Caffeine biosynthesis and adenine metabolism in transgenic Coffea canephora plants with reduced expression of N-methyltransferase genes

In anti-sense and RNA interference transgenic plants of Coffea canephora in which the expression of CaMXMT1 was suppressed, caffeine biosynthesis from [8-C-14]adenine was investigated, together with the overall metabolism of [8-C-14]adenine. Compared with wild type control plants, total purine alkaloid biosynthesis from adenine and conversion of theobromine to caffeine were both reduced in the transgenic plants. As found previously, [8-C-14]adenine was metabolised to salvage products (nucleotides and RNA), to degradation products (ureides and CO2) and to purine alkaloids (theobromine and caffeine). In the transgenic plants, metabolism of [8-C-14]adenine shifted from purine alkaloid synthesis to purine catabolism or salvage for nucleotides. HPLC analysis revealed a significantly reduced caffeine content in the transgenic plants. A small quantity (less than 20 nmol g(-1) fresh weight) of xanthosine had accumulated in at least one of the transgenic plants. (c) 2006 Elsevier Ltd. All rights reserved.