Codeinone Reductase Research Articles

RNAi-mediated replacement of morphine with the nonnarcotic alkaloid reticuline in opium poppy

We report on the silencing of codeinone reductase (COR) in the opium poppy, Papaver somniferum, using a chimeric hairpin RNA construct designed to silence all members of the multigene COR family through RNA interference (RNAi). After gene silencing, the precursor alkaloid (S)-reticuline-seven enzymatic steps upstream of codeinone-accumulated in transgenic plants at the expense of morphine, codeine, oripavine and thebaine. Methylated derivatives of reticuline also accumulated. Analysis verified loss of Cor gene transcript, appearance of 22-mer degradation products and reduction of enzyme activity. The surprising accumulation of (S)-reticuline suggests a feedback mechanism preventing intermediates from general benzylisoquinoline synthesis entering the morphine-specific branch. However transcript levels for seven other enzymes in the pathway, both before and after (S)-reticuline, were unaffected. This is the first report of gene silencing in transgenic opium poppy and of metabolic engineering to cause the high-yield accumulation of the nonnarcotic alkaloid reticuline.

The roles of latex and the vascular bundle in morphine biosynthesis in the opium poppy, Papaver somniferum.

The opium poppy, Papaver somniferum, is one of mankind's oldest medicinal plants. Opium poppy today is the commercial source of the narcotic analgesics morphine and codeine. Along with these two morphinans, opium poppy produces approximately eighty alkaloids belonging to various tetrahydrobenzylisoquinoline-derived classes. It has been known for over a century that morphinan alkaloids accumulate in the latex of opium poppy. With identification of many of the enzymes of alkaloid biosynthesis in this plant, biochemical data suggested involvement of multiple cell types in alkaloid biosynthesis in poppy. Herein the immunolocalization of five enzymes of alkaloid formation in opium poppy is reported: (R,S)-3'-hydroxy-N-methylcoclaurine 4'-O-methyltransferase central to the biosynthesis of tetrahydroisoquinoline-derived alkaloids, the berberine bridge enzyme of the sanguinarine pathway, (R,S)-reticuline 7-O-methyltransferase specific to laudanosine formation, and salutaridinol 7-O-acetyltransferase and codeinone reductase, which lead to morphine. In capsule and stem, both O-methyltransferases and the O-acetyltransferase are found predominantly in parenchyma cells within the vascular bundle, and codeinone reductase is localized to laticifers, the site of morphinan alkaloid accumulation. In developing root tip, both O-methyltransferases and the O-acetyltransferase are found in the pericycle of the stele, and the berberine bridge enzyme is localized to parenchyma cells of the root cortex. Laticifers are not found in developing root tip, and, likewise, codeinone reductase was not detected. These results provide cell-specific localization that gives a coherent picture of the spatial distribution of alkaloid biosynthesis in opium poppy.

A tale of three cell types: alkaloid biosynthesis is localized to sieve elements in opium poppy.

Opium poppy produces a diverse array of pharmaceutical alkaloids, including the narcotic analgesics morphine and codeine. The benzylisoquinoline alkaloids of opium poppy accumulate in the cytoplasm, or latex, of specialized laticifers that accompany vascular tissues throughout the plant. However, immunofluorescence labeling using affinity-purified antibodies showed that three key enzymes, (S)-N-methylcoclaurine 3'-hydroxylase (CYP80B1), berberine bridge enzyme (BBE), and codeinone reductase (COR), involved in the biosynthesis of morphine and the related antimicrobial alkaloid sanguinarine, are restricted to the parietal region of sieve elements adjacent or proximal to laticifers. The localization of laticifers was demonstrated using antibodies specific to the major latex protein (MLP), which is characteristic of the cell type. In situ hybridization showed that CYP80B1, BBE, and COR gene transcripts were found in the companion cell paired with each sieve element, whereas MLP transcripts were restricted to laticifers. The biosynthesis and accumulation of alkaloids in opium poppy involves cell types not implicated previously in plant secondary metabolism and dramatically extends the function of sieve elements beyond the transport of solutes and information macromolecules in plants.

Developmental and inducible accumulation of gene transcripts involved in alkaloid biosynthesis in opium poppy

Opium poppy (Papaver somniferum) produces a large number of benzylisoquinoline alkaloids, including morphine and sanguinarine, derived from tyrosine via the branch-point intermediate (S)-reticuline. Molecular clones for the three methlytransferases involved in (S)-reticuline biosynthesis, (S)-norcoclaurine-6-O-methyltransferase (6OMT), (S)-3′-hydroxy-N-methylcoclaurine-4′-O-methyltransferase (4′OMT), and (S)-coclaurine N-methyltransferase (CNMT), were isolated from opium poppy and shown to share extensive homology with the corresponding cDNAs from Japanese goldthread (Coptis japonica). These cDNAs were used together with previously isolated clones for tyrosine/dopa decarboxylase (TYDC), (S)-N-methylcoclaurine-3′-hydroxylase (CYP80B1), berberine bridge enzyme, (BBE), (7S)-salutaridinol 7-O-acetyltransferase (SAT), and codeinone reductase (COR), to compare the accumulation of gene transcripts encoding eight alkaloid biosynthetic enzymes in opium poppy. Transcript levels generally increased in developing seedlings and were consistently high in stems and flower buds, but were more variable in roots and leaves of mature plants. The accumulation of each transcript, with the exception of COR, showed a marked induction in response to elicitor treatment or wounding of cultured cells. Specific gene transcript levels often correlated with the accumulation of morphine or sanguinarine, with notable exceptions. Our data suggest some degree of coordination in the developmental and inducible regulation of alkaloid biosynthetic genes in opium poppy.

Molecular Characterization of the Salutaridinol 7-O-Acetyltransferase Involved in Morphine Biosynthesis in Opium Poppy Papaver somniferum

Salutaridinol 7-O-acetyltransferase (EC ) catalyzes the conversion of the phenanthrene alkaloid salutaridinol to salutaridinol-7-O-acetate, the immediate precursor of thebaine along the morphine biosynthetic pathway. We have isolated a cDNA clone that corresponds to the internal amino acid sequences of the native enzyme purified from a cell suspension culture of opium poppy Papaver somniferum. The recombinant enzyme acetylated the 7-hydroxyl moiety of salutaridinol in the presence of acetyl-CoA. The apparent K(m) value for salutaridinol was determined to be 9 microm and 54 microm for acetyl-CoA. The gene transcript was detected in extracts from Papaver orientale and Papaver bracteatum in addition to P. somniferum. Genomic DNA gel blot analysis indicated that there is likely a single copy of this gene in the P. somniferum genome. The amino acid sequence of salutaridinol 7-O-acetyltransferase is most similar (37% identity) to that of deacetylvindoline acetyltransferase of Catharanthus roseus. Salutaridinol 7-O-acetyltransferase is the second enzyme specific to morphine biosynthesis for which we have isolated a cDNA. Taken together with the other cDNAs cloned encoding norcoclaurine 6-O-methyltransferase, (S)-N-methylcoclaurine 3'-hydroxylase, the cytochrome P-450 reductase, and codeinone reductase, significant progress has been made toward accumulating genes of this pathway to enable the end goal of a biotechnological production of morphinan alkaloids.

Characterization of proteins in latex of the opium poppy (Papaver somniferum) using two-dimensional gel electrophoresis and microsequencing.

The opium poppy (Papaver somniferum) belongs to the group of latex-containing plants. Latex is the milky-like fluid within laticifer cells. In this study, poppy latex was analyzed with respect to ultrastructure, alkaloid, and protein content. The main goal of this project was the examination of the proteins by two-dimensional gel electrophoresis. In a proteomics approach, we investigated two main fractions of the latex, namely the cytosolic serum and the sedimented fraction containing the alkaloid-accumulating vesicles. Of the serum, representing the protein-rich part of the latex, 75 spots were analyzed by internal peptide microsequencing, followed by a database searching. For 69 proteins a function could be assigned due to homology to known proteins, whereas six spots could not be identified. Furthermore, codeinone reductase, a representative of the specific enzyme system in morphine biosynthesis, could be detected within the cytosolic serum fraction. In the vesicle-containing pellet, 23 protein spots were analyzed. An attempt was also made to separate the vesicle pellet by density centrifugation, followed by investigation of the alkaloid content, ultrastructure, and protein pattern. This study describes the first database of soluble proteins present in the latex of P. somniferum

Distribution of morphinan and benzo[ c]phenanthridine alkaloid gene transcript accumulation in Papaver somniferum

The opium poppy Papaver somniferum L. produces the antimicrobial benzo[ c]phenanthridine alkaloid sanguinarine and the narcotic analgesic morphinan alkaloid morphine. Transcripts of three genes of alkaloid biosynthesis in P. somniferum in developing seedlings, mature plants and plant cell suspension culture were monitored for temporal/spatial or for methyl jasmonate-induced accumulation by RNA gel blot analysis. These genes encoded ( S)- N-methylcoclaurine 3′-hydroxylase (CYP80B1) that is common to morphine and sanguinarine biosynthesis, the berberine bridge enzyme (BBE) that lies on the pathway to sanguinarine, and codeinone reductase (COR) the penultimate enzyme of morphine biosynthesis. In developing P. somniferum seedlings, the morphine precursor thebaine was present throughout the first twenty days of germination. In contrast, sanguinarine was present in detectable quantities only after day five after germination and continued to increase at least until day twenty. Accumulation of cyp80b1, bbe1 and cor1 gene transcripts paralleled these differences. In the mature poppy plant, cyp80b1, bbe1 and cor1 gene transcripts were detected in the root, the stem, the leaf lamina and the leaf mid rib. Only cyp80b1 and cor1, however, were found in the flower bud and the capsule. Consistent with the fact that sanguinarine accumulation, but not that of morphine, can be induced in opium poppy cell suspension culture by addition of methyl jasmonate to the culture medium, cyp80b1 and bbe1, but not cor1 transcript accumulated in response to elicitor treatment.