"tobacco plant or plant part, seed, tobacco product, methods to reduce the carcinogenic potential of a tobacco product, to reduce the level of nornicotine, or to reduce the rate of conversion of nicotine to nornicotine in a plant or part. of a tobacco plant and to identify a tobacco plant with low levels of nornicotin, isolated polynucleotide, isolated polypeptide and mutation in a gene encoding a cyp82e10 nicotine demethylase. "
"tobacco plant or plant part, seed, tobacco product, methods to reduce the carcinogenic potential of a tobacco product, to reduce the level of nornicotine, or to reduce the rate of conversion of nicotine to nornicotine in a plant or part. of a tobacco plant and to identify a tobacco plant with low levels of nornicotin, isolated polynucleotide, isolated polypeptide and mutation in a gene encoding a cyp82e10 nicotine demethylase. " Compositions and methods for reducing the level of nornicotine and n'-nitrosonornicotine (nnn) in tobacco plants and plant parts are provided. Compositions include polynucleotides and polypeptides isolated for root-specific cyp82e10 nicotine demethylases and variants thereof, which participate in the metabolic conversion of nicotine to nornicotine in these plants. Compositions of the invention also include plants or parts of tobacco plants, including a mutation in a gene encoding cyp82e10 nicotine demethylase, the mutation causing reduced expression or function of cyp82e10 necotine demethylase. Seeds of these tobacco plants, or progenies thereof, and tobacco products prepared from the tobacco plants of the invention, or from plant parts or their progenies, are also provided. Methods to reduce the level of nornicotine or to reduce the conversion rate of nicotine to nornicotine in a plant or part of a tobacco plant are also provided. The methods consist of introducing into the genome of a tobacco plant a mutation within at least one allele of each of the at least three nicotine demethylase genes, the mutation reducing expression of the nicotine demethylase gene, and a first These nicotine demethylase genes encode a root-specific nicotine demethylase that participates in the metabolic conversion of nicotine to nornicotine in a plant or part of a tobacco plant. The methods may be applied in the manufacture of tobacco products having reduced levels of nornicotine and its carcinogenic metabolite, nnn, and therefore reduced carcinogenic potential
