ISOLATION AND CHARACTERIZATION OF A WATER-STRESS-INDUCIBLE CDNA CLONEFROM SOLANUM CHACOENSE

A rich source of valuable genes are wild species. Solanum chacoense Bi tter with its extreme resistance to viruses, insects and drought, is a good example. In the present study, a stress gene, designated DS2, ha s been isolated from S. chacoense. We have shown that the expression o f the gene is organ-specific being detected in leaf, stem and stolen, but not in root, tuber or flower. Treatment of detached leaves with ab scisic acid (ABA), salicylic acid or methyl jasmonate resulted in only very moderate accumulation of DS2 mRNA. Thus, DS2 represents a very r are type of the water-stress-inducible genes whose signalling pathway is not primarily related to ABA. Based on DNA sequence analysis, DS2 e ncodes a putative protein starting with 20 amino acids homologous to t he ABA- and water-stress-inducible, ripening-related (ASR) proteins of tomato continued by an insert of 155 amino acids structurally similar to certain LEAs (late embryogenesis-abundant proteins) and ending in 88 amino acids homologous again to the ASR sequences and to an unpubli shed partial cDNA fragment isolated from the root of rice. The N-termi nal region of the DS2 protein is hydrophilic with ten 13-mer amino aci d motifs and random coil structure. In contrast, the C-terminus predic ts an cc-helix and possesses a bipartite nuclear targeting sequence mo tif. These data suggest that the function of the DS2 may be the protec tion of the nuclear DNA from desiccation.