Gene 'knockout' floors tobacco carcinogen

Dewey and Lewis add that nothing else in the plant changed – growth or resistance to insects or disease, for example – after they knocked out this specific gene.

While Lewis believes that varieties of burley tobacco with a silenced demethylase gene will exist within the next few years, the NC State researchers say burley tobacco has a number of other targets for their gene silencing method.

The research is sponsored by Philip Morris USA.

Note to editors: An abstract of the paper follows.

"RNA Interference (RNAi)-Induced Suppression of Nicotine Demethylase Activity Reduces Levels of a Key Carcinogen in Cured Tobacco Leaves"
Authors: Ramsey S. Lewis and Ralph E. Dewey, North Carolina State University; Anne M. Jack, Lily Gavilano, Balazs Siminszky and Lowell Bush, University of Kentucky; Jerry Morris, Vincent Robert and Alec Hayes, Philip Morris USA
Published: Online Feb. 14 in Plant Biotechnology Journal

Abstract: 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.