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.
Bertauche
N
N
Institut des Sciences Végétales, Centre National de la Recherche Scientifique (Unité Propre de Recherche 40), Gif-sur-Yvette, France.
Leung
J
J
Giraudat
J
J
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