Production of fungal cellulases and xylanases depends on stimulation of exogenous carbon sources under certain cultivation conditions; it is strictly controlled by regulatory networks comprising numerous transcriptional factors (TFs), signal sensors, and receptors. Induction of P. oxalicum strain HP7-1 using WB plus Avicel under SmF proved more favourable for cellulase and xylanase production than induction using WB alone [3]
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