The abi1-1 mutation blocks ABA signaling downstream of cADPR action

Authors

  • Yan Wu,

    1. Laboratory of Plant Molecular Biology, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA,
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    • Present address: Torrey Mesa Research Institute, Syngenta, 3115 Merryfield Row, San Diego, CA 92121, USA.

  • Juan Pablo Sanchez,

    1. Laboratory of Plant Molecular Biology, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA,
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  • Luis Lopez-Molina,

    1. Laboratory of Plant Molecular Biology, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA,
    2. Biology Department, City College, City University of New York, 138th Street and Convent Avenue New York, NY 10031, USA
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  • Axel Himmelbach,

    1. TU-München, Lehrstuhl für Botanik, Am Hochanger 4, D-85350, Freising, Germany, and
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  • Erwin Grill,

    1. TU-München, Lehrstuhl für Botanik, Am Hochanger 4, D-85350, Freising, Germany, and
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  • Nam-Hai Chua

    Corresponding author
    1. Laboratory of Plant Molecular Biology, The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA,
      For correspondence (fax +1 212 3278327; e-mail chua@rockvax.rockfeller.edu).
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For correspondence (fax +1 212 3278327; e-mail chua@rockvax.rockfeller.edu).

Summary

Arabidopsis thaliana abscisic acid insensitive 1-1 (abi1-1) is a dominant mutant that is insensitive to the inhibition of germination and growth by the plant hormone, abscisic acid (ABA). The mutation severely decreases the catalytic activity of the ABI1 type 2C protein phosphatase (PP2C). However, the site of action of the abi1-1/ABI1 in the ABA signal transduction pathway has not yet been determined. Using single cell assays, we showed that microinjecting mutant abi1-1 protein inhibited the activation of RD29A-GUS and KIN2-GUS in response to ABA, cyclic ADP-ribose (cADPR), and Ca2+. The inhibitory effect of the mutant protein, however, was reversed by co-microinjection of an excess amount of the ABI1 protein. In transgenic Arabidopsis plants, overexpression of abi1-1 rendered the plants insensitive to ABA during germination, whereas overexpression of ABI1 did not have any apparent effect. Moreover, transgenic plants overexpressing abi1-1 were blocked in the induction of ABA-responsive genes; however, overexpression of ABI1 did not affect gene expression. Taken together, our results demonstrate that abi1-1 is likely to be a dominant negative mutation and ABI1 likely acts downstream of cADPR in the ABA-signaling pathway. Our results on ABI1 overexpression in Arabidopsis are not compatible with a negative regulatory role of this phosphatase in ABA responses.

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