<p style="text-align: justify;">Transgenic cotton (<i>Gossypium hirsutum</i> L.) line BXN&trade; was developed using recombinant DNA techniques to be tolerant of herbicides in the oxynil family, principally bromoxynil (tradename Buctril&reg;). The oxynil family of herbicides is active against dicotyledonous plants by blocking electron flow during the light reaction of photosynthesis. This transgenic line was produced by inserting a gene that encodes for a bacterial enzyme, nitrilase, from <i>Klebsiella pneumoniae</i>. The nitrilase enzyme hydrolyses the herbicides ioxynil and bromoxynil into non-phytotoxic compounds. Specifically the nitrilase enzyme breaks down bromoxynil into 3,5 dibromo-4-hydroxybenzoic acid (DBHA), eliminating its herbicidal activity.</p>

<p style="text-align: justify;">An antibiotic resistance marker gene (<i>neo</i>) encoding the enzyme neomycin phosphotransferase II (NPTII), which inactivates aminoglycoside antibiotics such as kanamycin and neomycin, was also introduced into the genome of these transgenic lines. This gene was derived from a bacterial transposon (Tn5 transposable element from <i>Escherichia coli</i>) and was included as a selectable marker to identify transformed plants during tissue culture regeneration and multiplication. The expression of the <i>neo</i> gene in these plants has no agronomic significance and the safety of the NPTII enzyme as a food additive was evaluated by the United States Food and Drug Administration in 1994 (US FDA, 1994).</p>
