<p style="text-align: justify;">Maize line DAS-59122-7 was genetically modified to contain three novel genes, <i>cry</i>34Ab1 and <i>cry</i>35Ab1 for insect resistance, and <i>pat</i>, for herbicide tolerance used as a selectable marker. All three genes were introduced into the parental maize hybrid line Hi-II by <i>Agrobacterium</i>-mediated plant transformation.</p>

<p style="text-align: justify;">The <i>cry</i>34Ab1 and <i>cry</i>35Ab1 genes, isolated from the common soil bacterium <i>Bacillus thuringiensis</i> (<i>Bt</i>) strain PS149B1, produce the insect control proteins (delta-endotoxins) Cry34Ab1 and Cry35Ab1. Cry proteins, of which Cry34Ab1 and Cry35Ab1 are only two among many, act by selectively binding to specific sites localized on the lining of the midgut of susceptible insect species. Following binding, pores are formed that disrupt midgut ion flow, causing gut paralysis and eventual death due to bacterial sepsis. Cry34Ab1 and Cry35Ab1 are both lethal only when eaten by the larvae of coleopteran insects (<i>i.e.</i>, beetles), and its specificity of action is directly attributable to the presence of specific binding sites in the target insects. There are no binding sites for the delta-endotoxins of <i>B. thuringiensis</i> on the surface of mammalian intestinal cells, therefore, livestock animals and humans are not susceptible to these proteins.<br />
The <i>pat</i> gene introduced into DAS-59122-7 maize allows the use of the herbicide glufosinate ammonium as a breeding tool for selecting plants containing the <i>cry</i>34Ab1 and <i>cry</i>35Ab1 genes. The herbicidal mode of action of glufosinate ammonium is related to the activity of glutamine synthetase (GS), the enzyme required for the synthesis of the amino acid glutamine. L-phosphinothricin, the active ingredient of glufosinate ammonium, is a structural analog of glutamate, and acts as a competitive inhibitor. After application of the herbicide, L-phosphinothricin competes with glutamine for its active sites on GS. The results of the inhibition of GS are an accumulation of ammonia in the plant, a reduction in the synthesis of glutamine, and an inhibition of photosynthesis. This causes the death of plant cells, and eventually, the entire plant. The <i>pat</i> gene codes for the production of the enzyme phosphinothricin acetyl-transferase (PAT). This enzyme acetylates L-phosphinothricin rendering it inactive in the plant. The PAT enzyme is not known to have any toxic properties. The <i>pat</i> gene was isolated from the soil bacterium <i>Streptomyces viridochromogenes</i>, the same organism from which L-phosphinothricin was originally isolated.</p>
