Biosynthetic Pathways of Purine and Pyridine Alkaloids in Coffee Plants

Caffeine (1,3,7-N-trimethylxanthine) and trigonelline (1N-methylnicotinic acid) are major alkaloids in coffee plants. The key enzymes involved in the biosynthesis of these compounds are very closely related N-methyltransferases belonging to the motif B' family of methyltransferases. The major biosynthetic pathways of caffeine and trigonelline are summarized in this review, including new evidence obtained from recombinant enzymes. In addition, precursor supply pathways are discussed with newly obtained results. Transgenic plants produced by the modification of the expression of N-methyltransferase genes are also introduced.