Expression dynamics of mCry3A and eCry3.1Ab transgenes in Bt corn hybrids across growth and environments.

In 2017 and 2018, studies were conducted in Iowa, US across three environments with a history of greater than expected corn rootworm injury i.e., greater than one node of injury to (US EPA 2009) and one environment without rootworm injury, and at different growth stages, to determine the expression levels of mCry3A and eCry3.1Ab transgenes in the roots of different Bt corn hybrids namely the molecular stack (MZIR098), breeding stack (MIR604 × 5307), 5307 and MIR604. ELISA results showed that expressions of both mCry3A and eCry3.1Ab transgenes, were higher in the MZIR098 molecular stack and breeding stack (MIR604 × 5307), than the MIR604 and 5307 at V3 and VT growth stages over both years. To protect the roots from feeding damage by the corn rootworm larvae, expression of the transgenes must be high at the V3 growth stage. The expression of the transgene was significantly impacted by the stage of plant growth while the environments with greater than expected corn rootworm injury did not impact expression of the transgenes. It was found that the expression of mCry3A and eCry3.1Ab transgenes were high at the V3 plant growth stage compared to the VT growth stage. Stacking two or more genes together in the same plant such as the molecular and breeding stacks have the potential to protect roots in environments with higher-than-expected damage and slow down the evolution of resistance in field populations of rootworms.