Abstract
BackgroundTrichoderma reesei is one of the major producers of enzymes for the conversion of plant biomass to sustainable fuels and chemicals. Crude plant biomass can induce the production of CAZymes in T. reesei, but there is limited understanding of how the transcriptional response to crude plant biomass is regulated. In addition, it is unknown whether induction on untreated recalcitrant crude plant biomass (with a large diversity of inducers) can be sustained for longer. We investigated the transcriptomic response of T. reesei to the two industrial feedstocks, corn stover (CS) and soybean hulls (SBH), over time (4 h, 24 h and 48 h), and its regulatory basis using transcription factor deletion mutants (Δxyr1 and Δara1). We also investigated whether deletion of a xylulokinase gene (Δxki1) from the pentose catabolic pathway that converts potential inducers could lead to increased CAZyme gene expression.ResultsBy analyzing the transcriptomic responses using clustering as well as differential and cumulative expression of plant biomass degrading CAZymes, we found that corn stover induced a broader range and higher expression of CAZymes in T. reesei, while SBH induced more pectinolytic and mannanolytic transcripts. XYR1 was the major TF regulating CS utilization, likely due to the significant amount of d-xylose in this substrate. In contrast, ARA1 had a stronger effect on SBH utilization, which correlates with a higher abundance of l-arabinose in SBH that activates ARA1. Blocking pentose catabolism by deletion of xki1 led to higher expression of CAZyme encoding genes on both substrates at later time points. Surprisingly, this was also observed for Δara1 at later time points. Many of these genes were XYR1 regulated, suggesting that inducers for this regulator accumulated over time on both substrates.ConclusionOur data demonstrates the complexity of the regulatory system related to plant biomass degradation in T. reesei and the effect the feedstock composition has on this. Furthermore, this dataset provides leads to improve the efficiency of a T. reesei enzyme cocktail, such as by the choice of substrate or by deleting xki1 to obtain higher production of plant biomass degrading CAZymes.
Highlights
Trichoderma reesei is one of the major producers of enzymes for the conversion of plant biomass to sustainable fuels and chemicals
The regulatory and catabolic mutants had severely reduced growth on pure mono‐ and polysaccharides compared to the reference strain, but not on crude plant biomass Three T. reesei deletion mutants (Δxyr1, Δara1 and Δxki1) were phenotypically compared to the reference strain QM9414 by growth on various carbon sources, including mono- and disaccharides, polymers and crude plant biomass (Fig. 2)
XYR1 is the major transcription factor (TF) regulating the degradation of corn stover, while ARA1 more strongly affects soybean hulls utilization We initially analyzed the secretome profiles of the reference strain and what we considered phenotypically the most extreme mutant, Δxyr1, by SDS-PAGE gel analysis on later time points (24 h and 48 h), where we expected to see clear patterns
Summary
Trichoderma reesei is one of the major producers of enzymes for the conversion of plant biomass to sustainable fuels and chemicals. Crude plant biomass can induce the production of CAZymes in T. reesei, but there is limited understanding of how the transcriptional response to crude plant biomass is regulated. It is unknown whether induction on untreated recalcitrant crude plant biomass (with a large diversity of inducers) can be sustained for longer. Plant biomass is the most abundant renewable carbon source on Earth for conversion into biofuel and biochemicals by the biotechnology industry. It is composed of three major polysaccharides (cellulose, hemicellulose and pectin), and many different plant biomass degrading (PBD) enzymes are required for efficient degradation [1]. Sustaining induction for longer time periods will lead to higher overall CAZyme yields as well as a more diverse array of CAZymes and reduce enzyme production costs
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