• Open Access

Targeting expression of a fungal ferulic acid esterase to the apoplast, endoplasmic reticulum or golgi can disrupt feruloylation of the growing cell wall and increase the biodegradability of tall fescue (Festuca arundinacea)

Authors

  • Marcia M. de O. Buanafina,

    Corresponding author
    1. Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth University, Wales, UK
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  • Tim Langdon,

    1. Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth University, Wales, UK
    2. Institute of Biological and Rural Sciences, Plas Gogerddan, Aberystwyth University, Wales, UK
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  • Barbara Hauck,

    1. Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth University, Wales, UK
    2. Institute of Biological and Rural Sciences, Plas Gogerddan, Aberystwyth University, Wales, UK
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  • Sue Dalton,

    1. Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth University, Wales, UK
    2. Institute of Biological and Rural Sciences, Plas Gogerddan, Aberystwyth University, Wales, UK
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  • Emma Timms-Taravella,

    1. Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth University, Wales, UK
    2. Institute of Biological and Rural Sciences, Plas Gogerddan, Aberystwyth University, Wales, UK
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  • Phillip Morris

    1. Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth University, Wales, UK
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  • Present address: Marcia M. de O. Buanafina, Department of Biology, 208 Mueller Laboratory, Pennsylvania University, University Park, PA 16802, USA.

* Correspondence (fax 814-867-9131; e-mail mmb26@psu.edu)

Summary

In the cell walls of grasses, ferulic acid is esterified to arabinoxylans and undergoes oxidative reactions to form ferulates dimers, trimers and oligomers. Feruloylation of arabinoxylan is considered important not only because it leads to cross-linked xylans but also because ferulates may act as a nucleating site for the formation of lignin and hence link arabinoxylans to lignin by forming a lignin–ferulate–arabinoxylan complex. Such cross-linking is among the main factors inhibiting the release of fermentable carbohydrates from grasses either for ruminant nutrition or for biofuel production. We have found that significant reductions in the levels of monomeric and dimeric phenolics can be achieved in the growing cell walls during plant development in leaves of Festuca arundinacea by constitutive intracellular targeted expression of Aspergillus niger ferulic acid esterase (FAEA). We propose that this occurred by directly disrupting ester bonds linking phenolics to cell wall polysaccharides by apoplast targeting or by preventing excessive feruloylation of cell wall carbohydrates prior to their incorporation into the cell wall, by targeting to the Golgi membrane system. Plants with lower cell wall ferulate levels, which showed increased digestibility and increased rates of cellulase-mediated release of fermentable sugars, were identified. Targeting FAE to the Golgi was found to be more effective than targeting to the ER, which supports the current theories of the Golgi as the site of feruloylation of arabinoxylans. It is concluded that targeting FAEA expression to the Golgi or apoplast is likely to be an effective strategy for improving wall digestibility in grass species used for fodder or cellulosic ethanol production.

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