Insights into carotenoid accumulation using VIGS to block different steps of carotenoid biosynthesis in petals of California poppy

Viral-induced gene silencing of selected biosynthetic genes decreased overall carotenoid accumulation in California poppy. Regulation of carotenogenesis was linked with pigment sequestration, not changes in biosynthetic gene expression. Genes of carotenogenesis are well described, but understanding how they affect carotenoid accumulation has proven difficult because of plant lethality when the pigments are lacking. Here, we used a Tobacco Rattle Virus-based virus-induced-gene-silencing (VIGS) approach in California poppy (Eschscholzia californica) to investigate how silencing of the carotenoid biosynthetic pathway genes affects carotenoid metabolite accumulation and RNA transcript abundance of the carotenoid biosynthetic pathway genes. VIGS of upstream (PDS and ZDS) and downstream (βOH and ZEP) genes reduced transcript abundance of the targeted genes in the poppy petals while having no effect on abundance of the other carotenogenesis genes. Silencing of PDS, ZDS, βOH and ZEP genes reduced total pigment concentration by 75-90% and altered petal colour. HPLC and LC-MS measurements suggested that petal colour changes were caused by substantially altered pigment profiles and quantity. Carotenoid metabolites were different to those normally detected in wild-type petals accumulated but overall carotenoid concentration was less, suggesting the chemical form of carotenoid was important for whether it could be stored at high amounts. In poppy petals, eschscholtzxanthin and retro-carotene-triol were the predominant carotenoids, present mainly as esters. Specific esterification enzymes for specific carotenoids and/or fatty acids appear key for enabling petal carotenoids to accumulate to high amounts. Our findings argue against a direct role for carotenoid metabolites regulating carotenogenesis genes in the petals of California poppy as transcript abundance of carotenogenesis genes studied was unchanged, while the petal carotenoid metabolite profile changed substantially.

Evaluation of Manganese Chloride's Effect on Biosynthetic Properties of In Vitro Cultures of Eschscholzia californica Cham

The basal production of secondary metabolites in medicinal plants is limited. One of the effective approaches that encourages plants to produce a remarkable amount of precious compounds is an application of elicitors. Our work was focused on the elicitation of Eschscholzia californica Cham. suspension cultures using various concentrations of MnCl₂ (5; 10; 15 mg/L) with the aim of evaluating its effect on sanguinarine, chelerythrine, and macarpine production and gene expression of enzymes involved in the biosynthesis of mentioned secondary metabolites (BBE, 4′-OMT, CYP80B1) or in defense processes (LOX). Suspension cultures were exposed to elicitor for 24, 48, and 72 h. The content of alkaloids in phytomass was determined on the basis of their fluorescence properties. The relative mRNA expression of selected genes was analyzed using the ΔΔCt value method. PCR products were evaluated by melting curve analysis to confirm the specific amplification. Our results demonstrated that Eschscholzia californica Cham. cell suspension cultures evince sensitivity to the presence of MnCl₂ in growth media resulting in the increased production of benzophenanthridine alkaloids and gene expression of selected enzymes. Manganese chloride seems to be a potential elicitor supporting natural biosynthetic properties in plant cell cultures and can be applied for the sustained production of valuable secondary metabolites.

Modulation of benzylisoquinoline alkaloid biosynthesis by heterologous expression of CjWRKY1 in Eschscholzia californica cells

Transcription factors control many processes in plants and have high potentials to manipulate specialized metabolic pathways. Transcriptional regulation of the biosynthesis of monoterpenoid indole alkaloids (MIAs), nicotine alkaloids, and benzylisoquinoline alkaloids (BIAs) has been characterized using Catharanthus roseus, Nicotiana and Coptis plants. However, metabolic engineering in which specific transcription factors are used in alkaloid biosynthesis is limited. In this study, we characterized the effects of ectopic expression of CjWRKY1, which is a transcriptional activator with many targets in BIA biosynthesis in Coptis japonica (Ranunculaceae) and Eschscholzia californica (California poppy, Papaveraceae). Heterologous expression of CjWRKY1 in cultured California poppy cells induced increases in transcripts of several genes encoding BIA biosynthetic enzymes. Metabolite analyses indicated that the overexpression of the CjWRKY1 gene also induced increases in the accumulation of BIAs such as sanguinarine, chelerythrine, chelirubine, protopine, allocryptopine, and 10-hydroxychelerythrine in the culture medium. Previous characterization of EcbHLH1 and current results indicated that both transcription factors, WRKY1 and bHLH1, are substantially involved in the regulation of BIA biosynthesis. We discuss the function of CjWRKY1 in E. californica cells and its potential for metabolic engineering in BIA biosynthesis.

Unraveling Additional O-Methylation Steps in Benzylisoquinoline Alkaloid Biosynthesis in California Poppy (Eschscholzia californica)

California poppy (Eschscholzia californica), a member of the Papaveraceae family, produces many biologically active benzylisoquinoline alkaloids (BIAs), such as sanguinarine, macarpine and chelerythrine. Sanguinarine biosynthesis has been elucidated at the molecular level, and its biosynthetic genes have been isolated and used in synthetic biology approaches to produce BIAs in vitro. However, several genes involved in the biosynthesis of macarpine and chelerythrine have not yet been characterized. In this study, we report the isolation and characterization of a novel O-methyltransferase (OMT) involved in the biosynthesis of partially characterized BIAs, especially chelerythrine. A search of the RNA sequence database from NCBI and PhytoMetaSyn for the conserved OMT domain identified 68 new OMT-like sequences, of which the longest 22 sequences were selected based on sequence similarity. Based on their expression in cell lines with different macarpine/chelerythrine profiles, we selected three OMTs (G2, G3 and G11) for further characterization. G3 expression in Escherichia coli indicated O-methylation activity of the simple benzylisoquinolines, including reticuline and norreticuline, and the protoberberine scoulerine with dual regio-reactivities. G3 produced 7-O-methylated, 3'-O-methylated and dual O-methylated products from reticuline and norreticuline, and 9-O-methylated tetrahydrocolumbamine, 2-O-methylscoulerine and tetrahydropalmatine from scoulerine. Further enzymatic analyses suggested that G3 is a scoulerine-9-O-methyltransferase for the biosynthesis of chelerythrine in California poppy. In the present study, we discuss the physiological role of G3 in BIA biosynthesis.

The Vacuolar Proton-Cation Exchanger EcNHX1 Generates pH Signals for the Expression of Secondary Metabolism in Eschscholzia californica

Cell cultures of Eschscholzia californica react to a fungal elicitor by the overproduction of antimicrobial benzophenanthridine alkaloids. The signal cascade toward the expression of biosynthetic enzymes includes (1) the activation of phospholipase A2 at the plasma membrane, resulting in a peak of lysophosphatidylcholine, and (2) a subsequent, transient efflux of vacuolar protons, resulting in a peak of cytosolic H(+). This study demonstrates that one of the Na(+)/H(+) antiporters acting at the tonoplast of E. californica cells mediates this proton flux. Four antiporter-encoding genes were isolated and cloned from complementary DNA (EcNHX1-EcNHX4). RNA interference-based, simultaneous silencing of EcNHX1, EcNHX3, and EcNHX4 resulted in stable cell lines with largely diminished capacities of (1) sodium-dependent efflux of vacuolar protons and (2) elicitor-triggered overproduction of alkaloids. Each of the four EcNHX genes of E. californica reconstituted the lack of Na(+)-dependent H(+) efflux in a Δnhx null mutant of Saccharomyces cerevisiae. Only the yeast strain transformed with and expressing the EcNHX1 gene displayed Na(+)-dependent proton fluxes that were stimulated by lysophosphatidylcholine, thus giving rise to a net efflux of vacuolar H(+). This finding was supported by three-dimensional protein homology models that predict a plausible recognition site for lysophosphatidylcholine only in EcNHX1. We conclude that the EcNHX1 antiporter functions in the elicitor-initiated expression of alkaloid biosynthetic genes by recruiting the vacuolar proton pool for the signaling process.

Alkaloid metabolism in thrips-Papaveraceae interaction: recognition and mutual response

Frankliniella occidentalis (Pergande), the Western Flower Thrips (WFT), is a polyphagous and highly adaptable insect of the order Thysanoptera. It has a broad host range but is rarely found on Papaveraceae, which might be due to deterrent effects of alkaloids present in most species of this family. In order to test the adaptive potential of WFT, we investigated its interaction with two Papaveraceae offered as sole feeding source. We found that WFT are able to live and feed on leaves of Eschscholzia californica and Chelidonium majus. Both plants respond to thrips feeding by the enhanced production of benzophenanthridine alkaloids. Furthermore, cell cultures of E. californica react to water insoluble compounds prepared from adult thrips with enhanced alkaloid production. During feeding, WFT take up benzophenanthridine alkaloids from either plant and from an artificial feeding medium and convert them to their less toxic dihydroderivatives. This was shown in detail with sanguinarine, the most cytotoxic benzophenanthridine. A similar conversion is used in plants to prevent self-intoxication by their own toxins. We conclude that WFT causes a phytoalexin-like response in Papaveraceae, but is able to adapt to such host plants by detoxification of toxic alkaloids.

[Effect of abiotic elicitation on the sanguinarine production and polyphenol oxidase activity in the suspension culture of Eschscholtzia californica CHAM]

Elicitation of plant in vitro cultures represents a biotechnological tool to improve the production of secondary metabolites. In this study, the effect of AgNO3 and CdCl2 on the sanguinarine production by the suspension culture of Eschscholtzia californica CHAM. was investigated. Elicitors were added to the cultures at the 14th day of subcultivation and their effect on the sanguinarine production was evaluated after a 48 h exposure. AgNO3 at the concentration of 0.075 mmol.l-1 and CdCl2 at the concentration of 4 mmol.l-1 induced a ca. 5.2- and 5.6-multiple increase in sanguinarine synthesis, respectively. This amount represents probably the maximal production, because a further increase in the elicitors concentrations did not increase sanguinarine production. Both abiotic elicitors induced a polyphenol oxidase specific activity increase. Polyphenol oxidase is probably involved in the biosynthesis of sanguinarine at the level of dopamine formation. Dopamine is a precursor of (S)-norcoclaurine, the first intermediate with the benzylisoquinoline structure.

Molecular cloning and characterization of a cytochrome P450 in sanguinarine biosynthesis from Eschscholzia californica cells

Benzophenanthridine alkaloids, such as sanguinarine, are produced from reticuline, a common intermediate in benzylisoquinoline alkaloid biosynthesis, via protopine. Four cytochrome P450s are involved in the biosynthesis of sanguinarine from reticuline; i.e. cheilanthifoline synthase (CYP719A5; EC 1.14.21.2.), stylopine synthase (CYP719A2/A3; EC 1.14.21.1.), N-methylstylopine hydroxylase (MSH) and protopine 6-hydroxylase (P6H; EC 1.14.13.55.). In this study, a cDNA of P6H was isolated from cultured Eschscholzia californica cells, based on an integrated analysis of metabolites and transcript expression profiles of transgenic cells with Coptis japonica scoulerine-9-O-methyltransferase. Using the full-length candidate cDNA for P6H (CYP82N2v2), recombinant protein was produced in Saccharomyces cerevisiae for characterization. The microsomal fraction containing recombinant CYP82N2v2 showed typical reduced CO-difference spectra of P450, and production of dihydrosanguinarine and dihydrochelerythrine from protopine and allocryptopine, respectively. Further characterization of the substrate-specificity of CYP82N2v2 indicated that 6-hydroxylation played a role in the reaction.

Overproduction of alkaloid phytoalexins in California poppy cells is associated with the co-expression of biosynthetic and stress-protective enzymes

Many plant cells respond to pathogens by the induction of phytoalexin biosynthesis, but the underlying changes of gene expression are often obscured by their close linkage to the complex rearrangements during pathogen defense, especially the hypersensitive cell death. In root-derived cell cultures of Eschscholzia californica, the overproduction of cytotoxic benzophenanthridine alkaloids can be triggered by a minimum of pathogen pressure that does not evoke hypersensitive reactions. Such conditions activate a signal chain that is initiated by a short contact to low concentrations of yeast glycoprotein elicitor and includes a transient acidification of the cytoplasm. In contrast, high elicitor concentrations signal via an increase of jasmonate and trigger hypersensitive cell death, preceded by a drastic decay of translatable mRNAs. The main changes in protein and mRNA patterns caused by either signal path were compared by 2D proteomic separation, MS/MS sequencing and mRNA-in vitro translation. The four proteins showing the highest overexpression were identical between cells that received low or high-elicitor treatment and overlapped with the three proteins most up-regulated by artificial pH shifts. They comprised one biosynthetic enzyme (norcoclaurine:SAM 4' O-methyl-transferase) plus a unique combination of stress-protective proteins: a heat shock protein (hsp 70); a peptidyl-prolyl-cis/trans isomerase (cyclophilin); and a glyceraldehyde-3-phosphate dehydrogenase. It appears that overproduction of the benzophenanthridine phytoalexins requires the up-regulation of a rate-limiting biosynthetic enzyme plus the coordinated expression of a specific set of protective enzymes and thus is managed like an oxidative stress.

Over-expression of rate-limiting enzymes to improve alkaloid productivity

Benzylisoquinoline alkaloids are one of the most important groups of secondary metabolites and include the economically important analgesic morphine and the antimicrobial agent berberine. To improve the productivity of these alkaloids, we investigated the effects of putative rate-limiting step enzymes in alkaloid biosynthesis. We constructed several over-expression vectors for biosynthetic enzymes and introduced them into cultured California poppy, a model isoquinoline alkaloid-producing plant. HPLC/LC-MS analysis of transgenic cells revealed that these enzymes varied in their ability to increase alkaloid production. We describe the use of a rate-limiting step gene to improve alkaloid productivity.

The CRABS CLAW ortholog from California poppy (Eschscholzia californica, Papaveraceae), EcCRC, is involved in floral meristem termination, gynoecium differentiation and ovule initiation

The Arabidopsis transcription factor CRABS CLAW (CRC) is a major determinant of carpel growth and fusion, and, in concert with other redundantly acting genes, of floral meristem termination. Its rice ortholog, however, has additional functions in specifying carpel organ identity. We were interested in understanding the history of gene function modulation of CRC-like genes during angiosperm evolution. Here, we report the identification and functional characterization of EcCRC, the Californica poppy (Eschscholzia californica) CRC ortholog. The downregulation of EcCRC by virus-induced gene silencing (VIGS) produces additional organ whorls that develop exclusively into gynoecia, resulting in a reiteration of the fourth whorl. Additionally, defects in carpel polarity and ovule initiation are apparent, and the observed phenotype is restricted to the gynoecium. Our results further show that the history of CRC-like genes during angiosperm evolution is characterized by gains of function, independent of duplication processes in this gene subfamily. Moreover, our data indicate that the ancestral angiosperm CRC-like gene was involved in floral meristem termination and the promotion of abaxial cell fate in the gynoecium, and that in the lineage leading to Arabidopsis, additional genes have been recruited to adopt some of these functions, resulting in a high degree of redundancy.

The signal molecule lysophosphatidylcholine in Eschscholzia californica is rapidly metabolized by reacylation

In cultured cells of California poppy (Eschscholzia californica), lysophosphatidylcholine (LPC) triggers a signal path that finally induces alkaloid biosynthesis. LPC is transiently generated by elicitor-activated phospholipase A(2) of the plasma membrane. Externally added LPC is rapidly acylated by a membrane-bound enzyme that shows the highest specific activity in the purified plasma membrane. The fatty acid incorporated into the sn-2 position of LPC is preferentially linoleic (18:2), which is the most abundant acyl component in the PC species of Eschscholzia cells, but a minor component of the pool of free fatty acids. The fatty acid at the sn-1 position of LPC is less important for substrate specificity. The capacity of LPC acylation by intact cells or isolated plasma membranes by far exceeds the rate of LPC generation by activated phospholipase A(2) and is not limited by the availability of acyl donors. Metabolites other than phosphatidylcholine (PC) were not significantly produced from labeled LPC within 20 min, indicating that lysophospholipases are not significantly contributing to the short-time metabolism of LPC. It is concluded that reacylation to PC is the dominating process in the detoxication of LPC and ensures the transient character of its steady state concentrations, even at maximum phospholipase A(2) activities.

Differential induction of protein expression and benzophenanthridine alkaloid accumulation in Eschscholtzia californica suspension cultures by methyl jasmonate and yeast extract

Methyl jasmonate (MJ) and yeast extract (YE) induce protein expression and benzophenanthridine alkaloid accumulation in Eschscholtzia californica suspension cell cultures. One hundred microM MJ primarily induced dihydrosanguinarine 509.0+/-7.4 mg/l); 0.2 g/l YE induced sanguinarine (146.8+/- 3.8 mg/l) and an unknown compound. These results occur because dihydrobenzophenanthridine oxidase (DHBO) is induced by YE and not by MJ. YE and chitin (CHI) had similar effects on sanguinarine production and DHBO expression. Differential induction of secondary metabolites was shown in E. californica suspension cultures and the expression of proteins confirmed the metabolite results. Furthermore, treatment by various oligosaccharides helped us to understand the elicitation effect of YE in signal transduction pathways.

Regulatory interaction of the Galpha protein with phospholipase A2 in the plasma membrane of Eschscholzia californica

Plant heterotrimeric G-proteins are involved in a variety of signaling pathways, though only one alpha and a few betagamma isoforms of their subunits exist. In isolated plasma membranes of California poppy (Eschscholzia californica), the plant-specific Galpha subunit was isolated and identified immunologically and by homology of the cloned gene with that of several plants. In the same membrane, phospholipase A(2) (PLA(2)) was activated by yeast elicitor only if GTPgammaS (an activator of Galpha) was present. From the cholate-solubilized membrane proteins, PLA(2) was co-precipitated together with Galpha by a polyclonal antiserum raised against the recombinant Galpha. In this immunoprecipitate and in the plasma membrane (but not in the Galpha-free supernatant) PLA(2) was stimulated by GTPgammaS. Plasma membranes and immunoprecipitates obtained from antisense transformants with a low Galpha content allowed no such stimulation. An antiserum raised against the C-terminus (which in animal Galphas is located near the target coupling site) precipitated Galpha without any PLA(2) activity. Using non-denaturing PAGE, complexes of solubilized plasma membrane proteins were visualized that contained Galpha plus PLA(2) activity and dissociated at pH 9.5. At this pH, PLA(2) was no longer stimulated by GTPgammaS. It is concluded that a distinct fraction of the plasma membrane-bound PLA(2) exists in a detergent-resistant complex with Galpha that can be dissociated at pH 9.5. This complex allows the Galpha-mediated activation of PLA(2).

Large-scale identification of microRNAs from a basal eudicot (Eschscholzia californica) and conservation in flowering plants

MicroRNAs (miRNAs) negatively control gene expression by cleaving or inhibiting the translation of mRNA of target genes, and as such, they play an important role in plant development. Of the 79 plant miRNA families discovered to date, most are from the fully sequenced plant genomes of Arabidopsis, Populus and rice. Here, we identified miRNAs from leaves, roots, stems and flowers at different developmental stages of the basal eudicot species Eschscholzia californica (California poppy) using cloning and capillary sequencing, as well as ultrahigh-throughput pyrosequencing using the recently introduced 454 sequencing method. In total, we identified a minimum of 173 unique miRNA sequences belonging to 28 miRNA families and seven trans-acting small interfering RNAs (ta-siRNAs) conserved in eudicot and monocot species. miR529 and miR537, which have not yet been reported in eudicot species, were detected in California poppy; loci encoding these miRNAs were also found in Arabidopsis and Populus. miR535, which occurs in the moss Physcomitrella patens, was also detected in California poppy, but not in other angiosperms. Several potential miRNA targets were found in cDNA sequences of California poppy. Predicted target genes include transcription factors but also genes implicated in various metabolic processes and in stress defense. Comparative analysis of miRNAs from plants of phylogenetically-critical basal lineages aid the study of the evolutionary gains and losses of miRNAs in plants as well as their conservation, and lead to discoveries about the miRNAs of even well-studied model organisms.

Highly efficient virus-induced gene silencing (VIGS) in California poppy (Eschscholzia californica): an evaluation of VIGS as a strategy to obtain functional data from non-model plants

BACKGROUND AND AIMS

Eschscholzia californica (California poppy) is an emerging model plant for 'evo-devo' studies from the basal eudicot clade of Papaveraceae. California poppy has a relatively small genome, a short life cycle and, most importantly, it is amenable for transformation. However, since this transformation protocol is time consuming, virus-induced gene silencing (VIGS) was evaluated as a fast method to obtain functional data for California poppy genes.

METHODS

Commercially available California poppy plants were infiltrated with Agrobacterium tumefaciens carrying the tobacco rattle virus plasmids pTRV1 and pTRV2. pTRV2 contained part of the eschscholzia Phytoene Desaturase (EcPDS) gene whose loss of function results in photobleaching of the green parts of the plant and in a lack of floral coloration. The degree and duration of these symptoms was evaluated for vegetative rosettes and plants in flower.

KEY RESULTS

It is shown that VIGS is able to effectively down-regulate the EcPDS gene in eschscholzia. Various degrees of silencing were observed starting <2 weeks after infiltration with Agrobacterium tumefaciens in 92 % of the plants. Tissue with silencing symptoms also showed complete or strong reduction of EcPDS transcripts. Strong silencing resulted in almost completely white petals, fruits, shoots and leaves. Plants with a strong degree of silencing will eventually die off; however, others are able to produce EcPDS gene product even after a strong initial silencing and will recover. Silencing was found to be not always systemic, but was often restricted to certain organs or parts of organs.

CONCLUSIONS

VIGS is an effective, fast and transient method to down-regulate gene expression in eschscholzia. It serves well to detect prominent phenotypes which may become obvious even if some target gene transcript remains in the plant tissue. However, subtle phenotypes will be more difficult to detect, as extremely strong silencing effects occur in <10 % of all flowers from infected plants.

Enhanced benzophenanthridine alkaloid production and protein expression with combined elicitor in Eschscholtzia californica suspension cultures

Production of the benzophenanthridine alkaloids in Eschscholtzia californica suspension cell cultures was optimized by adding 0.5 mg methyl jasmonate (MJ) and 0.02 mg salicylic acid (SA)/g FCW after 7 days cultivation. Sanguinarine reached 24 mg/g DCW by such treatment; 10 times higher than in control cell cultures. MJ and SA induced expression of berberine bridge enzyme and 3'-hydroxy-(S)-N-methylcoclaurine-4'-O-methyltransferase, respectively. MJ plus SA induced over-expression of both enzymes.

Overexpression of Coptis japonica norcoclaurine 6-O-methyltransferase overcomes the rate-limiting step in Benzylisoquinoline alkaloid biosynthesis in cultured Eschscholzia californica

Benzylisoquinoline alkaloids are one of the most important secondary metabolite groups, and include the economically important analgesic morphine and the antimicrobial agent berberine. To improve the production of these alkaloids, we investigated the effect of the overexpression of putative rate-limiting step enzymes in benzylisoquinoline alkaloid biosynthesis. We introduced two O-methyltransferase [Coptis japonica norcoclaurine 6-O-methyltransferase (6OMT) and 3'-hydroxy-N-methylcoclaurine 4'-O-methyltransferase (4'OMT)] expression vectors into cultured California poppy cells to avoid the gene silencing effect of endogenous genes. We established 20 independent lines for 6OMT transformants and 15 independent lines for 4'OMT transformants. HPLC/liquid chromatography-mass spectrometry (LC-MS) analysis revealed that the overexpression of C. japonica 6OMT was associated with an average alkaloid content 7.5 times greater than that in the wild type, whereas the overexpression of C. japonica 4'OMT had only a marginal effect. Further characterization of 6OMT in California poppy cells indicated that a 6OMT-specific gene is missing and 4OMT catalyzes the 6OMT reaction with low activity in California poppy, which supports the notion that the 6OMT reaction is important for alkaloid biosynthesis in this plant species. We discuss the importance of 6OMT in benzylisoquinoline alkaloid biosynthesis and the potential for using a rate-limiting step gene to improve alkaloid production.

Molecular cloning and characterization of methylenedioxy bridge-forming enzymes involved in stylopine biosynthesis inEschscholzia californica

(S)-stylopine is an important intermediate in the biosynthesis of benzophenanthridine alkaloids, such as sanguinarine. Stylopine biosynthesis involves the sequential formation of two methylenedioxy bridges. Although the methylenedioxy bridge-forming P450 (CYP719) involved in berberine biosynthesis has been cloned from Coptis japonica[Ikezawa N, Tanaka M, Nagayoshi M, Shinkyo R, Sakaki T, Inouye K & Sato F (2003) J Biol Chem278, 38557-38565], no information is available regarding the genes for methylenedioxy bridge-forming enzymes in stylopine biosynthesis. Two cytochrome P450 cDNAs involved in stylopine biosynthesis were isolated using degenerate primers designed for C. japonica CYP719 from cultured Eschscholzia californica cells. Heterologous expression in Saccharomyces cerevisiae showed that both CYP719A2 and CYP719A3 had stylopine synthase activity to catalyze methylenedioxy bridge-formation from cheilanthifoline to stylopine, but not cheilanthifoline synthase activity to convert scoulerine to cheilanthifoline. Functional differences and expression patterns of CYP719A2 and CYP719A3 were examined to investigate their physiological roles in stylopine biosynthesis. Enzymatic analysis showed that CYP719A2 had high substrate affinity only toward (R,S)-cheilanthifoline, whereas CYP719A3 had high affinity toward three similar substrates (R,S)-cheilanthifoline, (S)-scoulerine, and (S)-tetrahydrocolumbamine. An expression analysis in E. californica plant tissues showed that CYP719A2 and CYP719A3 exhibited expression patterns similar to those of three stylopine biosynthetic genes (CYP80B1, berberine bridge enzyme, and S-adenosyl-l-methionine : 3'-hydroxy-N-methylcoclaurine 4'-O-methyltransferase), whereas the specific expression of CYP719A3 in root was notable. Treatment of E. californica seedlings with methyl jasmonate resulted in the coordinated induction of CYP719A2 and CYP719A3 genes. The physiological roles of CYP719A2 and CYP719A3 in stylopine biosynthesis are discussed.

Knockdown of berberine bridge enzyme by RNAi accumulates (S)-reticuline and activates a silent pathway in cultured California poppy cells

Reticuline is a key compound in the biosynthetic pathway for isoquinoline alkaloids in plants, which include morphine, codeine and berberine. We established cultured California poppy (Eschscholzia californica) cells, in which berberine bridge enzyme (BBE) was knocked down by RNA interference, to accumulate the important key intermediate reticuline. Both BBE mRNA accumulation and enzyme activity were effectively suppressed in transgenic cells. In these transgenic cells, end-products of isoquinoline alkaloid biosynthesis, such as sanguinarine, were considerably reduced and reticuline was accumulated at a maximum level of 310 mug/g-fresh weight. In addition, 1 g-fresh weight of these cells secreted significant amounts of reticuline into the medium, with a maximum level of 6 mg/20 mL culture medium. These cells also produced a methylated derivative of reticuline, laudanine, which could scarcely be detected in control cells. We discuss the potential application of RNAi technology in metabolic modification and the flexibility of plant secondary metabolism.

Analysis of secondary metabolites from eschscholtzia californica by high-performance liquid chromatography

A rapid and precise analytical HPLC method has been developed for screening the major benzophenanthridine alkaloids produced by cell cultures of Eschscholtzia califomica, namely, sanguinarine, chelirubine, macarpine, chelerythrine and chelilutine. Separation was achieved on a C18, reversed-phase column with gradient elution using acetonitrile and 50 mM phosphoric acid. Detection was performed by both fluorescence (lambda(ex) 330 nm, lambda(em) 570 nm) and photodiode array, leading to good selectivity and precision in determining peak purity. A simple and quick sample preparation protocol was elaborated involving a methanolic extraction for the measurement of intracellular concentrations of the alkaloids and a solid phase extraction for their quantification in culture medium. Owing to the non-availability of commercially standards, a method for the purification of chelirubine, macar pine and chelilutine by semi-preparative HPLC was developed. Coupled together, the isolation method and the analytical method were highly reliable for screening the alkaloids of interest produced by E. califomica.

The Galpha protein controls a pH-dependent signal path to the induction of phytoalexin biosynthesis in Eschscholzia californica

The function of a Galpha protein in the elicitation of phytoalexin (benzophenanthridine) biosynthesis was characterized in cultured cells of California poppy (Eschscholzia californica). Both the decrease of Galpha content via antisense transformation and the expression of recombinant anti-Galpha single-chain antibodies strongly impaired the induction of alkaloid biosynthesis by low elicitor concentrations. All transgenic cell types were deficient in two elicitor-triggered early signal events: activation of phospholipase A2 (PLA2) and efflux of vacuolar protons. The lacking H+ efflux could be restored (1) by adding lysophosphatidylcholine (LPC), a product of PLA2 activity, to vacuoles in situ and (2) by exposing intact cells to isotonic, near-neutral HEPES buffers. The latter treatment induced alkaloid biosynthesis in the absence of elicitor and in Galpha-deficient cells. We conclude that Galpha mediates the stimulation of PLA2 by low elicitor concentrations and that the resulting peak of LPC initiates a transient efflux of vacuolar protons. In this way, an acidic peak of the cytoplasmic pH is generated that causes the expression of enzymes of phytoalexin production independent of the hypersensitive response.

Conservation and divergence in the AGAMOUS subfamily of MADS-box genes: evidence of independent sub- and neofunctionalization events

The MADS-box gene AGAMOUS (AG) plays a key role in determining floral meristem and organ identities. We identified three AG homologs, EScaAG1, EScaAG2, and EScaAGL11 from the basal eudicot Eschscholzia californica (California poppy). Phylogenetic analyses indicate that EScaAG1 and EScaAG2 are recent paralogs within the AG clade, independent of the duplication in ancestral core eudicots that gave rise to the euAG and PLENA (PLE) orthologs. EScaAGL11 is basal to core eudicot AGL11 orthologs in a clade representing an older duplication event after the divergence of the angiosperm and gymnosperm lineages. Detailed in situ hybridization experiments show that expression of EScaAG1 and EScaAG2 is similar to AG; however, both genes appear to be expressed earlier in floral development than described in the core eudicots. A thorough examination of available expression and functional data in a phylogenetic context for members of the AG and AGL11 clades reveals that gene expression has been quite variable throughout the evolutionary history of the AG subfamily and that ovule-specific expression might have evolved more than twice. Although sub- and neofunctionalization are inferred to have occurred following gene duplication, functional divergence among orthologs is evident, as is convergence, among paralogs sampled from different species. We propose that retention of multiple AG homologs in several paralogous lineages can be explained by the conservation of ancestral protein activity combined with evolutionarily labile regulation of expression in the AG and AGL11 clades such that the collective functions of the AG subfamily in stamen and carpel development are maintained following gene duplication.

Intracellular pH signals in the induction of secondary pathways--the case of Eschscholzia californica

Transient peaks of the cytoplasmic pH are essential elements in a number of signal cascades that activate environmental responses or developmental processes in plant cells but little is known about the mechanisms of their generation. In many plant cells, elicitation of the hypersensitive response is preceded by a perturbation of the ionic balance at the plasma membrane including the inhibition of the proton pump and the influx of H+ from the apoplast. A basically different mechanism of cytoplasmic acidification that is fed by vacuolar protons has been discovered in cell suspensions of the California Poppy (Eschscholzia californica). These cells react to a yeast glycoprotein elicitor with the overproduction of benzophenanthridine alkaloids. Low elicitor concentrations trigger the biosynthesis of these phytoalexins without invoking elements of the hypersensitive response. Accumulated data support the existence of a signal path that includes the following steps: Links between the above events that connect them within a distinct signal path are substantiated by the phenotypes of transformed cell lines that either display lowered Galpha levels due to antisense transformation or express Galpha-binding antibodies in the cytoplasm. All of these cell lines lack the elicitor-activation of PLA2 and of vacuolar proton fluxes and show an impaired phytoalexin response to low elicitor concentrations. High elicitor concentrations trigger alkaloid biosynthesis via an increase of jasmonate at a pH-independent signal path.

A high-rate perfusion bioreactor for plant cells

A perfusion bioreactor allowing continuous extraction of secondary metabolites was designed and challenged for Eschscholtzia californica plant cell suspensions. Four sedimentation columns mounted inside a 2.5-L bioreactor separated single cells and cell aggregates from the culture medium. Cells were elicited with chitin at day 4 and the liquid medium free of cells and debris was then continuously pumped to the extraction columns containing fluidized XAD-7 resins, and then recirculated back to the cell suspension. A medium upward velocity corresponding to cell sedimentation velocity maintained a stable cell/medium separation front in the columns for sedimented cell volume (SCV) of 90% (70% packed cell volume, PCV). Two perfusion bioreactor cultures of 10 and 14 days were performed. A maximum dilution rate of 20.4/day was reached from day 4 to day 6, and was then reduced to 5/day at day 9 for 55% SCV. Control cultures were performed without and with free extraction resins into the cell suspension. Perfusion cultures showed similar specific growth rates of 0.24 +/- 0.04/day before and after elicitation. However, production level in the perfusion cultures was similar to that from the culture without resins with a maximum of 2.06 micromole/gDW total alkaloids, with 1.54 micromole/gDW in the resins. Cultures with free resins resulted in 30.94 micromole/gDW with 28.4 +/- 8.8 micromole/gDW in the resins. Difference in the cells nutritional state from elicitation was identified as a major cause in the production reduction. However, pathway to chelilutine was favored in the continuous extraction culture.

In situ extraction strategy affects benzophenanthridine alkaloid production fluxes in suspension cultures of Eschscholtzia californica

The effect of contact between cells and extractive phase on secondary metabolite production was investigated in two-phase suspension cultures of Eschscholtzia californica. A system was designed to extract benzophenanthridine alkaloids from the cell culture, without contact between XAD-7 resins and the cells: only medium was recirculated through a column packed with the extractive phase. This strategy was compared to the classic method of addition of resins directly into the cell suspension. Removal of the product directly from the medium enabled important increases in production of alkaloids, namely a 20-fold increase in sanguinarine production and a 10-fold increase in chelerythrine, with high recovery in the resin. The recirculation strategy greatly simplified the production process since the resins are easily recovered from the cell culture and enable harvest of product without termination of culture. However, due to limited flow rate, the recirculation strategy was slightly less effective than direct addition of resins into the cell suspension. In addition to enabling increased production, removal of secondary metabolites from the medium changed metabolic flux distribution, testifying to a complex control mechanism of production.

Development of a small-scale bioreactor: application to in vivo NMR measurement

A perfused bioreactor allowing in vivo NMR measurement was developed and validated for Eschscholtzia californica cells. The bioreactor was made of a 10-mm NMR tube. NMR measurement of the signal-to-noise ratio was optimized using a sedimented compact bed of cells that were retained in the bioreactor by a supporting filter. Liquid medium flow through the cell bed was characterized from a mass balance on oxygen and a dispersive hydrodynamic model. Cell bed oxygen demand for 4 h perfusion required a minimal medium flow rate of 0.8 mL/min. Residence time distribution assays at 0.8-2.6 mL/min suggest that the cells are subjected to a uniform nutrient environment along the cell bed. Cell integrity was maintained for all culture conditions since the release of intracellular esterases was not significant even after 4 h of perfusion. In vivo NMR was performed for (31)P NMR and the spectrum can be recorded after only 10 min of spectral accumulation (500 scans) with peaks identified as G-6P, F-6P, cytoplasmic Pi, vacuolar Pi, ATP(gamma) and ADP(beta), ATP(alpha) and ADP(alpha), NADP and NDPG, NDPG and ATP(beta). Cell viability was shown to be maintained as (31)P chemical shifts were constant with time for all the identified nuclei, thus suggesting constant intracellular pH.

Expression patterns of STM-like KNOX and Histone H4 genes in shoot development of the dissected-leaved basal eudicot plants Chelidonium majus and Eschscholzia californica (Papaveraceae)

Knotted-like homeobox (KNOX) genes encode important regulators of shoot development in flowering plants. In Arabidopsis, class I KNOX genes are part of a regulatory system that contributes to indeterminacy of shoot development, delimitation of leaf primordia and internode development. In other species, class I KNOX genes have also been recruited in the control of marginal blastozone fractionation during dissected leaf development. Here we report the isolation of class I KNOX genes from two species of the basal eudicot family Papaveraceae, Chelidonium majus and Eschscholzia californica. Sequence comparisons and expression patterns indicate that these genes are orthologs of SHOOTMERISTEMLESS (STM), a class I KNOX gene from Arabidopsis. Both genes are expressed in the center of vegetative and floral shoot apical meristems (SAM), but downregulated at leaf or floral organ initiating sites. While Eschscholzia californica STM (EcSTM) is again upregulated during acropetal pinna formation, in situ hybridization could not detect Chelidonium majus STM (CmSTM) transcripts at any stage of basipetal leaf development, indicating divergent evolution of STM gene function in leaves within Papaveraceae. Immunolocalization of KNOX proteins indicate that other gene family members may control leaf dissection in both species. The contrasting direction of pinna initiation in the two species was also investigated using Histone H4 expression. Leaves at early stages of development did not reveal notable differences in cell division activity of the elongating leaf axis, suggesting that differential meristematic growth may not play a role in determining the observed dissection patterns.

Critical influence ofEschscholzia californica cells nutritional state on secondary metabolite production

In this study, we investigated the influence of initial internal nutrient concentrations at the time of elicitation on the ability of Eschscholzia californica (EC) cells to produce alkaloids. Three EC cell suspensions cultivated in culture media differing in their PO4(3-) and NO3- contents were sampled daily for 12 days and analyzed for extracellular and intracellular nutrient concentrations. The ability of the cells to produce alkaloids was tested along the three cell suspension cultures. Sampled cells were then further cultured for 7 days in a production medium containing the elicitor and an extraction resin. The alkaloid production of the cells was measured 7 days post-elicitation. In the low-N medium, starch, glucose, and phosphate contents in the biomass was increased by 470, 1624 and 70%, respectively, 10 days after inoculation compared to the control culture in standard B5 medium. Cell concentration was significantly reduced from 10.3 to 8.6 millions cell/mL on this low-N medium compared to the control, nevertheless alkaloid production was multiplied by 39 at day 10 when cells were elicited. Cells grown on the low-N or low-P media accumulated 83% and 188% more carbon, respectively, than control cells at the end of the culture. This intracellular C was mainly stored in the form of starch in low-P medium and both in the form of starch and glucose in the low-N medium. The ability of EC cells to produce alkaloids upon elicitation was shown to be strongly dependent on the initial intracellular C and P content at the time of elicitation. This suggests that reproducibility and productivity during EC cell culture could be enhanced by manipulating the intracellular C and P content at the time of elicitation.

Selective desensitization of jasmonate- and pH-dependent signaling in the induction of benzophenanthridine biosynthesis in cells of Eschscholzia californica

The biosynthesis of benzophenanthridine alkaloids, phytoalexins of Eschscholzia californica, in cultured cells can be induced by a glycoprotein preparation from yeast, methyljasmonate, artificial acidification with permeant acids, or mild osmotic stress. Each of these stimuli strongly attenuated the subsequent response to the same stimulus (homologous desensitization). Elicitor contact and artificial acidification mutually desensitized the cells for either signal. In contrast, elicitor-treated cells maintained their responsiveness to methyljasmonate or hyperosmolarity (sorbitol). Elicitor concentrations that nearly saturated the alkaloid response did not cause a detectable increase of jasmonate content. Transient acidification of the cytoplasm is a necessary step of signaling by low elicitor concentrations but was not detectable after jasmonate treatment. Seen together, the data indicate the existence of a jasmonate-dependent and jasmonate-independent (Delta pH controlled) signal pathway towards the expression of benzophenanthridine biosynthesis. Selective desensitization allows either stimulus to activate a distinct share of the biosynthetic capacity of the cell and limits the accumulation of toxic defense metabolites.

Immunocytological localization of two enzymes involved in berberine biosynthesis

Using post-embedding immunogold techniques the cytological localization of the two branchpoint enzymes of isoquinoline biosynthesis, berberine bridge enzyme (BBE) and (S)-tetrahydroprotoberberine oxidase (STOX), was demonstrated. Electron-microscopic examination revealed their exclusive compartmentation within vesicles. After these vesicles have fused with the central vacuole, they release their contents, resulting in a characteristic electron-dense precipitate at the tonoplast. Vesicles of similar structure could be identified in young meristematic tissues of roots or shoots from different Berberis species and Papaver somniferum L. The appearance of electron-dense osmiophilic material is strictly correlated with the alkaloid content of the tissue. Immunocytological staining of P. somniferum tissue with antibodies directed against BBE led to a characteristic labeling of electron-dense aggregates in idioblasts that are not connected to the laticifer system. This localization demonstrates the strictly cytological separation of benzophenanthridine and morphine biosyntheses within this plant.