The BXN™ cotton line was genetically engineered to express
tolerance to oxynil herbicides, including bromoxynil and ioxynil.
Oxynil herbicides act by blocking electron flow during the light
reaction of photosynthesis, inhibiting cellular respiration in
dicotyledonous plants. Oxynil herbicides applied at rates
recommended for effective weed control are toxic to conventional
cotton varieties. The modified cotton line BXN™ contains the bxn
gene for oxynil tolerance, and allows farmers to use oxynil
herbicides for weed control in the cultivation of cotton.
The bxn gene was isolated from the bacterium Klebsiella pneumoniae
subspecies ozaenae and codes for the enzyme nitrilase, which
hydrolyses ioxynil and bromoxynil into non-toxic compounds. The
nitrilase encoding gene was introduced into the cotton genome using
Agrobacterium-mediated transformation, and the bacterial form of
the enzyme expressed in this transgenic cotton line functions the
same as that found in monocot plants such as corn, wheat and
barley.
The kanamycin-resistance gene (aphII), isolated from the bacterium
Escherichia coli codes for an enzyme (aminoglycoside
3'-phosphotransferase II) that phosphorylates kanamycin , thereby
preventing it from binding to ribosomes and rendering the cells
resistant. This protein is ubiquitous in the environment and it
degrades rapidly in vitro in simulated mammalian gastric and
intestinal fluids.
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