Transcriptome and Metabolome Analysis of Isoquinoline Alkaloid Biosynthesis of Coptis chinensis in Different Years

Coptis chinensis is a perennial herb of the Ranunculaceae family. The isoquinoline alkaloid is the main active component of C. chinensis, mainly exists in its rhizomes and has high clinical application potential. The in vitro synthesis of isoquinoline alkaloids is difficult because their structures are complex; hence, plants are still the main source of them. In this study, two-year and four-year rhizomes of C. chinensis were selected to investigate the effect of growth years on the accumulation of isoquinoline alkaloids. Two-year and four-year C. chinensis were selected for metabolomics detection and transcriptomic analysis. A total of 413 alkaloids were detected by metabolomics analysis, of which 92 were isoquinoline alkaloids. (S)-reticuline was a significantly different accumulated metabolite of the isoquinoline alkaloids biosynthetic pathway in C. chinensis between the two groups. The results of transcriptome analysis showed that a total of 464 differential genes were identified, 36 of which were associated with the isoquinoline alkaloid biosynthesis pathway of C. chinensis. Among them, 18 genes were correlated with the content of important isoquinoline alkaloids. Overall, this study provided a comprehensive metabolomic and transcriptomic analysis of the rapid growth stage of C. chinensis rhizome from the perspective of growth years. It brought new insights into the biosynthetic pathway of isoquinoline alkaloids and provided information for utilizing biotechnology to improve their contents in C. chinensis.

Coptisine, the Characteristic Constituent from Coptis chinensis, Exhibits Significant Therapeutic Potential in Treating Cancers, Metabolic and Inflammatory Diseases

Naturally derived alkaloids belong to a class of quite significant organic compounds. Coptisine, a benzyl tetrahydroisoquinoline alkaloid, is one of the major bioactive constituents in Coptis chinensis Franch., which is a famous traditional Chinese medicine. C. chinensis possesses many kinds of functions, including the ability to eliminate heat, expel dampness, purge fire, and remove noxious substances. In Asian countries, C. chinensis is traditionally employed to treat carbuncle and furuncle, diabetes, jaundice, stomach and intestinal disorders, red eyes, toothache, and skin disorders. Up to now, there has been plenty of research of coptisine with respect to its pharmacology. Nevertheless, a comprehensive review of coptisine-associated research is urgently needed. This paper was designed to summarize in detail the progress in the research of the pharmacology, pharmacokinetics, safety, and formulation of coptisine. The related studies included in this paper were retrieved from the following academic databases: The Web of Science, PubMed, Google scholar, Elsevier, and CNKI. The cutoff date was January 2023. Coptisine manifests various pharmacological actions, including anticancer, antimetabolic disease, anti-inflammatory disease, and antigastrointestinal disease effects, among others. Based on its pharmacokinetics, the primary metabolic site of coptisine is the liver. Coptisine is poorly absorbed in the gastrointestinal system, and most of it is expelled in the form of its prototype through feces. Regarding safety, coptisine displayed potential hepatotoxicity. Some novel formulations, including the [Formula: see text]-cyclodextrin-based inclusion complex and nanocarriers, could effectively enhance the bioavailability of coptisine. The traditional use of C. chinensis is closely connected with the pharmacological actions of coptisine. Although there are some disadvantages, including poor solubility, low bioavailability, and possible hepatotoxicity, coptisine is still a prospective naturally derived drug candidate, especially in the treatment of tumors as well as metabolic and inflammatory diseases. Further investigation of coptisine is necessary to facilitate the application of coptisine-based drugs in clinical practice.

Pharmacokinetics of Five Alkaloids and their Metabolites in Normal and Diabetic Rats after Oral Administration of Rhizoma coptidis

Rhizoma coptidis has been clinically used for a long time for the treatment of various diseases in China, such as hypertension, diabetes, and inflammation. Previous studies have shown that alkaloid components of Rhizoma coptidis extract could be extensively metabolized and the metabolites were also considered to be the therapeutic material basis. However, until now, pharmacokinetic studies of the in vivo metabolites have not been revealed yet. The aim of the present study was to characterize the pharmacokinetics and excretions of five main alkaloids (berberine, jatrorrhizine, palmatine, epiberberine, and coptisine) and their seven metabolites (berberrubine, demethyleneberberine, jatrorrhizine-3-O-β-D-glucuronide, thalifendine-10-O-β-D-glucuronide, berberrubine-9-O-β-D-glucuronide, demethyleneberberine-2-O-sulfate, and demethyleneberberine-2-O-β-D-glucuronide) in rats after oral administration of Rhizoma coptidis extract. Meanwhile, comparative pharmacokinetics and excretions of these analytes in diabetic model rats were also investigated, since Rhizoma coptidis is widely used for the treatment of diabetes. Our results showed that the in vivo existing forms of alkaloid components were phase II metabolites, highlighting the glucuronidation metabolic pathway. In diabetic model rats, the utilization of Rhizoma coptidis alkaloids was significantly increased and the biotransformation of berberine into berberrubine was significantly inhibited.

Shenlian (SL) Decoction, a Traditional Chinese Medicine Compound, May Ameliorate Blood Glucose via Mediating the Gut Microbiota in db/db Mice

Shenlian (SL) decoction is a herbal formula composed of Coptis and ginseng, of which berberine and ginsenoside are the main constituents. Even though SL decoction is widely used in treating diabetes in China, the mechanism of its antidiabetes function still needs further study. Gut microbiota disorder is one of the important factors that cause diabetes. To explore the effect of SL decoction on intestinal microbiota, gut microbiota of mice was analyzed by sequencing the gut bacterial 16S rRNA V3+V4 region and metagenomics. In this study, results demonstrated that SL decoction had a better hypoglycemic effect and β cell protection effect than either ginseng or Coptis chinensis. Alpha diversity analysis showed that all interventions with ginseng, Coptis, and SL decoction could reverse the increased diversity and richness of gut microbiota in db/db mice. PCoA analysis showed oral SL decoction significantly alters gut microbiota composition in db/db mice. 395 OTUs showed significant differences after SL treatment, of which 37 OTUs enriched by SL decoction showed a significant negative correlation with FBG, and 204 OTUs decreased by SL decoction showed a significant positive correlation with FBG. Results of KEGG analysis and metagenomic sequencing showed that SL decoction could reduce the Prevotellaceae, Rikenellaceae, and Helicobacteraceae, which were related to lipopolysaccharide biosynthesis, riboflavin metabolism, and peroxisome, respectively. It could also upregulate the abundance of Bacteroidaceae, which contributed to the metabolism of starch and sucrose as well as pentose-glucuronate interconversions. In the species level, SL decoction significantly upregulates the relative abundance of Bacteroides_acidifaciens which showed a significant negative correlation with FBG and was reported to be a potential agent for modulating metabolic disorders such as diabetes and obesity. In conclusion, SL decoction was effective in hypoglycemia and its mechanism may be related to regulating gut microbiota via upregulating Bacteroides_acidifaciens.

Analysis of the Coptis chinensis genome reveals the diversification of protoberberine-type alkaloids

Chinese goldthread (Coptis chinensis Franch.), a member of the Ranunculales, represents an important early-diverging eudicot lineage with diverse medicinal applications. Here, we present a high-quality chromosome-scale genome assembly and annotation of C. chinensis. Phylogenetic and comparative genomic analyses reveal the phylogenetic placement of this species and identify a single round of ancient whole-genome duplication (WGD) shared by the Ranunculaceae. We characterize genes involved in the biosynthesis of protoberberine-type alkaloids in C. chinensis. In particular, local genomic tandem duplications contribute to member amplification of a Ranunculales clade-specific gene family of the cytochrome P450 (CYP) 719. The functional versatility of a key CYP719 gene that encodes the (S)-canadine synthase enzyme involved in the berberine biosynthesis pathway may play critical roles in the diversification of other berberine-related alkaloids in C. chinensis. Our study provides insights into the genomic landscape of early-diverging eudicots and provides a valuable model genome for genetic and applied studies of Ranunculales.

Coptidis alkaloids extracted from Coptis chinensis Franch attenuate IFN-γ-induced destruction of bone marrow cells

Coptidis alkaloids are the primary active components of Coptis chinensis Franch. Clinical and pharmacodynamic studies have confirmed that Coptidis alkaloids have multiple therapeutic effects including anti-inflammatory, antioxidant and antitumor effects, and they are usually used to treat various inflammatory disorders and related diseases. Mouse bone marrow cells (BMCs) were isolated from BALB/c mice. Immune-mediated destruction of BMCs was induced by interferon (IFN) -γ. High-performance liquid chromatography-electrospray ionization/ mass spectrometry was used to analyze the ingredients of the aqueous extract from Coptis chinensis Franch. The results confirmed that Coptidis alkaloids were the predominant ingredients in the aqueous extract from Coptis chinensis. The functional mechanism of Coptidis alkaloids in inhibiting immune-mediated destruction of BMCs was studied in vitro. After Coptidis alkaloid treatment, the percentages of apoptotic BMCs and the proliferation and differentiation of helper T (Th) cells and regulatory T (Treg) cells were measured by flow cytometry. The expression and distribution of T-bet in BMCs were observed by immunofluorescence. Western blotting analysis was used to assay the expression of key molecules in the Fas apoptosis and Jak/Stats signaling pathways in BMCs. We identified five alkaloids in the aqueous extract of Coptis chinensis. The apoptotic ratios of BMCs induced by IFN-γ were decreased significantly after Coptidis alkaloid treatment. The levels of key molecules (Fas, Caspase-3, cleaved Caspase-3, Caspase-8 and Caspase-8) in Fas apoptosis signaling pathways also decreased significantly after treatment with low concentrations of Coptidis alkaloids. Coptidis alkaloids were also found to inhibit the proliferation of Th1 and Th17 cells and induce the differentiation of Th2 and Treg cells; further, the distribution of T-bet in BMCs was decreased significantly. In addition, the levels of Stat-1, phospho-Stat-1 and phospho-Stat-3 were also reduced after Coptidis alkaloid treatment. These results indicate that Coptidis alkaloids extracted by water decoction from Coptis chinensis Franch could inhibit the proliferation and differentiation of T lymphocytes, attenuate the apoptosis of BMCs, and suppress the immune-mediated destruction of the BMCs induced by pro-inflammatory cytokines.

Full-length transcriptome analysis of Coptis deltoidea and identification of putative genes involved in benzylisoquinoline alkaloids biosynthesis based on combined sequencing platforms

The study carry out comprehensive transcriptome analysis of C. deltoidea and exploration of BIAs biosynthesis and accumulation based on UHPLC-MS/MS and combined sequencing platforms. Coptis deltoidea is an important medicinal plant with a long history of medicinal use, which is rich in benzylisoquinoline alkaloids (BIAs). In this study, Ultra performance liquid chromatography-electrospray ionization tandem mass spectrometry (UHPLC-ESI-MS/MS) and combined sequencing platforms were performed for exploration of BIAs biosynthesis, accumulation and comprehensive transcriptome analysis of C. deltoidea. By metabolism profiling, the accumulation of ten BIAs was analyzed using UHPLC-MS/MS and different contents were observed in different organs. From transcriptome sequencing result, we applied single-molecule real-time (SMRT) sequencing to C. deltoidea and generated a total of 75,438 full-length transcripts. We proposed the candidate biosynthetic pathway of tyrosine, precursor of BIAs, and identified 64 full length-transcripts encoding enzymes putatively involved in BIAs biosynthesis. RNA-Seq data indicated that the majority of genes exhibited relatively high expression level in roots. Transport of BIAs was also important for their accumulation. Here, 9 ABC transporters and 2 MATE transporters highly homologous to known alkaloid transporters related with BIAs transport in roots and rhizomes were identified. These findings based on the combined sequencing platforms provide valuable genetic information for C. deltoidea and the results of transcriptome combined with metabolome analysis can help us better understand BIAs biosynthesis and transport in this medicinal plant. The information will be critical for further characterization of C. deltoidea transcriptome and molecular-assisted breeding for this medicinal plant with scarce resources.

Coptisine from Coptis chinensis exerts diverse beneficial properties: A concise review

Coptisine is a natural small-molecular compound extracted from Coptis chinensis (CC) with a history of using for thousands of years. This work aimed at summarizing coptisine's activity and providing advice for its clinical use. We analysed the online papers in the database of SciFinder, Web of Science, PubMed, Google scholar and CNKI by setting keywords as 'coptisine' in combination of 'each pivotal pathway target'. Based on the existing literatures, we find (a) coptisine exerted potential to be an anti-cancer, anti-inflammatory, CAD ameliorating or anti-bacterial drug through regulating the signalling transduction of pathways such as NF-κB, MAPK, PI3K/Akt, NLRP3 inflammasome, RANKL/RANK and Beclin 1/Sirt1. However, we also (b) observe that the plasma concentration of coptisine demonstrates obvious non-liner relationship with dosage, and even the highest dosage used in animal study actually cannot reach the minimum concentration level used in cell experiments owing to the poor absorption and low availability of coptisine. We conclude (a) further investigations can focus on coptisine's effect on caspase-1-involved inflammasome assembling and pyroptosis activation, as well as autophagy. (b) Under circumstance of promoting coptisine availability by pursuing nano- or microrods strategies or applying salt-forming process to coptisine, can it be introduced to clinical trial.

A multidrug and toxic compound extrusion transporter mediates berberine accumulation into vacuoles in Coptis japonica

Plants produce a large variety of alkaloids, which have diverse chemical structures and biological activities. Many of these alkaloids accumulate in vacuoles. Although some membrane proteins on tonoplasts have been identified as alkaloid uptake transporters, few have been characterized to date, and relatively little is known about the mechanisms underlying alkaloid transport and accumulation in plant cells. Berberine is a model alkaloid. Although all genes involved in berberine biosynthesis, as well as the master regulator, have been identified, the gene responsible for the final accumulation of berberine at tonoplasts has not been determined. This study showed that a multidrug and toxic compound extrusion protein 1 (CjMATE1) may act as a berberine transporter in cultured Coptis japonica cells. CjMATE1 was found to localize at tonoplasts in C. japonica cells and, in intact plants, to be expressed preferentially in rhizomes, the site of abundant berberine accumulation. Cellular transport analysis using a yeast expression system showed that CjMATE1 could transport berberine. Expression analysis showed that RNAi suppression of CjbHLH1, a master transcription factor of the berberine biosynthetic pathway, markedly reduced the expression of CjMATE1 in a manner similar to the suppression of berberine biosynthetic genes. These results strongly suggest that CjMATE1 is the transporter that mediates berberine accumulation in vacuoles.

Characterization of Coptis japonica CjABCB2, an ATP-binding cassette protein involved in alkaloid transport

Higher plants produce a large number of secondary metabolites. Among these are the alkaloids, a group of small nitrogen-containing molecules. Alkaloids often have strong biological activity that protects alkaloid-producing plants from herbivores, and often accumulate to high concentrations in a specific organelle of a particular organ in the producing plant. However, knowledge of the membrane transport mechanism of alkaloids is still limited. Coptis japonica, a perennial Ranunculaceous plant, produces the benzylisoquinoline alkaloid berberine. This alkaloid, though biosynthesized in root tissues, accumulates in the rhizome, suggesting translocation of the molecule via xylem. In this study, a gene encoding a ATP-binding cassette (ABC) protein of B-type, Cjabcb2, was isolated from C. japonica. Northern analysis showed that Cjabcb2 was preferentially expressed in the rhizome, which is the sink organ of berberine. Functional analysis of CjABCB2 using yeast suggested that CjABCB2 transports berberine in an inward direction. Membrane separation and in situ hybridization data indicated that CjABCB2 might be involved in translocation of berberine from the root to the rhizome by transporting berberine at the plasma membrane of cells around the xylem of the rhizome.

Characterization of plant functions using cultured plant cells, and biotechnological applications

Plant cell cultures are widely used in the micro-propagation of clonal plants, especially virus-free plants, and in the production of useful metabolites such as paclitaxel. On the other hand, the use of plant cell cultures for the more basic characterization of plant functions is rather limited due to the difficulties associated with functional differentiation in cell cultures. In this review, I overview our experience with functionally differentiated cultured plant cells and their characteristics, especially with regard to photoautotrophism and secondary metabolism. I emphasize the high potential of functionally differentiated cell cultures, as well as some of the pitfalls, in the characterization of plant functions and biotechnological applications.

[Effect of enhanced UV-B radiation on metabolism and berberine content of Coptis chinensis]

OBJECTIVE

To reveal the response of content berberine in root of Coptis chinensis to different intensity of UV-B radiation, and provide the theory basis for promoting the content of berberine.

METHOD

Four groups of UV-B radiation were set in the experiment which included: natural light control (0 W x m(-2)), UL (0.05 W x m(-2)), UM (0.10 W x m(-2)), UH (0.20 W x m(-2)). The special photosynthesis character, PPP pathway in the primary metabolism and lyrosinase activity, the changes of berberine in the root of C. chinensis were measured under different UV-B radiation.

RESULT

Photosynthetic pigment, qN, Fo, ETR, activity of glucose-6-phosphate dehydrogenase and the content of berberine in the root of C. chinensis, all of these parameters were lower than other groups under the UH radiation. However, under the UM radiation, C. chinensis protected itself from the light UV-B radiation by promoting the power of photosynthesis and PPP pathway in order to produce more NADPH and secondary metabolites.

CONCLUSION

C. chinensis increases its photosynthetic ability and PPP pathway which can furnish more precursor of secondary metabolites and NADPH that are needed in the secondary metabolism. Furthermore, the content of berberine increases correspondingly. The research provide the example for increasing the content of berberine in C. chinensis cultivation.

[Correlation analysis soil nutrition as sell as yield and active compounds of Coptis teeta]

The correlations between soil nutrition and yield as well as active compound contents of Coptis teeta were analyzed. The contents of 13 soil factors, rhizome biomass and the content of berberine, jatrorrhizine, and palmatine in rhizome of C. teeta were determined, and analyzed by factor analysis (FA) and correlation analysis (CA). FA showed that the first three factors accounted for 86.9% of the total variance. The contents of Ca, Mg, Fe, Mn, and Zn correlated with the first factor. The content of organic matter, N, available N, available P, and available K correlated with the second factor. CA showed that yield of C. teeta had a significant positive correlation with available P (r = 0.931) at 0.01 level, and available N (r = 0.703) at 0.05 level. The content of berberine of C. teeta had a significant positive correlation with available P (r = 0.680) at 0.05 level. The yield and berberine content of C. teeta were high in the soil with high contents of available N and available P.

[Dynamic accumulation of effective components and biomass of Coptis chinensis in Hongya county]

OBJECTIVE

To study the dynamic accumulation of the effective components and biomass of Coptis chinensis, so to provide the experimental date of optimal harvest time for C. chinensis in Hongya county.

METHOD

The samples of three to five years were gathered from the same field and time. The biomass was analyzed by weighed. The jatrorrhizine, columbamine, epiberberine, coptisine, palmatine and berberine in C. chinensis were analyzed by HPLC.

RESULT

With the increasing of years of growth, the rootstalk biomass of C. chinensis was increasing continuously. The biomass growth of four-year-old C. chinensis was the fastest in the year. From September to October was the fastest season of the growth of rootstalk. The dynamic accumulation in rootstalk C. chinensis had regularity in the certain extend. The contents of six alkaloids and all alkaloids in 4-year-old C. chinensis were more than that in 3-years-old and 5-year-old. The contents of six alkaloids were mostly highest in August. From July to December, there is no significant difference in the contents of columbamine, epiberberine, coptisine, palmatine, berberine and all alkaloids in 4-years-old C. chinensis.

CONCLUSION

According to the biomass and the accumulation pattern of the effective components in the C. chinensis, the optimal harvest time is from September to October of 4-year-old C. chinensis.

Isoquinoline alkaloid biosynthesis is regulated by a unique bHLH-type transcription factor in Coptis japonica

Specific plant species produce unique isoquinoline alkaloids (IQAs); however, the mechanism of their evolution and the regulation of their biosynthesis are largely unknown. We report here the isolation of a novel basic helix-loop-helix protein, CjbHLH1, from IQA-producing Coptis japonica. A BLAST search indicated that CjbHLH1 homologs were only found in plant species that produce IQAs. Transient RNA interference (RNAi) and overexpression of CjbHLH1 in C. japonica protoplasts revealed the activity of CjbHLH1 in transcription of IQA biosynthetic genes, and little activity in the transcription of genes involved in primary metabolism or the stress response. A chromatin immunoprecipitation experiment using CjbHLH1-specific antibodies revealed the direct interaction of CjbHLH1 with promoter sequences of IQA biosynthetic genes in vivo. We discuss the unique role of CjbHLH1 in IQA biosynthesis.

Identification of a WRKY protein as a transcriptional regulator of benzylisoquinoline alkaloid biosynthesis in Coptis japonica

Selected cultured Coptis japonica cells produce a large amount of the benzylisoquinoline alkaloid berberine. Previous studies have suggested that berberine productivity is controlled at the transcript level of biosynthetic genes. We have identified a regulator of transcription in berberine biosynthesis using functional genomics with a transient RNA interference (RNAi) and overexpression of the candidate gene. The 24 primary candidate clones were selected from 1,014 expressed sequence tags (ESTs) that were obtained from a C. japonica cell line producing high levels of berberine. Further characterization of the expression profiles of these ESTs suggested that five ESTs would be good candidates as regulators of berberine production. A newly developed transient RNAi system with C. japonica protoplasts indicated that double-stranded RNA of an EST clone significantly reduced the level of transcripts of 3'-hydroxy N-methylcoclaurine 4'-O-methyltransferase. Sequence analysis showed that this EST encoded a group-II WRKY, and we named it CjWRKY1. When the effects of double-stranded RNA of the CjWRKY1 gene were examined in detail, a marked reduction in the transcripts of all genes involved in berberine biosynthesis was detected, whereas little effect was found in the transcript levels of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and chorismate mutase (CM) that are associated with primary metabolism. Ectopic expression of CjWRKY1 cDNA in C. japonica protoplasts clearly increased the level of transcripts of all berberine biosynthetic genes examined compared with control treatment, whereas the levels of GAPDH and CM were not affected. The functional role of CjWRKY1 as a specific and comprehensive regulator of berberine biosynthesis is discussed.

In Vivo 15N-Enrichment of Metabolites in Suspension Cultured Cells and Its Application to Metabolomics

The incorporation of stable isotopes in suspension cultured cells is very simple and useful as a preliminary experimental method in the experimental scene of plant metabolomics to elucidate the metabolic profiles of mutants and transformants. Stable isotope methods would afford a dynamic explanation of turnover speed that would concern the metabolic flux. Utilization of suspension cultured cells allows genes to be easily induced or suppressed, culture conditions to be controlled, and samples to be easily prepared. Stable isotope tracing allows an index of metabolic flux to be obtained. Here we present an experiment feeding (15)N-labeled inorganic salts to Arabidopsis (cell line T87) and Coptis cultured cells. Results of a comparison of (15)N labeling ratios of amino acids derived from T87 cells cultured under light with those cultured in the dark corresponded to transcriptional expressions revealed by microarray experiments published previously, demonstrating the validity of this procedure. Furthermore, (15)N labeling ratios of Coptis cultured cells revealed arginine and lysine metabolism inhibition, which should result in inhibition of polyamine biosynthesis and cell division. This very simple experiment allowed us to uncover metabolic dynamic features of the plant cell. Therefore this method is very useful for forming working hypotheses and experimental design.

Micellar electrokinetic chromatography for separation of a mixture of coptis alkaloids, scute flavonoids, and rhubarb anthraquinones and bianthrones

Coptidis Rhizoma, Scutellariae Radix, and Rhei Rhizoma are three common Chinese herbs. There are many herbal formulas which contain either two or all three of the herbs mentioned above. Their bioactive components have already been identified, respectively. However, there is no report about separation of the 13 bioactive constituents of the three herbs at the same time. In order to assess these constituents of related Chinese herbal preparations, a micellar electrokinetic chromatography method was developed. While buffer pH and surfactant concentration affected the resolution of separation, acetonitrile percentage was found to significantly influence the resolution, peak shape, and elution window. Optimum separation of 13 compounds was achieved at pH 7.3 using a buffer mixture of 70% (v/v) 3 mM di-sodium tetraborate, 10 mM sodium dihydrogen phosphate, and 50 mM sodium deoxycholate with 30% (v/v) acetonitrile. When applying the developed method to analyze a model preparation, San-huang-xie-xin-tang, which contains all three herbs, 8 of the 13 bioactive constituents, could be determined. The present study proposed a method to assess San-huang-xie-xin-tang within short analysis time and also provided a possible starting point to evaluate related herbal preparations containing Coptidis Rhizoma, Scutellariae Radix, and Rhei Rhizoma.

[Dynamic change of soluble saccharides and amino acids during the growing period of Coptis chinensis]

OBJECTIVE

To study the changes of soluble saccharides and amino acids during the growing period of Coptis chinensis.

METHOD

Amino acid contents were estimated by Indene tri-ketone colorimetric method; saccharide contents were determined by anthracene ketone method.

RESULT AND CONCLUSION

The contents of soluble saccharides and amino acids in different organs were low in plants of 1-2 years old. And they were increased in plants of 3-4 years old. At maturation (5 years), the contents of amino acids kept on increasing in rhizome and flower stalk, while decreased in fibre and leaves, and the contents of soluble saccharides showed the downtrend in rhizome, leaves and fibre, except the uptrend in flower stalk.

Application of vanadate-induced nucleotide trapping to plant cells for detection of ABC proteins

The vanadate-induced nucleotide trapping technique, which has been conventionally used to characterize mammalian ATP-binding cassette (ABC) proteins, was applied to berberine-producing plant cell cultures, Thalictrum minus and Coptis japonica. One membrane protein at ca. 180 kDa was photoaffinity-labeled with 8-azido-[alpha-(32)P]ATP in the T. minus cells in the presence of vanadate, which was specifically induced by the addition of benzyladenine in a similar manner as the induction of berberine biosynthesis in these cell cultures, whereas three bands were observed in the C. japonica cells in the size region between 120 and 150 kDa corresponding to full-sized ABC protein. The benzyladenine-induced band in T. minus showed properties similar to those of human MDR1, including the recognition of berberine, which suggests that the ABC protein detected in T. minus takes this endogenous alkaloid as a putative substrate for transport. This is the first application of this technique to plant cells.

Involvement of CjMDR1, a plant multidrug-resistance-type ATP-binding cassette protein, in alkaloid transport in Coptis japonica

Alkaloids comprise one of the largest groups of plant secondary metabolites. Berberine, a benzylisoquinoline alkaloid, is preferentially accumulated in the rhizome of Coptis japonica, a ranunculaceous plant, whereas gene expression for berberine biosynthetic enzymes has been observed specifically in root tissues, which suggests that berberine synthesized in the root is transported to the rhizome, where there is high accumulation. We recently isolated a cDNA encoding a multidrug-resistance protein (MDR)-type ATP-binding cassette (ABC) transporter (Cjmdr1) from berberine-producing cultured C. japonica cells, which is highly expressed in the rhizome. Functional analysis of Cjmdr1 by using a Xenopus oocyte expression system showed that CjMDR1 transported berberine in an inward direction, resulting in a higher accumulation of berberine in Cjmdr1-injected oocytes than in the control. Typical inhibitors of ABC proteins, such as vanadate, nifedipine, and glibenclamide, as well as ATP depletion, clearly inhibited this CjMDR1-dependent berberine uptake, suggesting that CjMDR1 functioned as an ABC transporter. Conventional membrane separation methods showed that CjMDR1 was localized in the plasma membrane of C. japonica cells. In situ hybridization indicated that Cjmdr1 mRNA was expressed preferentially in xylem tissues of the rhizome. These findings strongly suggest that CjMDR1 is involved in the translocation of berberine from the root to the rhizome.

Molecular cloning of columbamine O-methyltransferase from cultured Coptis japonica cells

To identify all of the O-methyltransferase genes involved in isoquinoline alkaloid biosynthesis in Coptis japonica cells, we sequenced 1014 cDNA clones isolated from high-alkaloid-producing cultured cells of C. japonica. Among them, we found all three reported O-methyltransferases and an O-methyltransferase-like cDNA clone (CJEST64). This cDNA was quite similar to S-adenosyl-l-methionine:coclaurine 6-O-methyltransferase and S-adenosyl-l-methionine:isoflavone 7-O-methyltransferase. As S-adenosyl-l-methionine:columbamine O-methyltransferase, which catalyzes the conversion of columbamine to palmatine, is one of the remaining unelucidated components in isoquinoline alkaloid biosynthesis in C. japonica, we heterologously expressed the protein in Escherichia coli and examined the activity of columbamine O-methyltransferase. The recombinant protein clearly showed O-methylation activity using columbamine, as well as (S)-tetrahydrocolumbamine, (S)-, (R,S)-scoulerine and (R,S)-2,3,9,10-tetrahydroxyprotoberberine as substrates. This result clearly indicated that EST analysis was useful for isolating the candidate gene in a relatively well-characterized biosynthetic pathway. The relationship between the structure and substrate recognition of the O-methyltransferases involved in isoquinoline alkaloid biosynthesis, and a reconsideration of the biosynthetic pathway to palmatine are discussed.