Modified Switchgrass: Success in Biofuel-relevant Characteristics
Introduced traits remain stable for improved biofuel production in a field setting.
The development of near-term fossil fuel alternatives is needed to reduce carbon emissions and to ensure U.S. energy security. Switchgrass, a biofuel feedstock (biological material that can be converted into a fuel), is a perennial grass that is able to grow on marginal lands and has served as an adaptable lignocellulosic bioresource. Due to its complex composition, the plant cell wall is resistant to deconstruction to its component sugars, known as recalcitrance. Overcoming this recalcitrance is necessary to enable the economic feasibility of biofuel production. In this study, researchers evaluated the physiological and chemical effects of genetically modified switchgrass lignin in a three year field study.
Using a genetically modified line of switchgrass a team of scientists was able to demonstrate that biofuel-relevant characteristics remained stable while recalcitrance was reduced after three generations in the field. This is a vital step towards understanding how to overcome the recalcitrance problem and 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 lignin is considered a major contributor to recalcitrance. Researchers at the 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. A 35-84% higher sugar release was reported in the lignin modified plants after a 72-h enzymatic hydrolysis without pretreatment and a 25-32% increase in enzymatic sugar release (after hydrothermal pretreatment). For years 2 and 3 in the field, lignin modified plants had 12% and 14% reduced 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 were able to remain 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 Bioenergy Research Center supported by the Office of Biological and Environmental Research in the DOE Office of Science under Contract No. 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].