Biosynthesis and catabolism of caffeine in low-caffeine-containing species of Coffea

Leaves of Coffea salvatrix, Coffea eugenioides, and C. bengalensis contain similar to 3-7-fold lower levels of caffeine than those of Coffea arabica. There was more extensive biosynthesis of caffeine from [8-C-14]-adenine in young leaves of C. arabica than in C. salvatrix, C. eugenioides, and C. bengalensis. Degradation of [8-C-14]caffeine, which is negligible in leaves of C. arabica, was also very slow in C. salvatrix and C. bengalensis. In contrast, [8-C-14]caffeine was catabolized rapidly by young and mature leaves of C. eugenioides primarily by a caffeine --> theophylline --> 3-methylxanthine --> xanthine --> uric acid --> allantoin --> allantoic acid --> urea --> CO2 + NH3 pathway. These results indicate that the low caffeine accumulation in C. salvatrix, C. eugenioides, and C. bengalensis is a consequence of a slow rate of caffeine biosynthesis, whereas rapid degradation of caffeine also contributes to the low endogenous caffeine pool in C, eugenioides. The genes that regulate caffeine accumulation appear to be those encoding N-methyltransferase and caffeine (7-N) demethylase activities. The diversity of caffeine catabolism observed in C, arabica, C. salvatrix, C. eugenioides, and C. bengalensis, other species of Coffea, and Camellia sinensis is discussed.