Increased nicotianamine biosynthesis confers enhanced tolerance of high levels of metals, in particular nickel, to plants

Nicotianamine, a plant-derived chelator of metals, is produced by the trimerization of S-adenosylmethionine catalyzed by nicotianamine synthase. We established transgenic Arabidopsis and tobacco plants that constitutively overexpress the barley nicotianamine synthase gene. Nicotianamine synthase overexpression resulted in increased biosynthesis of nicotianamine in transgenic plants, which conferred enhanced tolerance of high levels of metals, particularly nickel, to plants. Promoter activities of four nicotianamine synthase genes in Arabidopsis were all increased in response to excess nickel, suggesting that nicotianamine plays an important role in the detoxification of nickel in plants. Furthermore, transgenic tobacco plants with a high level of nicotianamine grew well in a nickel-enriched serpentine soil without developing any symptoms of nickel toxicity. Our results indicate that nicotianamine plays a critical role in metal detoxification, and this can be a powerful tool for use in phytoremediation.