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A link between sterol biosynthesis, the cell wall, and cellulose in Arabidopsis

Authors

  • Kathrin Schrick,

    Corresponding author
    1. Department of Developmental Genetics, ZMBP (Center for Plant Molecular Biology), University of Tübingen, 72076 Tübingen, Germany,
      For correspondence (fax +1 909 607 8086; e-mail
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      Current address: Keck Graduate Institute of Applied Life Sciences, Claremont, CA 91711, USA.
  • Shozo Fujioka,

    1. RIKEN (The Institute of Physical and Chemical Research), Saitama 351-0198, Japan,
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  • Suguru Takatsuto,

    1. Department of Chemistry, Joetsu University of Education, Nigata 943-8512, Japan,
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  • York-Dieter Stierhof,

    1. Department of Developmental Genetics, ZMBP (Center for Plant Molecular Biology), University of Tübingen, 72076 Tübingen, Germany,
    2. Microscopy Facility, ZMBP (Center for Plant Molecular Biology), University of Tübingen, 72076 Tübingen, Germany, and
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  • Harald Stransky,

    1. Department of Plant Physiology, ZMBP (Center for Plant Molecular Biology), University of Tübingen, 72076 Tübingen, Germany
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  • Shigeo Yoshida,

    1. RIKEN (The Institute of Physical and Chemical Research), Saitama 351-0198, Japan,
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  • Gerd Jürgens

    1. Department of Developmental Genetics, ZMBP (Center for Plant Molecular Biology), University of Tübingen, 72076 Tübingen, Germany,
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For correspondence (fax +1 909 607 8086; e-mail Kathrin_Schrick@kgi.edu).
Current address: Keck Graduate Institute of Applied Life Sciences, Claremont, CA 91711, USA.

Summary

A crucial role for sterols in plant growth and development is underscored by the identification of three Arabidopsis sterol biosynthesis mutants that exhibit embryonic defects: fackel (fk), hydra1 (hyd1), and sterol methyltransferase 1/cephalopod (smt1/cph). We have taken a dual approach of sterol profiling and ultrastructural analysis to investigate the primary defects underlying the mutant phenotypes. Comprehensive gas chromatography (GC)–MS analysis of hyd1 in comparison to fk reveals an abnormal accumulation of unique sterol intermediates in each case. Sterol profiling of the fk hyd1 double mutant provides genetic evidence that FK C-14 reductase acts upstream of HYD1 C-8,7 isomerase. Despite distinct differences in sterol profiles, fk and hyd1 as well as smt1/cph share ultrastructural features such as incomplete cell walls and aberrant cell wall thickenings in embryonic and post-embryonic tissues. The common defects are coupled with ectopic callose and lignin deposits. We show that all three mutants exhibit a deficiency in cellulose, but are not reduced in pectin and sugars of the cell wall and cytosol. The sterol biosynthesis inhibitors 15-azasterol and fenpropimorph also cause cell wall gaps in dividing root cells and a reduction in bulk cellulose, corroborating that the cell wall abnormalities are due to altered sterol composition. Our results demonstrate that sterols are crucial for cellulose synthesis in the building of the plant cell wall.

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