Generation of tobacco lines with widely different reduction in nicotine levels via RNA silencing approaches

Issues related to the nicotine content of tobacco have been public concerns. Several reports have described decreasing nicotine levels by silencing the putrescine N-methyltransferase (PMT) genes, but the reported variations of nicotine levels among transgenic lines are relatively low in general. Here we describe the generation in tobacco (Nicotiana tabacum) lines with widely different, reduced nicotine levels using three kinds of RNA-silencing approaches. The relative efficacies of suppression were compared among the three approaches regarding the aspect of nicotine level in tobacco leaves. By suppressing expression of the PMT genes, over 200 transgenic lines were obtained with nicotine levels reduced by 9.1-96.7%. RNA interference (RNAi) was the most efficient method of reducing the levels of nicotine, whereas cosuppression and antisense methods were less effective. This report gives clues to the efficient generation of plants with a variety of metabolite levels, and the results demonstrate the relative efficiencies of various RNA-silencing methods.