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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

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. The following are the 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 Populusmore » 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. Finally, 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.« less
 [1] ;  [1] ;  [1] ;  [2] ;  [3] ;  [3] ;  [1] ;  [4] ;  [1] ;  [1] ;  [1] ;  [5] ;  [5] ;  [5] ;  [5] ;  [6] ;  [5] ;  [5] ;  [1] ;  [1]
  1. Univ. of Georgia, Athens, GA (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); ArborGen Inc., Ridgeville, SC (United States)
  4. Univ. of Georgia, Athens, GA (United States). Dept. of Plant Biology
  5. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States); National Renewable Energy Lab. (NREL), Golden, CO (United States)
  6. Univ. of Georgia, Athens, GA (United States)
Publication Date:
OSTI Identifier:
Report Number(s):
Journal ID: ISSN 1754-6834
Grant/Contract Number:
PS02-06ER64304; FG02-93ER20097
Accepted Manuscript
Journal Name:
Biotechnology for Biofuels
Additional Journal Information:
Journal Volume: 8; Journal ID: ISSN 1754-6834
BioMed Central
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States); Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
09 BIOMASS FUELS; 59 BASIC BIOLOGICAL SCIENCES biofuels; growth; pectin; Populus; saccharification; secondary cell wall; xylan; wood development