Compositions and methods for reducing the level of nornicotine and N&prime；-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.담배 식물 및 식물의 일부분에서 노르니코틴 및 N'-니트로소노르니코틴(NNN)의 수준을 낮추기 위한 조성물 및 방법을 제공한다. 상기 조성물은, 이들 식물에서 니코틴의 노르니코틴으로의 대사적 전환에 참여하는, 뿌리-특이적인 니코틴 탈메틸화 효소들, CYP82E10 및 이의 변이체에 대한 분리된 폴리뉴클레오티드 및 폴리펩타이드를 포함한다. 또한, 본 발명의 조성물은, CYP82E10 니코틴 탈메틸화 효소를 코딩하는 유전자에 돌연변이를 포함하는, 담배 식물 또는 이 식물의 일부를 포함
