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Title: A gene stacking approach leads to engineered plants with highly increased galactan levels in Arabidopsis

Background: Engineering of plants with a composition of lignocellulosic biomass that is more suitable for downstream processing is of high interest for next-generation biofuel production. Lignocellulosic biomass contains a high proportion of pentose residues, which are more difficult to convert into fuels than hexoses. Therefore, increasing the hexose/pentose ratio in biomass is one approach for biomass improvement. A genetic engineering approach was used to investigate whether the amount of pectic galactan can be specifically increased in cell walls of Arabidopsis fiber cells, which in turn could provide a potential source of readily fermentable galactose. Results: First it was tested if overexpression of various plant UDP-glucose 4-epimerases (UGEs) could increase the availability of UDP-galactose and thereby increase the biosynthesis of galactan. Constitutive and tissue-specific expression of a poplar UGE and three Arabidopsis UGEs in Arabidopsis plants could not significantly increase the amount of cell wall bound galactose. We then investigated co-overexpression of AtUGE2 together with the β-1,4-galactan synthase GalS1. Co-overexpression of AtUGE2 and GalS1 led to over 80% increase in cell wall galactose levels in Arabidopsis stems, providing evidence that these proteins work synergistically. Furthermore, AtUGE2 and GalS1 overexpression in combination with overexpression of the NST1 master regulator for secondary cellmore » wall biosynthesis resulted in increased thickness of fiber cell walls in addition to the high cell wall galactose levels. Immunofluorescence microscopy confirmed that the increased galactose was present as β-1,4-galactan in secondary cell walls. Conclusions: This approach clearly indicates that simultaneous overexpression of AtUGE2 and GalS1 increases the cell wall galactose to much higher levels than can be achieved by overexpressing either one of these proteins alone. Moreover, the increased galactan content in fiber cells while improving the biomass composition had no impact on plant growth and development and hence on the overall biomass amount. Thus, we could show that the gene stacking approach described here is a promising method to engineer advanced feedstocks for biofuel production.« less
Authors:
 [1] ;  [2] ;  [1] ;  [2] ;  [2] ;  [2] ;  [3]
  1. Joint BioEnergy Institute, Emeryville, CA (United States). Feedstocks Div.; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of Copenhagen, Frederiksberg (Denmark)
  2. Joint BioEnergy Institute, Emeryville, CA (United States). Feedstocks Div.; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
  3. Joint BioEnergy Institute, Emeryville, CA (United States). Feedstocks Div.; Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States)
Publication Date:
OSTI Identifier:
1213421
Grant/Contract Number:
AC02-05CH11231
Type:
Accepted Manuscript
Journal Name:
BMC Plant Biology
Additional Journal Information:
Journal Volume: 14; Journal Issue: 1; Journal ID: ISSN 1471-2229
Publisher:
BioMed Central
Research Org:
Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Biological and Environmental Research (BER) (SC-23)
Country of Publication:
United States
Language:
English
Subject:
09 BIOMASS FUELS; 60 APPLIED LIFE SCIENCES plant cell wall; UDP-glucose 4-epimerase; Galactan; Pectin; Arabidopsis; Populus; gene stacking; GalS1; NST1; artificial positive feedback loop