Novel food information: Bacillus thuringiensis (B.t) Cry34/35/Ab1 insect resistant, glufosinate-tolerant transformation corn event DAS-59122-7

On this page

• Background
• Introduction
• Development of the modified plant
• Characterization of the modified plant
• Product information
• Dietary exposure
• Nutrition
• Chemistry/toxicology
• Conclusion

Background

Health Canada has notified Dow AgroSciences Canada Inc. that it has no objection to the food use of Bacillus thuringiensis (B.t) Cry34/35/Ab1 insect resistant, glufosinate-tolerant transformation corn event DAS-59122-7. The Department conducted a comprehensive assessment of this corn 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 Canada Inc. and the evaluation by Heath Canada and contains no confidential business information.

Introduction

Dow AgroSciences has developed corn (Zea mays L.) lines based upon transformation event DAS-59122-7. Corn varieties containing this event express three novel proteins from three distinct genes. These genes are the cry34Ab1 and cry35Ab1 genes, which confer resistance to rootworm pests of corn and the phosphinotricin acetyltransferase (pat) gene, which confers tolerance to glufosinate ammonium herbicides. Health Canada has previously indicated no objection to the sale of glufosinate tolerant Corn (line 1507, event T14 and event T25), Canola (Event T45 and Event HCN92), Soybean (Line A5547-127 and line A2704-12) and Sugarbeet (Event T120-7), for human food applications in Canada. Like corn event DAS-59122-7, these lines express the pat gene which confers tolerance to glufosinate ammonium. Cry proteins have an almost sixty years history of use as a pesticide for agricultural purposes and have been widely used as a biocontrol agent in genetically modified crops.

Health Canada has previously issued letters of no objection to Cotton ( Event 281-24-236, Event 3006-210-23, Event 15985, Line 531 and line 757), Corn (line 1507, MON 863, MON 802, MON 810, MON 809, BT11, Line 176 and DBT 418), Tomato (Line 5345) and Potato (RBMT21-129, RBMT21-350, RBMT22-082, RBMT15-01, SEMT15-02, SEMT15-15, BT06, BT10, BT12, BT16, BT17, BT18, and BT23) all containing Cry proteins.

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 DAS-59122-7 was developed; how the composition and nutritional quality of corn varieties containing this event compared to non-modified and current commercial corn varieties; and what the potential is for corn lines 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 DAS-59122-7 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 line HI-II was genetically modified using Agrobacterium tumefaciens transformation. The transforming plasmid PHP17662 carried a transfer DNA (T-DNA) sequence comprised of the transgenes cry34Ab1, cry35Ab1 and pat under the control of additional genetic components. The genetic elements in the T-DNA region were the Ubiquitin promoter and 5' untranslated region and intron from Zea mays (UBIIZM PRO), a corn optimized synthetic version of the Cry34Ab1 coding region (cry34Ab1), the terminator sequence from Solanum tuberosum proteinase inhibitor II (PINII TERM), the root-preferred promoter from Triticum aestivum peroxidase (TA PEROXIDASE), a corn optimized synthetic version of the Cry35Ab1 coding region (cry35Ab1), the 35S promoter from the cauliflower mosaic virus, Strasbourg strain (CaMV 35S PRO), a synthetic plant optimized phophinothricin aceetyltransferase coding sequence from Streptomyces viridochromogenes (pat) and the 35S terminator from the cauliflower mosaic virus (CaMV 35S TERM).

Characterization of the modified plant

Southern blot analysis of the corn event DAS-59122-7 demonstrated the insertion of a single intact copy of the T-DNA region in the corn genome at a single locus. Southern blot analysis also demonstrated the integrity of the T-DNA region and its regulatory elements, as well as the absence of any plasmid derived sequences outside the T-DNA region, such as the spectinomycin resistance gene found in the plasmid backbone. The elements contained in the T-DNA region have been shown to be stable with no rearrangements through southern analysis and sequence analysis.

The stability of the inserted cry34Ab1, cry35Ab1 and pat genes was evaluated in multiple generations of corn grown at separate locations. The results of southern blot analysis and segregation data demonstrated the stability of the corn event DAS-59122-7 at the genomic level in different environments.

Characterization of the expressed proteins through Western blot analysis using polyclonal antibodies produced immunoreactive bands at the expected molecular weights for these proteins. Levels of Cry34Ab1, Cry35Ab1 and PAT expression were determined using ELISA for leaf, pollen, root, stalk, grain and whole plant samples. Expression of Cry34Ab1, Cry35Ab1 and PAT was detected in all tissues assayed, except that no PAT protein was detected in pollen.

Product information

Corn event DAS-59122-7 differs from its traditional counterpart by the addition of the cry34Ab1, cry35Ab1 and pat gene sequences into the genome, and the expression of the Cry34Ab1, Cry35Ab1 and PAT proteins coded for by these genes. The proteins encoded by these genes are expressed at different levels throughout the plant tissue and throughout the life of the plant.

Dietary exposure

The primary use of corn lines carrying event DAS-59122-7 will be for animal feed. This corn will be processed into food and industrial products such as ethyl alcohol by fermentation, cornmeal by dry milling and highly refined starch by wet milling processes. Food products derived from corn containing event DAS-59122-7 are expected to be used by the food industry in the same applications as food products derived from other commercial corn varieties.

Nutrition

Corn grain was analysed for proximates (including ADF and NDF), fatty acids (palmitic, stearic, oleic, linoleic and linolenic), amino acids (eighteen), minerals (nine), vitamins (beta-carotene, B1, riboflavin, folic acid, alpha, beta, delta, gamma and total tocopherols), secondary metabolites and anti-nutrients (inositol, raffinose, furfural, p-coumaric acid, ferulic acid, phytic acid and trypsin inhibitor).

The data presented showed no significant differences in proximate composition of grains from unsprayed test and control treatments. Most of the other comparisons showed few significant differences between test and control treatments. For analytes where some significant differences were observed, values were within literature ranges and the absolute differences were small and nutritionally insignificant.

Chemistry/toxicology

Based on the expression levels of these proteins in grain and dietary intake data, exposure to these proteins would be extremely low. The novel proteins were not homologous to known food allergens, as established by amino acid sequence comparisons with allergenic proteins from extensive computerized databases. In digestibility studies using simulated mammalian gastric fluid, the novel proteins were more rapidly digested than non-allergen protein controls. Based on the preceding evidence, the novel proteins expressed in this corn line do not share characteristics of known food allergens.

The LD₅₀ of the Cry34Ab1, Cry35Ab1 and PAT proteins (2700 mg/kg bw, 1850/mg/kg bw and 5000 mg/kg bw, respectively) were orders of magnitude greater than the dose range for this endpoint typically associated with protein toxins. Additionally, the PAT protein present in this corn event DAS-59122-7 has been extensively studied and has been found safe for consumption in food or feed according to a consensus document concerning the genes and associated enzymes that confer tolerance to phosphinothricin herbicide (OECD, 1999).

No introduced health concerns would be expected to be associated with the consumption of corn event DAS-59122-7 compared with its non-transgenic parent. DAS-59122-7 corn is deemed to be similar to the non-transgenic parental strain of corn in terms of being an acceptable food source.

Conclusion

Health Canada's review of the information presented in support of the food use of Bacillus thuringiensis (B.t) Cry34/35/Ab1 insect resistant, glufosinate-tolerant transformation corn event DAS-59122-7 concluded that this use does not raise concerns related to human food safety. Health Canada is of the opinion that corn containing event DAS-59122-7 is as safe and nutritious as current commercial corn varieties.

Health Canada's opinion deals only with the food use of Bacillus thuringiensis (B.t) Cry34/35/Ab1 insect resistant, glufosinate-tolerant transformation corn event DAS-59122-7. Issues related to its use as animal 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