LACCASE14 is required for the deposition of guaiacyl lignin and affects cell wall digestibility in poplar
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Biotechnology for Biofuels Open Access
RESEARCH
LACCASE14 is required for the deposition of guaiacyl lignin and affects cell wall digestibility in poplar Shifei Qin1, Chunfen Fan1, Xiaohong Li1, Yi Li1, Jian Hu1, Chaofeng Li1 and Keming Luo1,2*
Abstract Background: The recalcitrance of lignocellulosic biomass provided technical and economic challenges in the current biomass conversion processes. Lignin is considered as a crucial recalcitrance component in biomass utilization. An indepth understanding of lignin biosynthesis can provide clues to overcoming the recalcitrance. Laccases are believed to play a role in the oxidation of lignin monomers, leading to the formation of higher-order lignin. In plants, functions of only a few laccases have been evaluated, so little is known about the effect of laccases on cell wall structure and biomass saccharification. Results: In this study, we screened a gain-of-function mutant with a significant increase in lignin content from Arabidopsis mutant lines overexpressing a full-length poplar cDNA library. Further analysis confirmed that a Chinese white poplar (Populus tomentosa) laccase gene PtoLAC14 was inserted into the mutant, and PtoLAC14 could functionally complement the Arabidopsis lac4 mutant. Overexpression of PtoLAC14 promoted the lignification of poplar and reduced the proportion of syringyl/guaiacyl. In contrast, the CRISPR/Cas9-generated mutation of PtLAC14 results in increased the syringyl/guaiacyl ratios, which led to integrated enhancement on biomass enzymatic saccharification. Notably, the recombinant PtoLAC14 protein showed higher oxidized efficiency to coniferyl alcohol (precursor of guaiacyl unit) in vitro. Conclusions: This study shows that PtoLAC14 plays an important role in the oxidation of guaiacyl deposition on cell wall. The reduced recalcitrance of the PtoLAC14-KO lines suggests that PtoLAC14 is an elite target for cell wall engineering, and genetic manipulation of this gene will facilitate the utilization of lignocellulose. Keywords: Populus, Dwarf, Laccase, Lignin, Monolignol, Guaiacyl unit, Saccharification Background The plant cell wall represents an enormous renewable biomass resource for biochemical, biofuels and materials production on the earth [1, 2]. Plant cell wall is composed mainly of cellulose, hemicelluloses and lignin, as well as minor pectic polysaccharides and wall proteins *Correspondence: [email protected] † Shifei Qin and Chunfen Fan have made equal contribution to this work 1 Chongqing Key Laboratory of Plant Resource Conservation and Germplasm Innovation, School of Life Sciences, Southwest University, No. 2, Tiansheng Road, Beibei 400716, Chongqing, China Full list of author information is available at the end of the article
[3]. Cellulose and hemicellulose can be converted to bioethanol, biobutanol, and other products. For effective utilization of these carbohydrates, it is necessary to overcome the recalcitrance of cell wall. Lignocellulose recalcitrance is principally determined by cell wall composition, wall polymer fea
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