STRUCTURAL ORGANIZATION, EXPRESSION AND PROMOTER ACTIVITY OF A COLD-STRESS-INDUCIBLE GENE OF POTATO (SOLANUM-TUBEROSUM L)

Cold storage of potato tubers at 4 degrees C is associated with the ac cumulation of several cold-induced transcripts. By using a previously characterized cDNA (CI7) as probe, we isolated and sequenced the corre sponding ci7 gene. The putative promoter of ci7 contains sequence elem ents that have been shown to mediate expression of stress-responsive g enes of Arabidopsis thaliana. CI7 transcripts were differentially indu ced in response to cold, drought, high salt or exogenous ABA treatment in potato tubers and leaves. Whereas accumulation of CI7 transcript d uring cold storage occurred within days, induction of CI7 transcript i n response to drought, ABA and salt occurred rapidly within few hours. In tubers, accumulation of CI7 protein in response to abiotic stresse s and ABA was small when compared to transcript levels. In leaves, the CI7 protein was undetectable after all treatments tested. 3 kb of the 5'-flanking ci7 promoter region were fused to the GUS reporter gene a nd introduced into S, tuberosum plants. The analysis of tubers of inde pendent transgenic lines did not reveal significant induction of enzym atic GUS activity in induction of enzymatic GUS activity in response t o low temperature. When RNA gel blotting was used to analyze the level of induction of the GUS gene driven by the ci7 promoter, the heterolo gous GUS fusion was, however, strongly responsive to low temperature. Nuclear run-on transcription studies of the ci7 gene, in comparison wi th RNA gel blot analyses of the transgenic plants, indicated that most of the temperature-regulated expression of the ci7 gene in tubers may be accounted for by post-transcriptional control mechanisms.