Tomato (Solanum esculentum var. esculentum) became the first genetically modified organism to be sold as food. The sale of tomato (CGN-89564-2) was approved in 1992. These genetically modified tomatoes were made to be picked when red and could be transported without getting marks or being damaged. This should produce a tomato with more and better flavor than most other tomatoes that are picked before they are ripe. Ordinary tomatoes can withstand transport and processing until storage only when they are green. In order to be able to sell them on from storage to shops, ethylene gas is used to change the color to red. The taste may then be weak or absent. The first genetically modified tomatoes should therefore win on the market with both better durability and taste.
Four years later in 1996, these GMO tomatoes were introduced as tomato paste which could contain herbs and flavorings in the UK. About. 20% reduction in processing costs made the product compatible with other similar tomato paste products on the market until 1998. Public opinion may have changed after television information that the GMO process could cause more changes than those caused by a gene inserted to give the tomatoes a new traits. The public perception changed to something that products like these genetically modified tomatoes were not all they had been made out to be. This may have led to a large drop in supermarket demand for genetically modified tomato paste. The products went out of supermarkets in 1999.
Two genes have been inserted into CGN-89564-2, one of which is polygalacturonase in reverse orientation. Polygalacturonase (PG) is an enzyme that is produced naturally in tomato cells during the ripening stage of tomato development. PG is needed in tomato for the breakdown of pectin in cell walls and fruit softening. A gene for PG has been inserted that is reverse oriented. This is so that the mRNA strand from this inserted gene will later match and bind together with the tomato's natural "messenger RNA" (mRNA). This should prevent natural "messenger RNA" (mRNA) from being able to start production of the natural PG enzyme. This reduced functioning polygalacturonase enzyme activity, and breakdown of pectin in cell walls and fruit softening by up to 90%.
When the mRNA from the inserted gene (PG antisense mRNA) meets the mRNA from the natural gene (PG sense mRNA), the two strands will match and bind together. This effectively stops the natural PG sans mRNA from reaching its target for processing by the natural enzyme PG. PG antisense mRNA may also lead to some unknown side effects such as unknown peptides, metabolites and processes. The natural PG activity for fruit ripening is reduced and not completely stopped in the tomato (CGN-89564-2). Accumulation of the red tomato pigment and antioxidant lycopene is not completely prevented. Color development characteristic of red ripe fruit therefore occurs before it has to be picked and without the use of ethylene gas.
A gene from an antibiotic-resistant bacterium (Escherichia coli Tn5 transposon) has also been inserted. This inserted gene is to be able to produce a functioning neomycin phosphotransferase II enzyme. This enzyme enables transformed plants to metabolize neomycin and kanamycin antibiotics. This is mainly to be able to identify and select the genetically modified plants (those with antibiotic resistance as well as antisense oriented polygalacturonase) in cultures with added antibiotics. Both genes were inserted into tomato cells through a bacterium (Agrobacterium tumefaciens).
Links:
The case of the FLAVR SAVR tomato
Reference:
Krieger EK, Allen A., Gilbertson LA, Hiatt W., and Sanders RA. 2008. The Flavr Savr Tomato, an Early Example of RNAi Technology. HEART SCIENCE 43(3):962–964.
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