Tomato modified for delayed ripening

Delayed ripening tomatoes, created through introduction of a gene sequence encoding the enzyme 1-amino-cyclopropane-1-carboxylic acid synthase (ACC) that metabolises the precursor of the fruit ripening hormone ethylene. The neomycin phosphotransferase II (npt II) confers resistance to the antibiotic kanamycin.

Cultivar: 91103-114

pWTT2144/AccS

A 1088bp truncated segment of the Acc2 gene (designated AccS) was inserted into the host genome. The genetic element does not result in a functional protein and the expression of the AccS gene results in the sense suppression of the endogenous gene. The nos promoter is present as a duplicate tandem repeat of the 5' untranslated region of the nopaline synthase gene.

Southern blot analysis indicated that three copies of the T-DNA inserted at a single locus within the host genome in an inverted fashion. There was no incorporation of translatable plasmid DNA sequences outside of the T-DNA region.

The 1345-4 line of tomato (Lycopersicon esculentum) was developed through a specific genetic modification of cultivar 91103-114 to exhibit a decreased activity of the enzyme 1-aminocyclopropane-1- carboxylic acid (ACC) synthase. This endogenous enzyme is responsible for the conversion of s-adenosylmethionine to ACC, which is the immediate precursor of ethylene, a phytohormone known to play a key role in fruit ripening. The in situ accumulation of ethylene in the transgenic tomatoes is only about 1/50 the level found in the unmodified parental line and the fruit does not fully ripen unless an external source of ethylene is applied.

While not completely understood, the mechanism of "downregulation" of the endogenous ACC synthase gene is likely linked to the coordinate suppression of transcription of both the endogenous gene and the introduced truncated ACC synthase gene.