The DUF579 domain containing proteins IRX15 and IRX15-L affect xylan synthesis in Arabidopsis

Authors

  • Jacob K. Jensen,

    1. Department of Plant Biology, Michigan State University, East Lansing, MI 48824, USA
    2. DOE Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, WI 53706, USA
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  • Hoon Kim,

    1. DOE Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, WI 53706, USA
    2. Department of Biochemistry, University of Wisconsin, Madison, WI 53706, USA
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  • Jean-Christophe Cocuron,

    1. Department of Plant Biology, Michigan State University, East Lansing, MI 48824, USA
    2. DOE Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, WI 53706, USA
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  • Robert Orler,

    1. Department of Plant Biology, Michigan State University, East Lansing, MI 48824, USA
    2. DOE Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, WI 53706, USA
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  • John Ralph,

    1. DOE Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, WI 53706, USA
    2. Department of Biochemistry, University of Wisconsin, Madison, WI 53706, USA
    3. Department of Biological Systems Engineering, University of Wisconsin, Madison, WI 53706, USA
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  • Curtis G. Wilkerson

    Corresponding author
    1. Department of Plant Biology, Michigan State University, East Lansing, MI 48824, USA
    2. DOE Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, WI 53706, USA
    3. Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA
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(fax +1 517 353 1926; e-mail wilker13@msu.edu).

Summary

Xylan is the principal hemicellulose in the secondary cell walls of eudicots and in the primary and secondary cell walls of grasses and cereals. The biosynthesis of this important cell wall component has yet to be fully determined although a number of proteins have been shown to be required for xylan synthesis. To discover new genes involved in xylan biosynthesis we explored the psyllium (Plantago ovata Forsk) seed mucilaginous layer through EST profiling. This tissue synthesizes large amounts of a complex heteroxylan over a short period of time. By comparing abundant transcripts in this tissue with abundant transcripts specifically present during secondary cell wall formation in Arabidopsis thaliana, where glucuronoxylan biosynthesis is pronounced, we identified two Arabidopsis genes likely involved in xylan biosynthesis. These genes encode proteins containing a Domain of Unknown Function (DUF) 579 and were designated IRREGULAR XYLEM (IRX) 15 and IRX15-LIKE (IRX15-L). We obtained Arabidopsis T-DNA knockout lines for the two genes and analyzed their lower stems for changes in neutral monosaccharide composition. No changes were observed in each of these mutants, although the irx15 irx15-L double mutant displayed a moderate reduction in stem xylose. Further characterization of the irx15 irx15-L mutant revealed irregular secondary cell wall margins in fiber cells and a lower xylan degree of polymerization. Through these studies we conclude that IRX15 and IRX15-L function in a redundant manner and are involved in xylan biosynthesis.

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