Mechanisms of Molecular Regulation of Nicotine Biosynthesis

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Nicotine alkaloids are synthesized in the root of Nicotiana species, and their synthesis increases after insect attack, wounding and jasmonate treatment of the leaf. Putrescine N-methyltransferase (PMT) catalyzes the first committed step in nicotine biosynthesis. The expression patterns of the three Nicotiana sylvestris PMT genes (NsPMT1, NsPMT2, and NsPMT3) and of one Nicotiana sylvestris A622 gene are reported upon in this study. Transcripts of the NsPMT and A622 genes were detected only in the root, and were up-regulated by methyl jasmonate treatment. Ethylene antagonized the gene induction by jasmonate. When the 5'-flanking regions of NsPMT1, NsPMT2, NsPMT3 and A622 were fused independently to a β-glucuronidase reporter gene and introduced transgenes were expressed in the cortex, endodermis, and xylem in the root, as well as upregulated by methyl jasmonate treatment. These qualitatively similar patterns of expression for the NsPMT genes are achieved with only 0.25 kb of their 5'-flanking regions, which contain a short DNA sequence conserved among these four genes.