An abscisic-acid- and salt-stress-responsive rice cDNA from a novel plant gene family

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Abstract
A novel cDNA clone osr40c1, encoding a abscisic acid (ABA)-responsive 40-kDa protein previously associated with salt tolerance (Moons et al. `1995' Plant Physiol 107: 177–186), was isolated from roots of rice seedlings (Oryza sativa L.). Exogenously applied ABA and salt shock induced a marked increase of the osr40c1 transcript level in roots of seedlings whereas constant osr40c1 mRNA levels were found in the shoot. The root-specific salinity-induced osr40c1 mRNA accumulation was rapid and gradually declined upon prolonged salt shock. Plant growth regulators, signalling the wounding and the pathogen response, did not enhance osr40c1 expression, indicating a salt- and osmotic-stress-specific response. The encoded OSR40c1 protein was found to be hydrophilic, rich in histidine residues (6%) constituting putative metal-binding domains, and to consist of a duplicated domain of 151 amino acids (75% identical), that can form amphiphilic α-helical structures. The gene osr40c1 belongs to a multigene family. Two osr40 genes were isolated, osr40g2 and osr40g3, tandemly arranged in an 8-kb region of the rice genome. Antisera raised against a conserved OSR40 peptide recognized different OSR40 proteins that accumulated in roots upon exposure to salt stress. The OSR40 protein family included 29-kDa proteins and two 40-kDa proteins, the latter most probably corresponding to OSR40c1 and OSR40g2 with duplicated domain structures. The osr40g3 transcript encoded a single copy of the OSR40 domain and exhibited a shoot-specific expression. Results indicate that OSR40c1 plays a role in the adaptative response of roots to an hyper-osmotic environment and belongs to a novel plant protein family that most probably has structural functions.

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