ABA-Hypersensitive Germination1 encodes a protein phosphatase 2C, an essential component of abscisic acid signaling in Arabidopsis seed

Authors

  • Noriyuki Nishimura,

    1. Laboratory of Environmental Molecular Biology, RIKEN Wako Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan,
    2. Integrated Graduate School of Art and Science, Yokohama City University, 1-7-29 Suehiro, Tsurumi, Yokohama 230-0045, Japan,
    3. Gene Discovery Research Group, RIKEN Plant Science Center, 1-7-22 Tsurumi, Yokohama 230-0045, Japan, and
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    • Present address: Division of Biological Sciences, Cell and Developmental Biology Section, Center for Molecular Genetics, University of California, San Diego, 9500 Gilman Drive La Jolla, CA 92093-0116, USA.

  • Tomo Yoshida,

    1. Integrated Graduate School of Art and Science, Yokohama City University, 1-7-29 Suehiro, Tsurumi, Yokohama 230-0045, Japan,
    2. Gene Discovery Research Group, RIKEN Plant Science Center, 1-7-22 Tsurumi, Yokohama 230-0045, Japan, and
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  • Nobutaka Kitahata,

    1. Laboratory of Cellular Biochemistry, RIKEN Wako Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
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  • Tadao Asami,

    1. Laboratory of Cellular Biochemistry, RIKEN Wako Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
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  • Kazuo Shinozaki,

    1. Gene Discovery Research Group, RIKEN Plant Science Center, 1-7-22 Tsurumi, Yokohama 230-0045, Japan, and
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  • Takashi Hirayama

    Corresponding author
    1. Laboratory of Environmental Molecular Biology, RIKEN Wako Institute, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan,
    2. Integrated Graduate School of Art and Science, Yokohama City University, 1-7-29 Suehiro, Tsurumi, Yokohama 230-0045, Japan,
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(fax +81 45 508 7363; e-mail hirayama@gsc.riken.jp).

Summary

The phytohormone abscisic acid (ABA) regulates physiologically important stress and developmental responses in plants. To reveal the mechanism of response to ABA, we isolated several novel ABA-hypersensitive Arabidopsis thaliana mutants, named ahg (ABA-hypersensitive germination). ahg1-1 mutants showed hypersensitivity to ABA, NaCl, KCl, mannitol, glucose and sucrose during germination and post-germination growth, but did not display any significant phenotypes in adult plants. ahg1-1 seeds accumulated slightly more ABA before stratification and showed increased seed dormancy. Map-based cloning of AHG1 revealed that ahg1-1 has a nonsense mutation in a gene encoding a novel protein phosphatase 2C (PP2C). We previously showed that the ahg3-1 mutant has a point mutation in the AtPP2CA gene, which encodes another PP2C that has a major role in the ABA response in seeds (Yoshida et al., 2006b). The levels of AHG1 mRNA were higher in dry seeds and increased during late seed maturation – an expression pattern similar to that of ABI5. Transcriptome analysis revealed that, in ABA-treated germinating seeds, many seed-specific genes and ABA-inducible genes were highly expressed in ahg1-1 and ahg3-1 mutants compared with the wild-type. Detailed analysis suggested differences between the functions of AHG1 and AHG3. Dozens of genes were expressed more strongly in the ahg1-1 mutant than in ahg3-1. Promoter–GUS analyses demonstrated both overlapping and distinct expression patterns in seed. In addition, the ahg1-1 ahg3-1 double mutant was more hypersensitive than either monogenic mutant. These results suggest that AHG1 has specific functions in seed development and germination, shared partly with AHG3.

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