Molecular genetics of isoquinoline alkaloid biosynthesis in the opium poppy Papaver somniferum

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The opium poppy "Papaver somniferum" is still today one of our most important medicinal plants. Among the 80 alkaloids produced by this plant, three are medicinally important. These are the narcotic analgesic morphine, the analgesic and the antitussive codeine and the antitussive noscapine. The biosynthesis of codeine and morphine is almost completely elucidated at the enzyme level. Relatively little is understood, however, concerning the biosynthesis of noscapine. We also understand very little of how the alkaloid biosynthesis is regulated and of the biological role of these compounds in the plant. We are systematically isolating cDNAs that encode the unique enzymes of alkaloid biosynthesis in opium poppy. These cDNAs are functionally heterologously expressed in bacterial and insect cell cultures and characterized. We propose specifically herein to purify and partially sequence thebaine synthase of morphine biosynthesis, and to isolate the corresponding cDNA clone. We will also isolate cDNAs encoding methyltransferases specific to alkaloid biosynthesis in this plant. The seven cDNAs that we have isolated to date from "P. somniferum" will be used in situ hybridization and the encoded heterologous proteins in immunolocalization studies in order to identify the cellular sites of biosynthesis of some of the various classes of isoquinoline alkaloids (morphinan, benzo[c]phenanthridine, phtalideisoquinoline) produced by this plant. These results should provide the first insight as to how biosynthesis and accumulation of the various classes of these alkaloids is regulated in this plant.