Lewis Ramsey S, Jack Anne M, Morris Jerry W, Robert Vincent J M, Gavilano Lily B, Siminszky Balazs, Bush Lowell P, Hayes Alec J, Dewey Ralph E
Department of Crop Science, North Carolina State University, Raleigh, NC 27695, USA.
Plant Biotechnol J. 2008 May;6(4):346-54. doi: 10.1111/j.1467-7652.2008.00324.x. Epub 2008 Feb 14.
Technologies for reducing the levels of tobacco product constituents that may contribute to unwanted health effects are desired. Target compounds include tobacco-specific nitrosamines (TSNAs), a class of compounds generated through the nitrosation of pyridine alkaloids during the curing and processing of tobacco. Studies have reported the TSNA N'-nitrosonornicotine (NNN) to be carcinogenic in laboratory animals. NNN is formed via the nitrosation of nornicotine, a secondary alkaloid produced through enzymatic N-demethylation of nicotine. Strategies to lower nornicotine levels in tobacco (Nicotiana tabacum L.) could lead to a corresponding decrease in NNN accumulation in cured leaves. The major nicotine demethylase gene of tobacco has recently been isolated. In this study, a large-scale field trial was conducted to evaluate transgenic lines of burley tobacco carrying an RNA interference (RNAi) construct designed to inhibit the expression of this gene. Selected transgenic lines exhibited a six-fold decrease in nornicotine content relative to untransformed controls. Analysis of cured leaves revealed a commensurate decrease in NNN and total TSNAs. The inhibition of nicotine demethylase activity is an effective means of decreasing significantly the level of a key defined animal carcinogen present in tobacco products.
人们期望获得能够降低可能导致不良健康影响的烟草制品成分含量的技术。目标化合物包括烟草特有亚硝胺（TSNAs），这是一类在烟草调制和加工过程中由吡啶生物碱亚硝化产生的化合物。研究报告称，TSNA N'-亚硝基降烟碱（NNN）在实验动物中具有致癌性。NNN是由降烟碱亚硝化形成的，而降烟碱是尼古丁通过酶促N-去甲基化产生的一种仲生物碱。降低烟草（Nicotiana tabacum L.）中降烟碱水平的策略可能会导致烤烟叶中NNN积累相应减少。烟草的主要尼古丁去甲基化酶基因最近已被分离出来。在本研究中，进行了一项大规模田间试验，以评估携带旨在抑制该基因表达的RNA干扰（RNAi）构建体的白肋烟转基因株系。所选转基因株系的降烟碱含量相对于未转化对照降低了六倍。对烤烟叶的分析表明，NNN和总TSNAs含量相应降低。抑制尼古丁去甲基化酶活性是显著降低烟草制品中一种关键的已确定动物致癌物含量的有效手段。
