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Open Access Research

Enhanced characteristics of genetically modified switchgrass (Panicum virgatum L.) for high biofuel production

Hui Shen16, Charleson R Poovaiah26, Angela Ziebell36, Timothy J Tschaplinski6, Sivakumar Pattathil46, Erica Gjersing36, Nancy L Engle6, Rui Katahira37, Yunqiao Pu36, Robert Sykes36, Fang Chen16, Arthur J Ragauskas56, Jonathan R Mielenz6, Michael G Hahn46, Mark Davis36, C Neal Stewart26 and Richard A Dixon167*

Author Affiliations

1 Plant Biology Division, Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK, 73401, USA

2 Department of Plant Sciences, University of Tennessee, 2431 Joe Johnson Dr., Knoxville, TN, 37996, USA

3 National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO, 80401, USA

4 Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Rd., Athens, GA, 30602, USA

5 School of Chemistry & Biochemistry, Georgia Institute of Technology, 901 Atlantic Drive, 30332, Atlanta, GA, USA

6 BioEnergy Science Center (BESC), Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA

7 Present address: Department of Biological Sciences, University of North Texas, 1155 Union Circle, Denton, TX 76203, USA

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Biotechnology for Biofuels 2013, 6:71  doi:10.1186/1754-6834-6-71

Published: 7 May 2013

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.

Keywords:
Switchgrass; Bioenergy; Biofuel; Feedstock; Cellulosic ethanol; PvMYB4; Transcription factor; Cell wall; Recalcitrance; Lignin; Hemicellulose; Pectin