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

Abstract

SummaryTransgenic Panicum virgatum L. silencing (KD) or overexpressing (OE) specific genes or a small RNA (GAUT4‐KD, miRNA156‐OE, MYB4‐OE,COMT‐KD and FPGS‐KD) was grown in the field and aerial tissue analysed for biofuel production traits. Clones representing independent transgenic lines were established and senesced tissue was sampled after year 1 and 2 growth cycles. Biomass was analysed for wall sugars, recalcitrance to enzymatic digestibility and biofuel production using separate hydrolysis and fermentation. No correlation was found between plant carbohydrate content and biofuel production pointing to overriding structural and compositional elements that influence recalcitrance. Biomass yields were greater for all lines in the second year as plants establish in the field and standard amounts of biomass analysed from each line had more glucan, xylan and less ethanol (g/g basis) in the second‐ versus the first‐year samples, pointing to a broad increase in tissue recalcitrance after regrowth from the perennial root. However, biomass from second‐year growth of transgenics targeted for wall modification, GAUT4‐KD,MYB4‐OE,COMT‐KD and FPGS‐KD, had increased carbohydrate and ethanol yields (up to 12% and 21%, respectively) compared with control samples. The parental plant lines were found to have a significant impact on recalcitrance which can be exploited in future strategies. This summarizes progress towards generating next‐generation bio‐feedstocks with improved properties for microbial and enzymatic deconstruction, while providing a comprehensive quantitative analysis for the bioconversion of multiple plant lines in five transgenic strategies.

Transgenic miR156 switchgrass in the field: growth, recalcitrance and rust susceptibility

“…Ethanol yields were measured by separate hydrolysis and fermentation (SHF) as described previously (Dumitrache et al ., ). SHF experiments were performed in biological duplicate at a 5.0% (w/v) dry solids loading at 20 mL final volume.…”

Gene regulatory networks for lignin biosynthesis in switchgrass (Panicum virgatum)

“…Switchgrass (Panicum virgatum L.) has been selected as a major cellulosic feedstock for bioconversion to ethanol in the United States (Bouton, 2007). Manipulating cell walls in switchgrass through down-regulation of GAUT4 (galacturono-syltransferase4, involved in pectin biosynthesis), COMT (caffeic acid/5-hydroxyferulic acid 3-O-methyltransferase, involved in lignin biosynthesis) and FPGS (folylpolyglutamate synthase 1, involved in C1 metabolism) or overexpression of MYB4 (a repressor of lignin biosynthesis) in all cases leads to a reduction of cell wall recalcitrance and an increased efficiency of sugar release (Dumitrache et al, 2017). However, as a non-model organism, the lack of genetic information on secondary cell wall formation in switchgrass limits biotechnological approaches to feedstock development.…”

The miR156‐SPL4 module predominantly regulates aerial axillary bud formation and controls shoot architecture

“…Switchgrass (Panicum virgatum) is a C 4 perennial tetraploid bunchgrass that has been developed into a dedicated biofuel crop because of its high biomass yield, low agricultural input requirements and the ability to grow in marginal lands (Schmer et al, 2008;Hardin et al, 2013). Extensive efforts have been made to genetically improve switchgrass productivity and reduce biomass recalcitrance (Fu et al, 2011(Fu et al, , 2012Shen et al, 2013;Baxter et al, 2014;Dumitrache et al, 2017;Li et al, 2017;Liu et al, 2017). We have shown that overexpression of a microRNA156 (miR156) precursor in switchgrass resulted in various morphological alterations, and the degree of the morphological changes depends on the miR156 level (Fu et al, 2012).…”