Development and Characterization of a CP4 EPSPS-Based, Glyphosate-Tolerant Corn Event

Abstract

5-Enol-pyruvylshikimate-3-phosphate synthase from Agrobacterium sp. CP4 (CP4 EPSPS) confers tolerance to the nonselective herbicide glyphosate (marketed under the trade name Roundup11 Roundup Ready and Roundup herbicide are trademarks of the Monsanto Company.) when sufficiently expressed in transgenic plants. Dual CP4 EPSPS transgene cassettes were transformed into corn (Zea mays L.) under the transcriptional regulatory control of the rice (Oryza sativa L.) actin 1 (P-Ract1) and the enhanced Cauliflower mosaic virus 35S (P-e35S) promoters, respectively, to impart fully constitutive expression in corn. Resulting events were tested for lack of chlorosis and malformation injury after two sequential applications of 1.68 kg acid equivalents (a.e.) ha−1 glyphosate. Agronomic parameters, male fertility, appropriate Mendelian segregation of the trait, plus characteristics of the transgenic integration site were also evaluated. From this selection process, the NK603 event was chosen for commercialization as the event that embodied the most optimal profile of tolerance, agronomics, and molecular characteristics. The NK603 event exhibited high glyphosate tolerance from one transgenic locus bearing a single copy of the dual cassettes integrated into the corn genome with a minimum of target sequence disruption. Trait expression in the NK603 event has remained stable over more than eight generations as shown through tolerance testing, western blots of CP4 EPSPS accumulation, and Southern blot analysis of the transgene.