A rational approach to improving the biotechnological production of taxanes in plant cell cultures of Taxus spp

Eco-friendly approaches to phytochemical production: elicitation and beyond

Highly ameliorated phytochemicals from plants are recognized to have numerous beneficial effects on human health. However, obtaining secondary metabolites directly from wild plants is posing a great threat to endangered plant species due to their over exploitation. Moreover, due to complicated structure and stereospecificity chemical synthesis of these compounds is a troublesome procedure. As a result, sustainable and ecofriendly in vitro strategy has been adopted for phytochemicals production. But, lack of fully differentiated cells lowers down cultured cells productivity. Consequently, for enhancing yield of metabolites produced by cultured plant cells a variety of methodologies has been followed one such approach includes elicitation of culture medium that provoke stress responses in plants enhancing synthesis and storage of bioactive compounds. Nevertheless, for conclusive breakthrough in synthesizing bioactive compounds at commercial level in-depth knowledge regarding metabolic responses to elicitation in plant cell cultures is needed. However, technological advancement has led to development of molecular based approaches like metabolic engineering and synthetic biology which can serve as promising path for phytochemicals synthesis. This review article deals with classification, stimulating effect of elicitors on cultured cells, parameters of elicitors and action mechanism in plants, modern approaches like metabolic engineering for future advances.

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.

Transcriptomics and Physiological Analyses Reveal Changes in Paclitaxel Production and Physiological Properties in Taxus cuspidata Suspension Cells in Response to Elicitors

In this research, the cell growth, physiological, and biochemical reactions, as well as the paclitaxel production, of Taxus cuspidata suspension cells after treatment with polyethylene glycol (PEG), cyclodextrin (CD), or salicylic acid (SA) (alone or in combination) were investigated. To reveal the paclitaxel synthesis mechanism of T. cuspidata suspension cells under elicitor treatment, the transcriptomics of the Control group and P + C + S group (PEG + CD + SA) were compared. The results show that there were no significant differences in cell biomass after 5 days of elicitor treatments. However, the content of hydrogen peroxide (H2O2) and malondialdehyde (MDA), and the activities of phenylalanine ammonia-lyase (PAL) and polyphenol oxidase (PPO) after elicitor combination treatments were decreased compared with the single-elicitor treatment. Meanwhile, the antioxidant enzyme activity (superoxide dismutase (SOD), catalase (CAT), and peroxidase (PO)) and the contents of soluble sugar and soluble protein were increased after combination elicitor treatments. Additionally, the paclitaxel yield after treatment with the combination of all three elicitors (P + C + S) was 6.02 times higher than that of the Control group, thus indicating that the combination elicitor treatments had a significant effect on paclitaxel production in T. cuspidata cell suspension culture. Transcriptomics analysis revealed 13,623 differentially expressed genes (DEGs) between the Control and P + C + S treatment groups. Both GO and KEGG analyses showed that the DEGs mainly affected metabolic processes. DEGs associated with antioxidant enzymes, paclitaxel biosynthesis enzymes, and transcription factors were identified. It can be hypothesized that the oxidative stress of suspension cells occurred with elicitor stimulation, thereby leading to a defense response and an up-regulation of the gene expression associated with antioxidant enzymes, paclitaxel synthesis enzymes, and paclitaxel synthesis transcription factors; this ultimately increased the production of paclitaxel.

Increased paclitaxel recovery from Taxus baccata vascular stem cells using novel in situ product recovery approaches

In this study, several approaches were tested to optimise the production and recovery of the widely used anticancer drug Taxol® (paclitaxel) from culturable vascular stem cells (VSCs) of Taxus baccata, which is currently used as a successful cell line for paclitaxel production. An in situ product recovery (ISPR) technique was employed, which involved combining three commercial macro-porous resin beads (HP-20, XAD7HP and HP-2MG) with batch and semi-continuous cultivations of the T. baccata VSCs after adding methyl jasmonate (Me-JA) as an elicitor. The optimal resin combination resulted in 234 ± 23 mg of paclitaxel per kg of fresh-weight cells, indicating a 13-fold improved yield compared to the control (with no resins) in batch cultivation. This resin treatment was further studied to evaluate the resins' removal capacity of reactive oxygen species (ROS), which can cause poor cell growth or reduce product synthesis. It was observed that the ISPR cultivations had fourfold less intracellular ROS concentration than that of the control; thus, a reduced ROS concentration established by the resin contributed to increased paclitaxel yield, contrary to previous studies. These paclitaxel yields are the highest reported to date using VSCs, and this scalable production method could be applied for a diverse range of similar compounds utilising plant cell culture.

Polyploidy as a strategy to increase taxane production in yew cell cultures: Obtaining and characterizing a Taxus baccata tetraploid cell line

Novel approaches to optimize the production of plant specialized metabolites are crucial to reach maximum productivity of plant biofactories. Plant polyploidization frequently enhances protein synthesis and thereby increases the biosynthesis of specialized metabolites. Paclitaxel is a valuable anticancer agent scarcely produced in nature. Therefore, plant biofactories represent a sustainable alternative source of this compound and related taxanes. With the aim of improving the productivity of Taxus spp. cell cultures, we induced polyploidy in vitro by treating immature embryos of Taxus baccata with colchicine. To obtain the polyploid cell lines, calli were induced from T. baccata plantlets previously treated with colchicine and ploidy levels were accurately identified using flow cytometry. In terms of cell morphology, tetraploid cells were about 3-fold bigger than the diploid cells. The expression of taxane pathway genes was higher in the tetraploid cell line compared to the diploid cells. Moreover, taxane production was 6.2-fold higher and the production peak was achieved 8 days earlier than in the diploid cell line, indicating a higher productivity. The obtained tetraploid cell line proved to be highly productive, constituting a step forward towards the development of a bio-sustainable production system for this chemotherapeutic drug.

Effect of Methyl Jasmonate on the Growth and Biosynthesis of C13- and C14-Hydroxylated Taxoids in the Cell Culture of Yew (Taxus wallichiana Zucc.) of Different Ages

The effects of methyl jasmonate (MeJ) on growth and taxoid formation in the cell culture of Taxus wallichiana were investigated to elucidate the specifics of phytohormone action in dedifferentiated plant cells in vitro. The characteristics of the same suspension cell culture were compared in 2017 (the «young» culture) and in 2022 (the «old» culture)-1.5 or 6 years after culture induction, respectively. MeJ (100 µM) is added to the cell suspension at the end of the exponential growth phase. Cell culture demonstrated good growth (dry weight accumulation 10-18 g/L, specific growth rate µ = 0.15-0.35 day^-1) regardless of its «age», cultivation system, and MeJ addition. UPLC-ESI-MS analysis revealed the presence of C14-hydroxylated taxoids (yunnanxane, taxuyunnanine C, sinenxane C, and sinenxane B) in the cell biomass. The content of C14-OH taxoids increased from 0.2-1.6 mg/gDW in «young» culture to 0.6-10.1 mg/gDW in «old» culture. Yunnanxane was the main compound in «young» culture, while sinenxane C predominated in «old» culture. Without elicitation, small amounts of C13-OH taxoids (<0.05 mg/gDW) were found only in «young» cultures. MeJ addition to «young» culture had no effect on the content of C14-OH taxoids but caused a 10-fold increase in C13-OH taxoid production (up to 0.12-0.19 mg/gDW, comparable to the bark of yew trees). By contrast, MeJ added to «old» culture was not beneficial for the production of C13-OH taxoids but notably increased the content of C14-OH taxoids (1.5-2.0 times in flasks and 5-8 times in bioreactors). These findings suggest that hormonal signaling in dedifferentiated yew cells grown in vitro is different from that in plants and can be affected by the culture's age. This might be a result of the high level of culture heterogeneity and constant auto-selection for intensive proliferation, which leads to the predominant formation of C14-OH taxoids versus C13-OH taxoids and a modified cell response to exogenous MeJ treatment.

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.

Transcriptional regulatory network of high-value active ingredients in medicinal plants

High-value active ingredients in medicinal plants have attracted research attention because of their benefits for human health, such as the antimalarial artemisinin, anticardiovascular disease tanshinones, and anticancer Taxol and vinblastine. Here, we review how hormones and environmental factors promote the accumulation of active ingredients, thereby providing a strategy to produce high-value drugs at a low cost. Focusing on major hormone signaling events and environmental factors, we review the transcriptional regulatory network mediating biosynthesis of representative active ingredients. In this network, many transcription factors (TFs) simultaneously control multiple synthase genes; thus, understanding the molecular mechanisms affecting transcriptional regulation of active ingredients will be crucial to developing new breeding possibilities.

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.

Five Species of Taxus Karyotype Based on Oligo-FISH for 5S rDNA and (AG3T3)3

As a relict plant, Taxus is used in a variety of medicinal ingredients, for instance to treat a variety of cancers. Taxus plants are difficult to distinguish from one another due to their similar morphology; indeed, some species of Taxus cytogenetic data still are unclear. Oligo-FISH can rapidly and efficiently provide insight into the genetic composition and karyotype. This is important for understanding the organization and evolution of chromosomes in Taxus species. We analysed five Taxus species using two oligonucleotide probes. (AG₃T₃)₃ signals were distributed at the chromosome ends and the centromere of five species of Taxus. The 5S rDNA signal was displayed on two chromosomes of five species of Taxus. In addition to Taxus wallichiana var. mairei, 5S rDNA signals were found proximal in the remaining four species, which signals a difference in its location. The karyotype formula of Taxus wallichiana was 2n = 2x = 24m, its karyotype asymmetry index was 55.56%, and its arm ratio was 3.0087. Taxus × media's karyotype formula was 2n = 2x = 24m, its karyotype asymmetry index was 55.09%, and its arm ratio was 3.4198. The karyotype formula of Taxus yunnanensis was 2n = 2x = 24m, its karyotype asymmetry index was 55.56%, and its arm ratio was 2.6402. The karyotype formula of Taxus cuspidate was 2n = 2x = 24m, its karyotype asymmetry index was 54.67%, its arm ratio was 3.0135, and two chromosomes exhibited the 5S rDNA signal. The karyotype formula of T. wallichiana var. mairei was 2n= 2x = 22m + 2sm, its karyotype asymmetry index was 54.33%, and its arm ratio was 2.8716. Our results provide the karyotype analysis and physical genetic map of five species of Taxus, which contributes to providing molecular cytogenetics data for Taxus.

Transcription level differences in Taxus wallichiana var. mairei elicited by Ce3+, Ce4+ and methyl jasmonate

Taxol is a precious and effective anticancer drug. Cerium and methyl jasmonate (MJ) have been shown to increase the yield of taxol in taxus cells. However, the mechanisms of cerium-mediated and MJ-mediated taxol biosynthesis remain unknown. RNA-Seq was applied to study the overall regulation mechanism of cerium and MJ on taxol biosynthesis and analyze the differences among T. mairei cells elicited by Ce³⁺, Ce⁴⁺ and MJ on transcriptional level . Using sequence homology, 179 unigenes were identified as taxol synthesis genes. Under the condition of 100 μM MJ, taxol synthesis genes were up-regulated. Notably, taxol synthesis genes were down-regulated expression at 1 mM Ce³⁺ and 1 mM Ce⁴⁺. Differential expression genes involved in some related functions were analyzed, such as MAPK signaling pathway and plant-pathogen interaction. Sequence alignment and phylogenetic analysis of nine differentially expressed WRKYs in our data were carried out.

Factors affecting the growth, antioxidant potential, and secondary metabolites production in hazel callus cultures

Hazelnut is one of the most important nut plants recently suggested as a sustainable source for paclitaxel. In the present study, the effect of the concentration and combination of PGRs, different basal medium and ultrasonic waves on callus induction and growth, physiological characteristics, and taxol and baccatin III production in hazelnut callus cultures were investigated. The results indicated that combining 2,4-D (2 mg/L) and Kin (0.2 mg/L) with the sonication of explants for 1 min provides an optimized condition for callus induction and growth. Hazelnut explants exhibited different callus production and biochemical and metabolic characteristics depending on the basal medium type, ultrasound treatment, and inclusion of ascorbic acid in the medium. So that, the highest percentage of callogenesis (100%) observed in ½ MS + 1 min US, ½ MS + 150 mg/L AA, B5 + 1 min US and B5 + 150 mg/L AA, and also ½ MS salt + Nitsch vitamins + 150 mg/L AA. Furthermore, the highest callus growth (7.86 g FW) was obtained from ½ MS + 1 min US. The highest amount of baccatin III production (147.98 and 147.85 mg/L) was obtained from the WPM and MS basal media; the highest taxol production (44.89 mg/L) was observed in the WPM basal medium. The cultures in the MS, WPM, and MS salts + Nitsch vitamins media, had the highest H₂O₂ and MDA content, antioxidant enzymes activity, and phenolic compounds. In conclusion, culture media nutrient composition and concentration not only affect the cell growth and physiological status of the cultures but also improve secondary metabolites production and accumulation.

The Epigenetic Regulation in Plant Specialized Metabolism: DNA Methylation Limits Paclitaxel in vitro Biotechnological Production

Environmental conditions are key factors in the modulation of the epigenetic mechanisms regulating gene expression in plants. Specifically, the maintenance of cell cultures in optimal in vitro conditions alters methylation patterns and, consequently, their genetic transcription and metabolism. Paclitaxel production in Taxus x media cell cultures is reduced during its maintenance in in vitro conditions, compromising the biotechnological production of this valuable anticancer agent. To understand how DNA methylation influences taxane production, the promoters of three genes (GGPPS, TXS, and DBTNBT) involved in taxane biosynthesis have been studied, comparing the methylation patterns between a new line and one of ~14 years old. Our work revealed that while the central promoter of the GGPPS gene is protected from cytosine methylation accumulation, TXS and DBTNBT promoters accumulate methylation at different levels. The DBTNBT promoter of the old line is the most affected, showing a 200 bp regulatory region where all the cytosines were methylated. This evidence the existence of specific epigenetic regulatory mechanisms affecting the last steps of the pathway, such as the DBTNBT promoter. Interestingly, the GGPPS promoter, a regulatory sequence of a non-specific taxane biosynthetic gene, was not affected by this mechanism. In addition, the relationship between the detected methylation points and the predicted transcription factor binding sites (TFBS) showed that the action of TFs would be compromised in the old line, giving a further explanation for the production reduction in in vitro cell cultures. This knowledge could help in designing novel strategies to enhance the biotechnological production of taxanes over time.

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.

Identification and Optimization of a Novel Taxanes Extraction Process from Taxus cuspidata Needles by High-Intensity Pulsed Electric Field

Taxanes are a series of natural compounds with great application potential in antitumor therapy, whereas the lack of efficient taxanes extraction methods significantly hinders the development of taxanes. The high-intensity pulsed electric field (PEF) is a novel technology used to extract bioactive ingredients from food and other natural products. However, the prospect of using PEF for taxanes extraction remains to be elucidated. Herein, we extracted taxanes from Taxus cuspidata via PEF and explored the effects of seven extraction conditions on the yields of target compounds. The Placket–Burman design (PBD) assay revealed that electric field strength, pulse number, and particle size are key factors for taxanes extraction. The response surface methodology (RSM) and back-propagation neural network conjugated with genetic algorithm (GA-BP) were further used to model and predict the optimal extraction conditions, and GA-BP exerted higher reliability, leading to a maximum extraction yield of 672.13 μg/g under electric field strength of 16 kV/cm, pulse number of 8, particle size of 160 meshes, solid–liquid ratio of 1:60, a single extraction, centrifugal speed of 8000 r/min, and flow rate of 7 mL/min, which was 1.07–1.84 folds that of control, solid–liquid extraction (SL), and ultrasonic extraction (US) groups. Additionally, the scanning electron microscopy (SEM) results indicated that the sample particles extracted by PEF method exhibited a coarser surface morphology. Thus, we present for the first time that PEF is feasible for the extraction of taxanes from Taxus cuspidata and highlight the application value of the PBD, RSM, and GA-BP models in parameters optimization during extraction process.

Prospecting potential of endophytes for modulation of biosynthesis of therapeutic bioactive secondary metabolites and plant growth promotion of medicinal and aromatic plants

Medicinal and aromatic plants possess pharmacological properties (antidiabetes, anticancer, antihypertension, anticardiovascular, antileprosy, etc.) because of their potential to synthesize a wide range of therapeutic bioactive secondary metabolites. The concentration of bioactive secondry metabolites depends on plant species, local environment, soil type and internal microbiome. The internal microbiome of medicinal plants plays the crucial role in the production of bioactive secondary metabolites, namely alkaloids, steroids, terpenoids, peptides, polyketones, flavonoids, quinols and phenols. In this review, the host specific secondry metabolites produced by endophytes, their therapeutic properties and host-endophytes interaction in relation to production of bioactive secondry metaboloites and the role of endophytes in enhancing the production of bioactive secondry metabolites is discussed. How biological nitrogen fixation, phosphorus solubilization, micronutrient uptake, phytohormone production, disease suppression, etc. can play a vital role in enhacing the plant growth and development.The role of endophytes in enhancing the plant growth and content of bioactive secondary metabolites in medicinal and aromatic plants in a sustainable mode is highlighted.

Phenylpropanoids in Silybum marianum cultures treated with cyclodextrins coated with magnetic nanoparticles

The glucose oligosaccharide-derived cyclodextrins (CDs) are used for improving bioactive compound production in plant cell cultures because, in addition to their elicitation activity, CDs promote product removal from cells. However, despite these advantages, the industrial application of CDs is hampered by their high market price. A strategy to overcome this constraint was recently tested, in which reusable CD polymers coated with magnetic Fe3O4 nanoparticles were harnessed in Vitis vinifera cell cultures to produce t-resveratrol (t-R). In this study, we applied hydroxypropyl-β-CDs (HPCD) and HPCDs coated with magnetic nanoparticles (HPCD-EPI-MN) in methyl jasmonate (MJ)-treated transgenic Silybum marianum cultures ectopically expressing either a stilbene synthase gene (STS) or a chalcone synthase gene (CHS), and compared their effects on the yields of t-R and naringenin (Ng), respectively. HPCD-EPI-MN at 15 g/L stimulated the accumulation of metabolites in the culture medium of the corresponding transgenic cell lines, with up to 4 mg/L of t-R and 3 mg/L of Ng released after 3 days. Similar amounts were produced in cultures treated with HPCD. Concentrations higher than 15 g/L of HPCD-EPI-MN and prolonged incubation periods negatively affected cell growth and viability in both transgenic cell lines. Reutilization of HPCD-EPI-MN was possible in three elicitation cycles (72 h each), after which the polymer retained 25-30% of its initial efficiency, indicating good stability and reusability. Due to their capacity to adsorb metabolites and their recyclability, the application of magnetic CD polymers may reduce the costs of establishing efficient secondary metabolite production systems on a commercial scale. KEY POINTS: • Long-term transgenic S. marianum suspensions stably produce transgene products • t-R and Ng accumulated extracellularly in cultures elicited with HPCD and HPCD-EPI-MN • The recyclability of HPCD-EPI-MN for metabolite production was proven.

Characterization of lipid droplets from a Taxus media cell suspension and their potential involvement in trafficking and secretion of paclitaxel

Our paper describes the potential roles of lipid droplets of Taxus media cell suspension in the biosynthesis and secretion of paclitaxel and, therefore, highlights their involvement in improving its production. Paclitaxel (PTX) is a highly potent anticancer drug that is mainly produced using Taxus sp. cell suspension cultures. The main purpose of the current study is to characterize cellular LDs from T. media cell suspension with a particular focus on the biological connection of their associated proteins, the caleosins (CLOs), with the biosynthesis and secretion of PTX. A pure LD fraction obtained from T. media cells and characterized in terms of their proteome. Interestingly, the cellular LD in T. media sequester the PTX. This was confirmed in vitro, where about 96% of PTX (C⁰_PTX,_aq [mg L^-1]) in the aqueous solution was partitioned into the isolated LDs. Furthermore, silencing of CLO-encoding genes in the T. media cells led to a net decrease in the number and size of LDs. This coincided with a significant reduction in expression levels of TXS, DBAT and DBTNBT, key genes in the PTX biosynthesis pathway. Subsequently, the biosynthesis of PTX was declined in cell culture. In contrast, treatment of cells with 13-hydroperoxide C18:3, a substrate of the peroxygenase activity, induced the expression of CLOs, and, therefore, the accumulation of cellular LDs in the T. media cells cultures, thus increasing the PTX secretion. The accumulation of stable LDs is critically important for effective secretion of PTX. This is modulated by the expression of caleosins, a class of LD-associated proteins with a dual role conferring the structural stability of LDs as well as regulating lipidic bioactive metabolites via their enzymatic activity, thus enhancing the biosynthesis of PTX.

Metabolomics and Molecular Approaches Reveal Drought Stress Tolerance in Plants

Metabolic regulation is the key mechanism implicated in plants maintaining cell osmotic potential under drought stress. Understanding drought stress tolerance in plants will have a significant impact on food security in the face of increasingly harsh climatic conditions. Plant primary and secondary metabolites and metabolic genes are key factors in drought tolerance through their involvement in diverse metabolic pathways. Physio-biochemical and molecular strategies involved in plant tolerance mechanisms could be exploited to increase plant survival under drought stress. This review summarizes the most updated findings on primary and secondary metabolites involved in drought stress. We also examine the application of useful metabolic genes and their molecular responses to drought tolerance in plants and discuss possible strategies to help plants to counteract unfavorable drought periods.

Practical Enzymatic Production of Carbocycles

The Pd-catalyzed carbon-carbon bond formation pioneered by Heck in 1969 has dominated medicinal chemistry development for the ensuing fifty years. As the demand for more complex three-dimensional active pharmaceuticals continues to increase, preparative enzyme-mediated assembly, by virtue of its exquisite selectivity and sustainable nature, is poised to provide a practical and affordable alternative for accessing such compounds. In this minireview, we summarize recent state-of-the-art developments in practical enzyme-mediated assembly of carbocycles. When appropriate, background information on the enzymatic transformation is provided and challenges and/or limitations are also highlighted.

The Taxus genome provides insights into paclitaxel biosynthesis

The ancient gymnosperm genus Taxus is the exclusive source of the anticancer drug paclitaxel, yet no reference genome sequences are available for comprehensively elucidating the paclitaxel biosynthesis pathway. We have completed a chromosome-level genome of Taxus chinensis var. mairei with a total length of 10.23 gigabases. Taxus shared an ancestral whole-genome duplication with the coniferophyte lineage and underwent distinct transposon evolution. We discovered a unique physical and functional grouping of CYP725As (cytochrome P450) in the Taxus genome for paclitaxel biosynthesis. We also identified a gene cluster for taxadiene biosynthesis, which was formed mainly by gene duplications. This study will facilitate the elucidation of paclitaxel biosynthesis and unleash the biotechnological potential of Taxus.

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.

Developing a Yeast Platform Strain for an Enhanced Taxadiene Biosynthesis by CRISPR/Cas9

Paclitaxel is an important diterpenoid commonly used as an anticancer drug. Although the paclitaxel biosynthetic pathway has been mostly revealed, some steps remain to be elucidated. The difficulties in plant transformations and the scarcity of the precursor of paclitaxel, (+)-taxa-4(5), 11(12)-diene (taxadiene), have hindered the full comprehension of paclitaxel biochemistry and, therefore, its production by biotechnological approaches. One solution is to use the budding yeast, Saccharomyces cerevisiae, as a platform to elucidate the paclitaxel biosynthesis. As taxadiene is a diterpenoid, its common precursor, geranylgeranyl pyrophosphate (GGPP), needs to be increased in yeast. In this study, we screened various GGPP synthases (GGPPS) to find the most suitable GGPPS for taxadiene production in yeast. We also optimized the taxadiene production by increasing the flux toward the terpenoid pathway. Finally, to remove selection markers, we integrated the required genes using a CRISPR/Cas9 system in the yeast genome. Our result showed that a titer of 2.02 ± 0.40 mg/L (plasmid) and 0.41 ± 0.06 mg/L (integrated) can be achieved using these strategies. This platform strain can be used to readily test the gene candidates for microbial paclitaxel biosynthesis in the future.

Effects of different factors on friable callus induction and establishment of cell suspension culture of Hovenia dulcis (Rhamnaceae)

Abstract Medicinal plants are an important therapeutic option for a large share of the world’s population. To establish an in vitro culture system for the production of secondary metabolites from Hovenia dulcis, we studied the effect of auxins, cytokinins, absence of light, and silver nitrate on the development of friable callus. Callus cultures were established for the first time and used to obtain cell suspension cultures. Supplementation with KIN (Kinetin) produced calli with both compact and friable areas, while the addition of TDZ (Thidiazuron) only produced compact callus. The maintenance of cultures in the dark induced a slight enhancement on friability when the auxin PIC (Picloram) was present in the culture medium. The addition of silver nitrate promoted the formation of friable calli. Dry weight analysis showed no significant differences in biomass growth, and, therefore, 2.0 mg.L-1 was considered the most suitable treatment. The presence of silver nitrate was not required for the establishment of cell suspension cultures. Dry weight analysis of cell suspensions showed higher biomass production in the absence of silver nitrate. PIC promoted 100% of cell suspension culture formation in the absence of silver nitrate, and higher biomass production was observed with the lowest concentration (0.625 mg.L-1). No morphological differences were observed among the different concentrations of PIC. Phytochemical screening showed the presence of saponins, flavonoids, flavonols and catechins in the extracts obtained from H. dulcis calli. These results show that the cell cultures herein established are potential sources for the production of H. dulcis secondary metabolites of medicinal interest.

Selection and validation of reference genes for quantitative gene expression normalization in Taxus spp

Quantitative real-time PCR (qRT-PCR) is commonly used to measure gene expression to further explore gene function, while suitable reference genes must be stably expressed under different experimental conditions to obtain accurate and reproducible data for relative quantification. Taxol or paclitaxel is an important anticancer compound mainly identified in Taxus spp. The molecular mechanism of the regulation of taxol biosynthesis is current research goal. However, in the case of Taxus spp., few reports were published on screening suitable reference genes as internal controls for qRT-PCR. Here, eight reference genes were selected as candidate reference genes for further study. Common statistical algorithms geNorm, NormFinder, BestKeeper, ΔCt, and RefFinder were used to analyze the data from samples collected from a cell line of Taxus × media under various experimental conditions and from tissues of Taxus chinensis var. mairei. The expression patterns of TcMYC under salicylic acid treatment differed significantly, with the best and worst reference genes in the cell line. This study screened out suitable reference genes (GAPDH1 and SAND) under different treatments and tissues for the accurate and reliable normalization of the qRT-PCR expression data of Taxus spp. At the same time, this study will aid future research on taxol biosynthesis-related genes expression in Taxus spp., and can also be directly used to other related species.

The effect of β-cyclocitral treatment on the carotenoid content of transgenic Marsh grapefruit (Citrus paradisi Macf.) suspension-cultured cells

This work reports the development of suspension culture system of transgenic Marsh grapefruit (Citrus paradisi Macf., Rutaceae) callus overexpressing bacterial phytoene synthase; and the use of this suspension culture to investigate the effects of β-cyclocitral on carotenoid content and composition. At a β-cyclocitral concentration of 0.5 mM and after ten days cultivation, analysis of the carotenoids showed a significant increase in the content of β-, α-carotene, and phytoene predominantly. The maximal increase in total provitamin A carotenoids content following β-cyclocitral application was ~2-fold higher than the control, reaching 245.8 μg/g DW. The trend for increased transcript levels of biosynthetic genes PSY and ZDS correlated with the enhancement of the content of these carotenes following β-cyclocitral treatment and GC-MS based metabolite profiling showed significant changes of metabolite levels across intermediary metabolism. These findings suggest that β-cyclocitral can act as a chemical elicitor, to enhance the formation of carotenes in citrus suspension-cultured cells (SCC), which could be utilized in studying the regulation of carotenoid biosynthesis and biotechnological application to the renewable production of nutritional carotenoids.

Enhancing Salt Tolerance of Plants: From Metabolic Reprogramming to Exogenous Chemical Treatments and Molecular Approaches

Plants grow on soils that not only provide support for root anchorage but also act as a reservoir of water and nutrients important for plant growth and development. However, environmental factors, such as high salinity, hinder the uptake of nutrients and water from the soil and reduce the quality and productivity of plants. Under high salinity, plants attempt to maintain cellular homeostasis through the production of numerous stress-associated endogenous metabolites that can help mitigate the stress. Both primary and secondary metabolites can significantly contribute to survival and the maintenance of growth and development of plants on saline soils. Existing studies have suggested that seed/plant-priming with exogenous metabolites is a promising approach to increase crop tolerance to salt stress without manipulation of the genome. Recent advancements have also been made in genetic engineering of various metabolic genes involved in regulation of plant responses and protection of the cells during salinity, which have therefore resulted in many more basic and applied studies in both model and crop plants. In this review, we discuss the recent findings of metabolic reprogramming, exogenous treatments with metabolites and genetic engineering of metabolic genes for the improvement of plant salt tolerance.

Effective Production of Phenolic Compounds with Health Benefits in Pigeon Pea [Cajanus cajan (L.) Millsp.] Hairy Root Cultures

Phenolic compounds in pigeon pea possess various biological properties beneficial to human health. In this study, pigeon pea hairy root cultures (PPHRCs) were developed as an effective in vitro platform for the production of phenolic compounds. A high-productive hairy root line was screened and characterized, and its culture conditions were optimized in terms of biomass productivity and phenolic yield. The comparative profiling of 10 phenolic compounds in PPHRCs and pigeon pea natural resources (seeds, leaves, and roots) was achieved by ultra-high-performance liquid chromatography-tandem mass spectrometry analysis. The total phenolic yield in PPHRCs (3278.44 μg/g) was much higher than those in seeds (68.86 μg/g) and roots (846.03 μg/g), and comparable to leaves (3379.49 μg/g). Notably, PPHRCs exhibited superiority in the yield of the most important health-promoting compound cajaninstilbene acid (2996.23 μg/g) against natural resources (4.42-2293.31 μg/g). Overall, PPHRCs could serve as promising potential alternative sources for the production of phenolic compounds with nutraceutical/medicinal values.

A Novel Hydroxylation Step in the Taxane Biosynthetic Pathway: A New Approach to Paclitaxel Production by Synthetic Biology

Engineered plant cell lines have the potential to achieve enhanced metabolite production rates, providing a high-yielding source of compounds of interest. Improving the production of taxanes, pharmacologically valuable secondary metabolites of Taxus spp., is hindered by an incomplete knowledge of the taxane biosynthetic pathway. Of the five unknown steps, three are thought to involve cytochrome P450-like hydroxylases. In the current work, after an in-depth in silico characterization of four candidate enzymes proposed in a previous cDNA-AFLP assay, TB506 was selected as a candidate for the hydroxylation of the taxane side chain. A docking assay indicated TB506 is active after the attachment of the side chain based on its affinity to the ligand 3'N-dehydroxydebenzoyltaxol. Finally, the involvement of TB506 in the last hydroxylation step of the paclitaxel biosynthetic pathway was confirmed by functional assays. The identification of this hydroxylase will contribute to the development of alternative sustainable paclitaxel production systems using synthetic biology techniques.

Enhanced bioactive compound production in broccoli cells due to coronatine and methyl jasmonate is linked to antioxidative metabolism

Elicited broccoli suspension-cultured cells (SCC) provide a useful system for obtaining bioactive compounds, including glucosinolates (GS) and phenolic compounds (PCs). In this work, coronatine (Cor) and methyl jasmonate (MJ) were used to increase the bioactive compound production in broccoli SCC. Although the use of Cor and MJ in secondary metabolite production has already been described, information concerning how elicitors affect cell metabolism is scarce. It has been suggested that Cor and MJ trigger defence reactions affecting the antioxidative metabolism. In the current study, the concentration of 0.5 μM Cor was the most effective treatment for increasing both the total antioxidant capacity (measured as ferulic acid equivalents) and glucosinolate content in broccoli SCC. The elicited broccoli SCC also showed higher polyphenol oxidase activity than the control cells. Elicitation altered the antioxidative metabolism of broccoli SCC, which displayed biochemical changes in antioxidant enzymes, a decrease in the glutathione redox state and an increase in lipid peroxidation levels. Furthermore, we studied the effect of elicitation on the protein profile and observed an induction of defence-related proteins. All of these findings suggest that elicitation not only increases bioactive compound production, but it also leads to mild oxidative stress in broccoli SCC that could be an important factor triggering the production of these compounds.

Methyljasmonate Elicitation Increases Terpenoid Indole Alkaloid Accumulation in Rhazya stricta Hairy Root Cultures

Methyl jasmonate is capable of initiating or improving the biosynthesis of secondary metabolites in plants and therefore has opened up a concept for the biosynthesis of valuable constituents. In this study, the effect of different doses of methyl jasmonate (MeJA) elicitation on the accumulation of terpenoid indole alkaloids (TIAs) in the hairy root cultures of the medicinal plant, Rhazya stricta throughout a time course (one-seven days) was investigated. Gas chromatography-mass spectrometry (GC-MS) analyses were carried out for targeted ten major non-polar alkaloids. Furthermore, overall alterations in metabolite contents in elicited and control cultures were investigated applying proton nuclear magnetic resonance (1H NMR) spectroscopy. Methyl jasmonate caused dosage- and time course-dependent significant rise in the accumulation of TIAs as determined by GC-MS. The contents of seven alkaloids including eburenine, quebrachamine, fluorocarpamine, pleiocarpamine, tubotaiwine, tetrahydroalstonine, and ajmalicine increased compared to non-elicited cultures. However, MeJA-elicitation did not induce the accumulation of vincanine, yohimbine (isomer II), and vallesiachotamine. Furthermore, principal component analysis (PCA) of 1H NMR metabolic profiles revealed a discrimination between elicited hairy roots and control cultures with significant increase in total vindoline-type alkaloid content and elevated levels of organic and amino acids. In addition, elicited and control samples had different sugar and fatty acid profiles, suggesting that MeJA also influences the primary metabolism of R. stricta hairy roots. It is evident that methyl jasmonate is applicable for elevating alkaloid accumulation in "hairy root" organ cultures of R. strica.

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.

Advances in the Regulation of In Vitro Paclitaxel Production: Methylation of a Y-Patch Promoter Region Alters BAPT Gene Expression in Taxus Cell Cultures

Plant cell biofactories represent a promising solution to the increasing demand for plant-derived compounds, but there are still limiting factors that prevent optimal production, including the loss of yield during in vitro maintenance. Our results reveal a clear correlation between genomic methylation levels and a progressive decline in taxane production in Taxus spp. cell cultures. A comparative study of two cell lines, one 10 years old and low productive and the other new and high productive, revealed important differences in appearance, growth, taxane accumulation and expression levels of several taxane biosynthetic genes. Differences in taxane content and gene expression profile indicate an altered pathway regulation and that the BAPT gene, located in the center of the expression network of taxane biosynthetic genes, is active in a potentially flux-limiting step. The methylation patterns of the BAPT gene were studied in both cell lines by bisulfite sequencing, which revealed high rates of CHH methylated cytosines on the core promoter. Using a bioinformatics approach, this hotspot was identified as a Y-patch promoter element. The Y-patch may play a key role in the epigenetic regulation of the taxane biosynthetic pathway, which would open up novel genetic engineering strategies toward stable and high productivity.

Comparative Transcriptome Analysis Revealed the Tissue-Specific Accumulations of Taxanes among Three Experimental Lines of Taxus yunnanensis

Taxus yunnanensis (Yew) is known for natural anticancer metabolite paclitaxel (Taxol) and its biosynthesis pathway in yew species still needs to be completely elucidated. In the current study, productions of paclitaxel and 10-DAB III from three different tissues (needle, branch, and root) of T. yunnanensis wild type (WT) and two new cultivars Zhongda-1 (Zd1) and Zhongda-2 (Zd2) were determined, and significant tissue differences in contents of the taxanes were observed among the three experimental lines. The much higher 10-DAB III and lower paclitaxel contents in needle of Zd2 when compared with that of Zd1 indicated the low conversion from 10-DAB III to paclitaxel in the needle of Zd2. In order to uncover the mechanisms of the tissue-specific biosynthesis of the taxanes, transcriptome analysis of cultivar Zd2 was conducted, and the previously reported transcriptome data of Zd1 and WT were used to perform a comparison. The enhancement of TDAT and T10βH side biosynthetic pathway in roots of Zd2 in early taxane synthesis might lead to the biosynthesis of other toxoids, while the preference of T13αH route in the needle and branch of Zd2 was mainly responsible for the tissue-specific reinforced biosynthesis of 10-DAB III and paclitaxel in Zd2. Different from Zd1, the tissue-specific pattern of paclitaxel biosynthesis genes in Zd2 was similar to WT. However, the lower transcript abundance of final steps genes (TBT, DBAT, BAPT, and DBTNBT) of the paclitaxel biosynthesis pathway in Zd2 than in Zd1 might further promote 10-DAB III accumulation in Zd2.

Effect of in vitro morphogenesis on the production of podophyllotoxin derivatives in callus cultures of Linum album

The anticancer compound podophyllotoxin and other related lignans can be produced in Linum album in vitro cultures, although their biosynthesis varies according to the degree of differentiation of the plant material. In general, L. album cell cultures do not form the same lignans as roots or other culture systems. Our aim was to explore how the lignan-producing capacity of organogenic cell masses is affected by the conditions that promote their formation and growth. Thus, L. album biomass obtained from plantlets was cultured in darkness or light, with or without the addition of plant growth regulators, and the levels of podophyllotoxin, methoxypodophyllotoxin and other related lignans were determined in each of these conditions. The organogenic capacity of the cell biomass grown in the different conditions was studied directly and also with light and scanning electronic microscopy, leading to the observation of.several somatic embryos and well-formed shoots. The main lignan produced was methoxypodophyllotoxin, whose production was clearly linked to the organogenic capacity of the cell biomass, which to a lesser extent was also the case for podophyllotoxin.

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.

Identification of potential genes that contributed to the variation in the taxoid contents between two Taxus species (Taxus media and Taxus mairei)

Taxol is currently a valuable anticancer drug; however, the accumulated mixture of taxoids can vary greatly among Taxus species. So far, there is very little genomic information for the genus Taxus, except for Taxus baccata. Transcriptome analysis is a powerful approach to explore the different regulatory mechanisms underlying the taxoid biosynthesis pathway in Taxus species. First, we quantified the variation in the taxoid contents between Taxus media and Taxus mairei. The contents of paclitaxel and 10-deacetylpaclitaxel in T. media are higher than that in T. mairei. Then, the transcriptome profiles of T. media and T. mairei were analyzed to investigate the altered expressions. A total of 20,704 significantly differentially expressed genes (DEGs), including 9865 unigenes predominantly expressed in T. media and 10,839 unigenes predominantly expressed in T. mairei, were identified. In total, 120 jasmonic acid-related DEGs were analyzed, suggesting variations in 'response to JA stimulus' and 'JA biosynthetic process' pathways between T. media and T. mairei. Furthermore, a number of genes related to the precursor supply, taxane skeleton formation and hydroxylation, and C13-side chain assembly were also identified. The differential expression of the candidate genes involved in taxoid biosynthetic pathways may explain the variation in the taxoid contents between T. media and T. mairei.

A rational approach for the improvement of biomass production and lipid profile in cacao cell suspensions

Cocoa butter (CB) is produced in the seeds of Theobroma cacao representing 50% of its dry weight. The lipid composition plays an important role in the physicochemical, rheological, and sensory properties of the CB, making this fat a valuable resource for the production of chocolates, cosmetics, and pharmaceuticals. In this paper, are described experimental strategies used for a rational improvement of biomass production and fatty acids in cacao cell suspension cultures. First, the lipid profile in four cacao varieties is characterized, and then, one variety is selected to induce cell suspensions using a direct method without previous establishment of a callus phase. To improve growth and total fat production in cell suspension cultures, modified DKW media and newly designed media culture, based on the mineral concentrations of cacao seeds (cacao biomass production, "CBP"), are analyzed and compared. In addition, the effect of acetate in the lipid profile of cell suspensions is evaluated. Ultrastructural histological analysis of lipid vesicles in cacao seeds and cell suspensions is also performed. The results will show that it is feasible to establish cacao suspensions without the calli step and increase the biomass production by selecting a suitable cacao variety and tissue and also applying a new culture media formulation. In addition, it is possible to synthesize fatty acids in cell cultures and modify the lipid profile adding a precursor of the novo biosynthesis of fatty acids such as the acetate. Transmission electronic microscopy examinations and differential interference contrast microscopy analysis will demonstrate that lipid vesicles are the main reserve substance in both cacao seeds and cell suspensions.

Bioconversion of stilbenes in genetically engineered root and cell cultures of tobacco

It is currently possible to transfer a biosynthetic pathway from a plant to another organism. This system has been exploited to transfer the metabolic richness of certain plant species to other plants or even to more simple metabolic organisms such as yeast or bacteria for the production of high added value plant compounds. Another application is to bioconvert substrates into scarcer or biologically more interesting compounds, such as piceatannol and pterostilbene. These two resveratrol-derived stilbenes, which have very promising pharmacological activities, are found in plants only in small amounts. By transferring the human cytochrome P450 hydroxylase 1B1 (HsCYP1B1) gene to tobacco hairy roots and cell cultures, we developed a system able to bioconvert exogenous t-resveratrol into piceatannol in quantities near to mg L-1. Similarly, after heterologous expression of resveratrol O-methyltransferase from Vitis vinifera (VvROMT) in tobacco hairy roots, the exogenous t-resveratrol was bioconverted into pterostilbene. We also observed that both bioconversions can take place in tobacco wild type hairy roots (pRiA4, without any transgene), showing that unspecific tobacco P450 hydroxylases and methyltransferases can perform the bioconversion of t-resveratrol to give the target compounds, albeit at a lower rate than transgenic roots.

An optimized biotechnological system for the production of centellosides based on elicitation and bioconversion of Centella asiatica cell cultures

Centella asiatica is a herbaceous plant of Asian traditional medicine. Besides wound healing, this plant is recommended for the treatment or care of various skin conditions such as dry skin, leprosy, varicose ulcers, eczema, and/or psoriasis. Triterpene saponins, known as centellosides, are the main metabolites associated with these beneficial effects. Considering the interest in these high value active compounds, there is a need to develop biosustainable and economically viable processes to produce them. Previous work using C. asiatica plant cell culture technology demonstrated the efficient conversion of amyrin derivatives into centellosides, opening a new way to access these biomolecules. The current study was aimed at increasing the production of centellosides in C. asiatica plant cell cultures. Herein, we report the application of a new elicitor, coronatine, combined with the addition of amyrin-enriched resins as potential sustainable precursors in the centelloside pathway, for a positive synergistic effect on centelloside production. Our results show that coronatine is a powerful elicitor for increasing centelloside production and that treatments with sustainable natural sources of amyrins enhance centelloside yields. This process can be scaled up to an orbitally shaken CellBag, thereby increasing the capacity of the system for producing biomass and centellosides.

Plant Metabolic Engineering Strategies for the Production of Pharmaceutical Terpenoids

Pharmaceutical terpenoids belong to the most diverse class of natural products. They have significant curative effects on a variety of diseases, such as cancer, cardiovascular diseases, malaria and Alzheimer's disease. Nowadays, elicitors, including biotic and abiotic elicitors, are often used to activate the pathway of secondary metabolism and enhance the production of target terpenoids. Based on Agrobacterium-mediated genetic transformation, several plant metabolic engineering strategies hold great promise to regulate the biosynthesis of pharmaceutical terpenoids. Overexpressing terpenoids biosynthesis pathway genes in homologous and ectopic plants is an effective strategy to enhance the yield of pharmaceutical terpenoids. Another strategy is to suppress the expression of competitive metabolic pathways. In addition, global regulation which includes regulating the relative transcription factors, endogenous phytohormones and primary metabolism could also markedly increase their yield. All these strategies offer great opportunities to enhance the supply of scarce terpenoids drugs, reduce the price of expensive drugs and improve people's standards of living.

In silico metabolic network analysis of Arabidopsis leaves

Background

During the last decades, we face an increasing interest in superior plants to supply growing demands for human and animal nutrition and for the developing bio-based economy. Presently, our limited understanding of their metabolism and its regulation hampers the targeted development of desired plant phenotypes. In this regard, systems biology, in particular the integration of metabolic and regulatory networks, is promising to broaden our knowledge and to further explore the biotechnological potential of plants.

Results

The thale cress Arabidopsis thaliana provides an ideal model to understand plant primary metabolism. To obtain insight into its functional properties, we constructed a large-scale metabolic network of the leaf of A. thaliana. It represented 511 reactions with spatial separation into compartments. Systematic analysis of this network, utilizing elementary flux modes, investigates metabolic capabilities of the plant and predicts relevant properties on the systems level: optimum pathway use for maximum growth and flux re-arrangement in response to environmental perturbation. Our computational model indicates that the A. thaliana leaf operates near its theoretical optimum flux state in the light, however, only in a narrow range of photon usage. The simulations further demonstrate that the natural day-night shift requires substantial re-arrangement of pathway flux between compartments: 89 reactions, involving redox and energy metabolism, substantially change the extent of flux, whereas 19 reactions even invert flux direction. The optimum set of anabolic pathways differs between day and night and is partly shifted between compartments. The integration with experimental transcriptome data pinpoints selected transcriptional changes that mediate the diurnal adaptation of the plant and superimpose the flux response.

Conclusions

The successful application of predictive modelling in Arabidopsis thaliana can bring systems-biological interpretation of plant systems forward. Using the gained knowledge, metabolic engineering strategies to engage plants as biotechnological factories can be developed.

Electronic supplementary material

The online version of this article (doi:10.1186/s12918-016-0347-3) contains supplementary material, which is available to authorized users.

Jasmonates: signal transduction components and their roles in environmental stress responses

Jasmonates, oxylipin-type plant hormones, are implicated in diverse aspects of plant growth development and interaction with the environment. Following diverse developmental and environmental cues, jasmonate is produced, conjugated to the amino acid isoleucine and perceived by a co-receptor complex composed of the Jasmonate ZIM-domain (JAZ) repressor proteins and an E3 ubiquitin ligase complex containing the F-box CORONATINE INSENSITIVE 1 (COI1). This event triggers the degradation of the JAZ proteins and the release of numerous transcription factors, including MYC2 and its homologues, which are otherwise bound and inhibited by the JAZ repressors. Here, we will review the role of the COI1, JAZ and MYC2 proteins in the interaction of the plant with its environment, illustrating the significance of jasmonate signalling, and of the proteins involved, for responses to both biotic stresses caused by insects and numerous microbial pathogens and abiotic stresses caused by adverse climatic conditions. It has also become evident that crosstalk with other hormone signals, as well as light and clock signals, plays an important role in the control and fine-tuning of these stress responses. Finally, we will discuss how several pathogens exploit the jasmonate perception and early signalling machinery to decoy the plants defence systems.

Synthetic biology for production of natural and new-to-nature terpenoids in photosynthetic organisms

With tens of thousands of characterized members, terpenoids constitute the largest class of natural compounds that are synthesized by all living organisms. Several terpenoids play primary roles in the maintenance of cell membrane fluidity, as pigments or as phytohormones, but most of them function as specialized metabolites that are involved in plant resistance to herbivores or plant-environment interactions. Terpenoids are an essential component of human nutrition, and many are economically important pharmaceuticals, aromatics and potential next-generation biofuels. Because of the often low abundance in their natural source, as well as the demand for novel terpenoid structures with new or improved bioactivities, terpenoid biosynthesis has become a prime target for metabolic engineering and synthetic biology projects. In this review we focus on the creation of new-to-nature or tailor-made plant-derived terpenoids in photosynthetic organisms, in particular by means of combinatorial biosynthesis and the activation of silent metabolism. We reflect on the characteristics of different potential photosynthetic host organisms and recent advances in synthetic biology and discuss their utility for the (heterologous) production of (novel) terpenoids.

Seasonal-based temporal changes fluctuate expression patterns of TXS, DBAT, BAPT and DBTNBT genes alongside production of associated taxanes in Taxus baccata

Environmental cues have synergistic or antagonistic regulatory roles on transcription activity and taxanes accumulation in yew, though DBAT activity is less influenced, could be accordingly a rate-limiting enzyme. The current work was undertaken to elucidate the consequences of some environmental cues (i.e., day length, temperature, sunlight and relative humidity) on the expression patterns of TXS, DBAT, BAPT and DBTNBT genes contributed to the taxol biosynthetic pathway along with the accumulation of some taxanes in needles and stems of Taxus baccata over year 2013-2014. In both tissues, light intensity and temperature correlated with the production of 10-DAB III and total taxanes, and TXS activity, while a lack of significant association was deduced for day length and relative humidity. Furthermore, in both tissues, a weak correlation was observed between BAC III and light intensity, temperature, day length and relative humidity, and the corresponding gene, DBAT. Surprisingly, DBAT activity was not co-induced with TXS in both tissues, and remained expressed at basal levels over year, supporting that the conversion of 10-DAB III into BAC III could presumably be a rate limiting step in the taxol biosynthetic pathway. Similar to BAC III, no strong correlation was detected between production of taxol in both tissues and all the meteorological data, while the corresponding genes BAPT and DBTNBT, in some cases, exhibited significant correlated results. Notably, despite higher activities of BAPT and DBTNBT in both tissues over year, taxol production was still in small quantities, probably owing to the low amounts of its precursors rather than low volumes of BAPT and DBTNBT transcripts. The results, altogether, could provide us new insights towards the potential regulatory roles of environmental cues on the production of taxanes in yew trees.

Medicinal Bioprospecting of the Amazon Rainforest: A Modern Eldorado?

Ignorant of the New World, Europeans believed in El Dorado, a hidden city of immense wealth in gold. Many consider the Amazonian forest to be a medicinal treasure chest and potentially the largest drug dispensary in the world. Yet, the quest to obtain drugs from indigenous tropical plants remains elusive. Here, we assess the potential of new technologies to tap into the metabolic diversity of tropical plants. We also consider how regulations affect access to plant resources. We conclude that, although the road to this medicinal El Dorado may be long and arduous, many other smaller but still valuable finds are hidden along the way.

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.