First published online December 16, 2005; 10.1104/pp.105.070318
Plant Physiology 140:127-139 (2006)
© 2006 American Society of Plant Biologists
DEVELOPMENT AND HORMONE ACTION
The Protein Phosphatase AtPP2CA Negatively Regulates Abscisic Acid Signal Transduction in Arabidopsis, and Effects of abh1 on AtPP2CA mRNA1,[W]
Josef M. Kuhn2,
Aurélien Boisson-Dernier2,
Marie B. Dizon,
Mohammad H. Maktabi and
Julian I. Schroeder*
Division of Biological Sciences, Cell and Developmental Biology Section, and Center for Molecular Genetics, University of California, La Jolla, California 92093–0116
To identify new loci in abscisic acid (ABA) signaling, we screened a library of 35S::cDNA Arabidopsis (Arabidopsis thaliana)-expressing lines for ABA-insensitive mutants in seed germination assays. One of the identified mutants germinated on 2.5 µM ABA, a concentration that completely inhibits wild-type seed germination. Backcrosses and F2 analyses indicated that the mutant exhibits a dominant phenotype and that the ABA insensitivity was linked to a single T-DNA insertion containing a 35S::cDNA fusion. The inserted cDNA corresponds to a full-length cDNA of the AtPP2CA gene, encoding a protein phosphatase type 2C (PP2C). Northern-blot analyses demonstrated that the AtPP2CA transcript is indeed overexpressed in the mutant (named PP2CAox). Two independent homozygous T-DNA insertion lines, pp2ca-1 and pp2ca-2, were recovered from the Arabidopsis Biological Resource Center and shown to lack full-length AtPP2CA expression. A detailed characterization of PP2CAox and the T-DNA disruption mutants demonstrated that, whereas ectopic expression of a 35S::AtPP2CA fusion caused ABA insensitivity in seed germination and ABA-induced stomatal closure responses, disruption mutants displayed the opposite phenotype, namely, strong ABA hypersensitivity. Thus our data demonstrate that the PP2CA protein phosphatase is a strong negative regulator of ABA signal transduction. Furthermore, it has been previously shown that the AtPP2CA transcript is down-regulated in the ABA-hypersensitive nuclear mRNA cap-binding protein mutant abh1. We show here that down-regulation of AtPP2CA in abh1 is not due to impaired RNA splicing of AtPP2CA pre-mRNA. Moreover, expression of a 35S::AtPP2CA cDNA fusion in abh1 partially suppresses abh1 hypersensitivity, and the data further suggest that additional mechanisms contribute to ABA hypersensitivity of abh1.
1 This work was supported by National Institutes of Health (R01GM060396) and National Science Foundation (MCB0417118) grants (to J.I.S.), and by a European Molecular Biology Organization fellowship (to J.M.K.).
2 These authors contributed equally to the paper.
The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Julian I. Schroeder (julian{at}biomail.ucsd.edu).
[W] The online version of this article contains Web-only data.
Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.105.070318.
* Corresponding author; email julian{at}biomail.ucsd.edu; fax 858–534–7108.
Received August 24, 2005;
returned for revision October 13, 2005;
accepted October 23, 2005.
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