An approach to the molecular mechanism of methyl jasmonate and vanadyl sulphate elicitation in Taxus baccata cell cultures: The role of txs and bapt gene expression

Overexpression of BAPT and DBTNBT genes in Taxus baccata in vitro cultures to enhance the biotechnological production of paclitaxel

Paclitaxel is one of the most effective anticancer drugs ever developed. Although the most sustainable approach to its production is provided by plant cell cultures, the yield is limited by bottleneck enzymes in the taxane biosynthetic pathway: baccatin-aminophenylpropanoyl-13-O-transferase (BAPT) and 3'-N-debenzoyltaxol N-benzoyltransferase (DBTNBT). With the aim of enhancing paclitaxel production by overcoming this bottleneck, we obtained distinct lines of Taxus baccata in vitro roots, each independently overexpressing either of the two flux-limiting genes, BAPT or DBTNBT, through a Rhizobium rhizogenes A4-mediated transformation. Due to the slow growth rate of the transgenic Taxus roots, they were dedifferentiated to obtain callus lines and establish cell suspensions. The transgenic cells were cultured in a two-stage system and stimulated for taxane production by a dual elicitation treatment with 1 μm coronatine plus 50 mm of randomly methylated-β-cyclodextrins. A high overexpression of BAPT (59.72-fold higher at 48 h) and DBTNBT (61.93-fold higher at 72 h) genes was observed in the transgenic cell cultures, as well as an improved taxane production. Compared to the wild type line (71.01 mg/L), the DBTNBT line produced more than four times higher amounts of paclitaxel (310 mg/L), while the content of this taxane was almost doubled in the BAPT line (135 mg/L). A transcriptional profiling of taxane biosynthetic genes revealed that GGPPS, TXS and DBAT genes were the most reactive to DBTNBT overexpression and the dual elicitation, their expression increasing gradually and constantly. The same genes exhibited a pattern of isolated peaks of expression in the elicited BAPT-overexpressing line.

The advent of plant cells in bioreactors

Ever since agriculture started, plants have been bred to obtain better yields, better fruits, or sustainable products under uncertain biotic and abiotic conditions. However, a new way to obtain products from plant cells emerged with the development of recombinant DNA technologies. This led to the possibility of producing exogenous molecules in plants. Furthermore, plant chemodiversity has been the main source of pharmacological molecules, opening a field of plant biotechnology directed to produce high quality plant metabolites. The need for different products by the pharma, cosmetics agriculture and food industry has pushed again to develop new procedures. These include cell production in bioreactors. While plant tissue and cell culture are an established technology, beginning over a hundred years ago, plant cell cultures have shown little impact in biotechnology projects, compared to bacterial, yeasts or animal cells. In this review we address the different types of bioreactors that are currently used for plant cell production and their usage for quality biomolecule production. We make an overview of Nicotiana tabacum, Nicotiana benthamiana, Oryza sativa, Daucus carota, Vitis vinifera and Physcomitrium patens as well-established models for plant cell culture, and some species used to obtain important metabolites, with an insight into the type of bioreactor and production protocols.

Exploring the Interplay between Metabolic Pathways and Taxane Production in Elicited Taxus baccata Cell Suspensions

Taxus cell cultures are a reliable biotechnological source of the anticancer drug paclitaxel. However, the interplay between taxane production and other metabolic pathways during elicitation remains poorly understood. In this study, we combined untargeted metabolomics and elicited Taxus baccata cell cultures to investigate variations in taxane-associated metabolism under the influence of 1 µM coronatine (COR) and 150 µM salicylic acid (SA). Our results demonstrated pleiotropic effects induced by both COR and SA elicitors, leading to differential changes in cell growth, taxane content, and secondary metabolism. Metabolite annotation revealed significant effects on N-containing compounds, phenylpropanoids, and terpenoids. Multivariate analysis showed that the metabolomic profiles of control and COR-treated samples are closer to each other than to SA-elicited samples at different time points (8, 16, and 24 days). The highest level of paclitaxel content was detected on day 8 under SA elicitation, exhibiting a negative correlation with the biomarkers kauralexin A2 and taxusin. Our study provides valuable insights into the intricate metabolic changes associated with paclitaxel production, aiding its potential optimization through untargeted metabolomics and an evaluation of COR/SA elicitor effects.

Physiological and metabolic traits of Taxol biosynthesis of endophytic fungi inhabiting plants: Plant-microbial crosstalk, and epigenetic regulators

Attenuating the Taxol productivity of fungi with the subculturing and storage under axenic conditions is the challenge that halts the feasibility of fungi to be an industrial platform for Taxol production. This successive weakening of Taxol productivity by fungi could be attributed to the epigenetic down-regulation and molecular silencing of most of the gene clusters encoding Taxol biosynthetic enzymes. Thus, exploring the epigenetic regulating mechanisms controlling the molecular machinery of Taxol biosynthesis could be an alternative prospective technology to conquer the lower accessibility of Taxol by the potent fungi. The current review focuses on discussing the different molecular approaches, epigenetic regulators, transcriptional factors, metabolic manipulators, microbial communications and microbial cross-talking approaches on restoring and enhancing the Taxol biosynthetic potency of fungi to be industrial platform for Taxol production.

Switching cell fate by the actin-auxin oscillator in Taxus: cellular aspects of plant cell fermentation

Paclitaxel synthesis in Taxus cells correlates with a cell-fate switch that leads to vacuoles of a glossy appearance and vermiform mitochondria. This switch depends on actin and apoplastic respiratory burst. Plant cell fermentation, the production of valuable products in plant cell culture, has great potential as sustainable alternative to the exploitation of natural resources for compounds of pharmaceutical interest. However, the success of this approach has remained limited, because the cellular aspects of metabolic competence are mostly unknown. The production of the anti-cancer alkaloid Paclitaxel has been, so far, the most successful case for this approach. In the current work, we map cellular aspects of alkaloid synthesis in cells of Taxus chinensis using a combination of live-cell imaging, quantitative physiology, and metabolite analysis. We show evidence that metabolic potency correlates with a differentiation event giving rise to cells with large vacuoles with a tonoplast that is of a glossy appearance, agglomerations of lipophilic compounds, and multivesicular bodies that fuse with the plasma membrane. Cellular features of these glossy cells are bundled actin, more numerous peroxisomes, and vermiform mitochondria. The incidence of glossy cells can be increased by aluminium ions, and this increase is significantly reduced by the actin inhibitor Latrunculin B, and by diphenylene iodonium, a specific inhibitor of the NADPH oxidase Respiratory burst oxidase Homologue (RboH). It is also reduced by the artificial auxin Picloram. This cellular fingerprint matches the implications of a model, where the differentiation into the glossy cell type is regulated by the actin-auxin oscillator that in plant cells acts as dynamic switch between growth and defence.

Gene expression pattern and taxane biosynthesis in a cell suspension culture of Taxus baccata L. subjected to light and a phenylalanine ammonia lyase (PAL) inhibitor

Taxus baccata L. cell culture is a promising commercial method for the production of taxanes with anti-cancer activities. In the present study, a T. baccata cell suspension culture was exposed to white light and 2-aminoindan-2-phosphonic acid (AIP), a phenylalanine ammonia lyase (PAL) inhibitor, and the effects of this treatment on cell growth, PAL activity, total phenol content (TPC), total flavonoid content (TFC), taxane production and the expression of some key taxane biosynthetic genes (DXS, GGPPS, T13OH, BAPT, DBTNBT) as well as the PAL were studied. Light reduced cell growth, whereas AIP slightly improved it. Light increased PAL activity up to 2.7-fold relative to darkness. The highest TPC (24.89 mg GAE/g DW) and TFC (66.94 mg RUE/g DW) were observed in cultures treated with light and AIP. Light treatment also resulted in the maximum content of total taxanes (154.78 μg/g DW), increasing extracellular paclitaxel and cephalomannin (3.3-fold) and intracellular 10-deacetyl paclitaxel (2.5-fold). Light significantly increased the expression level of PAL, DBTNBT, BAPT, and T13αOH genes, whereas it had no effect on the expression of DXS, a gene active at the beginning of the taxane biosynthetic pathway. AIP had no significant effect on the expression of the target genes. In conclusion, the light-induced activation of PAL transcription and altered expression of relevant biosynthetic genes reduced cell growth and increased the content of total phenolic compounds and taxanes. These findings can be applied to improve taxane production in controlled cultures and bioreactors.

Insights into the control of taxane metabolism: Molecular, cellular, and metabolic changes induced by elicitation in Taxus baccata cell suspensions

More knowledge is needed about the molecular/cellular control of paclitaxel (PTX) production in Taxus spp. cell cultures. In this study, the yield of this anticancer agent in Taxus baccata cell suspensions was improved 11-fold after elicitation with coronatine (COR) compared to the untreated cells, and 18-fold when co-supplemented with methyl-β-cyclodextrins (β-CDs). In the dual treatment, the release of taxanes from the producer cells was greatly enhanced, with 81.6% of the total taxane content being found in the medium at the end of the experiment. The experimental conditions that caused the highest PTX production also induced its maximum excretion, and increased the expression of taxane biosynthetic genes, especially the flux-limiting BAPT and DBTNBT. The application of COR, which activates PTX biosynthesis, together with β - CDs, which form inclusion complexes with PTX and related taxanes, is evidently an efficient strategy for enhancing PTX production and release to the culture medium. Due to the recently described role of lipid droplets (LDs) in the trafficking and accumulation of hydrophobic taxanes in Taxus spp. cell cultures, the structure, number and taxane storage capacity of these organelles was also studied. In elicited cultures, the number of LDs increased and they mainly accumulated taxanes with a side chain, especially PTX. Thus, PTX constituted up to 50-70% of the total taxanes found in LDs throughout the experiment in the COR + β - CD-treated cultures. These results confirm that LDs can store taxanes and distribute them inside and outside cells.

Application of Priming Strategy for Enhanced Paclitaxel Biosynthesis in Taxus × Media Hairy Root Cultures

Despite huge progress in biotechnological approaches to paclitaxel production, Taxus spp. in vitro culture productivity still remains a challenge. This could be solved by developing a new strategy engaging mechanisms of the primed defence response joined with subsequent elicitation treatment to circumvent limitations in paclitaxel biosynthesis. The hairy roots were primed by preincubation with β-aminobutyric acid (BABA) for 24 h or 1 week, and then elicited with methyl jasmonate (MeJA) or a mixture of MeJA, sodium nitroprusside and L-phenylalanine (MIX). The effect of priming was evaluated on a molecular level by examination of the expression profiles of the four genes involved in paclitaxel biosynthesis, i.e., TXS (taxadiene synthase), BAPT (baccatin III: 3-amino, 3-phenylpropanoyltransferase), DBTNBT (3′-N-debenzoyl-2-deoxytaxol-N-benzoyltransferase) and PAM (phenylalanine aminomutase), as well as rolC (cytokinin-β-glucosidase), originated from the T-DNA of Agrobacterium rhizogenes. The maximum paclitaxel yield was achieved in cultures primed with BABA for 1 week and elicited with MIX (3179.9 ± 212 µg/g dry weight), which corresponded to the highest expression levels of TXS and BAPT genes. Although BABA itself induced the investigated gene expression over control level, it was not translated into paclitaxel production. Nevertheless, preincubation with BABA essentially affected paclitaxel yield, and the duration of BABA pretreatment seemed to have the most pronounced impact on its productivity.

Improved biotechnological production of paclitaxel in Taxus media cell cultures by the combined action of coronatine and calix[8]arenes

Paclitaxel (PTX), a widely used anticancer agent, is found in the inner bark of several Taxus species, although at such low levels that its extraction is ecologically unsustainable. Biotechnological platforms based on Taxus sp. cell cultures offer an eco-friendlier approach to PTX production, with yields that can be improved by elicitation. However, the also limited excretion of target compounds from the producer cells to the medium hampers their extraction and purification. In this context, we studied the effect of treating T. media cell cultures with the elicitor coronatine (COR) and calix[8]arenes (CAL), nanoparticles that can host lipophilic compounds within their macrocyclic scaffold. The highest taxane production (103.5 mg.L^-1), achieved after treatment with COR (1 μM) and CAL (10 mg.L^-1), was 15-fold greater than in the control, and PTX represented 82% of the total taxanes analyzed. Expression levels of the flux-limiting PTX biosynthetic genes, BAPT and DBTNBT, increased after the addition of COR, confirming its elicitor action, but not CAL. The CAL treatment significantly enhanced taxane excretion, especially when production levels were increased by COR; 98% of the total taxanes were found in the culture medium after COR + CAL treatment. By forming complexes with PTX, the nanoparticles facilitated its excretion to the medium, and by protecting cells from PTX toxicity, its intra-and extra-cellular degradation may have been avoided. The addition of COR and CAL to T. media cell cultures is therefore a bio-sustainable and economically viable system to improve the yield of this important anticancer compound.

Biotechnological approaches to the production of plant-derived promising anticancer agents: An update and overview

The plant kingdom is a rich source of bioactive compounds, many of which have been used since pre-history for their therapeutic properties to treat a range of illnesses. These metabolites have recently attracted attention to their antineoplastic activities to treat various cancers relying on different mechanisms. Some of these molecules are glycosides, which have proven useful as anti-cancer agents, namely podophyllotoxin (PPT) anaryltetralin lignan or alkaloids. There are three primary forms of alkaloids, such as indole alkaloids (vincristine and vinblastine from Catharanthus roseus), quinoline alkaloid (camptothecin from Camptotheca acuminata), and diterpenoid alkaloid (taxol and it's analogous from Taxus and Corylus species). This review considers various plant biotechnology approaches used to enhance the production of these anticancer molecules in different species. In this regard, many in vitro culture techniques such as stimulation of suspension culture and hairy roots are being used to investigate the effects of plant growth regulators and elicitors on various explants.

Comparison of elicitor-based effects on metabolic responses of Taxus × media hairy roots in perfluorodecalin-supported two-phase culture system

Two lines of Taxus × media hairy roots harbouring or not the TXS transgene demonstrated diverse gene expression and taxane yield during cultivation in PFD-supported two liquid-phase culture system. Two lines of Taxus × media hairy roots were subjected to single or twice-repeated supplementation with methyl jasmonate, sodium nitroprusside, L-phenylalanine, and sucrose feeding. One line harboured transgene of taxadiene synthase (ATMA), while the second (KT) did not. Both hairy root lines were cultured in two-phase culture systems containing perfluorodecalin (PFD) in aerated or degassed form. The relationship between TXS (taxadiene synthase), BAPT (baccatin III: 3-amino, 3-phenylpropanoyltransferase), and DBTNBT (3'-N-debenzoyl-2-deoxytaxol-N-benzoyltransferase) genes and taxane production was analysed. The ATMA and KT lines differed in their potential for taxane accumulation, secretion, and taxane profile. In ATMA biomass, both paclitaxel and baccatin III were detected, while in KT roots only paclitaxel. The most suitable conditions for taxane production for ATMA roots were found in single-elicited supported with PFD-degassed cultures (2 473.29 ± 263.85 µg/g DW), whereas in KT roots in single-elicited cultures with PFD-aerated (470.08 ± 25.15 µg/g DW). The extracellular levels of paclitaxel never exceeded 10% for ATMA roots, while for KT increased up to 76%. The gene expression profile was determined in single-elicited cultures supported with PFD-degassed, where in ATMA roots, the highest taxane yield was obtained, while in KT the lowest one. The gene expression pattern in both investigated root lines differed substantially what resulted in taxane yield characterized particular lines. The highest co-expression of TXS, BAPT and DBTNBT genes noted for ATMA roots harvested 48 h after elicitation corresponded with their higher ability for taxane production in comparison with the effects observed for KT roots.

Transcriptome profiling reveals specific patterns of paclitaxel synthesis in a new Taxus yunnanensis cultivar

The difference in contents of paclitaxel and 10-deacetylbaccatin III (10-DABIII) in needles between wildtype (WT) and a new cultivar (Zhongdayihao, ZD1) of Taxus yunnanensis was examined. Transcriptome profiling was conducted for different tissues of the ZD1 and WT to illustrate the regulation mechanism of paclitaxel biosynthesis. It was observed that average contents of paclitaxel and 10-DABIII in ZD1 were 4 folds and 32 folds higher than those in WT, respectively. More significant elevations of differential expressed genes (DEGs) from paclitaxel biosynthesis pathway were revealed in ZD1 rather than WT, which should be responsible for the higher contents of paclitaxel and 10-DABIII in the ZD1. Special tissues-dependent expression patterns of paclitaxel biosynthesis DEGs in ZD1 compared to WT were unraveled. The relative higher expressions of paclitaxel biosynthesis genes in needles than other tissues supported the higher content of paclitaxel and 10-DABIII content in needles of ZD1. Attenuation of plant hormone signal transduction pathway led to the lower expression of TFs in ZD1 rather than WT. Besides, the significant negative correlations between differential expressed TFs and DEGs from paclitaxel biosynthesis pathway displayed a possibly negative regulation pattern of these TFs on paclitaxel biosynthesis pathway genes. These results provided new insights into the molecular process of paclitaxel synthesis in Taxus.

Perfluorodecalins and Hexenol as Inducers of Secondary Metabolism in Taxus media and Vitis vinifera Cell Cultures

Plant cell cultures constitute a potentially efficient and sustainable tool for the production of high added-value bioactive compounds. However, due to the inherent restrictions in the expression of secondary metabolism, to date the yields obtained have generally been low. Plant cell culture elicitation can boost production, sometimes leading to dramatic improvements in yield, as well as providing insight into the target biosynthetic pathways and the regulation of the genes involved. Among the secondary compounds successfully being produced in biotechnological platforms are taxanes and trans-resveratrol (t-R). In the current study, perfluorodecalins (PFDs) and hexenol (Hex) were tested for the first time with Taxus media and Vitis vinifera cell cultures to explore their effect on plant cell growth and secondary metabolite production, either alone or combined with other elicitors already established as highly effective, such as methyl jasmonate (MeJa), coronatine (Coro) or randomly methylated β-cyclodextrins (β-CDs). The total taxane content at the peak of production in T. media cell cultures treated with PFDs together with Coro plus β-CDs was 3.3-fold higher than in the control, whereas the t-R production in MeJa and β-CD-treated V. vinifera cell cultures increased 552.6-fold compared to the extremely low-yielding control. Hex was ineffective as an elicitor in V. vinifera cell cultures, and in T. media cell suspensions it blocked the taxol production but induced a clear enhancement of baccatin III. Regarding biosynthetic gene expression, a strong positive relationship was observed between the transcript level of targeted genes and taxol production in the T. media cell cultures, but not with t-R production in the elicited V. vinifera cell cultures.

Elicitation, an Effective Strategy for the Biotechnological Production of Bioactive High-Added Value Compounds in Plant Cell Factories

Plant in vitro cultures represent an attractive and cost-effective alternative to classical approaches to plant secondary metabolite (PSM) production (the “Plant Cell Factory” concept). Among other advantages, they constitute the only sustainable and eco-friendly system to obtain complex chemical structures biosynthesized by rare or endangered plant species that resist domestication. For successful results, the biotechnological production of PSM requires an optimized system, for which elicitation has proved one of the most effective strategies. In plant cell cultures, an elicitor can be defined as a compound introduced in small concentrations to a living system to promote the biosynthesis of the target metabolite. Traditionally, elicitors have been classified in two types, abiotic or biotic, according to their chemical nature and exogenous or endogenous origin, and notably include yeast extract, methyl jasmonate, salicylic acid, vanadyl sulphate and chitosan. In this review, we summarize the enhancing effects of elicitors on the production of high-added value plant compounds such as taxanes, ginsenosides, aryltetralin lignans and other types of polyphenols, focusing particularly on the use of a new generation of elicitors such as coronatine and cyclodextrins.

Transcript profiling of jasmonate-elicited Taxus cells reveals a β-phenylalanine-CoA ligase

Plant cell cultures constitute eco-friendly biotechnological platforms for the production of plant secondary metabolites with pharmacological activities, as well as a suitable system for extending our knowledge of secondary metabolism. Despite the high added value of taxol and the importance of taxanes as anticancer compounds, several aspects of their biosynthesis remain unknown. In this work, a genomewide expression analysis of jasmonate-elicited Taxus baccata cell cultures by complementary DNA-amplified fragment length polymorphism (cDNA-AFLP) indicated a correlation between an extensive elicitor-induced genetic reprogramming and increased taxane production in the targeted cultures. Subsequent in silico analysis allowed us to identify 15 genes with a jasmonate-induced differential expression as putative candidates for genes encoding enzymes involved in five unknown steps of taxane biosynthesis. Among them, the TB768 gene showed a strong homology, including a very similar predicted 3D structure, with other genes previously reported to encode acyl-CoA ligases, thus suggesting a role in the formation of the taxol lateral chain. Functional analysis confirmed that the TB768 gene encodes an acyl-CoA ligase that localizes to the cytoplasm and is able to convert β-phenylalanine, as well as coumaric acid, into their respective derivative CoA esters. β-phenylalanyl-CoA is attached to baccatin III in one of the last steps of the taxol biosynthetic pathway. The identification of this gene will contribute to the establishment of sustainable taxol production systems through metabolic engineering or synthetic biology approaches.

Changes in gene transcription and taxane production in elicited cell cultures of Taxus × media and Taxus globosa

The response of two Taxus cell systems to the action of cyclodextrin (CD) and coronatine (CORO), supplied to the culture medium either separately or together, was studied. Two-stage Taxus globosa and Taxus media cell cultures were established and the elicitors were added at the beginning of the second stage. Growth, taxane production, and the expression of known taxol biosynthetic genes, including the recently characterized CoA ligase gene, were studied. Although CORO reduced the growth capacity of both cell lines, CD apparently counteracted this negative effect. Taxane production was significantly enhanced by the simultaneous addition of CD and CORO to the medium. The total taxane production in the T. media cell line was more than double that of T. globosa, but in the latter more than 90% of the taxanes produced were excreted to the medium. Individual taxane patterns also differed: at the height of production, the main taxanes in T. globosa cultures were cephalomannine and 10-deacetyltaxol, and in T. media, taxol and baccatin III. The low transcript levels of taxane biosynthetic genes found in T. globosa cells mirrored the lower taxane production in these cultures, while a high expression was strongly correlated with a high taxane production in T. media.

Synergistic effect of cyclodextrins and methyl jasmonate on taxane production in Taxus x media cell cultures

Methyl jasmonate and cyclodextrins are proven effective inducers of secondary metabolism in plant cell cultures. Cyclodextrins, which are cyclic oligosaccharides, can form inclusion complexes with nonhydrophilic secondary products, thus increasing their excretion from the producer cells to the culture medium. In the present work, using a selected Taxus x media cell line cultured in a two-stage system, the relationship between taxane production and the transcript profiles of several genes involved in taxol metabolism was studied to gain more insight into the mechanism by which these two elicitors regulate the biosynthesis and excretion of taxol and related taxanes. Gene expression was not clearly enhanced by the presence of cyclodextrins in the culture medium and variably induced by methyl jasmonate, but when the culture was supplemented with both elicitors, a synergistic effect on transcript accumulation was observed. The BAPT and DBTNBT genes, which encode the last two transferases involved in the taxol pathway, appeared to control limiting biosynthetic steps. In the cell cultures treated with both elicitors, the produced taxanes were found mainly in the culture medium, which limited retroinhibition processes and taxane toxicity for the producer cells. The expression level of a putative ABC gene was found to have increased, suggesting it played a role in the taxane excretion. Taxol biosynthesis was clearly increased by the joint action of methyl jasmonate and cyclodextrins, reaching production levels 55 times higher than in nonelicited cultures.

Taximin, a conserved plant-specific peptide is involved in the modulation of plant-specialized metabolism

Small peptides play important roles in the signalling cascades that steer plant growth, development and defence, and often crosstalk with hormonal signalling. Thereby, they also modulate metabolism, including the production of bioactive molecules that are of high interest for human applications. Yew species (Taxus spp.) produce diterpenes such as the powerful anticancer agent paclitaxel, the biosynthesis of which can be stimulated by the hormone jasmonate, both in whole plants and cell suspension cultures. Here, we identified Taximin, as a gene encoding a hitherto unreported, plant-specific, small, cysteine-rich signalling peptide, through a transcriptome survey of jasmonate-elicited T. baccata suspension cells grown in two-media cultures. Taximin expression increased in a coordinated manner with that of paclitaxel biosynthesis genes. Tagged Taximin peptides were shown to enter the secretory system and localize to the plasma membrane. In agreement with this, the exogenous application of synthetic Taximin peptide variants could transiently modulate the biosynthesis of taxanes in T. baccata cell suspension cultures. Importantly, the Taximin peptide is widely conserved in the higher plant kingdom with a high degree of sequence conservation. Accordingly, Taximin overexpression could stimulate the production of nicotinic alkaloids in Nicotiana tabacum hairy root cultures in a synergistic manner with jasmonates. In contrast, no pronounced effects of Taximin overexpression on the specialized metabolism in Medicago truncatula roots were observed. This study increases our understanding of the regulation of Taxus diterpene biosynthesis in particular and plant metabolism in general. Ultimately, Taximin might increase the practical potential of metabolic engineering of medicinal plants.

Induction of extracellular defense-related proteins in suspension cultured-cells of Daucus carota elicited with cyclodextrins and methyl jasmonate

Suspension cultured-cells (SCC) of Daucus carota were used to evaluate the effect of methyl jasmonate and cyclodextrins, separately or in combination, on the induction of defense responses, particularly the accumulation of pathogenesis-related proteins. A comparative study of the extracellular proteome (secretome) between control and elicited carrot SCC pointed to the presence of amino acid sequences homologous to glycoproteins which have inhibitory activity against the cell-wall-degrading enzymes secreted by pathogens and/or are induced when carrot cells are exposed to a pathogen elicitor. Other amino acid sequences were homologous to Leucine-Rich Repeat domain-containing proteins, which play an essential role in defense against pathogens, as well as in the recognition of microorganisms, making them important players in the innate immunity of this plant. Also, some tryptic peptides were shown to be homologous to a thaumatin-like protein, showing high specificity to abiotic stress and to different reticuline oxidase-like proteins that displayed high levels of antifungal activity, suggesting that methyl jasmonate and cyclodextrins could play a role in mediating defense-related gene product expression in SCC of D. carota. Apart from these elicitor-inducible proteins, we observed the presence of PR-proteins in both control and elicited carrot SCC, suggesting that their expression is mainly constitutive. These PR-proteins are putative class IV chitinases, which also have inhibitory activity against pathogen growth and the class III peroxidases that participate in response to environmental stress (e.g. pathogen attack and oxidative), meaning that they are involved in defense responses triggered by both biotic and abiotic factors.

Correlation analysis of the taxane core functional group modification, enzyme expression, and metabolite accumulation profiles under methyl jasmonate treatment

Metabolomic and transcriptomic profiling data were obtained and integrated to elucidate the crucial network controls on taxol and its precursor biosynthesis during the taxane core functionalization within methyl jasmonate (MJ)-induced Taxus chinensis cells. Twelve metabolites were identified using liquid chromatography-electrospray ionization-mass spectrometry. These metabolites contain taxol (paclitaxel), baccatin III (B-III) and its analogs, a group structurally bearing multiple free hydroxyls (TAX), and another group of multiple acyl taxanes (MAT), including taxuyunnanine C (TC) and its analogs. The metabolomic profile showed a higher increase in TAX than in MAT. Particularly, the ratio of B-III and taxol to the total taxane content increased more significantly in TAX than in MAT. The MAT proportion did not significantly change, although they are predominant components in cell cultures compared with TAX. Quantitative real-time polymerase chain reaction (qRT-RCR) was used to determine the transcription level of 20 genes, among which 11 were reported responsible for taxol biosynthesis and 9 were obtained from our previous transcriptomic data. The total expression levels of hydroxylase after 24 h and 6 days were higher than those of acylase. The principal component analysis (PCA) results validated the metabolomic analysis data, indicating that hydroxylation was more crucial than acylation for controlling the flux toward TAX biosynthesis. Furthermore, the PCA contribution comparison showed that two undefined genes of OHX1 and ACX3 might have good potential in TAX upregulation and MAT downregulation. To the best of our knowledge, this study provides the first experimental evidence on the contribution of total hydroxylation to taxane biosynthesis.

Coronatine, a more powerful elicitor for inducing taxane biosynthesis in Taxus media cell cultures than methyl jasmonate

Coronatine is a toxin produced by the pathogen Pseudomonas syringae. This compound has received much attention recently for its potential to act as a plant growth regulator and elicitor of plant secondary metabolism. To gain more insight into the mechanism by which elicitors can affect the biosynthesis of paclitaxel (Px) and related taxanes, the effect of coronatine (Cor) and methyl jasmonate (MeJA) on Taxus media cell cultures has been studied. For this study, a two-stage cell culture was established, in which cells were first cultured for 14 days in a medium optimised for growth, after which the cells were transferred to medium optimised for secondary metabolite production. The two elicitors were added to the medium at the beginning of the second stage. Total taxane production in the cell suspension was significantly enhanced by both elicitors, increasing from a maximum level of 8.14mg/L in control conditions to 21.48mg/L (day 12) with MeJA and 77.46mg/L (day 16) with Cor. Expression analysis indicated that the txs, t13oh, t2oh, t7oh, dbat, pam, bata and dbtnbt genes were variably induced by the presence of the elicitors. Genes encoding enzymes involved in the formation of the polihydroxylated hypothetical intermediate (TXS, T13OH, T2OH, T7OH) and the phenylalanoil CoA chain (PAM) were stronger induced than those encoding enzymes catalysing the last steps of the Px biosynthetic pathway (DBAT, BAPT and DBTNBT). Notably, although taxane accumulation differed qualitatively and quantitatively following MeJA- or Cor-elicitation, gene expression induction patterns were similar, inferring that both elicitors may involve distinct but yet uncharacterised regulatory mechanisms.

The relationship between TXS, DBAT, BAPT and DBTNBT gene expression and taxane production during the development of Taxus baccata plantlets

Taxol and related taxane accumulation in plants is regulated by the expression of genes involved in their biosynthesis. Although the metabolic pathway leading to taxol has been almost completely elucidated, comparatively little is known about the rate-limiting steps and their regulation. In this paper we report on a study of taxane production in Taxus baccata plantlets grown in vitro for 1 year. The relationship between taxane patterns and the expression of genes encoding the enzymes taxadiene synthase (TXS), 10-deacetylbaccatin III-10β-O-acetyltransferase (DBAT), baccatin III 13-O-(3-amino-3-phenylpropanoyl) transferase (BAPT) and 3'-N-debenzoyl-2'-deoxytaxol-N-benzoyltransferase (DBTNBT), involved in early and late steps of the taxane pathway, has been considered. A far higher content was found in the aerial part of the plantlets than in the roots. The most abundant taxane in the aerial parts was 10-deacetylbaccatin III, which increased as the plantlets grew, indicating a low conversion to baccatin III and taxol. In contrast, the levels of 10-deacetylbaccatin III in the roots remained lower than those of taxol. These results correlated with transcript accumulation of the studied genes, since in the aerial parts the expression of DBAT, which codes for the enzyme that converts 10-deacetylbaccatin III into baccatin III, did not increase with the age of plantlets, unlike that of TXS, BAPT and DBTNBT, suggesting that this gene controls a rate-limiting step in the taxane biosynthetic pathway. The lower taxane levels found in the roots also correlated with gene expression, since only the early pathway gene TXS was induced in this organ during the 1-year growth period.