ARCHIVED - Colorado Potato Beetle And Potato Virus Y Resistant Potato Lines SEMT15-02, SEMT15-15, RBMT15-101

FD/OFB-099-127-A
October 1999


Health Canada has notified Monsanto Canada Inc. that it has no objection to the food use of the transgenic NewLeaf-Y™ potato cultivars Shepody (SEMT15-02, SEMT15-15) and Russet Burbank (RBMT15-101), which have been developed to be resistant to the Colorado potato beetle (CPB) and to resist infection by the plant potyvirus, potato virus Y (PVY). The Department conducted a comprehensive assessment of the Shepody and Russet Burbank NewLeaf-Y™ potato cultivars 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.

Background:

The following provides a summary regarding the Monsanto Canada Inc. notification to Health Canada and contains no confidential business information.

1. Introduction

The NewLeaf-Y™ potato (Solanum tuberosum) lines SEMT15-02, SEMT15-15 and RBMT15-101 were developed through a specific genetic modification of cultivars Shepody and Russet Burbank to be CPB (Leptinotarsa decemlineata Say.) resistant and to resist infection by PVY. The novel lines produce a version of the insecticidal protein, CryIIIA, derived from Bacillus thuringiensis, as well as the coat protein (CP) from the ordinary (O) strain of potato virus Y (PVY-O). Delta-endotoxins, such as the CryIIIA protein expressed in Shepody and Russet Burbank NewLeaf-Y™ potatoes, act by selectively binding to specific receptors localized on the brush border midgut epithelium of susceptible insect species. Following binding, cation-specific pores are formed that disrupt midgut ion flow and thereby cause paralysis and death. CryIIIA and related endotoxins are insecticidal only to lepidopteran or coleopteran insects and their specificity of action is directly attributable to the presence of specific receptors in the target insects. There are no receptors for delta-endotoxins of B. thuringiensis on the surface of mammalian intestinal cells, therefore, livestock animals and humans are not susceptible to these proteins. PVY is the type member of the potyvirus group and is an aphid-transmissible RNA virus that commonly infects potato causing serious disease and economic loss. The introduced viral sequences do not result in the formation of any infectious particles, nor does their expression result in any disease pathology. The genetically modified potato cultivars exhibit the trait of resistance to infection and subsequent disease caused by PVY through a process that is related to viral cross-protection.

2. Development of the Modified Plant

The transgenic Shepody and Russet Burbank potato lines were created through two separate Agrobacterium-mediated transformation events in which the transfer DNA (T-DNA) contained the genes encoding the CryIIIA protein from B. thuringiensis subsp. tenebrionis and the CP from PVY-O. In addition, the T-DNA contained sequences encoding the enzyme neomycin phosphotransferase II (NPTII). The expression of NPTII activity was used as a selectable trait for screening transformed plants for the presence of the cryIIIA and PVY-O CP genes. Additional DNA outside of the T-DNA border sequences was incorporated into the genome of Shepody lines SEMT15-02 and SEMT15-15. These lines also contain the aad gene that encodes the enzyme 3''(9)-O-aminoglycoside adenylyltransferase, which confers bacterial resistance to spectinomycin and streptomycin. The aad gene was not expressed in plant tissue, but was present on the Ti plasmid as a selectable trait for screening bacterial colonies for the presence of plasmid vector. The NewLeaf-Y™ Shepody and Russet Burbank cultivars produce three novel proteins: CryIIIA, PVY-O CP and NPTII.

3. Product Information

The constitutive expression of CryIIIA protein was demonstrated in each of the transgenic NewLeaf-Y™ Shepody and Russet Burbank cultivars. On average, the amounts of CryIIIA protein produced in the leaves and tubers of SEMT15-02, SEMT15-15 and RBMT15-101 were comparable to the concentrations previously reported for NewLeaf™ Atlantic and Russet Burbank cultivars. The expression of PVY-O CP in either leaves or tubers from any of these transgenic lines was undetectable at a threshold of 2 ng/mg fresh weight tissue. In contrast, the accumulation of CP in plants naturally infected with PVY-O is readily detectable using enzyme linked immunosorbent assay (ELISA) or Western immunoblot analysis. It is not uncommon for commercial potato plantings to be significantly infected by PVY-O and thus the human consumption of viral CP from these sources is likely to be much higher than the exposure due to consumption of NewLeaf-Y™ potatoes. The presence of NPTII protein has been judged to be insignificant with respect to any human health risk due to exposure. Solanine and chaconine are the principal glycoalkaloids commonly found in potato tubers. Analyses of total glycoalkaloid (TGA) levels in each of the transgenic lines demonstrated that in each case the level was below the administrative guideline of 20 mg/100g fresh weight that has previously been established for TGA in potato. Other than resistance to CPB and infection by PVY, the disease, pest and other agronomic characteristics of the NewLeaf-Y™ Shepody and Russet Burbank lines were comparable to their non-transgenic parental cultivars.

4. Dietary Exposure

Potatoes are considered to be a staple food for many Canadians, constituting up to 37% of the total average vegetable intake. The genetic modification present in the SEMT15-02, SEMT15-15 and RBMT15-101 transgenic lines will not result in any change in the consumption pattern for potatoes. Due to their protection from CPB damage and resistance to infection by PVY, the NewLeaf-Y™ Shepody and Russet Burbank cultivars are expected to replace some existing commercial potato cultivars in all potato product applications. Hence, they will provide an alternate or additional choice to consumers and food manufacturers.

5. Nutrition

The analysis of macro- and micronutrients from SEMT15-02, SEMT15-15 and RBMT15-101 transgenic lines revealed only small differences with the respective values from non-transgenic controls and in each case the level was within the normal range of variation reported for commercial potatoes. The consumption of products from NewLeaf-Y™ Shepody and Russet Burbank potatoes will have no significant impact on the nutritional quality of the Canadian food supply.

6. Safety

a) Potential Toxicity:

The amino acid sequence of the CryIIIA protein expressed in NewLeaf-Y™ potatoes is closely related to the sequence of the same proteins that are present in strains of B. thuringiensis that have been used for over 30 years as commercial organic microbial insecticides. An analysis of the amino acid sequences of the inserted CryIIIA protein and PVY-O CP did not show homologies with known mammalian protein toxins and they are not judged to have any potential for human toxicity. The history of known safe consumption of PVY-O CP from virus-infected plant products provides additional evidence of lack of toxicity.

b) Potential Allergenicity:

The CryIIIA protein and PVY-O CP do not possess characteristics typical of known protein allergens. There were no regions of homology when the sequences of these introduced proteins were compared to the amino acid sequences of known protein allergens. Unlike known protein allergens, the CryIIIA protein is rapidly degraded by acid and/or enzymatic hydrolysis when exposed to simulated gastric or intestinal fluids. The CryIIIA protein and PVY-O CP are extremely unlikely to be allergenic.

CONCLUSION:

Health Canada's review of the information presented in support of the food use of CPB and PVY resistant SEMT15-02, SEMT15-15 and RBMT15-101 potato lines concluded that they do not raise concerns related to human food safety. Health Canada is of the opinion that products from NewLeaf-Y™ Shepody and NewLeaf-Y™ Russet Burbank potato cultivars are as safe and nutritious as those available from current commercial potato cultivars.

Health Canada's opinion pertains only to the food use of these CPB and PVY resistant potato lines. Issues related to growing NewLeaf-Y™ Shepody and NewLeaf-Y™ Russet Burbank potatoes 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
Food Directorate
Health Protection Branch
Health Canada
Tunney's Pasture
Ottawa, Ontario K1A 0L2
Telephone: (613) 941-5535
Facsimile: (613) 952-6400

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