Metabolic engineering of novel lignin in biomass crops

Authors

  • Ruben Vanholme,

    1. Department of Plant Systems Biology, VIB, Gent, Belgium
    2. Department of Plant Biotechnology and Bioinformatics, Ghent University, Gent, Belgium
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  • Kris Morreel,

    1. Department of Plant Systems Biology, VIB, Gent, Belgium
    2. Department of Plant Biotechnology and Bioinformatics, Ghent University, Gent, Belgium
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  • Chiarina Darrah,

    1. Department of Plant Systems Biology, VIB, Gent, Belgium
    2. Department of Plant Biotechnology and Bioinformatics, Ghent University, Gent, Belgium
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  • Paula Oyarce,

    1. Department of Plant Systems Biology, VIB, Gent, Belgium
    2. Department of Plant Biotechnology and Bioinformatics, Ghent University, Gent, Belgium
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  • John H. Grabber,

    1. USDA-Agricultural Research Service, US Dairy Forage Research Center, Madison, WI, USA
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  • John Ralph,

    1. Departments of Biochemistry and Biological Systems Engineering, the Wisconsin Bioenergy Initiative, and the DOE Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, WI, USA
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  • Wout Boerjan

    Corresponding author
    1. Department of Plant Biotechnology and Bioinformatics, Ghent University, Gent, Belgium
    • Department of Plant Systems Biology, VIB, Gent, Belgium
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Author for correspondence:

Wout Boerjan

Tel: +32 (0)9 331 38 81

Email: wout.boerjan@psb.vib-ugent.be

Abstract

Contents

 Summary978
I.Introduction979
II.Phenolic metabolism979
III.Lignin biosynthesis and structure983
IV.Alternative lignin monomers for biofuel applications985
V.Candidate alternative monolignols in biomimetic systems991
VI.From phenolic profiling to lignomics992
VII.Phenolic pathway engineering towards alternative monolignols993
 Acknowledgements994
 References994

Summary

Lignin, a phenolic polymer in the secondary wall, is the major cause of lignocellulosic biomass recalcitrance to efficient industrial processing. From an applications perspective, it is desirable that second-generation bioenergy crops have lignin that is readily degraded by chemical pretreatments but still fulfill its biological role in plants. Because plants can tolerate large variations in lignin composition, often without apparent adverse effects, substitution of some fraction of the traditional monolignols by alternative monomers through genetic engineering is a promising strategy to tailor lignin in bioenergy crops. However, successful engineering of lignin incorporating alternative monomers requires knowledge about phenolic metabolism in plants and about the coupling properties of these alternative monomers. Here, we review the current knowledge about lignin biosynthesis and the pathways towards the main phenolic classes. In addition, the minimal requirements are defined for molecules that, upon incorporation into the lignin polymer, make the latter more susceptible to biomass pretreatment. Numerous metabolites made by plants meet these requirements, and several have already been tested as monolignol substitutes in biomimetic systems. Finally, the status of detection and identification of compounds by phenolic profiling is discussed, as phenolic profiling serves in pathway elucidation and for the detection of incorporation of alternative lignin monomers.

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