Arabidopsis genes IRREGULAR XYLEM (IRX15) and IRX15L encode DUF579-containing proteins that are essential for normal xylan deposition in the secondary cell wall

Authors

  • David Brown,

    1. University of Manchester, Faculty of Life Science, Oxford Road, Manchester M13 9PT, UK
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    • These authors contributed equally to this work.

    • Present address: Biodomain, Shell Projects and Technologies, Shell Research Ltd, Shell Technology Centre, CH1 3SH, UK.

  • Raymond Wightman,

    1. University of Manchester, Faculty of Life Science, Oxford Road, Manchester M13 9PT, UK
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    • These authors contributed equally to this work.

  • Zhinong Zhang,

    1. Department of Biochemistry, University of Cambridge, Building O, Downing Site, Cambridge CB2 1QW, UK
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  • Leonardo D. Gomez,

    1. University of York, CNAP, Biology Department, Wentworth Way, York YO10 5DD, UK
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  • Ivan Atanassov,

    1. University of Manchester, Faculty of Life Science, Oxford Road, Manchester M13 9PT, UK
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    • Present address: AgroBioInstitute, 8 Dragan Tzankov, Sofia 1618, Bulgaria.

  • John-Paul Bukowski,

    1. University of Manchester, Faculty of Life Science, Oxford Road, Manchester M13 9PT, UK
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    • Present address: University of Copenhagen, Københavns Biocenter, BRIC, Ole Maaløes Vej 5, 2200 København N, Denmark.

  • Theodora Tryfona,

    1. Department of Biochemistry, University of Cambridge, Building O, Downing Site, Cambridge CB2 1QW, UK
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  • Simon J. McQueen-Mason,

    1. University of York, CNAP, Biology Department, Wentworth Way, York YO10 5DD, UK
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  • Paul Dupree,

    1. Department of Biochemistry, University of Cambridge, Building O, Downing Site, Cambridge CB2 1QW, UK
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  • Simon Turner

    Corresponding author
    1. University of Manchester, Faculty of Life Science, Oxford Road, Manchester M13 9PT, UK
      (fax +44 161 275 3938; e-mail Simon.turner@manchester.ac.uk).
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(fax +44 161 275 3938; e-mail Simon.turner@manchester.ac.uk).

Summary

There are 10 genes in the Arabidopsis genome that contain a domain described in the Pfam database as domain of unknown function 579 (DUF579). Although DUF579 is widely distributed in eukaryotic species, there is no direct experimental evidence to assign a function to it. Five of the 10 Arabidopsis DUF579 family members are co-expressed with marker genes for secondary cell wall formation. Plants in which two closely related members of the DUF579 family have been disrupted by T-DNA insertions contain less xylose in the secondary cell wall as a result of decreased xylan content, and exhibit mildly distorted xylem vessels. Consequently we have named these genes IRREGULAR XYLEM 15 (IRX15) and IRX15L. These mutant plants exhibit many features of previously described xylan synthesis mutants, such as the replacement of glucuronic acid side chains with methylglucuronic acid side chains. By contrast, immunostaining of xylan and transmission electron microscopy (TEM) reveals that the walls of these irx15 irx15l double mutants are disorganized, compared with the wild type or other previously described xylan mutants, and exhibit dramatic increases in the quantity of sugar released in cell wall digestibility assays. Furthermore, localization studies using fluorescent fusion proteins label both the Golgi and also an unknown intracellular compartment. These data are consistent with irx15 and irx15l defining a new class of genes involved in xylan biosynthesis. How these genes function during xylan biosynthesis and deposition is discussed.

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