Development and Characterization of a Cotton (<i>Gossypium hirsutum</i> L.) Event with Enhanced Reproductive Resistance to Glyphosate

Abstract

Glyphosate is a broad spectrum herbicide that inhibits the activity of endogenous plant 5‐enolpyruvylshikimate‐3‐phosphate synthase (EPSPS). Glyphosate resistance has been engineered in multiple crops by constitutive expression of an EPSPS variant from Agrobacterium sp. CP4 (CP4 EPSPS) that binds glyphosate less efficiently. The first glyphosate‐resistant cotton ( Gossypium hirsutum L.) event, MON 1445, was developed utilizing this CP4 EPSPS and commercially introduced in 1997. Due to insufficient expression of CP4 EPSPS in male reproductive tissues, over‐the‐top glyphosate applications must be limited to the four‐leaf stage of growth. In an attempt to generate events with complete constitutive expression, multiple constructs consisting of different promoters driving cp4 epsps were transformed into cotton. The MON 88913 event was identified as providing exceptional vegetative and reproductive resistance to glyphosate based on more than 8 yr of field testing. Cotton containing MON 88913 has a comparable agronomic profile to the respective negative isoline, the event is stably inherited over multiple generations, and the insertion site is simple with minimal disruption of the cotton genome. As a result, the MON 88913 event was commercially introduced in 2006 as Roundup Ready Flex Cotton (Monsanto Co., St. Louis, MO).