Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Novel promoter sequences enabling fruit-specific expression of transgenes in tomato

Two promoters were analyzed for expression for expression in tomato fruits. The promoters of the soluble starch synthase 3 gene (SSS3) from potato and of the glucan phosphorylase gene (Pho1) from broad bean, respectively, were analysed during tomato fruit development.

Fruit development was divided into 10 stages depending on size and colour of the fruits. First samples were taken one week after flowering (stage I). Stage VI corresponds to the breaker stage (green colour changes to yellow). Stage X represents a fully ripe fruit. From each stage slices were stained in X-Gluc and later compared with results from quantitative MUG analyses. For each time point 15 samples were collected from different fruits for a quantitative MUG assay.

SSS3 and Pho1 promoters show a comparable expression pattern. During fruit development GUS activity increases and achieves highest values at stage VI (about 25 nmol MU/min mg protein). In stages VII–X GUS activity decrease to about 5 nmol MU/min mg protein. X-Gluc staining suggested that blue staining occurred throughout the whole fruit including the vasculature.

These results reveal that both promoters can be used for metabolic engineering tomato fruits. The E8 promoter is frequently found in the literature and has been shown to be induced at the onset of ripening. This contrasts with SSS3 and Pho1 promoters as these drive highest GUS expression in green fruits which then decreases during ripening. Thus the promoters can be complementary used to the E8 promoter.

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