AN ABSCISIC-ACID-RESPONSIVE AND SALT-STRESS-RESPONSIVE RICE CDNA FROMA NOVEL PLANT GENE FAMILY

A novel cDNA clone osr40c1, encoding a environment and belongs to a no vel plant protein family that most probably has structural functions. abscisic acid (ABA)-responsive 40-kDa protein previously associated wi th salt tolerance (Moons et al. '1995' Plant Physiol 107: 177-186), wa s isolated from roots of rice seedlings (Oryza sativa L.). Exogenously applied ABA and salt shock induced a marked increase of the asr40c1 t ranscript level in roots of seedlings whereas constant osr40c1 mRNA le vels were found in the shoot. The root-specific salinity-induced osr40 c1 mRNA accumulation was rapid and gradually declined upon prolonged s alt shock. Plant growth regulators, signalling the wounding and the pa thogen response, did not enhance osr40c1 expression, indicating a salt - and osmotic-stress-specific response. The encoded OSR40c1 protein wa s found to be hydrophilic, rich in histidine residues (6%) constitutin g putative metal-binding domains, and to consist of a duplicated domai n of 151 amino acids (75% identical), that can form amphiphilic a-heli cal structures. The gene osr40c1 belongs to a multigene family. Two os r40 genes were isolated, osr40g2 and osr40g3, tandemly arranged in an 8-kb region of the rice genome. Antisera raised against a conserved OS R40 peptide recognized different OSR40 proteins that accumulated in ro ots upon exposure to salt stress. The OSR40 protein family included 29 -kDa proteins and two 40-kDa proteins, the latter most probably corres ponding to OSR40c1 and OSR40g2 with duplicated domain structures. The osr40g3 transcript encoded a single copy of the OSR40 domain and exhib ited a shoot-specific expression. Results indicate that OSR40c1 plays a role in the adaptative response of roots to an hyper-osmotic environ ment and belongs to a novel plant protein family that most probably ha s structural functions.