Hybridization of downregulated-COMT transgenic switchgrass lines with field selected switchgrass for improved biomass traits

Authors: BAXTER, HOLLY - University Of Tennessee; Alexander, Lisa; MAZAREI, MITRA - University Of Tennessee; HAYNES, ELLEN - University Of Tennessee; TURNER, GEOFFREY - University Of North Texas; SYKES, ROBERT - National Renewable Energy Laboatory; DECKER, STEPHEN - National Renewable Energy Laboatory; DAVIS, MARK - National Renewable Energy Laboatory; DIXON, RICHARD - University Of North Texas; WANG, ZENG-YU - Samuel Roberts Noble Foundation, Inc; STEWART, NEAL - University Of Tennessee

Submitted to: Euphytica
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/31/2015
Publication Date: 1/21/2016
Citation: Baxter, H.L., Alexander, L.W., Mazarei, M., Haynes, E., Turner, G.B., Sykes, R.W., Decker, S.R., Davis, M.F., Dixon, R.A., Wang, Z., Stewart, N.C. 2016. Hybridization of downregulated-COMT transgenic switchgrass lines with field selected switchgrass for improved biomass traits. Euphytica. 209:341-355.

Interpretive Summary: The United States Department of Energy’s renewable fuel standards require an increase in energy production from renewable sources. Switchgrass (Panicum virgatum, L.), a warm-season C4 perennial grass species native to North America, has significant potential as a renewable source of fuel due to its wide range of adaptation, high biomass potential on marginal land, and high nutrient- and water-use efficiency. Despite favorable economic and environmental traits, large-scale deployment of switchgrass as sustainable and cost-competitive sources of fuel will rely on improvements to feedstock quality, biomass productivity, and other desirable agronomic traits. In particular, recent breeding and biotechnology efforts with switchgrass have focused on improving biomass composition for bioconversion. For instance, downregulated caffeic acid 3-O-methyltransferase (COMT) switchgrass produced significantly more biomass and biofuel than the non-transgenic progenitor line. In the present study we sought to further improve biomass characteristics by crossing the downregulated COMT T1 lines with high-yielding switchgrass accessions in two genetic backgrounds (‘Alamo’ and ‘Kanlow’). Crosses and T2 progeny analysis were made under greenhouse conditions to assess maternal effects, plant morphology, yield and cell wall traits. T2 transgenic hybrids were 7% shorter at 80 days after sowing and produced 43% less biomass than non-transgenic null-segregant hybrids. Cell wall-related differences included lower lignin content, reduced S/G ratio, and a 12% increase in total sugar release in the T2 transgenic hybrids compared to non-transgenic null segregants. This is the first study to evaluate the feasibility of transferring the low-recalcitrance traits associated with a transgenic switchgrass line into high-yielding field varieties in an attempt to improve growth-related traits. Our results provide insights into the possible improvement of switchgrass productivity via biotechnology paired with plant breeding for line improvement for bioenergy.

Technical Abstract: Transgenic switchgrass (Panicum virgatum L.) has been produced for improved cell walls for biofuels. Downregulated caffeic acid 3-O-methyltransferase (COMT) switchgrass produced significantly more biomass and biofuel than the non-transgenic progenitor line. In the present study we sought to further improve biomass characteristics by crossing the downregulated COMT T1 lines with high-yielding switchgrass accessions in two genetic backgrounds (‘Alamo’ and ‘Kanlow’). Crosses and T2 progeny analysis were made under greenhouse conditions to assess maternal effects, plant morphology, yield and cell wall traits. Female parent type influenced morphology but had no effect on cell wall traits. T2 hybrids produced with T1 COMT-downregulated switchgrass as the female parent were taller, produced more tillers, and had 63% more dry weight biomass compared to those produced using the field selected wild type as the female parent. Transgene status (presence or absence of transgene) influenced both growth and cell wall traits. T2 transgenic hybrids were 7% shorter at 80 days after sowing and produced 43% less biomass than non-transgenic null-segregant hybrids. Cell wall-related differences included lower lignin content, reduced S/G ratio, and a 12% increase in total sugar release in the T2 transgenic hybrids compared to non-transgenic null segregants. This is the first study to evaluate the feasibility of transferring the low-recalcitrance traits associated with a transgenic switchgrass line into high-yielding field varieties in an attempt to improve growth-related traits. Our results provide insights into the possible improvement of switchgrass productivity via biotechnology paired with plant breeding for line improvement for bioenergy.