Silencing Folylpolyglutamate Synthetase1 (FPGS1) in Switchgrass (Panicum virgatum L.) Improves Lignocellulosic Biofuel Production

Abstract

Switchgrass (Panicum virgatum L.) is a lignocellulosic perennial grass with great potential in bioenergy field. Lignocellulosic bioenergy crops are mostly resistant to cell wall deconstruction, and therefore yield suboptimal levels of biofuel. The one-carbon pathway (also known as C1 metabolism) is critical for polymer methylation, including that of lignin and hemicelluloses in cell walls. Folylpolyglutamate synthetase (FPGS) catalyzes a biochemical reaction that leads to the formation of folylpolyglutamate, an important cofactor for many enzymes in the C1 pathway. In this study, the putatively novel switchgrass PvFPGS1 gene was identified and its functional role in cell wall composition and biofuel production was examined by RNAi knockdown analysis. The PvFPGS1-downregulated plants were analyzed in the field over three growing seasons. Transgenic plants with the highest reduction in PvFPGS1 expression grew slower and produced lower end-of-season biomass. Transgenic plants with low-to-moderate reduction in PvFPGS1 transcript levels produced equivalent biomass as controls. There were no significant differences observed for lignin content and syringyl/guaiacyl lignin monomer ratio in the low-to-moderately reduced PvFPGS1 transgenic lines compared with the controls. Similarly, sugar release efficiency was also not significantly different in these transgenic lines compared with the control lines. However, transgenic plants produced up to 18% more ethanol while maintaining congruent growth and biomass as non-transgenic controls. Severity of rust disease among transgenic and control lines were not different during the time course of the field experiments. Altogether, the unchanged lignin content and composition in the low-to-moderate PvFPGS1-downregulated lines may suggest that partial downregulation of PvFPGS1 expression did not impact lignin biosynthesis in switchgrass. In conclusion, the manipulation of PvFPGS1 expression in bioenergy crops may be useful to increase biofuel potential with no growth penalty or increased susceptibility to rust in feedstock.

Sorghum Brown Midrib19 (Bmr19) Gene Links Lignin Biosynthesis to Folate Metabolism

“…A FPGS in switchgrass ( Panicum virgatum ) encoded by Pavir.Ib00114 ( PvFPGS1 ) with high homology (93.8% identical + positively scoring residues in alignment according to Phytozome v.12) to sorghum Bmr19 was targeted by RNAi to either knock-down or knock-out the activity of one of three FPGS in transgenic plants evaluated in the field for harvestable biomass and ethanol yield [ 47 ]. Transgenic lines in which PvFPGS1 expression was essentially knocked out had severe consequences on plant biomass yield.…”

“…However, in certain of these transgenic switchgrass lines ethanol yield was improved by as much as 18%. This was despite no obvious improvement in sugar release efficiency in these transgenics relative to control [ 47 ]. The authors of the switchgrass study monitored global gene expression in their transgenic lines through RNA-seq and speculate that the increased ethanol yield in their low-to-moderate PvFPGS1 knock-down transgenics may be due to perturbations in gene expression through metabolite feedback that alter the expression of genes whose products ultimately affect the level of lignin polymerization in cell walls rather than the actual production of monolignols [ 47 ].…”

Lignocellulolytic Biocatalysts: The Main Players Involved in Multiple Biotechnological Processes for Biomass Valorization

“…In order to increase the feasibility of using microorganisms in biofuel production, recent research has sought to develop high-yield microorganisms for plant biomass degradation. In this scenario, genetic engineering of lignocellulosic biomass is one of the main strategies to increase biofuels [ 300 , 304 , 305 ]. On the other hand, genetic engineering and metabolic modulation of lignocellulolytic microorganisms is also an important strategy to improve both their enzymatic production and microorganism’s tolerance to inhibitors produced during the pretreatment step and to elevated temperature required conditions [ 300 , 306 , 307 , 308 , 309 , 310 ].…”

Activity of Cytosolic Ascorbate Peroxidase (APX) from Panicum virgatum against Ascorbate and Phenylpropanoids

“…Switchgrass plants can experience significant oxidative stress when infested with insects [ 28 ] or microbes [ 29 ], and it is likely that PviAPX1 plays a central role in mitigating oxidative stress. Considerable resources have been devoted to improving switchgrass biomass yields and quality [ 30 , 31 , 32 , 33 ]. Although vegetative biomass was targeted for biochemical conversion to ethanol [ 34 ], switchgrass biomass is suitable for producing butanol [ 35 ], or products derived by pyrolysis [ 36 ].…”