Near-term fossil fuel alternatives could reduce carbon emissions and ensure U.S. energy security. One alternative uses switchgrass, a perennial plant, that is able to grow on marginal lands. Sugars released by processing switchgrass can be turned into fuel. Due to its complex composition, the plant cell wall resists deconstruction into sugars. This resistance is called recalcitrance. Overcoming recalcitrance is vital to enable economically feasible biofuel production. Using a genetically modified line of switchgrass, scientists reduced recalcitrance while increasing sugar release over three generations.
This research is a vital step towards understanding how to overcome the recalcitrance problem. This work thus has the potential to reduce economic barriers to cost-effective biofuel production.
The plant cell wall is primarily made up of three biopolymers: lignin, hemicellulose and cellulose. Lignin’s complex architecture provides structural support and pathogen defense, but it is due to these functions that lignin is considered a major contributor to recalcitrance. Researchers at the U.S. Department of Energy’s (DOE) BioEnergy Science Research Center (BESC) silenced the caffeic acid O-methyltransferase (COMT) gene in the lignin biosynthesis pathway and demonstrated over three growing seasons that the genetically modified plants retained both reduced cell wall recalcitrance and lignin content in comparison to the non-transgenic controls. The team reported a 35 percent to 84 percent higher sugar release in the lignin-modified plants after a 72-hour enzymatic hydrolysis without pretreatment and a 25 percent to 32 percent increase in enzymatic sugar release (after hydrothermal pretreatment). For years 2 and 3 in the field, the team reported lignin-modified plants had 12 percent and 14 percent less lignin content, respectively. This study demonstrated the important traits associated with the COMT-silenced field-grown switchgrass are an increase in cell wall accessibility for sugar release and a reduction in lignin content. These traits remained durable in the field for 3 years in field trials. This research helps to provide a mechanistic understanding of lignin-modified switchgrass relevant to DOE’s energy and environmental missions.
This work was supported by the BioEnergy Science Center, a U.S. Department of Energy (DOE) Bioenergy Research Center supported by the Office of Biological and Environmental Research in the DOE Office of Science under contract DE-AC05-00OR22725.
M. Li, Y. Pu, C. Yoo, E. Gjersing, S.R. Decker, C. Doeppke, T. Shollenberger, T.J. Tschaplinski, N.L. Engle, R.W. Sykes, M.F. Davis, H.L. Baxter, M. Mazarei, C. Fu, R.A. Dixon, Z. Wang, C.N. Stewart, and A.J. Ragauskas, “Study of traits and recalcitrance reduction of field-grown COMT down-regulated switchgrass.” Biotechnology for Biofuels 10, 12 (2017). [DOI: 10.1186/s13068-016-0695-7]