ARCHIVED - Delayed ripening tomato line 1345-4
Novel Food Information - Food Biotechnology
Health Canada has notified DNA Plant Technology Corporation that it has no objection to the food use of the transgenic tomato line 1345-4 which has been developed to exhibit reduced ethylene accumulation and thus delayed ripening. The Department conducted a comprehensive assessment of this novel variety according to its Guidelines for the Safety Assessment of Novel Foods (September 1994). These guidelines are based upon internationally accepted principles for establishing the safety of foods derived from genetically modified organisms.
The following provides a summary regarding the DNA Plant Technology Corporation notification to Health Canada and contains no confidential business information.
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 sadenosylmethionine 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.
2. Development of the Modified Plant
The inbred line 1345-4 tomato was created by Agrobacterium-mediated transformation in which the transfer-DNA (T-DNA) contained a 3'-truncated open reading frame corresponding to the sequence of the ACC synthase encoding gene from "Golden Nugget" tomato. The expression of this truncated ACC synthase gene was controlled by inclusion of sequences from the 35S promoter of cauliflower mosaic virus and the 3'-polyadenylation signal from the nopaline synthase (nos) gene from Agrobacterium tumefaciens. In addition, the T-DNA contained sequences encoding the enzyme neomycin phosphotransferase II (NPTII) from the Tn5 transposon of Escherichia coli, strain K12, under the control of the nos promoter from A. tumefaciens. The expression of NPTII activity was used as a selectable trait to screen transformed plants for the presence of the truncated ACC synthase gene. There was no incorporation of translatable plasmid DNA sequences outside of the T-DNA region.
3. Product Information
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. While transcription of the truncated ACC synthase gene was detected in transgenic tomato tissues, no expression of a protein product was detectable. The presence of NPTII protein has been judged to be insignificant with respect to any human health risk due to exposure.
Alpha-tomatine is the principal naturally occurring glycoalkaloid in tomato, and the level of a-tomatine decreases as the fruit matures so that the amounts in vine-ripened red tomatoes are negligible. The concentration of a-tomatine in immature tomatoes from transgenic line 1345-4 was 1.13-1.37 mg/100g fresh weight tissue, as compared with 3.37-3.59 mg/100g fresh weight tissue for the unmodified 91103- 114 parental line. For ripe red tomatoes, the amounts of a-tomatine from each of these lines were 0.11 and 0.07 mg/100g fresh weight tissue, respectively. Other than reduced ACC synthase activity, the disease, pest and other agronomic characteristics of the transgenic 1435-4 line was comparable to the unmodified parental line.
4. Dietary Exposure
The human consumption of the modified tomato line 1345-5 will be as both fresh and processed tomato products. Fresh market tomatoes are eaten whole and sliced or diced in a variety of foods. Processed tomatoes are consumed in the form of soups, preserves, ketchup, paste and prepared sauces. The genetic modification of these novel hybrids will not result in any change in the consumption pattern for fresh or processed tomato products. Line 1345-4 is expected to replace other tomato cultivars currently in use due to improved quality and handling characteristics. Hence, it will provide an alternate or additional choice to consumers and food manufacturers.
The analysis of nutrients from the novel 1345-4 line and the non-transgenic 91103-114 parental line did not reveal any significant differences in the levels of macro- and micronutrients. The consumption of this product will, therefore, have no significant impact on the nutritional quality of the Canadian food supply.
The reduced synthesis of native ACC synthase arising as a result of the coordinate suppression of ACC synthase gene transcription by introduction of a truncated ACC synthase gene sequence is not judged to have any potential for additional human toxicity or allergenicity.
Health Canada's review of the information presented in support of the food use of delayed ripening tomato line 1345-4 concluded that this transgenic tomato does not raise concerns related to human food safety. Health Canada is of the opinion that the products from tomato line 1345-4 are as safe and nutritious as those available from current commercial tomato cultivars.
Health Canada's opinion pertains only to the food use of tomato line 1345-4. Issues related to growing delayed ripening tomatoes in Canada and their use as animal feed are addressed separately through existing regulatory processes in the Canadian Food Inspection Agency.
This Novel Food Information document has been prepared to summarize the opinion regarding the subject product provided by the Food Directorate, Health Protection Branch, Health Canada. This opinion is based upon the comprehensive review of information submitted by the petitioner according to the Guidelines for the Safety Assessment of Novel Foods.
For further information, please contact:
Office of Food Biotechnology
Health Protection Branch
Ottawa, Ontario K1A 0L2
Telephone: (613) 941-5535
Facsimile: (613) 952-6400
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