Novel food information: (mo)Cry1F insect resistant, glufosinate tolerant corn event TC6275

On this page:

• Background
• Introduction
• Development of the modified plant
• Characterization of the modified plant
• Product Information
• Dietary Exposure
• Nutrition
• Toxicology
• Conclusion

Background

Health Canada has notified Dow AgroSciences Canada Inc. that it has no objection to the sale of food derived from corn lines containing the transformation event TC6275, which exhibit both the insect resistant and glufosinate tolerant traits. The Department conducted a comprehensive assessment of this corn event 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 with novel traits.

The following provides a summary of the notification from Dow AgroSciences, and the evaluation by Heath Canada and contains no confidential business information.

Introduction

Dow AgroSciences has developed corn (Zea mays) lines based upon transformation event TC6275. Corn plants containing this vector stacked trait event express two novel proteins: phosphinothricin acetyl-transferase (PAT) which confers tolerance to glufosinate herbicides, and the Cry1F protein which exhibits insecticidal activity against certain Lepidopteran pests such as the European Corn Borer (Ostrinia nublialis).

Health Canada has previously indicated no objection to the sale of the insect resistant, glufosinate tolerant corn event 1507 expressing the Cry1F and PAT proteins for human food applications. The Cry1F protein from event 1507 is identical to that expressed in TC6275. The PAT protein from event 1507 is a variant sharing 85% amino acid sequence identity with that expressed in TC6275. Health Canada has also previously indicated no objection to the sale of the single trait glufosinate tolerant corn event DLL25 for human food applications. The PAT protein from event DLL25 is identical to that expressed in TC6275.

The safety assessment performed by Food Directorate evaluators was conducted according to Health Canada's Guidelines for the Safety Assessment of Novel Foods. The assessment considered: how corn event TC6275 was developed; how the composition and nutritional quality of corn grain derived from plants containing this event compare to non-modified corn; and what the potential is for food products derived from plants containing this event to be toxic or cause allergic reactions.

The Food Directorate has a legislated responsibility for pre-market assessment of novel foods and novel food ingredients as detailed in Division 28 of Part B of the Food and Drug Regulations (Novel Foods). Foods derived from corn lines containing event TC6275 are considered novel foods under the following part of the definition of novel foods: "c) a food that is derived from a plant, animal or microorganism that has been genetically modified such that

1. the plant, animal or microorganism exhibits characteristics that were not previously observed in that plant, animal or microorganism."

Development of the modified plant

Corn event TC6275 was developed through Agrobacterium-mediated transformation of corn embryo derived tissue followed by negative selection on culture media containing the herbicide glufosinate. TC6275 is a single insertional event containing two tandem expression cassettes, one for the (mo)cry1F gene and one for the bar gene:

The constitutive expression of a synthetic, maize codon-optimized variant of the cry1F gene from Bacillus thuringiensis var. aizawai [(mo)cry1F] was controlled by the ubiquitin 1 promoter (P-ZmUbi1) from corn. The above ubiquitin 1 promoter includes the corresponding untranslated leader (exon1) and intron1 sequences that contribute to transcript stability. The polyadenylation sequence is derived from the 3' untranslated region of the Proteinase Inhibitor II gene (T-PINII) from potato.

The bar gene expression cassette is composed of the Cauliflower Mosaic Virus 35S promoter, including upstream enhancer sequences (P-e35S), the alcohol dehydrogenase intron 1 sequence (I-Adh1) from maize, the bar gene from Streptomyces hygroscopicus encoding phosphinothricin N-acetyltransferase (PAT), and the 3' untranslated region of the Proteinase Inhibitor II gene (T-PINII) from potato.

Characterization of the modified plant

Southern blot and PCR analysis of corn containing the event TC6275 demonstrated the insertion of one copy of the T-DNA of plasmid PHP12537 in the corn genome. Southern blot analysis also demonstrated the integrity of the (mo)cry1F and bar genes and regulatory elements, as well as the absence of plasmid-derived sequences outside of the T-DNA region.

The genetic stability of the inserted (mo)cry1F and bar gene cassettes were evaluated in different corn germplasm backgrounds over seven generations of conventional breeding at various locations. The results obtained demonstrate the heritability and stability of the event TC6275 at the genomic level.

Product information

Corn event TC6275 differs from its traditional counterparts by the addition of the (mo)cry1F and bar gene sequences into the genome, and the expression of the Cry1F and PAT proteins. The proteins encoded by these two genes are expressed at different levels in various tissues throughout the plant and throughout the life of the plant.

Dietary exposure

The levels of Cry1F and PAT proteins in maize grain grown under North American conditions average 1.04 ng/mg and 5.94 ng/mg, respectively, on a dry weight basis. The levels of Cry1F and PAT proteins in maize grain sampled from a study in Chile average 2.14 ng/mg and 23 ng/mg, respectively, on a dry weight basis. It is expected that maize grain from TC6275 will be used in applications similar to that derived from other maize varieties. In North America, maize food products for human consumption are found mainly in the form of processed foods containing maize derived ingredients such as high fructose corn syrup, starch, oil, and flour.

Nutrition

The analysis of nutrients from corn lines containing event TC6275, control, and conventional corn did not reveal any significant differences in the levels of proximates, and selected fatty acids, amino acids, minerals, vitamins, and antinutrients. In each case the level of each respective component was comparable to the control or within the reported range for conventional corn. The consumption of products from corn event TC6275 will have no significant impact on the nutritional quality of the Canadian food supply.

Toxicology

The potential for toxicity for Cry1F and PAT proteins expressed in corn lines containing event TC6275 was considered remote. This conclusion was based on the low amount of Cry1F and PAT proteins found in corn grain, the absence of demonstrated acute toxicity to Cry1F and PAT in mice at doses orders of magnitude greater than the range associated with proteins, the lack of sequence homology between known toxins and the Cry1F and PAT proteins, and the likelihood that the Cry1F and PAT proteins will be degraded under conditions similar to those in the human gastrointestinal tract. There were no additional health concerns regarding endogenous toxins from food products derived from corn lines containing event TC6275 when compared to non-transgenic varieties.

The possibility that the Cry1F and PAT proteins would be allergenic in corn lines containing event TC6275 was also considered unlikely. This was based on the lack of sequence homology of the Cry1F and PAT proteins to any known allergens, and the rapid digestion of both proteins in simulated gastric fluids. These results suggest that foods derived from corn lines containing event TC6275 would not pose any greater allergenic risk than non-transgenic corn.

At the expected level of consumption, there was no greater concern with corn lines containing event TC6275 than non-transgenic corn, with respect to its potential for toxicity or allergenicity.

Conclusion

Health Canada's review of the information presented in support of the food use of corn lines containing event TC6275 concluded that the food use of corn lines containing this event does not raise concerns related to safety. Health Canada is of the opinion that corn lines containing event TC6275 are as safe and nutritious as current commercial corn lines.

Health Canada's opinion deals only with the human food use of corn lines containing event TC6275. Issues related to its use as livestock feed have been 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 Products and Food 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 (September 1994).

For further information, please contact:

Novel Foods Section
Food Directorate
Health Products and Food Branch
Health Canada, PL2204A1
251 Frederick Banting Driveway
Ottawa, Ontario K1A 0K9
bmh-bdm@hc-sc.gc.ca