APPLE ACC-OXIDASE AND POLYGALACTURONASE - RIPENING-SPECIFIC GENE-EXPRESSION AND PROMOTER ANALYSIS IN TRANSGENIC TOMATO

Levels of 1-aminocyclopropane-1-carboxylate (ACC) oxidase and polygala cturonase (PG) mRNAs were characterized during ripening of Royal Gala, Braeburn and Granny Smith apples. Both ACC-oxidase and PG mRNAs were up-regulated in ripening fruit of all three cultivars. Expression in R oyal Gala was detected earlier than in Braeburn and Granny Smith, rela tive to internal ethylene concentration. Genomic clones corresponding to the ACC-oxidase and PG mRNAs expressed in ripe apple fruit were iso lated and ca. 2 kb of each promoter was sequenced. The start point of transcription in each gene was mapped by primer extension, and sequenc es homologous to elements in other ethylene-responsive or PG promoters were identified. The fruit specificity of the apple ACC-oxidase and P G promoters was investigated in transgenic tomato plants using a neste d set of promoter fragments fused to the B-glucuronidase (gusA) report er gene. For the ACC-oxidase gene, 450 bp of 5' promoter sequence was sufficient to drive GUS expression, although this expression was not s pecific to ripening fruit. Larger fragments of 1966 and 1159 bp showed both fruit and ripening specificity. For the PG gene, promoter fragme nts of 1460 and 532 bp conferred ripening-specific expression in trans genic tomato fruit. However GUS expression was down-regulated by 2356 bp of promoter, suggesting the presence of a negative regulatory eleme nt between positions -1460 and -2356.