<p style="text-align: justify;">Tobacco (<i>Nicotina tabacum</i>) was grown commercially in 127 countries in 2004, with a combined production of 6.5 million metric tonnes. The major producers of tobacco were China, Brazil, India, the United States, Zimbabwe, Turkey and Indonesia. This cultivated plant is thought to be a hybrid of <i>N. sylvestris</i> and <i>N. tomentosiformis</i>. All Nicotiana species are characterized by the presence of nicotine and other alkaloids.</p>

<p style="text-align: justify;">Tobacco is processed into cigarettes, cigars, snuff, and chewing tobacco. Tobacco is widely regarded as being highly addictive due to the presence of high (20000 ppm to 30000 ppm) levels of nicotine in conventional varieties. It is generally agreed that reducing the level of nicotine delivered by tobacco products will reduce dependence on tobacco, which is commonly regarded as large contributor to cancerous diseases and premature mortality worldwide.</p>

<p style="text-align: justify;">The transgenic tobacco line Vector 21-41 was developed to reduce nicotine levels below those thought to be addictive. Vector 21-41 routinely contains 20 fold less nicotine than conventional varieties and also produces 15 fold less mutagenic and carcinogenic Tobacco Specific Nitrosamines. An antisense strategy was used to downregulate expression of the enzyme responsible for the production of nicotinic acid, a nicotine precursor. Specifically the antisense configuration of <i>NtQPT1</i> a gene coding for quinolinic acid phosphoribosyltransferase (QPTase) was inserted into Burley 21 LA (a low-alkaloid variety) via <i>Agrobacterium</i>-mediated transformation.</p>

<p style="text-align: justify;">Vector 21-41 was field tested in the U.S. and Argentina. Vector 21-41 did not prove to be substantially different than the parental line: Burley 21 LA or Burley 21, in terms of agronomic performance. Vector 21-41 did exhibit susceptibility to fungal diseases such as blue mold and insects, but this was not substantially different from the parental line and could be controlled by conventional practices.</p>

<p style="text-align: justify;">In field trials, Vector 21-41 leaves had 700 to 1500 ppm nicotine, while conventional varieties grown in the same conditions produced 10000 to 30000 ppm nicotine. The percentage of reducing sugars was increased in Vector 21-41 compared to conventional varieties almost two-fold.</p>

<p style="text-align: justify;">Due to the nature of the tobacco plant and cultivation methods currently used, it was not thought that Vector 21-41 posed an undue environmental risk. Tobacco is usually a self-pollinating plant, being possessed of tubular flowers and not prone to wind pollination. As well, out-crossing with related species is rare and these species are not generally found in areas where tobacco is grown.</p>

<p style="text-align: justify;">Cultivation of tobacco is not conducive to outcrossing. Most growers do not save tobacco seed, preferring to rely on certified seed for planting. As well, in commercial production, the flowers are removed prior to anthesis, pollen shed or seed development to encourage leaf growth. Vegetative reproduction in tobacco is rare in field conditions.</p>

<p style="text-align: justify;">An antibiotic resistance marker gene (<i>nptII</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 plants. 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>nptII</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>

<p style="text-align: justify;">Vector 21-41 is not expected to impact biodiversity or to become a weed nuisance. The transformation does not convey any competitive advantage to the plant nor does it allow the production of tobacco outside areas currently under tobacco cultivation. It has no known adverse effects on animals or insects feeding on the plant.</p>
