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Ancestral expression patterns and evolutionary diversification of YABBY genes in angiosperms

Authors

  • Toshihiro Yamada,

    Corresponding author
    1. Department of Life Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa 920-1192, Japan
    2. Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
      (fax 81 76 264 6207; e-mail ptilo@mb.infoweb.ne.jp).
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    • These authors contributed equally to this work.

  • Shin’ya Yokota,

    1. Department of Life Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa 920-1192, Japan
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    • These authors contributed equally to this work.

  • Yumiko Hirayama,

    1. Department of Botany, National Museum of Nature and Science, Tsukuba 305-0005, Japan
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  • Ryoko Imaichi,

    1. Department of Chemical and Biological Sciences, Japan Women’s University, Tokyo 112-8681, Japan
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  • Masahiro Kato,

    1. Department of Botany, National Museum of Nature and Science, Tsukuba 305-0005, Japan
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  • Charles S. Gasser

    1. Department of Molecular and Cellular Biology, University of California, Davis, CA 95616, USA
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(fax 81 76 264 6207; e-mail ptilo@mb.infoweb.ne.jp).

Summary

Lateral organ growth in seed plants is controlled in part by members of the YABBY (YAB) and class III homeodomain/leucine zipper (HD-ZIPIII) families of transcription factors. HD-ZIPIII genes appear to play a conserved role in such organs, but YAB genes have diversified, with some members of the family having specialized functions in leaves, carpels or ovule integuments. The ancestral expression patterns and timing of divergence of the various classes of YAB genes remain to be established. We isolated and evaluated the expression of one HD-ZIPIII and five YAB genes representing the five major YAB gene classes from Cabomba caroliniana, a member of the earliest-diverging angiosperms. Consistent with observations in eudicots, the FILAMENTOUS FLOWER (FIL) and YABBY5 (YAB5) genes of C. caroliniana were expressed in the abaxial regions of the leaf where new laminar segments arise, and the patterns of expression were mutually exclusive to those of HD-ZIPIII, indicating that these expression patterns are ancestral. Expression of CRABS CLAW (CRC) in the abaxial carpel wall, and of INNER NO OUTER (INO) in the abaxial outer integument of ovules was also conserved between eudicots and C. caroliniana, indicating that these patterns are primitive. However, the CRC gene was also expressed in other floral organs in C. caroliniana, and expression in stamens was also observed in another early-diverging species, Amborella trichopoda, indicating that carpel-specific expression was acquired after divergence of the Nymphaeales. The expression data and phylogeny for YAB genes suggest that the ancestral YAB gene was expressed in proliferating tissues of lateral organs.

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