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.
Original language | English |
---|---|
Article number | 41 |
Journal | Biotechnology for Biofuels |
Volume | 8 |
Issue number | 1 |
DOIs | |
State | Published - 2015 |
Bibliographical note
Publisher Copyright:© 2015 Biswal et al.; licensee BioMed Central.
Funding
We thank Lee Gunter for validation of constructs containing amplified gene targets from P. trichocarpa leaf cDNA libraries, Rick Nelson for directing the BESC transformation pipeline and critical review of the manuscript, Will Rottmann for overseeing the Populus transformation pipeline, Sheilah Dixon Huckabee for administrative assistance, and the CCRC Analytical Services for glycosyl residue linkage analysis. The authors also thank Crissa Doeppke, Melissa Glenn, Kimberly Mazza, Logan Schuster, and Kevin Cowley for preparation of samples for the HTP biomass recalcitrance pipeline and Breeanna R. Urbanowicz for providing the poplar cDNA. The generation of the CCRC series of plant cell wall glycan-directed monoclonal antibodies used in this work was supported by the US National Science Foundation Plant Genome Program (DBI-0421683 and IOS-0923992). The research was funded by The BioEnergy Science Center (BESC) Grant DE-PS02-06ER64304 and partially by the Department of Energy Center Grant DE-FG02-93ER20097. The BioEnergy Science Center is a U.S. Department of Energy Bioenergy Research Center supported by the Office of Biological and Environmental Research in the DOE Office of Science.
Funders | Funder number |
---|---|
BioEnergy Science Center | DE-PS02-06ER64304 |
Department of Energy Center | DE-FG02-93ER20097 |
U.S. Department of Energy Bioenergy Research Center | |
National Science Foundation | IOS-0923992, DBI-0421683 |
Directorate for Biological Sciences | 0421683, 0923992 |
Office of Science | |
Biological and Environmental Research |
Keywords
- Biofuel
- Growth
- Pectin
- Populus
- Saccharification
- Secondary cell wall
- Wood development
- Xylan