Isolation of 3 salt-induced low-abundance cDNAs from light-grown callus of Mesembryanthemum crystallinum by suppression subtractive hybridization

A technique combining suppression polymerase chain reaction with suppression subtractive hybridization was used to clone low-abundance transcripts that showed enhanced expression during salt stress in light-grown callus of Mesembryanthemum crystallinum L., the ice plant. Three salt-induced cDNAs were selected by the prolonged film exposure time when analyzed by northern blotting. All of them showed different response kinetics to 200 mM NaCl, but were all expressed at increased levels in the presence of high salts at the cellular level, Analysis of nucleic acid and deduced amino acid sequences of these cDNAs revealed that they encoded a protein involved in K+ uptake (suppressor of K+ transport growth defect [SKD1]), an enzyme in the ubiquitin-mediated proteolytic cycle (ubiquitin-conjugating enzyme [UBC]; EC 6.3.2.19), and a low-molecular mass basic stress-induced protein, The SKD1-like gene was constitutively expressed in the root and up-regulated in the leaf upon salt stress, The levels of other two transcripts remained relatively unchanged in the leaf and increased in the root by high salt. The possible roles of these gene products in the mechanism of salt tolerance in this halophyte are discussed.