Roundup Ready™ maize

The NK603 line of maize was developed to allow the use of glyphosate, the active ingredient in the herbicide Roundup®, as a weed control option. NK603 contains a form of the plant enzyme 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) that allows the plant to survive the otherwise lethal application of glyphosate.

PV-ZMGT32

Notes about the Other(s) sequence(s) specific to this LMO

The plant expression plasmid vector, PV-ZMGT32 contains two adjacent plant gene expression cassettes each containing a single copy of the cp4 epsps. In the first (5' end) expression cassette, the cp4 epsps gene is under the regulation of the rice actin promoter (P-Ract1) and the rice actin intron (I-Ract1). The second cassette, which is fused to the 3' end of the first, consists of the cp4epsps gene regulated by the enhanced cauliflower mosaic virus 35S promoter (e35S) (P-e35S is a 0.61Kb long sequence containing the promoter and leader for the cauliflower mosaic virus (CaMV) 35S RNA containing the duplicated enhancer region. This modification was made to enhance the activity of this promoter in plants.) and intron from the corn heat shock protein 70 (HSP70). Both expression cassettes incorporate the 3'untranslated region of the nopaline synthase gene (nos 3') for signal polyadenylation.

The vector also contains the nptII gene encoding kanamycin resistance allowing selection of bacteria containing the plasmid, and an origin of replication (ori) necessary for replicating the plasmid in Escherichia coli. For the transformation through particle bombardment, a fragment of the vector (obtained after digestion with the restriction enzyme MluI) was used which contains only the two cp4 epsps gene expression cassettes. Therefore, the nptII gene and the origin of replication were not inserted into NK603.

Corn NK603 contains one insertion site containing a single copy of the linear DNA of PV-ZMGT32 used for transformation. Both cp4 epsps gene cassettes within the single insert which are intact.

Glyphosate specifically binds to and inactivates the enzyme EPSPS, which is part of an important plant biochemical pathway called the shikimate pathway. The shikimate pathway is involved in the biosynthesis of the aromatic amino acids tyrosine, phenylalanine and tryptophan, as well as other aromatic compounds. When conventional plants are treated with glyphosate they cannot produce the aromatic amino acids essential to their survival. The modified maize line permits farmers to use glyphosate-containing herbicides for weed control in the cultivation of maize. The EPSPS enzyme is present in all plants, bacteria and fungi, but not in animals, which do not synthesize their own aromatic amino acids. Thus, EPSPS is normally present in food derived from plant and microbial sources.