Two‐year field analysis of reduced recalcitrance transgenic switchgrass

Abstract

SummarySwitchgrass (Panicum virgatum L.) is a leading candidate for a dedicated lignocellulosic biofuel feedstock owing to its high biomass production, wide adaptation and low agronomic input requirements. Lignin in cell walls of switchgrass, and other lignocellulosic feedstocks, severely limits the accessibility of cell wall carbohydrates to enzymatic breakdown into fermentable sugars and subsequently biofuels. Low-lignin transgenic switchgrass plants produced by the downregulation of caffeic acid O-methyltransferase (COMT), a lignin biosynthetic enzyme, were analysed in the field for two growing seasons. COMT transcript abundance, lignin content and the syringyl/guaiacyl lignin monomer ratio were consistently lower in the COMT-down-regulated plants throughout the duration of the field trial. In general, analyses with fully established plants harvested during the second growing season produced results that were similar to those observed in previous greenhouse studies with these plants. Sugar release was improved by up to 34% and ethanol yield by up to 28% in the transgenic lines relative to controls. Additionally, these results were obtained using senesced plant material harvested at the end of the growing season, compared with the young, green tissue that was used in the greenhouse experiments. Another important finding was that transgenic plants were not more susceptible to rust (Puccinia emaculata). The results of this study suggest that lignin down-regulation in switchgrass can confer real-world improvements in biofuel yield without negative consequences to biomass yield or disease susceptibility.

Silencing CHALCONE SYNTHASE in Maize Impedes the Incorporation of Tricin into Lignin and Increases Lignin Content

“…more hemicellulose in low-lignin plants) has been reported. Stems of low-lignin transgenic switchgrass (Panicum virgatum) down-regulated for COMT had increased amounts of xylan, the predominant hemicellulose component in switchgrass, both when plants were cultivated in the greenhouse (Fu et al, 2011) and in the field (Baxter et al, 2014). In brachypodium (Brachypodium distachyon), the reduced lignin content of a mutant for the ligninspecific laccase BdLAC5 was compensated for by a slight increase in the content of hemicellulose, whereas the amount of cellulose remained unchanged (Wang et al, 2015b).…”

Transgenic switchgrass (Panicum virgatum L.) targeted for reduced recalcitrance to bioconversion: a 2‐year comparative analysis of field‐grown lines modified for target gene or genetic element expression

“…Reduction in bioconversion to ethanol corresponds to a broad increase in biomass recalcitrance of unknown mechanism theorized as plant tissue ‘hardening’ from environmental exposure and regrowth in the field over years from the perennial root. Data indicating this were reported for transgenic lines modifying PvMYB and COMT expression (Baxter et al ., 2014, 2015). Our report extends this observation as a general trend affecting all transgenic and control switchgrass lines studied within BESC.…”

“…Replicates were arranged in a completely randomized design in all fields except for FPGS, which was arranged in a randomized block design. Fields were maintained as described previously (Baxter et al ., 2014). Briefly, no fertilizers or herbicides were applied for the duration of the field trail and weeding was performed by hand or tillage.…”

Relationships between Biomass Composition and Liquid Products Formed via Pyrolysis

“…For example, lignin is an important target for genetic engineering for pyrolysis since the major lignin-derived products have a lower O:C ratio, a higher energy value, and are more stable than sugar-derived products (Tanger et al, 2013;Mante et al, 2014). Some important genes that participate in or regulate lignin synthesis have already been modified in energy crops without major interference with plant biomass yield (Baxter et al, 2014(Baxter et al, , 2015reviewed in Bartley et al, 2014). However, current genetic engineering strategies are focused on developing low lignin biomass for saccharification and biochemical conversion to fuels.…”