Development and field assessment of transgenic hybrid switchgrass for improved biofuel traits

Authors: Alexander, Lisa; HATCHER, CATHERINE - University Of Tennessee; MAZAREI, MITRA - University Of Tennessee; HAYNES, ELLEN - University Of Tennessee; BAXTER, HOLLY - University Of Tennessee; KIM, KEONHEE - University Of Tennessee; HAMILTON, CHOO - University Of Tennessee; SYKES, ROBERT - National Renewable Energy Laboatory; TURNER, GEOFFREY - National Renewable Energy Laboatory; DAVIS, MARK - National Renewable Energy Laboatory; DIXON, RICHARD - University Of North Texas; WANG, ZENG-YU - Samuel Roberts Noble Foundation, Inc; LABBE, NICOLE - University Of Tennessee; STEWART, C.NEAL JR - University Of Tennessee

Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2020
Publication Date: 1/22/2020
Publication URL: https://handle.nal.usda.gov/10113/6820435
Citation: Alexander, L.W., Hatcher, Catherine, Mazarei, Mitra, Haynes, Ellen, Baxter, Holly, Kim, Keonhee, Hamilton, Choo, Sykes, Robert, Turner, Geoffrey, Davis, Mark, Dixon, Richard, Wang, Zeng-Yu, Labbe, Nicole, Stewart, C.Neal Jr 2020. Development and field assessment of transgenic hybrid switchgrass for improved biofuel traits. Euphytica. 216:25. https://doi.org/10.1007/s10681-020-2558-3.
DOI: https://doi.org/10.1007/s10681-020-2558-3

Interpretive Summary: Switchgrass is a promising biofuel crop due to its high yield per acre, ability to grow widely across the U.S., and low fertilizer and pesticide requirements. However, its cell walls contain large amounts of lignin, a molecule that inhibits enzymes from reaching carbohydrates in the cell wall and producing fermentable sugar, which can limit its use as a biofuel crop. Current pre-treatments used to digest the cell wall are expensive. Scientists at the University of Tennessee developed transgenic hybrid switchgrass varieties with less lignin in cell walls but that retained its high yield and disease resistance. These high-yielding, low-lignin genotypes will reduce the costs associated with biomass processing and facilitate the adoption of switchgrass as a biofuel source.

Technical Abstract: Despite the economic and environmental advantages of switchgrass as a lignocellulosic feedstock, high costs associated with pretreatment and conversion of biomass to biofuel currently prevent switchgrass from being an economically competitive fuel source. Development of commercially useful bioenergy switchgrass cultivars requires reducing recalcitrance during bioprocessing without compromising biomass yield. Low-lignin transgenic switchgrass plants have been produced via down-regulation of caffeic acid O-methyltransferase (COMT), a lignin biosynthetic enzyme, or by over-expression of the MYB4 transcription factor, a repressor of the lignin biosynthetic pathway. Hybrids between these low-lignin transgenics and field-selected ‘Alamo’ switchgrass showed reduced lignin in greenhouse studies. The aim of this study was to evaluate parents and selected hybrids obtained from COMT and MYB4 hybrid families under field conditions for agronomic performance and biomass quality. Plant height, width, number of tillers, dry weight, cell wall composition, and sugar release were measured during the establishment year (2014) and second growing season (2015). For COMT x ‘Alamo’ hybrids, biomass yield of the transgenic hybrids was not significantly different from the wild-type ‘Alamo’ parent selected for high biomass, lignin was reduced by 10%, S/G ratio decreased by 27% and sugar release increased between 20% and 44%. MYB x ‘Alamo’ hybrids showed a reduction in biomass yield with no subsequent decrease in S/G ratio or increase in sugar release. These results show that combining low-lignin transgenics with a breeding and selection program for biomass yield will allow for the deployment of effective transgenes in high-yielding genetic backgrounds.