title: Downregulation of GAUT12 in Populus deltoides by RNA silencing results in reduced recalcitrance, increased growth and reduced xylan and pectin in a woody biofuel feedstock.
abstract: BACKGROUND
  The inherent recalcitrance of woody bioenergy feedstocks is a major challenge for their use as a source of second-generation biofuel. Secondary cell walls that constitute the majority of hardwood biomass are rich in cellulose, xylan, and lignin. The interactions among these polymers prevent facile accessibility and deconstruction by enzymes and chemicals. Plant biomass that can with minimal pretreatment be degraded into sugars is required to produce renewable biofuels in a cost-effective manner.
  
  
  RESULTS
  GAUT12/IRX8 is a putative glycosyltransferase proposed to be involved in secondary cell wall glucuronoxylan and/or pectin biosynthesis based on concomitant reductions of both xylan and the pectin homogalacturonan (HG) in Arabidopsis irx8 mutants. Two GAUT12 homologs exist in Populus trichocarpa, PtGAUT12.1 and PtGAUT12.2. Knockdown expression of both genes simultaneously has been shown to reduce xylan content in Populus wood. We tested the proposition that RNA interference (RNAi) downregulation of GAUT12.1 alone would lead to increased sugar release in Populus wood, that is, reduced recalcitrance, based on the hypothesis that GAUT12 synthesizes a wall structure required for deposition of xylan and that cell walls with less xylan and/or modified cell wall architecture would have reduced recalcitrance. Using an RNAi approach, we generated 11 Populus deltoides transgenic lines with 50 to 67% reduced PdGAUT12.1 transcript expression compared to wild type (WT) and vector controls. Ten of the eleven RNAi lines yielded 4 to 8% greater glucose release upon enzymatic saccharification than the controls. The PdGAUT12.1 knockdown (PdGAUT12.1-KD) lines also displayed 12 to 52% and 12 to 44% increased plant height and radial stem diameter, respectively, compared to the controls. Knockdown of PdGAUT12.1 resulted in a 25 to 47% reduction in galacturonic acid and 17 to 30% reduction in xylose without affecting total lignin content, revealing that in Populus wood as in Arabidopsis, GAUT12 affects both pectin and xylan formation. Analyses of the sugars present in sequential cell wall extracts revealed a reduction of glucuronoxylan and pectic HG and rhamnogalacturonan in extracts from PdGAUT12.1-KD lines.
  
  
  CONCLUSIONS
  The results show that downregulation of GAUT12.1 leads to a reduction in a population of xylan and pectin during wood formation and to reduced recalcitrance, more easily extractable cell walls, and increased growth in Populus.
authors: Department of Biochemistry and Molecular Biology, University of Georgia, B122 Life Sciences Bldg., Athens, GA 30602 USA ; Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Road, Athens, GA 30602 USA ; DOE-BioEnergy Science Center (BESC), Oak Ridge, USA.
authors: Ajaya K
authors: AK
authors: Biswal
authors: Department of Plant Biology, University of Georgia, 2502 Miller Plant Sciences, Athens, GA 30602 USA ; Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Road, Athens, GA 30602 USA ; DOE-BioEnergy Science Center (BESC), Oak Ridge, USA.
authors: Zhangying
authors: Z
authors: Hao
authors: Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Road, Athens, GA 30602 USA ; DOE-BioEnergy Science Center (BESC), Oak Ridge, USA.
authors: Sivakumar
authors: S
authors: Pattathil
authors: DOE-BioEnergy Science Center (BESC), Oak Ridge, USA ; Bioscience Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831 USA.
authors: Xiaohan
authors: X
authors: Yang
authors: DOE-BioEnergy Science Center (BESC), Oak Ridge, USA ; ArborGen Inc., 2011 Broadbank Ct, Ridgeville, SC 29472 USA.
authors: Kim
authors: K
authors: Winkeler
authors: DOE-BioEnergy Science Center (BESC), Oak Ridge, USA ; ArborGen Inc., 2011 Broadbank Ct, Ridgeville, SC 29472 USA.
authors: Cassandra
authors: C
authors: Collins
authors: Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Road, Athens, GA 30602 USA ; DOE-BioEnergy Science Center (BESC), Oak Ridge, USA.
authors: Sushree S
authors: SS
authors: Mohanty
authors: Department of Plant Biology, University of Georgia, 2502 Miller Plant Sciences, Athens, GA 30602 USA.
authors: Elizabeth A
authors: EA
authors: Richardson
authors: Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Road, Athens, GA 30602 USA ; DOE-BioEnergy Science Center (BESC), Oak Ridge, USA.
authors: Ivana
authors: I
authors: Gelineo-Albersheim
authors: Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Road, Athens, GA 30602 USA ; DOE-BioEnergy Science Center (BESC), Oak Ridge, USA.
authors: Kimberly
authors: K
authors: Hunt
authors: Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Road, Athens, GA 30602 USA ; DOE-BioEnergy Science Center (BESC), Oak Ridge, USA.
authors: David
authors: D
authors: Ryno
authors: DOE-BioEnergy Science Center (BESC), Oak Ridge, USA ; National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401-3305 USA.
authors: Robert W
authors: RW
authors: Sykes
authors: DOE-BioEnergy Science Center (BESC), Oak Ridge, USA ; National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401-3305 USA.
authors: Geoffrey B
authors: GB
authors: Turner
authors: DOE-BioEnergy Science Center (BESC), Oak Ridge, USA ; National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401-3305 USA.
authors: Angela
authors: A
authors: Ziebell
authors: DOE-BioEnergy Science Center (BESC), Oak Ridge, USA ; National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401-3305 USA.
authors: Erica
authors: E
authors: Gjersing
authors: Department of Plant Biology, University of Georgia, 2502 Miller Plant Sciences, Athens, GA 30602 USA.
authors: Wolfgang
authors: W
authors: Lukowitz
authors: DOE-BioEnergy Science Center (BESC), Oak Ridge, USA ; National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401-3305 USA.
authors: Mark F
authors: MF
authors: Davis
authors: DOE-BioEnergy Science Center (BESC), Oak Ridge, USA ; National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO 80401-3305 USA.
authors: Stephen R
authors: SR
authors: Decker
authors: Department of Plant Biology, University of Georgia, 2502 Miller Plant Sciences, Athens, GA 30602 USA ; Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Road, Athens, GA 30602 USA ; DOE-BioEnergy Science Center (BESC), Oak Ridge, USA.
authors: Michael G
authors: MG
authors: Hahn
authors: Department of Biochemistry and Molecular Biology, University of Georgia, B122 Life Sciences Bldg., Athens, GA 30602 USA ; Complex Carbohydrate Research Center, University of Georgia, 315 Riverbend Road, Athens, GA 30602 USA ; DOE-BioEnergy Science Center (BESC), Oak Ridge, USA.
authors: Debra
authors: D
authors: Mohnen
keywords: Biofuel; Growth; Pectin; Populus; Saccharification; Secondary cell wall; Wood development; Xylan