Compositions and methods for reducing the level of
nornicotine and N′-nitrosonornicotine (NNN) in tobacco plants and
plant parts thereof are provided. The compositions comprise isolated polynucleotides and polypeptides for a root-specific
nicotine demethylases, CYP82E10, and variants thereof, that are involved in the
metabolic conversion of
nicotine to
nornicotine in these plants. Compositions of the invention also include tobacco plants, or
plant parts thereof, comprising a
mutation in a
gene encoding a CYP82E10
nicotine demethylase, wherein the
mutation results in reduced expression or function of the CYP82E10 nicotine
demethylase. Seed of these tobacco plants, or progeny thereof, and tobacco products prepared from the tobacco plants of the invention, or from
plant parts or progeny thereof, are also provided. Methods for reducing the level of
nornicotine, or reducing the rate of conversion of nicotine to nornicotine, in a tobacco plant, or
plant part thereof are also provided. The methods comprise introducing into the
genome of a tobacco plant a
mutation within at least one
allele of each of at least three nicotine
demethylase genes, wherein the mutation reduces expression of the nicotine demethylase
gene, and wherein a first of these nicotine demethylase genes encodes a root-specific nicotine demethylase involved in the
metabolic conversion of nicotine to nornicotine in a tobacco plant or a
plant part thereof. The methods find use in the production of tobacco products that have reduced levels of nornicotine and its carcinogenic
metabolite, NNN, and thus reduced carcinogenic potential for individuals consuming these tobacco products or exposed to secondary
smoke derived from these products.