<p style="text-align: justify;">The maize line DAS-06275-8 (hereafter referred to as <b>TC-6275</b>) was genetically modified to contain two novel genes, <i>cry</i>1F and <i>bar</i>, for insect resistance and herbicide tolerance respectively. Both 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>1F gene, isolated from the common soil bacterium <i>Bacillus thuringiensis</i> (<i>Bt</i>) var. <i>aizawai</i>, produces the insect control protein Cry1F, a delta-endotoxin. Cry proteins, of which Cry1F is only one, 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. Cry1F is lethal only when eaten by the larvae of lepidopteran insects (moths and butterflies), 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. The Cry1F protein expressed in TC-6275 provides protection against European corn borer (ECB), southwestern corn borer (SWCB), fall armyworm (FAW), black cutworm (BCW), and some control of corn earworm (CEW).</p>

<p style="text-align: justify;">The <i>bar</i> gene in TC-6275 confers tolerance to glufosinate ammonium. This herbicide can therefore be applied to TC-6275 as a weed control option, and can also be used as a selection tool for successful transformants containing the insect-tolerant <i>cry</i>1F gene. The herbicide tolerance of TC-6275 is due to the expression of a protein, phosphinothricin-acetyl-transferase (PAT), which confers tolerance to the active ingredient L-phosphinothricin in glufosinate ammonium. The <i>bar</i> gene was isolated from <i>Streptomyces hygroscopius</i>, a gram-positive soil bacterium.</p>

<p style="text-align: justify;">Glufosinate ammonium is a post-emergence, broad-spectrum contact herbicide and plant dessicant. L-Phosphinothricin was first isolated as bialaphos, an antibiotic synthesized during the fermentation of <i>Streptomyces hygroscopicus</i> or <i>S.viridochromogenes</i>. In herbicidal formulations, L-Phosphinothricin is a component of the glufosinate ammonium, which is chemically-synthesized. Glufosinate ammonium is a racemic mixture of L-phosphinothricin, the herbicidal active moiety, and its D-enantiomer. L-phosphinothricin is structurally similar to glutamate, the substrate of glutamine synthetase (GS), an enzyme that catalyzes the synthesis of glutamine from glutamate and ammonia. L-phosphinothricin inhibits the activity of GS irreversibly by binding to its active sites. The inhibition of GS caused by the application of glufosinate ammonium to plants results in the accumulation of ammonia, the reduction in the levels of glutamine, and the inhibition of photosynthesis, all of which results in the death of the plant. Plants transformed with the <i>bar</i> gene express the enzyme phosphinothricin-acetyl-transferase (PAT) which acetylates L-phosphinothricin into a non-phytotoxic metabolite (N-acetyl-L-glufosinate).</p>
