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Open Access Research

Lignin monomer composition affects Arabidopsis cell-wall degradability after liquid hot water pretreatment

Xu Li1, Eduardo Ximenes2, Youngmi Kim2, Mary Slininger2, Richard Meilan3, Michael Ladisch24* and Clint Chapple1*

Author Affiliations

1 Department of Biochemistry, Purdue University, West Lafayette, IN 47907, USA

2 Department of Agricultural and Biological Engineering and the Laboratory of Renewable Resources Engineering, Purdue University, West Lafayette, IN 47907, USA

3 Department of Forestry and Natural Resources, Purdue University, West Lafayette, IN 47907, USA

4 Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN 47907, USA

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Biotechnology for Biofuels 2010, 3:27  doi:10.1186/1754-6834-3-27

Published: 2 December 2010

Abstract

Background

Lignin is embedded in the plant cell wall matrix, and impedes the enzymatic saccharification of lignocellulosic feedstocks. To investigate whether enzymatic digestibility of cell wall materials can be improved by altering the relative abundance of the two major lignin monomers, guaiacyl (G) and syringyl (S) subunits, we compared the degradability of cell wall material from wild-type Arabidopsis thaliana with a mutant line and a genetically modified line, the lignins of which are enriched in G and S subunits, respectively.

Results

Arabidopsis tissue containing G- and S-rich lignins had the same saccharification performance as the wild type when subjected to enzyme hydrolysis without pretreatment. After a 24-hour incubation period, less than 30% of the total glucan was hydrolyzed. By contrast, when liquid hot water (LHW) pretreatment was included before enzyme hydrolysis, the S-lignin-rich tissue gave a much higher glucose yield than either the wild-type or G-lignin-rich tissue. Applying a hot-water washing step after the pretreatment did not lead to a further increase in final glucose yield, but the initial hydrolytic rate was doubled.

Conclusions

Our analyses using the model plant A. thaliana revealed that lignin composition affects the enzymatic digestibility of LHW pretreated plant material. Pretreatment is more effective in enhancing the saccharification of A. thaliana cell walls that contain S-rich lignin. Increasing lignin S monomer content through genetic engineering may be a promising approach to increase the efficiency and reduce the cost of biomass to biofuel conversion.