2,4-D and alkaloid accumulation in periwinkle cell suspensions

Cell type matters: competence for alkaloid metabolism differs in two seed-derived cell strains of Catharanthus roseus

Since the discovery of the anticancer drugs vinblastine and vincristine, Catharanthus roseus has been intensively studied for biosynthesis of several terpene indole alkaloids (TIAs). Due to their low abundance in plant tissues at a simultaneously high demand, modes of production alternative to conventional extraction are mandatory. Plant cell fermentation might become one of these alternatives, yet decades of research have shown limited success to certain product classes, leading to the question: how to preserve the intrinsic ability to produce TIAs (metabolic competence) in cell culture? We used the strategy to use the developmental potency of mature embryos to generate such strains. Two cell strains (C1and C4) from seed embryos of Catharanthus roseus were found to differ not only morphologically, but also in their metabolic competence. This differential competence became manifest not only under phytohormone elicitation, but also upon feeding with alkaloid pathway precursors. The more active strain C4 formed larger cell aggregates and was endowed with longer mitochondria. These cellular features were accompanied by higher alkaloid accumulation in response to methyl jasmonate (MeJA) elicitation. The levels of catharanthine could be increased significantly, while the concurrent vindoline branch of the pathway was blocked, such that no bisindole alkaloids were detectable. By feeding vindoline to MeJA-elicited C4 cells, vincristine became detectable; however, only to marginal amounts. In conclusion, these results show that cultured cells are not "de-differentiated", but can differ in metabolic competence. In addition to elicitation and precursor feeding, the cellular properties of the "biomatter" are highly relevant for the success of plant cell fermentation.

Quantification of Anti-Addictive Alkaloids Ibogaine and Voacangine in In Vivo- and In Vitro-Grown Plants of Two Mexican Tabernaemontana Species

Tabernaemontana alba and Tabernaemontana arborea are Apocynaceae species used in Mexican traditional medicine for which little phytochemical information exists. In this study, preliminary gas chromatography/mass spectrometry analyses of different organs obtained from wild plants of both species identified a total of 10 monoterpenoid indole alkaloids (MIAs) and one simple indole alkaloid, nine of which were reported for the first time in these species. Furthermore, callus cultures were established from T. alba leaf explants and regeneration of whole plants was accomplished via somatic embryogenesis. The anti-addictive MIAs ibogaine and voacangine were then quantified by gas chromatography with flame ionization detection in wild plants of both species, as well as greenhouse-grown plants, in vitro-grown plantlets and embryogenic callus of T. alba. Ibogaine and voacangine were present in most samples taken from the whole plants of both species, with stem and root barks showing the highest concentrations. No alkaloids were detected in callus samples. It was concluded that T. alba and T. arborea are potentially viable sources of ibogaine and voacangine, and that these MIAs can be produced through somatic embryogenesis and whole plant regeneration of T. alba. Approaches to increase MIA yields in whole plants and to achieve alkaloid production directly in cell cultures are discussed.

A bitter herbal medicine Gentiana scabra root extract stimulates glucagon-like peptide-1 secretion and regulates blood glucose in db/db mouse

ETHNOPHARMACOLOGICAL RELEVANCE

Gentiana scabra root extract (GS) is frequently prescribed as an internal remedy in traditional Korean medicine for treatment of diabetes mellitus. GS contains bitter iridoid glycosides including loganic acid, gentiopicrin, trifloroside, and rindoside. We previously reported that the intestinal bitter taste sensation stimulates GLP-1 secretion, and thereupon hypothesized that the blood glucose regulatory effect of GS is due to its GLP-1 secreting effect in enteroendocrine L cells.

MATERIALS AND METHOD

We studied GLP-1 secreting effect of GS treatment and its cellular downstream mechanism in human enteroendocrine NCI-H716 cells using the G protein-coupled receptor (GPCR) pathway inhibitors. Intracellular calcium assay also demonstrated the signal transduction pathway stimulated by the GS treatment. Using db/db mice, we performed oral glucose tolerance test (OGTT) to examine the blood glucose lowering effect of GS administration. We also collected the mouse plasma during the OGTT to measure the GLP-1 and insulin levels.

RESULT

We demonstrated dose-dependent GLP-1 secreting effect of GS on the NCI-H716 cells. The GLP-1 secreting effect of GS is mediated by the G protein βγ-subunit and inositol triphosphate. Using db/db mice, we found that the effect of GS on lowering blood glucose is due to its GLP-1 secretion, and consequential insulinotropic effect. The chemical fingerprint of GS was obtained through a direct analysis in realtime mass spectrometry (DART-MS) and high-performance liquid chromatography (HPLC)/MS. Through the GLP-1 secretion study, we found that loganic acid, an iridoid glycoside, contributes to the GLP-1 secreting effect of GS.

CONCLUSION

The findings of this study highlight the potential of exploiting the antidiabetic effect of GS on type 2 diabetes mellitus patients.

Biosynthesis and regulation of terpenoid indole alkaloids in Catharanthus roseus

Catharanthus roseus produces a wide range of terpenoid indole alkaloids (TIA). Many of them, such as vinblastine and vincristine, have significant bioactivity. They are valuable chemotherapy drugs used in combination with other drugs to treat lymphoma and leukemia. The TIA biosynthetic pathway has been investigated for many years, for scientific interest and for their potential in manufacturing applications, to fulfill the market demand. In this review, the progress and perspective of C. roseus TIA biosynthesis and its regulating enzymes are described. In addition, the culture condition, hormones, signaling molecules, precursor feeding on the accumulation of TIA, and gene expression are also evaluated and discussed.

Inducing effect of dihydroartemisinic acid in the biosynthesis of artemisinins with cultured cells of Artemisia annua by enhancing the expression of genes

Artemisinin has been used in the production of "artemisinin combination therapies" for the treatment of malaria. Feeding of precursors has been proven to be one of the most effective methods to enhance artemisinin production in plant cultured cells. At the current paper, the biosynthesis of artemisinin (ART) and its four analogs from dihydroartemisinic acid (DHAA) in suspension-cultured cells of Artemisia annua were investigated. ARTs were detected by HPLC/GC-MS and isolated by various chromatography methods. The structures of four DHAA metabolites, namely, dihydro-epi-deoxyarteannuin B, arteannuin I, arteannuin K, and 3-β-hydroxy-dihydro-epi-deoxyarteannuin B, were elucidated by physicochemical and spectroscopic analyses. The correlation between gene expression and ART content was investigated. The results of RT-PCR showed that DHAA could up-regulate expression of amorpha-4,11-diene synthase gene (ADS), amorpha-4,11-diene C-12 oxidase gene (CYP71AV1), and farnesyl diphosphate synthase gene (FPS) (3.19-, 7.21-, and 2.04-fold higher than those of control group, resp.), which indicated that biosynthesis processes from DHAA to ART were enzyme-mediated.

Molecular cloning and functional characterization of Catharanthus roseus hydroxymethylbutenyl 4-diphosphate synthase gene promoter from the methyl erythritol phosphate pathway

The Madagascar periwinkle produces monoterpenoid indole alkaloids (MIA) of high interest due to their therapeutical values. The terpenoid moiety of MIA is derived from the methyl erythritol phosphate (MEP) and seco-iridoid pathways. These pathways are regarded as the limiting branch for MIA biosynthesis in C. roseus cell and tissue cultures. In previous studies, we demonstrated a coordinated regulation at the transcriptional and spatial levels of genes from both pathways. We report here on the isolation of the 5'-flanking region (1,049 bp) of the hydroxymethylbutenyl 4-diphosphate synthase (HDS) gene from the MEP pathway. To investigate promoter transcriptional activities, the HDS promoter was fused to GUS reporter gene. Agrobacterium-mediated transformation of young tobacco leaves revealed that the cloned HDS promoter displays a tissue-specific GUS staining restricted to the vascular region of the leaves and limited to a part of the vein that encompasses the phloem in agreement with the previous localization of HDS transcripts in C. roseus aerial organs. Further functional characterizations in stably or transiently transformed C. roseus cells allowed us to identify the region that can be consider as the minimal promoter and to demonstrate the induction of HDS promoter by several hormonal signals (auxin, cytokinin, methyljasmonate and ethylene) leading to MIA production. These results, and the bioinformatic analysis of the HDS 5'-region, suggest that the HDS promoter harbours a number of cis-elements binding specific transcription factors that would regulate the flux of terpenoid precursors involved in MIA biosynthesis.

Characterization and subcellular localization of geranylgeranyl diphosphate synthase from Catharanthus roseus

The enzyme geranylgeranyl diphosphate synthase (GGPS: EC 2.5.1.1, EC 2.5.1.10, EC 2.5.1.29) catalyses the formation of geranylgeranyl diphosphate (GGPP) from isopentenyl diphosphate and dimethylallyl diphosphate via three successive condensation reactions. A full-length nucleotide sequence of GGPS (named CrGGPS) was cloned from the medicinal plant Catharanthus roseus. The deduced polypeptide has 383 amino acids with a calculated mass of 41.6 kDa and possesses prenyltransferase signatures characteristic of plant type II GGPS. The enzyme was characterized by functional complementation in carotenoid accumulating strains of Escherichia coli. When cultures of Catharanthus cell lines were treated with methyljasmonate, no specific increase in transcript levels were observed. In plants, GGPS are encoded by a small multigene family and the isoforms have been shown to be localized in three different subcellular compartments: chloroplast, endoplasmic reticulum and mitochondria. We investigated the subcellular distribution of CrGGPS through transient transformations of C. roseus cells with a yellow fluorescent protein-fused construct. Our results clearly indicate that CrGGPS is located to plastids within stroma and stromules.

Two distinct intracellular Ca2+-release components act in opposite ways in the regulation of the auxin-dependent MIA biosynthesis in Catharanthus roseus cells

Calcium-mediated signalling is ubiquitous in both animals and plants. Changes in cytoplasmic free Ca(2+) concentration couple diverse arrays of stimuli to their specific responses, the specificity of the stimulus being determined by integrated actions between multiple Ca(2+) mobilization pathways. In this work, a pharmacological approach is reported, aimed at deciphering the role of calcium as a second messenger in the transduction pathway leading to the inhibitory effect of 2,4-dichlorophenoxyacetic acid (2,4-D), in regulating monoterpene indole alkaloid (MIA) biosynthesis in Catharanthus roseus cells. It is demonstrated here that auxin-dependent MIA biosynthesis is differentially regulated by two distinct calcium release components from internal stores in C. roseus showing pharmacological profiles similar to those displayed by animal RyR and IP3 channels. MIA biosynthesis is stimulated by caffeine (Ca(2+)-release activator through RyR channels) and by heparin and TMB8 (Ca(2+)-release inhibitors of IP3 channels) whereas MIA biosynthesis is inhibited by mastoparan (Ca(2+)-release activator of IP3 channels) and by ruthenium red and DHBP (Ca(2+)-release inhibitors of RyR channels). Furthermore, calcium, as 2,4-D, acts on MIA biosynthesis by regulating the monoterpene moiety of the MIA biosynthesis pathway since calcium channel modulators preferentially modulate g10h expression, the gene encoding the enzyme of the secoiridoid monoterpene pathway, that is the major target of 2,4-D action. In addition, the simultaneous use of caffeine (an activator of RyR channel in animals) and TMB8 (an inhibitor of the IP3 channel) in 2,4-D treated cells triggers a synergistic effect on MIA accumulation. This finding suggests an opposite and co-ordinated action of multiple Ca(2+)-release pathways in 2,4-D signal transduction, adding a new level of complexity to calcium signalling in plants and questioning the existence of RyR and IP3 channels in plants.

Proteins prenylated by type I protein geranylgeranyltransferase act positively on the jasmonate signalling pathway triggering the biosynthesis of monoterpene indole alkaloids in Catharanthus roseus

In Catharanthus roseus, the first step of monoterpenoid indole alkaloids (MIA) biosynthesis results from the condensation of the indole precursor tryptamine with the terpenoid precursor secologanin. Secologanin biosynthesis requires two successive biosynthetic pathways, the plastidial methyl-D: -erythritol 4-phosphate (MEP) pathway and the monoterpene secoiridoid pathway. In C. roseus cell culture, the expression of several genes encoding enzymes of these two pathways is dramatically down-regulated by auxin, while strongly enhanced by cytokinin and methyl-jasmonate. Furthermore, our previous studies have shown that protein prenylation events are also involved in the transcriptional activation of some of these genes. In the present work, we investigate the involvement of protein prenylation in the jasmonate signalling pathway leading to MIA biosynthesis. Inhibition of protein prenyltransferase down-regulates the methyl-jasmonate-induced expression of MEP and monoterpene secoiridoid pathway genes and thus abolishes MIA biosynthesis. Jointly, it also inhibits the methyl-jasmonate-induced expression of the AP2/ERF transcription factor ORCA3 that acts as a central regulator of MIA biosynthesis. Finally, a specific silencing of protein prenyltransferases mediated by RNA interference in C. roseus cells shows that inhibition of type I protein geranylgeranyltransferase (PGGT-I) down-regulates the methyl-jasmonate-induced expression of ORCA3, suggesting that PGGT-I prenylated proteins are part of the early steps of jasmonate signalling leading to MIA biosynthesis.

Influence of Auxins and Sucrose in Monoterpenoid Oxindole Alkaloid Production by Uncaria tomentosa Cell Suspension Cultures

Growth and alkaloid production in Uncaria tomentosa cell suspension cultures were studied in Murashige and Skoog medium supplemented with 10 microM 2,4-dichlorophenoxyacetic acid, 10 microM kinetin, and 58 mM sucrose for maintenance and with 10 microM indole-3-acetic acid, 10 microM kinetin, and 58 mM sucrose for production. A U. tomentosa pale Uth-3 cell line, cultured in the production medium, showed a reduced lag phase and a specific growth rate (mu) of 0.27 day(-1), while cells growing in the maintenance medium showed mu = 0.20 day(-1). U. tomentosa cells growing in the production medium produced monoterpenoid oxindole alkaloids (MOA) in amounts of 10.2 +/- 1.6 microg g(-1) dry weight (DW). The chemical profile of MOA produced by in vitro cell cultures was similar to that found in the plant. After 10 subcultures, maximum MOA production decreased to 2.0 +/- 0.7 microg g(-1) DW, while tryptamine alkaloids (TA) were produced with a maximum of 6.2 +/- 0.4 microg g(-1) DW. The increase of initial sucrose concentration up to 145 mM in the production medium enhanced the cell biomass by 3.2-fold (from 10.2 +/- 0.1 to 32.8 +/- 1.1 g DW L(-1)), reduced mu from 0.27 to 0.23 day(-1), and provoked a substantial accumulation of TA (23.1 +/- 4.7 microg g(-1) DW). A high sucrose concentration stimulated MOA production in the maintenance medium (2.7 +/- 0.5 microg g(-1) DW), even in the presence of 2,4-dichlorophenoxyacetic acid.

Transcription factor Agamous-like 12 from Arabidopsis promotes tissue-like organization and alkaloid biosynthesis in Catharanthus roseus suspension cells

In Catharanthus roseus, monomeric terpenoid indole alkaloids (TIAs) are biosynthesized in specific tissues, particularly in roots, but failed to be produced by in vitro undifferentiated suspension cells. In this paper, we describe the impact of the root-specific MADS-box transcription factor Agamous-like 12 (Agl12) from Arabidopsis thaliana on the differentiation of suspension cells from C. roseus. The expression of Agl12 is sufficient to promote an organization of suspension cells into globular parenchyma-like aggregates but is insufficient by itself to induce complete morphological root differentiation. Agl12 expression selectively increases the expression of genes encoding enzymes involved in the early biosynthesis steps of the terpenic precursor of alkaloids. The transgenic cell lines expressing Agl12 produced significant amounts of ajmalicine, an antihypertensive TIA that normally accumulates in C. roseus roots. The present paper indicates that transcription factors involved in tissue or organ differentiation may constitute new metabolic engineering tools that could help to design in vitro cultured cells able to produce specific valuable secondary metabolites.

Epidermis is a pivotal site of at least four secondary metabolic pathways in Catharanthus roseus aerial organs

Catharanthus roseus produces a wide range of secondary metabolites, some of which present high therapeutic values such as antitumoral monoterpenoid indole alkaloids (MIAs), vinblastine and vincristine, and the hypotensive MIA, ajmalicine. We have recently shown that a complex multicellular organisation of the MIA biosynthetic pathway occurred in C. roseus aerial organs. In particular, the final steps of both the secoiridoid-monoterpene and indole pathways specifically occurred in the epidermis of leaves and petals. Chorismate is the common precursor of indole and phenylpropanoid pathways. In an attempt to better map the spatio-temporal organisation of diverse secondary metabolisms in Catharanthus roseus aerial organs, we studied the expression pattern of genes encoding enzymes of the phenylpropanoid pathway (phenylalanine ammonia-lyase [PAL, E.C. 4.3.1.5], cinnamate 4-hydroxylase [C4H, E.C. 1.14.13.11] and chalcone synthase [CHS, E.C. 2.3.1.74]). In situ hybridisation experiments revealed that CrPAL and CrC4H were specifically localised to lignifying xylem, whereas CrPAL, CrC4H and CrCHS were specifically expressed in the flavonoid-rich upper epidermis. Interestingly, these three genes were co-expressed in the epidermis (at least the upper, adaxial one) together with three MIA-related genes, indicating that single epidermis cells were capable of concomitantly producing a wide range of diverse secondary metabolites (e.g. flavonoïds, indoles, secoiridoid-monoterpenes and MIAs). These results, and data showing co-accumulation of flavonoids and alkaloids in single cells of C. roseus cell lines, indicated the spatio-temporal feasibility of putative common regulation mechanisms for the expression of these genes involved in at least four distinct secondary metabolisms.

CaaX-prenyltransferases are essential for expression of genes involvedin the early stages of monoterpenoid biosynthetic pathway in Catharanthus roseus cells

CaaX-prenyltransferases (CaaX-PTases) catalyse the covalent attachment of isoprenyl groups to conserved cysteine residues located at the C-terminal CaaX motif of a protein substrate. This post-translational modification is required for the function and/or subcellular localization of some transcription factors and components of signal transduction and membrane trafficking machinery. CaaX-PTases, including protein farnesyltransferase (PFT) and type-I protein geranylgeranyltransferase (PGGT-I), are heterodimeric enzymes composed of a common alpha subunit and a specific beta subunit. We have established RNA interference cell lines targeting the beta subunits of PFT and PGGT-I, respectively, in the Catharanthus roseus C20D cell line, which synthesizes monoterpenoid indole alkaloids in response to auxin depletion from the culture medium. In both types of RNAi cell lines, expression of a subset of genes involved in the early stage of monoterpenoid biosynthetic pathway (ESMB genes), including the MEP pathway, is strongly decreased. The role of CaaX-PTases in ESMB gene regulation was confirmed by using the general prenyltransferase inhibitor s-perillyl alcohol (SP) and the specific PFT inhibitor Manumycin A on the wild type line. Furthermore, supplementation of SP inhibited cells with monoterpenoid intermediates downstream of the steps encoded by the ESMB genes restores monoterpenoid indole alkaloids biosynthesis. We conclude that protein targets for both PFT and PGGT-I are required for the expression of ESMB genes and monoterpenoid biosynthesis in C. roseus, this represents a non previously described role for protein prenyltransferase in plants.