Regulations governing the safety assessment of genetically engineered (GE) crops require studies that measure the expression levels of the transgene products (proteins and double-stranded RNA) in the GE crop; furthermore, the regulations also often mandate the inclusion of an entry of the GE crop that is sprayed with the herbicide to which tolerance was engineered and a non-sprayed entry of the GE crop in said studies. The hypothesized unique risk of altered transgene expression in response to application of herbicides related to herbicide-tolerant GE crops, compared with application of other herbicides, is not readily apparent. Field studies were conducted with GE maize, soybean, and cotton breeding stacks containing multiple herbicide tolerance traits; studies included plots that were sprayed with the trait-related herbicides and plots that were unsprayed. The GE herbicide-tolerance traits and complimentary herbicides investigated here comprise the majority of those that are currently in commercial use. Transgene product expression was characterized in crop tissues that were collected throughout the growing season. Results confirm the expectation, which is based on the fact that modes of action and regulatory elements in the genetic constructs of the herbicide-tolerance traits are well understood, that applying herbicides associated with GE herbicide-tolerance traits does not meaningfully affect transgene expression. These findings call into question the routine requirement for the inclusion of herbicide sprayed and non-sprayed entries in transgene-expression studies designed to support risk assessment.
Keywords: Coefficient of identity; Genetically engineered (GE) breeding stacks; Herbicide-tolerant crops; Safety assessment; Transgene expression.
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