Abstract
Background: Lignocellulosic biomass is one of the most promising renewable and clean energy resources to reduce greenhouse gas emissions and dependence on fossil fuels. However, the resistance to accessibility of sugars embedded in plant cell walls (so-called recalcitrance) is a major barrier to economically viable cellulosic ethanol production. A recent report from the US National Academy of Sciences indicated that, "absent technological breakthroughs", it was unlikely that the US would meet the congressionally mandated renewable fuel standard of 35 billion gallons of ethanol-equivalent biofuels plus 1 billion gallons of biodiesel by 2022. We here describe the properties of switchgrass (Panicum virgatum) biomass that has been genetically engineered to increase the cellulosic ethanol yield by more than 2-fold. Results: We have increased the cellulosic ethanol yield from switchgrass by 2.6-fold through overexpression of the transcription factor PvMYB4. This strategy reduces carbon deposition into lignin and phenolic fermentation inhibitors while maintaining the availability of potentially fermentable soluble sugars and pectic polysaccharides. Detailed biomass characterization analyses revealed that the levels and nature of phenolic acids embedded in the cell-wall, the lignin content and polymer size, lignin internal linkage levels, linkages between lignin and xylans/pectins, and levels of wall-bound fucose are all altered in PvMYB4-OX lines. Genetically engineered PvMYB4-OX switchgrass therefore provides a novel system for further understanding cell wall recalcitrance. Conclusions: Our results have demonstrated that overexpression of PvMYB4, a general transcriptional repressor of the phenylpropanoid/lignin biosynthesis pathway, can lead to very high yield ethanol production through dramatic reduction of recalcitrance. MYB4-OX switchgrass is an excellent model system for understanding recalcitrance, and provides new germplasm for developing switchgrass cultivars as biomass feedstocks for biofuel production.
Original language | English |
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Article number | 71 |
Journal | Biotechnology for Biofuels |
Volume | 6 |
Issue number | 1 |
DOIs | |
State | Published - 2013 |
Funding
We thank Lisa Jackson and David Huhman for GC-MS analysis of lignin monomers, Tui Ray for assistance with qRT-PCR analysis, Choo Hamilton and Miguel Rodriguez for assistance with ethanol fermentations and HPLC, Jeffrey Miller for assistance with glycome profiling, Dr. Stephen Webb for assistance with statistical analysis, and Professor Rick Nelson and Dr. Yuhong Tang for critical reading of the manuscript. This work was supported by the BioEnergy Science Center, a US Department of Energy Bioenergy Research Center, through the Office of Biological and Environmental Research in the DOE Office of Science. This manuscript has been co-authored by a contractor of the U.S. Government under contract DE-AC05-00OR22725. The CCRC series of plant glycan-directed monoclonal antibodies used in this project were generated with the support of the NSF Plant Genome Program (DCB-041683 and IOS-0923992).
Keywords
- Bioenergy
- Biofuel
- Cell wall
- Cellulosic ethanol
- Feedstock
- Hemicellulose
- Lignin
- Pectin
- PvMYB4
- Recalcitrance
- Switchgrass
- Transcription factor