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

Biotechnology for Biofuels

Ajaya K Biswal¹  Zhangying Hao¹  Sivakumar Pattathil¹  Xiaohan Yang⁴  Kim Winkeler⁵  Cassandra Collins⁵  Sushree S Mohanty¹  Elizabeth A Richardson²  Ivana Gelineo-Albersheim¹  Kimberly Hunt¹  David Ryno¹  Robert W Sykes³  Geoffrey B Turner³  Angela Ziebell³  Erica Gjersing³  Wolfgang Lukowitz²  Mark F Davis³  Stephen R Decker³  Michael G Hahn¹  Debra Mohnen¹ 

[1] DOE-BioEnergy Science Center (BESC), Oak Ridge, USA

[2] Department of Plant Biology, University of Georgia, 2502 Miller Plant Sciences, Athens 30602, GA, USA

[3] National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden 80401-3305, CO, USA

[4] Bioscience Division, Oak Ridge National Laboratory, Oak Ridge 37831, TN, USA

[5] ArborGen Inc., 2011 Broadbank Ct, Ridgeville 29472, SC, USA

关键词: Wood development;    Xylan;    Secondary cell wall;    Saccharification;    Populus;    Pectin;    Growth;    Biofuel;   

Others  :  1145279
DOI  :  10.1186/s13068-015-0218-y

 received in 2014-09-16, accepted in 2015-02-03,  发布年份 2015

【 摘 要 】

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.

【 授权许可】

   
2015 Biswal et al.; licensee BioMed Central.

【 图 表 】

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