Downregulation of a UDP-Arabinomutase Gene in Switchgrass (Panicum virgatumL.) Results in Increased Cell Wall Lignin While Reducing Arabinose-Glycans.
Background:Switchgrass (Panicum virgatumL.) is a C4perennial prairie grass and a dedicated feedstock for lignocellulosic biofuels. Saccharification and biofuel yields are inhibited by the plant cell wall's natural recalcitrance against enzymatic degradation. Plant hemicellulose polysaccharides such as arabinoxylans structurally support and cross-link other cell wall polymers. Grasses predominately have Type II cell walls that are abundant in arabinoxylan, which comprise nearly 25% of aboveground biomass. A primary component of arabinoxylan synthesis is uridine diphosphate (UDP) linked to arabinofuranose (Araf). A family of UDP-arabinopyranose mutase (UAM)/reversible glycosylated polypeptides catalyze the interconversion between UDP-arabinopyranose (UDP-Arap) and UDP-Araf.Results:The expression of a switchgrass arabinoxylan biosynthesis pathway gene,PvUAM1, was decreased via RNAi to investigate its role in cell wall recalcitrance in the feedstock.PvUAM1encodes a switchgrass homolog of UDP-arabinose mutase, which converts UDP-Arapto UDP-Araf. Southern blot analysis revealed each transgenic line contained between one to at least seven T-DNA insertions, resulting in some cases, a 95% reduction of nativePvUAM1transcript in stem internodes. Transgenic plants had increased pigmentation in vascular tissues at nodes, but were otherwise similar in morphology to the non-transgenic control. Cell wall-associated arabinose was decreased in leaves and stems by over 50%, but there was an increase in cellulose. In addition, there was a commensurate change in arabinose side chain extension. Cell wall lignin composition was altered with a concurrent increase in lignin content and transcript abundance of lignin biosynthetic genes in mature tillers. Enzymatic saccharification efficiency was unchanged in the transgenic plants relative to the control.Conclusion:Plants with attenuatedPvUAM1transcript had increased cellulose and lignin in cell walls. A decrease in cell wall-associated arabinose was expected, which was likely caused by fewer Arafresidues in the arabinoxylan. The decrease in arabinoxylan may cause a compensation response to maintain cell wall integrity by increasing cellulose and lignin biosynthesis. In cases in which increased lignin is desired, e.g., feedstocks for carbon fiber production, downregulatedUAM1coupled with altered expression of other arabinoxylan biosynthesis genes might result in even higher production of lignin in biomass.
Department of Plant Sciences, University of Tennessee, KnoxvilleTN, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak RidgeTN, USA.
Jonathan D
JD
Willis
BioEnergy Science Center, Oak Ridge National Laboratory, Oak RidgeTN, USA; Complex Carbohydrate Research Center, University of Georgia, AthensGA, USA.
James A
JA
Smith
Department of Plant Sciences, University of Tennessee, KnoxvilleTN, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak RidgeTN, USA.
Mitra
M
Mazarei
BioEnergy Science Center, Oak Ridge National Laboratory, Oak RidgeTN, USA; The Samuel Roberts Noble Foundation, ArdmoreOK, USA.
Ji-Yi
JY
Zhang
BioEnergy Science Center, Oak Ridge National Laboratory, Oak RidgeTN, USA; The National Renewable Energy Laboratory, GoldenCO, USA.
Geoffrey B
GB
Turner
BioEnergy Science Center, Oak Ridge National Laboratory, Oak RidgeTN, USA; The National Renewable Energy Laboratory, GoldenCO, USA.
Stephen R
SR
Decker
BioEnergy Science Center, Oak Ridge National Laboratory, Oak RidgeTN, USA; The National Renewable Energy Laboratory, GoldenCO, USA.
Robert W
RW
Sykes
Department of Plant Sciences, University of Tennessee, KnoxvilleTN, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak RidgeTN, USA.
Charleson R
CR
Poovaiah
Department of Plant Sciences, University of Tennessee, KnoxvilleTN, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak RidgeTN, USA.
Holly L
HL
Baxter
Department of Plant Sciences, University of Tennessee, KnoxvilleTN, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak RidgeTN, USA.
David G J
DG
Mann
BioEnergy Science Center, Oak Ridge National Laboratory, Oak RidgeTN, USA; The National Renewable Energy Laboratory, GoldenCO, USA.
Mark F
MF
Davis
BioEnergy Science Center, Oak Ridge National Laboratory, Oak RidgeTN, USA; The Samuel Roberts Noble Foundation, ArdmoreOK, USA.
Michael K
MK
Udvardi
BioEnergy Science Center, Oak Ridge National Laboratory, Oak RidgeTN, USA; Complex Carbohydrate Research Center, University of Georgia, AthensGA, USA.
Maria J
MJ
Peña
BioEnergy Science Center, Oak Ridge National Laboratory, Oak RidgeTN, USA; Complex Carbohydrate Research Center, University of Georgia, AthensGA, USA.
Jason
J
Backe
BioEnergy Science Center, Oak Ridge National Laboratory, Oak RidgeTN, USA; Complex Carbohydrate Research Center, University of Georgia, AthensGA, USA; Plant Biology, University of Georgia, AthensGA, USA.
Maor
M
Bar-Peled
Department of Plant Sciences, University of Tennessee, KnoxvilleTN, USA; BioEnergy Science Center, Oak Ridge National Laboratory, Oak RidgeTN, USA.
C N
CN
Stewart
UDP-arabinopyranose mutase/reversible glycosylated polypeptide; biofuel; hemicellulose arabinoxylan; recalcitrance; switchgrass