Protein phosphatase activity of abscisic acid insensitive 1 (ABI1) protein from Arabidopsis thaliana.
Mutations at the ABI1 (abscisic acid insensitive 1) locus of the plant Arabidopsis thaliana cause a reduction in sensitivity to the plant hormone abscisic acid. The sequence of ABI1 predicts a protein composed of an N-terminal domain that contains motifs for an EF-hand Ca(2+)-binding site, and a C-terminal domain with similarities to protein serine/threonine phosphatases 2C. We report here two sets of experimental evidence that indicate that ABI1 has typical protein phosphatase 2C activity. First, expression of the ABI1 C-terminal domain partially complemented the temperature-sensitive growth defect of a Saccharomyces cerevisiae protein phosphatase 2C mutant. Second, recombinant proteins that contained the ABI1 C-terminal domain displayed in vitro phosphatase activity towards 32P-labelled casein, and this activity displayed Mg2+ or Mn2+ dependence and okadaic acid insensitivity typical of protein phosphatases 2C. Characterisation of recombinant proteins that contained various portions of ABI1 indicated that the putative EF-hand motif is unlikely to mediate Ca2+ regulation of the ABI1 phosphatase activity at physiological Ca2+ concentrations, and may represent in EF-hand analogue rather than an EF-hand homologue. The abil-l mutation appeared to cause significant reduction in the phosphatase activity of ABI1. These results are discussed in relation to the dominant phenotype of abil-l over the wild-type allele in plants, and to the possible role of ABI1 in abscisic acid signalling.
Institut des Sciences Végétales, Centre National de la Recherche Scientifique (Unité Propre de Recherche 40), Gif-sur-Yvette, France.
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Bertauche
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Leung
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Giraudat
D000040:Abscisic Acid / Q000494:pharmacology*; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology*; D029681:Arabidopsis Proteins; D001665:Binding Sites / Q000235:genetics; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D003001:Cloning, Molecular; D003598:Cytoskeletal Proteins; D004591:Electrophoresis, Polyacrylamide Gel; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004926:Escherichia coli / Q000235:genetics; D005656:Fungal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005816:Genetic Complementation Test; D018257:Helix-Loop-Helix Motifs; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed / Q000235:genetics; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D010749:Phosphoprotein Phosphatases / Q000737:chemistry / Q000378:metabolism*; D054648:Protein Phosphatase 2; D000071636:Protein Phosphatase 2C; D029701:Saccharomyces cerevisiae Proteins; D016415:Sequence Alignment
D029681:Arabidopsis Proteins; D003598:Cytoskeletal Proteins; D004791:Enzyme Inhibitors; D005656:Fungal Proteins; D018398:Homeodomain Proteins; D029701:Saccharomyces cerevisiae Proteins; D000040:Abscisic Acid; C087434:ABI1 protein, Arabidopsis; C087358:PTC1 protein, S cerevisiae; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2; D000071636:Protein Phosphatase 2C; D002118:Calcium