Short-chain dehydrogenase/reductase catalyzing the final step of noscapine biosynthesis is localized to laticifers in opium poppy

Metabolomics and transcriptomics reveal the mechanism of alkaloid synthesis in Corydalis yanhusuo bulbs

Corydalis yanhusuo W.T. Wang is a traditional herb. Benzylisoquinoline alkaloids (BIAs) are the main pharmacological active ingredients that play an important role in sedation, relieving pain, promoting blood circulation, and inhibiting cancer cells. However, there are few studies on the biosynthetic pathway of benzylisoquinoline alkaloids in Corydalis yanhusuo, especially on some specific components, such as tetrahydropalmatine. We carried out widely targeted metabolome and transcriptomic analyses to construct the biosynthetic pathway of benzylisoquinoline alkaloids and identified candidate genes. In this study, 702 metabolites were detected, including 216 alkaloids. Protoberberine-type and aporphine-type alkaloids are the main chemical components in C. yanhusuo bulbs. Key genes for benzylisoquinoline alkaloids biosynthesis, including 6-OMT, CNMT, NMCH, BBE, SOMT1, CFS, SPS, STOX, MSH, TNMT and P6H, were successfully identified. There was no significant difference in the content of benzylisoquinoline alkaloids and the expression level of genes between the two suborgans (mother-bulb and son-bulb). The expression levels of BIA genes in the expansion stage (MB-A and SB-A) were significantly higher than those in the maturity stage (MB-C and SB-C), and the content of benzylisoquinoline alkaloids was consistent with the pattern of gene regulation. Five complete single genes were likely to encode the functional enzyme of CoOMT, which participated in tetrahydropalmatine biosynthesis in C. yanhusuo bulbs. These studies provide a strong theoretical basis for the subsequent development of metabolic engineering of benzylisoquinoline alkaloids (especially tetrahydropalmatine) of C. yanhusuo.

Phloem-specific localization of benzylisoquinoline alkaloid metabolism in opium poppy

Opium poppy is the only commercial source of the narcotic analgesics morphine and codeine, and semi-synthetic derivatives of the natural opiate precursor thebaine, including oxycodone and the opioid antagonist naloxone. The plant also accumulates the vasodilator and antitussive agents papaverine and noscapine, respectively, which together with morphine, codeine and thebaine comprise the major benzylisoquinoline alkaloids (BIAs) in opium poppy. A majority of enzymes involved in the highly branched BIA metabolism in opium poppy have now been discovered, with many specifically localized to sieve elements of the phloem based on immunofluorescence labeling techniques. Transcripts corresponding to sieve element-localized biosynthetic enzymes were detected in companion cells, as expected. The more recent application of shotgun proteomics has shown that several enzymes operating late in the morphine and noscapine biosynthetic pathways occur primarily in laticifers that are adjacent or proximal to sieve elements. BIA biosynthesis and accumulation in opium poppy involves three phloem cell types and implicates the translocation of key pathway intermediates between sieve elements and laticifers. The recent isolation of uptake transporters associated with laticifers supports an apoplastic rather than a symplastic route for translocation. In spite of the extensive elucidation of BIA biosynthetic enzymes in opium poppy, additional transporters and other auxiliary proteins are clearly necessary to support the complex spatial organization and dynamics involved in product formation and sequestration. In this review, we provide an update of BIA metabolism in opium poppy with a focus on the role of phloem in the biosynthesis of the major alkaloids.

Biosynthesis and synthetic biology of psychoactive natural products

Psychoactive natural products play an integral role in the modern world. The tremendous structural complexity displayed by such molecules confers diverse biological activities of significant medicinal value and sociocultural impact. Accordingly, in the last two centuries, immense effort has been devoted towards establishing how plants, animals, and fungi synthesize complex natural products from simple metabolic precursors. The recent explosion of genomics data and molecular biology tools has enabled the identification of genes encoding proteins that catalyze individual biosynthetic steps. Once fully elucidated, the "biosynthetic pathways" are often comparable to organic syntheses in elegance and yield. Additionally, the discovery of biosynthetic enzymes provides powerful catalysts which may be repurposed for synthetic biology applications, or implemented with chemoenzymatic synthetic approaches. In this review, we discuss the progress that has been made toward biosynthetic pathway elucidation amongst four classes of psychoactive natural products: hallucinogens, stimulants, cannabinoids, and opioids. Compounds of diverse biosynthetic origin - terpene, amino acid, polyketide - are identified, and notable mechanisms of key scaffold transforming steps are highlighted. We also provide a description of subsequent applications of the biosynthetic machinery, with an emphasis placed on the synthetic biology and metabolic engineering strategies enabling heterologous production.

Benzylisoquinoline alkaloid analysis using high-resolution Orbitrap LC-MSn

Benzylisoquinoline alkaloids (BIAs) have profound implications on human health owing to their potent pharmacological properties. Notable naturally occurring BIAs are the narcotic analgesics morphine, the cough suppressant codeine, the potential anticancer drug noscapine, the muscle relaxant papaverine, and the antimicrobial sanguinarine, all of which are produced in opium poppy (Papaver somniferum). Thebaine, an intermediate in the biosynthesis of codeine and morphine, is used in the manufacture of semisynthetic opiates, including oxycodone and naloxone. As the only commercial source of pharmaceutical opiates, opium poppy has been the focus of considerable research to understand BIA metabolism in the plant. The elucidation of several BIA biosynthetic pathways has enabled the development of synthetic biology platforms aimed at the alternative commercial production of valuable phytochemicals in microorganisms. The detection and identification of BIA pathway products and intermediates in complex extracts is essential for the continuing advancement of research in plant specialized metabolism and microbial synthetic biology. Herein, we report the use of liquid chromatography coupled with linear trap quadrupole and high-resolution Orbitrap multistage mass spectrometry to characterize 44 authentic BIAs using collision-induced dissociation (CID), higher-energy collisional dissociation (HCD), and pulsed Q collision-induced dissociation (PQD) MS² fragmentation, with MS² CID followed by MS³ and MS⁴ fragmentation. Our deep library of diagnostic spectral data constitutes a valuable resource for BIAs identification. In addition, we identified 22 BIAs in opium poppy latex and roots extracts.

An integrated strategy to identify genes responsible for sesquiterpene biosynthesis in turmeric

Metabolic module, gene expression pattern and PLS modeling were integrated to precisely identify the terpene synthase responsible for sesquiterpene formation. Functional characterization confirmed the feasibility and sensitivity of this strategy. Plant secondary metabolite biosynthetic pathway elucidation is crucial for the production of these compounds with metabolic engineering. In this study, an integrated strategy was employed to predict the gene function of sesquiterpene synthase (STS) genes using turmeric as a model. Parallel analysis of gene expression patterns and metabolite modules narrowed the candidates into an STS group in which the STSs showed a similar expression pattern. The projections to latent structures by means of partial least squares model was further employed to establish a clear relationship between the candidate STS genes and metabolites and to predict three STSs (ClTPS16, ClTPS15 and ClTPS14) involved in the biosynthesis of several sesquiterpene skeletons. Functional characterization revealed that zingiberene and β-sesquiphellandrene were the major products of ClTPS16, and β-eudesmol was produced by ClTPS15, both of which indicated the accuracy of the prediction. Functional characterization of a control STS, ClTPS1, produced a small amount of β-sesquiphellandrene, as predicted, which confirmed the sensitivity of metabolite module analysis. This integrated strategy provides a methodology for gene function predictions, which represents a substantial improvement in the elucidation of biosynthetic pathways in nonmodel plants.

A Hedychium coronarium short chain alcohol dehydrogenase is a player in allo-ocimene biosynthesis

An enzyme is crucial for the formation of Hedychium coronarium scent and defense responses, which may be responsible for the biosynthesis of allo-ocimene in H. coronarium. Hedychium coronarium can emit a strong scent as its main scent constituents are monoterpenes and their derivatives. Among these derivatives, allo-ocimene is not only a very important volatile substance in flower aroma, but is also crucial to plant defense. However, the molecular mechanism of allo-ocimene biosynthesis has not been characterized in plants. In this study, a new alcohol dehydrogenase gene, HcADH, was cloned. The amino acid sequences encoded by HcADH contained the most conserved motifs of short chain alcohol dehydrogenase/reductases (SDRs), which included NAD⁺ binding domain, TGxxx[AG]xG and active site YxxxK. Real-time PCR analyses showed that the HcADH was highly expressed in the outer labellum but was almost undetectable in vegetative organs. The change in its expression level in petals was positively correlated with the emission pattern of allo-ocimene during flower development. HcADH expression coincides also the release level of allo-ocimene among different Hedychium species. Although HcADH is not expressed in the leaves, HcADH expression and allo-ocimene release in leaves can be induced by mechanical wounding or methyl jasmonate (MeJA) treatment. In addition, the expression of HcADH induced by mechanical wounding can be prevented by acetylsalicylic acid, a jasmonic acid biosynthesis inhibitor, suggesting that jasmonic acid might participate in the transmission of wounding signals. Using the Barley stripe mosaic virus (BSMV)-VIGS method, it was found that BSMV:HcADH₃₃₅ inoculation was able to down-regulate HcADH expression, decreasing only the release of allo-ocimene in flowers while the content of other volatile substances did not decrese. In vitro characterization showed that recombinant HcADH can catalyze geraniol into citral, and citral is an intermediate of allo-ocimene biosynthesis. HcADH may be responsible for the biosynthesis of allo-ocimene in H. coronarium, which is crucial for the formation of H. coronarium scent and defense function.

Comparative analysis of the root and leaf transcriptomes in Chelidonium majus L

Chelidonium majus is a traditional medicinal plant, which commonly known as a rich resource for the major benzylisoquinoline alkaloids (BIAs), including morphine, sanguinarine, and berberine. To understand the biosynthesis of C. majus BIAs, we performed de novo transcriptome sequencing of its leaf and root tissues using Illumina technology. Following comprehensive evaluation of de novo transcriptome assemblies produced with five programs including Trinity, Bridger, BinPacker, IDBA-tran, and Velvet/Oases using a series of k-mer sizes (from 25 to 91), BinPacker was found to produce the best assembly using a k-mer of 25. This study reports the results of differential gene expression (DGE), functional annotation, gene ontology (GO) analysis, classification of transcription factor (TF)s, and SSR and miRNA discovery. Our DGE analysis identified 6,028 transcripts that were up-regulated in the leaf, and 4,722 transcripts that were up-regulated in the root. Further investigations showed that most of the genes involved in the BIA biosynthetic pathway are significantly expressed in the root compared to the leaf. GO analysis showed that the predominant GO domain is "cellular component", while TF analysis found bHLH to be the most highly represented TF family. Our study further identified 10 SSRs, out of a total of 39,841, that showed linkage to five unigenes encoding enzymes in the BIA pathway, and 10 conserved miRNAs that were previously not detected in this plant. The comprehensive transcriptome information presented herein provides a foundation for further explorations on study of the molecular mechanisms of BIA synthesis in C. majus.

Heterodimeric O-methyltransferases involved in the biosynthesis of noscapine in opium poppy

Noscapine biosynthesis in opium poppy involves three characterized O-methyltransferases (OMTs) and a fourth responsible for the 4'-methoxyl on the phthalide isoquinoline scaffold. The first three enzymes are homodimers, whereas the latter is a heterodimer encoded by two linked genes (OMT2 and OMT3). Neither OMT2 nor OMT3 form stable homodimers, but yield a substrate-specific heterodimer when their genes are co-expressed in Escherichia coli. The only substrate, 4'-O-desmethyl-3-O-acetylpapaveroxine, is a seco-berbine pathway intermediate that undergoes ester hydrolysis subsequent to 4'-O-methylation leading to the formation of narcotine hemiacetal. In the absence of 4'-O-methylation, a parallel pathway yields narcotoline hemiacetal. Dehydrogenation produces noscapine and narcotoline from the corresponding hemiacetals. Phthalide isoquinoline intermediates with a 4'-hydroxyl (i.e. narcotoline and narcotoline hemiacetal), or the corresponding 1-hydroxyl on protoberberine intermediates, were not accepted. Norcoclaurine 6OMT, which shares 81% amino acid sequence identity with OMT3, also formed a functionally similar heterodimer with OMT2. Suppression of OMT2 transcript levels in opium poppy increased narcotoline accumulation, whereas reduced OMT3 transcript abundance caused no detectable change in the alkaloid phenotype. Opium poppy chemotype Marianne accumulates high levels of narcotoline and showed no detectable OMT2:OMT3 activity. Compared with the active subunit from the Bea's Choice chemotype, Marianne OMT2 exhibited a single S122Y mutation in the dimerization domain that precluded heterodimer formation based on homology models. Both subunits contributed to the formation of the substrate-binding domain, although site-directed mutagenesis revealed OMT2 as the active subunit. The occurrence of physiologically relevant OMT heterodimers increases the catalytic diversity of enzymes derived from a smaller number of gene products.

Short-chain dehydrogenase/reductase governs steroidal specialized metabolites structural diversity and toxicity in the genus Solanum

Thousands of specialized, steroidal metabolites are found in a wide spectrum of plants. These include the steroidal glycoalkaloids (SGAs), produced primarily by most species of the genus Solanum, and metabolites belonging to the steroidal saponins class that are widespread throughout the plant kingdom. SGAs play a protective role in plants and have potent activity in mammals, including antinutritional effects in humans. The presence or absence of the double bond at the C-5,6 position (unsaturated and saturated, respectively) creates vast structural diversity within this metabolite class and determines the degree of SGA toxicity. For many years, the elimination of the double bond from unsaturated SGAs was presumed to occur through a single hydrogenation step. In contrast to this prior assumption, here, we show that the tomato GLYCOALKALOID METABOLISM25 (GAME25), a short-chain dehydrogenase/reductase, catalyzes the first of three prospective reactions required to reduce the C-5,6 double bond in dehydrotomatidine to form tomatidine. The recombinant GAME25 enzyme displayed 3β-hydroxysteroid dehydrogenase/Δ^5,4 isomerase activity not only on diverse steroidal alkaloid aglycone substrates but also on steroidal saponin aglycones. Notably, GAME25 down-regulation rerouted the entire tomato SGA repertoire toward the dehydro-SGAs branch rather than forming the typically abundant saturated α-tomatine derivatives. Overexpressing the tomato GAME25 in the tomato plant resulted in significant accumulation of α-tomatine in ripe fruit, while heterologous expression in cultivated eggplant generated saturated SGAs and atypical saturated steroidal saponin glycosides. This study demonstrates how a single scaffold modification of steroidal metabolites in plants results in extensive structural diversity and modulation of product toxicity.

The effects of promoter variations of the N-Methylcanadine 1-Hydroxylase (CYP82Y1) gene on the noscapine production in opium poppy

Noscapine is an antitumor alkaloid produced in opium poppy (Papaver somniferum) and some members of the Papaveraceae family. It has been primarily used for its antitussive effects; more recently, its anticancer properties were shown. Herein, we detected an SSR embedded in the promoter region of the CYP82Y1 gene, which was found to be the first committed-step enzyme in the noscapine biosynthesis pathway, using the MISA program. Some collected ecotypes of P. somniferum were investigated for understanding of SSRs role in the regulation of gene expression and metabolite content. Quantitative PCR showed that a variation in the motif repeat number (either a decrease or increase) down-regulated the expression of the CYP82Y1 gene. Furthermore, the analysis of noscapine content suggested that a variation in the promoter region influence noscapine amount. Moreover, P. bracteatum was analyzed in both transcript and metabolite levels, and illustrated much less expression and metabolite level in comparison to P. somniferum. By exploiting the transcriptome data from the eight genera of the Papaveraceae family, we found that noscapine biosynthesis genes are present in P. bracteatum and are not shared in other genera of the Papaveraceae family. This results may explain production of a confined metabolite within a genus.

Integrated omics analysis of specialized metabolism in medicinal plants

Medicinal plants are a rich source of highly diverse specialized metabolites with important pharmacological properties. Until recently, plant biologists were limited in their ability to explore the biosynthetic pathways of these metabolites, mainly due to the scarcity of plant genomics resources. However, recent advances in high-throughput large-scale analytical methods have enabled plant biologists to discover biosynthetic pathways for important plant-based medicinal metabolites. The reduced cost of generating omics datasets and the development of computational tools for their analysis and integration have led to the elucidation of biosynthetic pathways of several bioactive metabolites of plant origin. These discoveries have inspired synthetic biology approaches to develop microbial systems to produce bioactive metabolites originating from plants, an alternative sustainable source of medicinally important chemicals. Since the demand for medicinal compounds are increasing with the world's population, understanding the complete biosynthesis of specialized metabolites becomes important to identify or develop reliable sources in the future. Here, we review the contributions of major omics approaches and their integration to our understanding of the biosynthetic pathways of bioactive metabolites. We briefly discuss different approaches for integrating omics datasets to extract biologically relevant knowledge and the application of omics datasets in the construction and reconstruction of metabolic models.

Engineering biosynthesis of the anticancer alkaloid noscapine in yeast

Noscapine is a potential anticancer drug isolated from the opium poppy Papaver somniferum, and genes encoding enzymes responsible for the synthesis of noscapine have been recently discovered to be clustered on the genome of P. somniferum. Here, we reconstitute the noscapine gene cluster in Saccharomyces cerevisiae to achieve the microbial production of noscapine and related pathway intermediates, complementing and extending previous in planta and in vitro investigations. Our work provides structural validation of the secoberberine intermediates and the description of the narcotoline-4'-O-methyltransferase, suggesting this activity is catalysed by a unique heterodimer. We also reconstitute a 14-step biosynthetic pathway of noscapine from the simple alkaloid norlaudanosoline by engineering a yeast strain expressing 16 heterologous plant enzymes, achieving reconstitution of a complex plant pathway in a microbial host. Other engineered yeasts produce previously inaccessible pathway intermediates and a novel derivative, thereby advancing protoberberine and noscapine related drug discovery.

Comparative analysis of transcription factor gene families from Papaver somniferum: identification of regulatory factors involved in benzylisoquinoline alkaloid biosynthesis

Opium poppy (Papaver somniferum L.), known for biosynthesis of several therapeutically important benzylisoquinoline alkaloids (BIAs), has emerged as the premier organism to study plant alkaloid metabolism. The most prominent molecules produced in opium poppy include narcotic analgesic morphine, the cough suppressant codeine, the muscle relaxant papaverine and the anti-microbial agent sanguinarine and berberine. Despite several health benefits, biosynthesis of some of these molecules is very low due to tight temporal and spatial regulation of the genes committed to their biosynthesis. Transcription factors, one of the prime regulators of secondary plant product biosynthesis, might be involved in controlled biosynthesis of BIAs in P. somniferum. In this study, identification of members of different transcription factor gene families using transcriptome datasets of 10 cultivars of P. somniferum with distinct chemoprofile has been carried out. Analysis suggests that most represented transcription factor gene family in all the poppy cultivars is WRKY. Comparative transcriptome analysis revealed differential expression pattern of the members of a set of transcription factor gene families among 10 cultivars. Through analysis, two members of WRKY and one member of C3H gene family were identified as potential candidates which might regulate thebaine and papaverine biosynthesis, respectively, in poppy.

Identification and expression analyses of MYB and WRKY transcription factor genes in Papaver somniferum L

Papaver somniferum L. is an herbaceous, annual and diploid plant that is important from pharmacological and strategic point of view. The cDNA clones of two putative MYB and WRKY genes were isolated (GeneBank accession numbers KP411870 and KP203854, respectively) from this plant, via the nested-PCR method, and characterized. The MYB transcription factor (TF) comprises 342 amino acids, and exhibits the structural features of the R2R3MYB protein family. The WRKY TF, a 326 amino acid-long polypeptide, falls structurally into the group II of WRKY protein family. Quantitative real-time PCR (qRT-PCR) analyses indicate the presence of these TFs in all organs of P. somniferum L. and Papaver bracteatum L. Highest expression levels of these two TFs were observed in the leaf tissues of P. somniferum L. while in P. bracteatum L. the espression levels were highest in the root tissues. Promoter analysis of the 10 co-expressed gene clustered involved in noscapine biosynthesis pathway in P. somniferum L. suggested that not only these 10 genes are co-expressed, but also share common regulatory motifs and TFs including MYB and WRKY TFs, and that may explain their common regulation.

The Noscapine Chronicle: A Pharmaco-Historic Biography of the Opiate Alkaloid Family and its Clinical Applications

Given its manifold potential therapeutic applications and amenability to modification, noscapine is a veritable "Renaissance drug" worthy of commemoration. Perhaps the only facet of noscapine's profile more astounding than its versatility is its virtual lack of side effects and addictive properties, which distinguishes it from other denizens of Papaver somniferum. This review intimately chronicles the rich intellectual and pharmacological history behind the noscapine family of compounds, the length of whose arms was revealed over decades of patient scholarship and experimentation. We discuss the intriguing story of this family of nontoxic alkaloids, from noscapine's purification from opium at the turn of the 19th century in Paris to the recent torrent of rationally designed analogs with tremendous anticancer potential. In between, noscapine's unique pharmacology; impact on cellular signaling pathways, the mitotic spindle, and centrosome clustering; use as an antimalarial drug and cough suppressant; and exceptional potential as a treatment for polycystic ovarian syndrome, strokes, and diverse malignancies are catalogued. Seminal experiments involving some of its more promising analogs, such as amino-noscapine, 9-nitronoscapine, 9-bromonoscapine, and reduced bromonoscapine, are also detailed. Finally, the bright future of these oftentimes even more exceptional derivatives is described, rounding out a portrait of a truly remarkable family of compounds.

Unlocking the diversity of alkaloids in Catharanthus roseus: nuclear localization suggests metabolic channeling in secondary metabolism

The extraordinary chemical diversity of the plant-derived monoterpene indole alkaloids, which include vinblastine, quinine, and strychnine, originates from a single biosynthetic intermediate, strictosidine aglycone. Here we report for the first time the cloning of a biosynthetic gene and characterization of the corresponding enzyme that acts at this crucial branchpoint. This enzyme, an alcohol dehydrogenase homolog, converts strictosidine aglycone to the heteroyohimbine-type alkaloid tetrahydroalstonine. We also demonstrate how this enzyme, which uses a highly reactive substrate, may interact with the upstream enzyme of the pathway.

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Tetrahydroalstonine synthase catalyzes the formation of a plant-derived alkaloid

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Tetrahydroalstonine synthase is localized to the nucleus

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Tetrahydroalstonine synthase and the preceding pathway enzyme interact

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Discovery of a gene controlling structural diversity of monoterpene indole alkaloids

Noscapine comes of age

Noscapine is a phthalideisoquinoline alkaloid, which represents a class of plant specialized metabolites within the large and structurally diverse group of benzylisoquinoline alkaloids. Along with the narcotic analgesic morphine, noscapine is a major alkaloid in the latex of opium poppy (Papaver somniferum) that has long been used as a cough suppressant and has undergone extensive investigation as a potential anticancer drug. Cultivated opium poppy plants remain the only commercial source of noscapine. Despite its isolation from opium more than two centuries ago, the almost complete biosynthesis of noscapine has only recently been established based on an impressive combination of molecular genetics, functional genomics, and metabolic biochemistry. In this review, we provide a historical account of noscapine from its discovery through to initial investigations of its formation in opium poppy. We also describe recent breakthroughs that have led to an elucidation of the noscapine biosynthetic pathway, and we discuss the pharmacological properties that have prompted intensive evaluation of the potential pharmaceutical applications of noscapine and several semi-synthetic derivatives. Finally, we speculate on the future potential for the production of noscapine using metabolic engineering and synthetic biology in plants and microbes.

Acetylation serves as a protective group in noscapine biosynthesis in opium poppy

We have characterized four sequential enzymes that transform 1-hydroxy-N-methylcanadine to narcotoline hemiacetal, completing our elucidation of noscapine biosynthesis in opium poppy. Two cytochromes P450 catalyze hydroxylations at C13 and C8 on the protoberberine scaffold, the latter step inducing ring opening and the formation of an aldehyde moiety. Acetylation at C13 before C8 hydroxylation introduces a protective group subsequently hydrolyzed by a carboxylesterase, which triggers rearrangement to a cyclic hemiacetal.

Benzylisoquinoline alkaloid biosynthesis in opium poppy

Opium poppy (Papaver somniferum) is one of the world's oldest medicinal plants and remains the only commercial source for the narcotic analgesics morphine, codeine and semi-synthetic derivatives such as oxycodone and naltrexone. The plant also produces several other benzylisoquinoline alkaloids with potent pharmacological properties including the vasodilator papaverine, the cough suppressant and potential anticancer drug noscapine and the antimicrobial agent sanguinarine. Opium poppy has served as a model system to investigate the biosynthesis of benzylisoquinoline alkaloids in plants. The application of biochemical and functional genomics has resulted in a recent surge in the discovery of biosynthetic genes involved in the formation of major benzylisoquinoline alkaloids in opium poppy. The availability of extensive biochemical genetic tools and information pertaining to benzylisoquinoline alkaloid metabolism is facilitating the study of a wide range of phenomena including the structural biology of novel catalysts, the genomic organization of biosynthetic genes, the cellular and sub-cellular localization of biosynthetic enzymes and a variety of biotechnological applications. In this review, we highlight recent developments and summarize the frontiers of knowledge regarding the biochemistry, cellular biology and biotechnology of benzylisoquinoline alkaloid biosynthesis in opium poppy.

CYP82Y1 is N-methylcanadine 1-hydroxylase, a key noscapine biosynthetic enzyme in opium poppy

Noscapine is a phthalideisoquinoline alkaloid investigated for its potent pharmacological properties. Although structurally elucidated more than a century ago, the biosynthesis of noscapine has not been established. Radiotracer studies have shown that noscapine is derived from the protoberberine alkaloid (S)-scoulerine and has been proposed to proceed through (S)-N-methylcanadine. However, pathway intermediates involved in the conversion of N-methylcanadine to noscapine have not been identified. We report the isolation and characterization of the cytochrome P-450 CYP82Y1, which catalyzes the 1-hydroxylation of N-methylcanadine to 1-hydroxy-N-methylcanadine. Comparison of transcript and metabolite profiles of eight opium poppy chemotypes revealed four cytochrome P-450s, three from the CYP82 and one from the CYP719 families, that were tightly correlated with noscapine accumulation. Recombinant CYP82Y1 was the only enzyme that accepted (R,S)-N-methylcanadine as a substrate with strict specificity and high affinity. As expected, CYP82Y1 was abundantly expressed in opium poppy stems where noscapine accumulation is highest among plant organs. Suppression of CYP82Y1 using virus-induced gene silencing caused a significant reduction in the levels of noscapine, narcotoline, and a putative downstream secoberbine intermediate and also resulted in increased accumulation of the upstream pathway intermediates scoulerine, tetrahydrocolum-bamine, canadine, and N-methylcanadine. The combined biochemical and physiological data support the 1-hydroxylation of (S)-N-methylcanadine catalyzed by CYP82Y1 as the first committed step in the formation of noscapine in opium poppy.