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The caffeine biosynthetic pathway in coffee plants has been proposed to involve three distinct N-methyltransferases, xanthosine methyltransferase (XMT), 7-N-methylxanthine methyltransferase (MXMT; theobromine synthase), and 3,7-dimethylxanthine methyltransferase (DXMT; caffeine synthase). We previously isolated all corresponding cDNAs designated as CaXMT1, CaMXMT1, CaMXMT2 and CaDXMT1, respectively, and showed that caffeine was indeed synthesized in vitro by the combination of their gene products. In order to regulate caffeine biosynthesis in planta, we suppressed expression of CaMXMT1 by the double stranded RNA interference (RNAi) method. For this purpose, we first established a protocol for efficient somatic embryogenesis of Coffea arabica and C. canephora, and then Agrobacterium-mediated transformation techniques. The RNAi transgenic lines of embryogenic tissues …