Biosynthesis and Catabolism of Purine Alkaloids

A limited number of plant species accumulate purine alkaloids, such as caffeine and theobromine, which are synthesized from xanthosine, a catabolite of purine nucleotides. The main biosynthetic pathway is a sequence consisting of xanthosine -> 7-methylxanthosine -> 7-methylxanthine -> theobromine -> caffeine. This review summarizes the occurrence of purine alkaloids in the plant kingdom, the caffeine biosynthesis routes from purine precursors, the enzymes and genes of N-methyltransferases, key enzymes of caffeine biosynthesis, caffeine catabolism and the possible ecological role of caffeine. Finally, we introduce transgenic plants in which caffeine production is either suppressed or induced by the introduction of caffeine encoded genes. Such plants have the potential to be used for the production of decaffeinated coffee and tea or as natural pesticides in agriculturally important crops.