<p style="text-align: justify;">The maize hybrid DK404SR was developed to allow the use of sethoxydim, the active ingredient in the herbicide Poast&reg;, for the control of annual and perennial grasses in maize crops. DK404SR originated from a somaclonal variant selected from embryo tissue and expresses a modified version of acetyl-CoA-carboxylase (ACCase) enzyme.</p>

<p style="text-align: justify;">ACCase is a key enzyme in the fatty acid biosynthesis pathway, necessary for the synthesis and maintenance of membranes and for the incorporation of fatty acids into triacylglycerides. The enzyme is inhibited by cyclohexanedione herbicides, such as sethoxydim, resulting in a lethal disruption of lipid biosynthesis. The mutant ACCase gene encodes for a modified version of acetyl-CoA-carboxylase enzyme in which the sethoxydim binding site is altered such that the ACCase enzyme is not inhibited by the sethoxydim herbicide, yet still retains its normal catalytic properties in fatty acid synthesis. The modified maize plants also demonstrated some level of cross-tolerance to the related herbicides, aryloxyphenoxypropionates, including haloxyfop (not registered in Canada), fluazifop (Venture) and quizalofop (Assure). These herbicides all have the same mode of action through ACCase inhibition. Natural tolerance to sethoxydim herbicide is found in several broadleaved plants and grasses and includes annual ryegrass, green foxtail and red fescue.</p>
