Glyphosate resistance

From: Heck et al. 2005. Development and Characterization of a CP4 EPSPS-Based, Glyphosate-Tolerant Corn Event: Crop Sci. 45:329-339 (2005).

"Two key elements needed for the development of commercially viable glyphosate-tolerant crops are

• a resistant target enzyme
• and sufficient expression of that enzyme within the transgenic plant

5-Enol-pyruvylshikimate-3-phosphate synthase (EPSPS) is the target enzyme for glyphosate inhibition within the aromatic amino acid biosynthetic pathway.

• Disruption of this pathway not only creates a deficiency in protein synthetic precursors, it also affects many other plant cell components that are derived from intermediates and derivatives of this pathway (e.g., auxins, lignans, flavonoids, anthocyanins, and quinones).
• Therefore, a crop plant must be engineered with a resistant enzyme to maintain flux through this pathway for uninhibited growth and development.

Numerous candidate EPSPS enzymes from native and mutagenized microbial and plant sources were examined in an effort to select an enzyme with high catalytic efficiency in the presence of glyphosate (Ruff et al., 1991; Barry et al., 1992).

• Agrobacterium sp. strain CP4 EPSPS (CP4 EPSPS) was found to be an exceptional enzyme during this screening process (Barry et al., 1992; Padgette et al., 1995) and is the transgenic EPSPS protein produced in glyphosate-tolerant Roundup Ready soybean, cotton, and canola.

Transgenic expression of CP4 EPSPS within these crops provided the appropriate support to the aromatic amino acid biosynthetic pathway without negative impact on yield, compositional qualities, and nutritional value of the harvested product (Delannay et al., 1995; Hammond et al., 1995; Harrison et al., 1996; Padgette et al., 1995; Nida et al., 1996b)."