Cell Biology and Metabolism
Novel Plant Ca2+-binding Protein Expressed in Response to Abscisic Acid and Osmotic Stress (∗)

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A cDNA corresponding to an mRNA which accumulates in germinating rice seeds in response to the phytohormone abscisic acid was isolated by differential hybridization. Northern blotting indicated that the mRNA also accumulates in vegetative tissues in response to treatment with abscisic acid and to osmotic stress. Sequencing identified a major open reading frame encoding a novel protein of 27.4 kDa. The identity of the open reading frame was confirmed by comparing the translation products of cellular, hybrid-selected, and in vitro transcribed RNAs and by immunoprecipitation. Western blotting of cellular extracts indicated that the protein is associated with microsomal or membrane fractions. Data base searches indicated that it contains a conserved Ca2+-binding, EF-hand motif and that related proteins are similarly expressed in Arabidopsis thaliana. A fusion protein purified from Escherichia coli containing the putative EF-hand region was shown to bind Ca2+ in blot binding assays. These data identify a novel gene family encoding proteins involved in the response of plants to abscisic acid and osmotic stress.

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This work was supported by a fellowship from the Humbolt Foundation (to F. M.-U.), and by grants from the Danish Agricultural and Veterinary Research Council(13-4946-1) (to K. S.) and from the Danish Natural Science Research Council(11-1119-1) (to J. M.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank(™)/EMBL Data Bank with accession number(s) X89891.