Evaluating the Potential for Adverse Interactions Within Genetically Engineered Breeding Stacks

Steiner HY, Halpin C, Jez JM, Kough J, Parrott W, Underhill L, Weber N, Hannah LC
Plant Physiology
January 1, 2013

Task Force #9

Plant Physiology. 2013;161:1587-1594

Abstract: Crops containing a single transgenic event are subjected to extensive safety assessments before authorization. These assessments evaluate the resulting phenotype for food and feed safety, cognizant that the phenotype is the result of interactions of the transgenes and their products with the tens of thousands of endogenous genes and their products. Genetically engineered (GE) stacks (also known as stacked or combined events) are produced by combining two or more single transgenic events by conventional breeding. The potential for interactions between the products of the events in a GE stack that impact food and feed safety can be evaluated in the context of conventional breeding of non-GE plants. Conventional breeding recombines tens of thousands of genes and alleles in the genome, and does so with a long history of safety. The numerous interactions between the products of endogenous genes are largely unknown and therefore currently do not lend themselves to experimental testing. In contrast, the functions of transgenes are known in great detail relative to endogenous genes, so such evaluation can be based on testable hypotheses concerning possible interactions between single events in a stack. Since interactions between events and the endogenous genes were evaluated for single events, safety assessment of GE stacks should focus on potential interactions between the products of the transgenes. Guiding questions are provided for consideration in formulating hypotheses regarding food and feed safety issues resulting from interactions between the products of combined events, and examples are included to aid in clarifying the use of these questions.

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