Developmental Methylome of the Medicinal Plant Catharanthus roseus Unravels the Tissue-Specific Control of the Monoterpene Indole Alkaloid Pathway by DNA Methylation.

Catharanthus roseus produces a wide spectrum of monoterpene indole alkaloids (MIAs). MIA biosynthesis requires a tightly coordinated pathway involving more than 30 enzymatic steps that are spatio-temporally and environmentally regulated so that some MIAs specifically accumulate in restricted plant parts. The first regulatory layer involves a complex network of transcription factors from the basic Helix Loop Helix (bHLH) or AP2 families. In the present manuscript, we investigated whether an additional epigenetic layer could control the organ-, developmental- and environmental-specificity of MIA accumulation. We used Whole-Genome Bisulfite Sequencing (WGBS) together with RNA-seq to identify differentially methylated and expressed genes among nine samples reflecting different plant organs and experimental conditions. Tissue specific gene expression was associated with specific methylation signatures depending on cytosine contexts and gene parts. Some genes encoding key enzymatic steps from the MIA pathway were found to be simultaneously differentially expressed and methylated in agreement with the corresponding MIA accumulation. In addition, we found that transcription factors were strikingly concerned by DNA methylation variations. Altogether, our integrative analysis supports an epigenetic regulation of specialized metabolisms in plants and more likely targeting transcription factors which in turn may control the expression of enzyme-encoding genes.

The genuine localization of indole alkaloids in Vinca minor and Catharanthus roseus.

Based on the occurrence of indole alkaloids in so-called "chloroform leaf surface extracts", it was previously deduced that these alkaloids are present in the cuticle at the leaf surface of Catharanthus roseus and Vinca minor. As no symplastic markers were found in these extracts this deduction seemed to be sound. However, since chloroform is known to destroy biomembranes very rapidly, these data have to be judged with scepticism. We reanalyzed the alleged apoplastic localization of indole alkaloids by employing slightly acidic aqueous surface extracts and comparing the corresponding alkaloid patterns with those of aqueous total leaf extracts. Whereas in the "chloroform leaf surface extracts" all alkaloids are present in the same manner as in the total leaf extracts, no alkaloids occur in the aqueous leaf surface extracts. These results clearly show that chloroform had rapidly destroyed cell integrity, and the related extracts also contain the alkaloids genuinely accumulated within the protoplasm. The related decompartmentation was verified by the massively enhanced concentration of amino acids in aqueous surface extracts of chloroform treated leaves. Furthermore, the chloroform-induced cell disintegration was vividly visualized by confocal laser scanning microscopical analyses, which clearly displayed a strong decrease in the chlorophyll fluorescence in chloroform treated leaves. These findings unequivocally display that the indole alkaloids are not located in the apoplastic space, but exclusively are present symplastically within the cells of V. minor and C. roseus leaves. Accordingly, we have to presume that also other leaf surface extracts employing organic solvents have to be re-investigated.

The complexity of intercellular localisation of alkaloids revealed by single-cell metabolomics.

Catharanthus roseus is a medicinal plant well known for producing bioactive compounds such as vinblastine and vincristine, which are classified as terpenoid indole alkaloids (TIAs). Although the leaves of this plant are the main source of these antitumour drugs, much remains unknown on how TIAs are biosynthesised from a central precursor, strictosidine, to various TIAs in planta. Here, we have succeeded in showing, for the first time in leaf tissue of C. roseus, cell-specific TIAs localisation and accumulation with 10 µm spatial resolution Imaging mass spectrometry (Imaging MS) and live single-cell mass spectrometry (single-cell MS). These metabolomic studies revealed that most TIA precursors (iridoids) are localised in the epidermal cells, but major TIAs including serpentine and vindoline are localised instead in idioblast cells. Interestingly, the central TIA intermediate strictosidine also accumulates in both epidermal and idioblast cells of C. roseus. Moreover, we also found that vindoline accumulation increases in laticifer cells as the leaf expands. These discoveries highlight the complexity of intercellular localisation in plant specialised metabolism.

Expression analysis of Cell wall invertase under abiotic stress conditions influencing specialized metabolism in Catharanthus roseus.

Catharanthus roseus is a commercial source for anti-cancer terpenoid indole alkaloids (TIAs: vincristine and vinblastine). Inherent levels of these TIAs are very low, hence research studies need to focus on enhancing their levels in planta. Since primary metabolism provides precursors for specialized-metabolism, elevating the former can achieve higher amounts of the latter. Cell Wall Invertase (CWIN), a key enzyme in sucrose-metabolism catalyses the breakdown of sucrose into glucose and fructose, which serve as carbon-skeleton for specialized-metabolites. Understanding CWIN regulation could unravel metabolic-engineering approaches towards enhancing the levels of TIAs in planta. Our study is the first to characterize CWIN at gene-expression level in the medicinal plant, C. roseus. The CWINs and their inter-relationship with sucrose and TIA metabolism was studied at gene and metabolite levels. It was found that sucrose-supplementation to C. roseus leaves significantly elevated the monomeric TIAs (vindoline, catharanthine) and their corresponding genes. This was further confirmed in cross-species, wherein Nicotiana benthamiana leaves transiently-overexpressing CrCWIN2 showed significant upregulation of specialized-metabolism genes: NbPAL2, Nb4CL, NbCHS, NbF3H, NbANS, NbHCT and NbG10H. The specialized metabolites- cinnamic acid, coumarin, and fisetin were significantly upregulated. Thus, the present study provides a valuable insight into metabolic-engineering approaches towards augmenting the levels of therapeutic TIAs.

Vacuole-Targeted Proteins: Ins and Outs of Subcellular Localization Studies.

Accurate and efficient demonstrations of protein localizations to the vacuole or tonoplast remain strict prerequisites to decipher the role of vacuoles in the whole plant cell biology and notably in defence processes. In this chapter, we describe a reliable procedure of protein subcellular localization study through transient transformations of Catharanthus roseus or onion cells and expression of fusions with fluorescent proteins allowing minimizing artefacts of targeting.

Isolation of Vacuoles from the Leaves of the Medicinal Plant Catharanthus roseus.

The isolation of vacuoles is an essential step to unravel the important and complex functions of this organelle in plant physiology. Here, we describe a method for the isolation of vacuoles from Catharanthus roseus leaves involving a simple procedure for the isolation of protoplasts, and the application of a controlled osmotic/thermal shock to the naked cells, leading to the release of intact vacuoles, which are subsequently purified by density gradient centrifugation. The purity of the isolated intact vacuoles is assayed by microscopy, western blotting, and measurement of vacuolar (V)-H+-ATPase hydrolytic activity. Finally, membrane functionality and integrity is evaluated by measuring the generation of a transtonoplast pH gradient by the V-H+-ATPase and the V-H+-pyrophosphatase, also producing further information on vacuole purity.

The bHLH transcription factor BIS1 controls the iridoid branch of the monoterpenoid indole alkaloid pathway in Catharanthus roseus.

Plants make specialized bioactive metabolites to defend themselves against attackers. The conserved control mechanisms are based on transcriptional activation of the respective plant species-specific biosynthetic pathways by the phytohormone jasmonate. Knowledge of the transcription factors involved, particularly in terpenoid biosynthesis, remains fragmentary. By transcriptome analysis and functional screens in the medicinal plant Catharanthus roseus (Madagascar periwinkle), the unique source of the monoterpenoid indole alkaloid (MIA)-type anticancer drugs vincristine and vinblastine, we identified a jasmonate-regulated basic helix-loop-helix (bHLH) transcription factor from clade IVa inducing the monoterpenoid branch of the MIA pathway. The bHLH iridoid synthesis 1 (BIS1) transcription factor transactivated the expression of all of the genes encoding the enzymes that catalyze the sequential conversion of the ubiquitous terpenoid precursor geranyl diphosphate to the iridoid loganic acid. BIS1 acted in a complementary manner to the previously characterized ethylene response factor Octadecanoid derivative-Responsive Catharanthus APETALA2-domain 3 (ORCA3) that transactivates the expression of several genes encoding the enzymes catalyzing the conversion of loganic acid to the downstream MIAs. In contrast to ORCA3, overexpression of BIS1 was sufficient to boost production of high-value iridoids and MIAs in C. roseus suspension cell cultures. Hence, BIS1 might be a metabolic engineering tool to produce sustainably high-value MIAs in C. roseus plants or cultures.

Effects of Adding Vindoline and MeJA on Production of Vincristine and Vinblastine, and Transcription of their Biosynthetic Genes in the Cultured CMCs of Catharanthus roseus.

Vincristine and vinblastine were found by Liquid Chromatography-Mass Spectrometry (LC-MS) in Catharanthus roseuscambial meristem cells (CMCs) jointly treated with 0.25 mM vindoline and methyl jasmonate (MeJA), suggesting that C. roseus CMCs contain a complete set of the enzymes which are in response to convert vindoline into vincristine and vinblastine. Based on the facts that the transcript levels of vindoline-biosynthetic genes (STR, SGD and D4H) were up-regulated instead of being down-regulated by adding itself to the culture, and that the transcriptional factor ORCA3 was up-regulated simultaneously, we further confirmed that the transcription of STR, SGD, D4H was manipulated by ORCA3.

Synergistic and cytotoxic action of indole alkaloids produced from elicited cell cultures of Catharanthus roseus.

CONTEXT: Catharanthus roseus (L.) G. Don (Apocynaceae) is a medicinal plant that produces more than 130 alkaloids, with special attention given to the production of the anti-hypertensive monomeric indole alkaloids, serpentine and ajmalicine, and the antitumor dimeric alkaloids, vinblastine and vincristine. OBJECTIVE: This study evaluated the cytotoxic activity of the indole alkaloid-enriched bioactive extract obtained from suspension cultured-cells of C. roseus elicited with methyl jasmonate (MJ) and cyclodextrins (CDs) in three cell lines: JURKAT E.6 human lymphocytic leukemia, THP-1 human monocytic leukemia and BL 1395 non-tumor human B-cell line. MATERIALS AND METHODS: An indole alkaloid-enriched bioactive extract was obtained from C. roseus cell cultures elicited with MJ and CDs. The indole alkaloids were identified using an HPLC-diode array system coupled to a time-of-flight mass spectrometer using electrospray ionization (ESI) source. The cytotoxic assays were made using the colorimetric assay 2, 3-bis (2-methoxy-4-nitro-5-sulfophenyl)-S-[(phenylamino)carbonyl]-2 tetrazolium hydroxide (XTT). RESULTS: Four indole alkaloids were identified (catharanthine, ajmalicine, tabersonine and lochnericine) but only catharanthine and ajmalicine were quantified. The concentration of the indole alkaloid-enriched bioactive extract that inhibited cell growth by 50% was 211 and 210 ng/mL for the JURKAT E.6 and THP-1 cell lines, respectively. DISCUSSION AND CONCLUSION: The results confirm that the powerful antitumor activity of this indole alkaloid-enriched bioactive extract is not due to the effect of a single compound but depends on the synergistic action of the four compounds identified.

Gene-to-metabolite networks for terpenoid indole alkaloid biosynthesis in Catharanthus roseus cells.

Rational engineering of complicated metabolic networks involved in the production of biologically active plant compounds has been greatly impeded by our poor understanding of the regulatory and metabolic pathways underlying the biosynthesis of these compounds. Whereas comprehensive genome-wide functional genomics approaches can be successfully applied to analyze a select number of model plants, these holistic approaches are not yet available for the study of nonmodel plants that include most, if not all, medicinal plants. We report here a comprehensive profiling analysis of the Madagascar periwinkle (Catharanthus roseus), a source of the anticancer drugs vinblastine and vincristine. Genome-wide transcript profiling by cDNA-amplified fragment-length polymorphism combined with metabolic profiling of elicited C. roseus cell cultures yielded a collection of known and previously undescribed transcript tags and metabolites associated with terpenoid indole alkaloids. Previously undescribed gene-to-gene and gene-to-metabolite networks were drawn up by searching for correlations between the expression profiles of 417 gene tags and the accumulation profiles of 178 metabolite peaks. These networks revealed that the different branches of terpenoid indole alkaloid biosynthesis and various other metabolic pathways are subject to differing hormonal regulation. These networks also served to identify a select number of genes and metabolites likely to be involved in the biosynthesis of terpenoid indole alkaloids. This study provides the basis for a better understanding of periwinkle secondary metabolism and increases the practical potential of metabolic engineering of this important medicinal plant.

Production of anthocyanins by Catharanthus roseus.

A stable cell suspension line of Catharanthus roseus producing anthocyanin was obtained. In this strain it was found that approximately 30% of cells regularly accumulated these metabolites and that anthocyanin accumulation occurred between the second half of log phase and the stationary phase of the culture growth cycle. The anthocyanins in the suspension cultures were compared with those biosynthetized in the flowers both of regenerated by somatic embryogenesis and field-grown plants. Six anthocyanins were identified in all the examined samples, three 3-O-glucosides and three 3-O-(6-O-p-coumaroyl) glucosides of petunidin, malvidin and hirsutidin. The hirsutidin coumaroyl glucoside has not been reported previously, and was predominat in all samples. The anthocyanin relative content was similar for cell suspensions and flowers from regenerated plants but different from field-grown plant flowers; instead, the total content was almost the same for the two flower types and higher compared to suspension culture content.

Effect of precursor feeding on alkaloid accumulation by a tryptophan decarboxylase over-expressing transgenic cell line T22 of Catharanthus roseus.

To obtain more insight into the regulation of terpenoid indole alkaloid (TIA) biosynthesis in Catharanthus roseus (L.) G. Don cell cultures and particularly to identify possible rate limiting steps, a transgenic cell line over-expressing tryptophan decarboxylase (Tdc), and thus having a high level of tryptamine, was fed with various amounts of precursors (tryptophan, tryptamine, loganin and secologanin) in different time schedules and analyzed for TIA production. When these precursors were added to this culture it was found that the optimal time for supplying the precursors was at inoculation of the cells into the production medium. Alkaloid accumulation by line T22 was enhanced by addition of loganin or secologanin; however, the secologanin feeding was less effective. Tryptamine or tryptophan alone had no effect on TIA accumulation. The over-expression of Tdc causes this cell line to produce quite large quantities of alkaloids after feeding loganin or secologanin. However, in combination with tryptophan or tryptamine, feeding of these precursors resulted in an even further increase of alkaloid accumulation and under optimal conditions line T22 accumulated around 1200 micromol l(-1) of TIAs whereas the control cultures accumulated less than 10 micromol l(-1) TIAs.

Influence of fungal elicitors on production of ajmalicine by cell cultures of Catharanthus roseus.

Suspension cultures of Catharanthus roseus (C. roseus) were elicited with fungal cell wall fragments of Aspergillus niger (A. niger), Fusarium moniliforme (F. moniliforme), and Trichoderma viride (T. viride). The effects of elicitor dosage, exposures time, and age of subculture on ajmalicine accumulation were studied. A higher concentration of elicitor extract responded positively to C. roseus suspension cultures. Ajmalicine accumulation increased by about 3-fold when cells were treated with A. niger, F.moniliforme, and T. viride. The maximum ajmalicine production (75 microg g(-1) dry weight (DW)) was observed in cells treated with T. viride. Cell cultures were elicited with 5% preparation of A. niger, F. moniliforme, and T. viride and exposed for 24, 48, 72, and 96 h. for elicitation. Suspension cultures elicited with T. viride for 48 h showed a 3-fold increase (87 microg g(-1) DW) in ajmalicine contents, whereas A. niger and F. moniliforme synthesized a 2-fold increase in alkaloid and yielded 52 and 56 microg g(-1) DW ajmalicine, respectively. C. roseus cells of different age (5,10, 15, 20, and 25 days old) were treated with a 5% elicitor of A. niger, F. moniliforme, and T. viride and investigated elicitors activity at different age of cell cultures. Maximum yield 166 microg g(-1) DW of ajmalicine was synthesized in 20 day old suspension cultures treated with T. viride. A longer period of incubation of cell cultures with elicitors adversely affected the ajmalicine synthesis.

Sequential solubilization of proteins precipitated with trichloroacetic acid in acetone from cultured Catharanthus roseus cells yields 52% more spots after two-dimensional electrophoresis.

Sample preparation is still the most critical step in two-dimensional gel electrophoresis (2-DE), and needs to be optimized for each type of sample. To analyze the proteome of the medicinal plant Catharanthus roseus, we developed and evaluated a sequential solubilization procedure for the solubilization of proteins after precipitation in trichloroacetic acid and acetone. The procedure includes solubilization with a conventional urea buffer followed by a stronger solubilizing buffer containing thiourea. The sequential solubilization of the precipitated proteins results in very different spot patterns following 2-DE. The number of protein spots which could be detected in both samples of the sequential solubilization was only about 10% of the total number of spots. Compared to solubilization in a single step, the total number of spots that could be detected in the sequential solubilization procedure was increased by 52%. The method described is simple and is applicable to different types of plant tissue.