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 Roundup1) 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.

Molecular Plant Breeding as the Foundation for 21st Century Crop Improvement

“…Each of these glyphosate-tolerant maize events also illustrates another benefit of biotechnology, where new combinations of regulatory sequences (e.g. the cauliflower mosaic virus 35S and rice actin1 promoters) may be used to achieve optimal trait expression with respect to overall activity and tissue distribution relative to what might be possible with endogenous genes (Heck et al, 2005).…”

Editor’s Choice: Crop Genome Plasticity and Its Relevance to Food and Feed Safety of Genetically Engineered Breeding Stacks

“…For example, over 1,300 initial transformation events were screened to identify the commercialized glyphosate-tolerant maize event NK603 (Heck et al, 2005). Events destined for commerce are thoroughly characterized for stable trait expression during breeding and are only advanced if the trait is stable over generations (Mumm and Walters, 2001).…”

“…To further evaluate the phenotypic stability of a lead event in a seed-propagated crop, field trials are conducted following multiple rounds of self-pollination or backcrosses into elite varieties (Padgette et al, 1995;Mumm and Walters, 2001;Heck et al, 2005). Such evaluations further help to uncover any stability concerns with a particular event before commercialization.…”

Herbicide selectivity by differential metabolism: considerations for reducing crop damages

“…Exercise care in relation to product (chemicals) interaction, mainly herbicides and organo-phosphorate insecticides applied together or at short intervals between applications (Porpiglia et al, 1990;Morton et al, 1991); c. Use antidotes or safeners, always when recommended (Devine et al, 1993;Hatzios & Burgos, 2004;Foloni et al, 2005); d. Whenever possible, rank herbicide applications according to selectivity, starting with products with enzymatic insensitivity, such as ACCase inhibitor (Turner & Pernich, 2002) in soybean, cotton and dry beans; e. Adopt genetically modified crops tolerant to herbicides (Pline-Srnic, 2005;Heck et al, 2005).…”