Stimulation of artemisinin synthesis by combined cerebroside and nitric oxide elicitation in Artemisia annua hairy roots

Influence of Abiotic and Biotic Elicitors on Organogenesis, Biomass Accumulation, and Production of Key Secondary Metabolites in Asteraceae Plants

The medicinal plants of the Asteraceae family are a valuable source of bioactive secondary metabolites, including polyphenols, phenolic acids, flavonoids, acetylenes, sesquiterpene lactones, triterpenes, etc. Under stressful conditions, the plants develop these secondary substances to carry out physiological tasks in plant cells. Secondary Asteraceae metabolites that are of the greatest interest to consumers are artemisinin (an anti-malarial drug from Artemisia annua L.-sweet wormwood), steviol glycosides (an intense sweetener from Stevia rebaudiana Bert.-stevia), caffeic acid derivatives (with a broad spectrum of biological activities synthesized from Echinacea purpurea (L.) Moench-echinacea and Cichorium intybus L.-chicory), helenalin and dihydrohelenalin (anti-inflammatory drug from Arnica montana L.-mountain arnica), parthenolide ("medieval aspirin" from Tanacetum parthenium (L.) Sch.Bip.-feverfew), and silymarin (liver-protective medicine from Silybum marianum (L.) Gaertn.-milk thistle). The necessity to enhance secondary metabolite synthesis has arisen due to the widespread use of these metabolites in numerous industrial sectors. Elicitation is an effective strategy to enhance the production of secondary metabolites in in vitro cultures. Suitable technological platforms for the production of phytochemicals are cell suspension, shoots, and hairy root cultures. Numerous reports describe an enhanced accumulation of desired metabolites after the application of various abiotic and biotic elicitors. Elicitors induce transcriptional changes in biosynthetic genes, leading to the metabolic reprogramming of secondary metabolism and clarifying the mechanism of the synthesis of bioactive compounds. This review summarizes biotechnological investigations concerning the biosynthesis of medicinally essential metabolites in plants of the Asteraceae family after various elicitor treatments.

Integrated mRNA and miRNA Transcriptome Analysis Suggests a Regulatory Network for UV-B-Controlled Terpenoid Synthesis in Fragrant Woodfern (Dryopteris fragrans)

Fragrant woodfern (Dryopteris fragrans) is a medicinal plant rich in terpenoids. Ultraviolet-B (UV–B) light could increase concentration of terpenoids. The aim of this study was to analyze how UV–B regulates the terpenoid synthesis of the molecular regulatory mechanism in fragrant woodfern. In this study, compared with the control group, the content of the terpenes was significantly higher in fragrant woodfern leaves under UV–B treatment for 4 days (d). In order to identify how UV–B regulates the terpenoid metabolic mechanism in fragrant woodfern, we examined the mRNAs and small RNAs in fragrant woodfern leaves under UV–B treatment. mRNA and miRNA–seq identified 4533 DEGs and 17 DEMs in the control group compared with fragrant woodfern leaves under UV–B treatment for 4 d. mRNA–miRNA analysis identified miRNA target gene pairs consisting of 8 DEMs and 115 miRNAs. The target genes were subjected to GO and KEGG analyses. The results showed that the target genes were mainly enriched in diterpene biosynthesis, terpenoid backbone biosynthesis, plant hormone signal transduction, MEP pathway and MVA pathway, in which miR156 and miR160 regulate these pathways by targeting DfSPL and DfARF, respectively. The mRNA and miRNA datasets identified a subset of candidate genes. It provides the theoretical basis that UV–B regulates the terpenoid synthesis of the molecular regulatory mechanism in fragrant woodfern.

Biotechnological Approaches for Production of Artemisinin, an Anti-Malarial Drug from Artemisia annua L

Artemisinin is an anti-malarial sesquiterpene lactone derived from Artemisia annua L. (Asteraceae family). One of the most widely used modes of treatment for malaria is an artemisinin-based combination therapy. Artemisinin and its associated compounds have a variety of pharmacological qualities that have helped achieve economic prominence in recent years. So far, research on the biosynthesis of this bioactive metabolite has revealed that it is produced in glandular trichomes and that the genes responsible for its production must be overexpressed in order to meet demand. Using biotechnological applications such as tissue culture, genetic engineering, and bioreactor-based approaches would aid in the upregulation of artemisinin yield, which is needed for the future. The current review focuses on the tissue culture aspects of propagation of A. annua and production of artemisinin from A. annua L. cell and organ cultures. The review also focuses on elicitation strategies in cell and organ cultures, as well as artemisinin biosynthesis and metabolic engineering of biosynthetic genes in Artemisia and plant model systems.

Application of Hairy Root Culture for Bioactive Compounds Production in Medicinal Plants

Medicinal plants are rich sources of natural bioactive compounds used to treat many diseases. With the development of the health industry, the market demands for Chinese medicine have been rapidly increasing in recent years. However, over-utilization of herbal plants would cause serious ecological problems. Therefore, an effective approach should be developed to produce the pharmaceutically important natural drugs. Hairy root culture induced by Agrobacterium rhizogenes has been considered to be an effective tool to produce secondary metabolites that are originally biosynthesized in the roots or even in the aerial organs of mature plants. This review aims to summarize current progress on medicinal plant hairy root culture for bioactive compounds production. It presents the stimulating effects of various biotic and abiotic elicitors on the accumulation of secondary metabolites. Synergetic effects by combination of different elicitors or with other strategies are also included. Besides, the transgenic system has promising prospects to increase bioactive compounds content by introducing their biosynthetic or regulatory genes into medicinal plant hairy root. It offers great potential to further increase secondary metabolites yield by the integration of manipulating pathway genes with elicitors and other strategies. Then advances on two valuable pharmaceuticals production in the hairy root cultures are illustrated in detail. Finally, successful production of bioactive compounds by hairy root culture in bioreactors are introduced.

Nitric oxide donor sodium nitroprusside-induced transcriptional changes and hypocrellin biosynthesis of Shiraia sp. S9

Background

Nitric oxide (NO) is a ubiquitous signaling mediator in various physiological processes. However, there are less reports concerning the effects of NO on fungal secondary metabolites. Hypocrellins are effective anticancer photodynamic therapy (PDT) agents from fungal perylenequinone pigments of Shiraia. NO donor sodium nitroprusside (SNP) was used as a chemical elicitor to promote hypocrellin biosynthesis in Shiraia mycelium cultures.

Results

SNP application at 0.01–0.20 mM was found to stimulate significantly fungal production of perylenequinones including hypocrellin A (HA) and elsinochrome A (EA). SNP application could not only enhance HA content by 178.96% in mycelia, but also stimulate its efflux to the medium. After 4 days of SNP application at 0.02 mM, the highest total production (110.34 mg/L) of HA was achieved without any growth suppression. SNP released NO in mycelia and acted as a pro-oxidant, thereby up-regulating the gene expression and activity of reactive oxygen species (ROS) generating NADPH oxidase (NOX) and antioxidant enzymes, leading to the increased levels of superoxide anion (O₂⁻) and hydrogen peroxide (H₂O₂). Gene ontology (GO) analysis revealed that SNP treatment could up-regulate biosynthetic genes for hypocrellins and activate the transporter protein major facilitator superfamily (MFS) for the exudation. Moreover, SNP treatment increased the proportion of total unsaturated fatty acids in the hypha membranes and enhanced membrane permeability. Our results indicated both cellular biosynthesis of HA and its secretion could contribute to HA production induced by SNP.

Conclusions

The results of this study provide a valuable strategy for large-scale hypocrellin production and can facilitate further understanding and exploration of NO signaling in the biosynthesis of the important fungal metabolites.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01581-8.

Regulation of glutamine synthetase activity by transcriptional and posttranslational modifications negatively influences ganoderic acid biosynthesis in Ganoderma lucidum

Glutamine synthetase (GS), a central nitrogen metabolic enzyme, plays important roles in the nitrogen regulation network and secondary metabolism in fungi. However, the mechanisms by which external nitrogen sources regulate fungal GS activity have not been determined. Here, we found that GS activity was inhibited under nitrate conditions in Ganoderma lucidum. By constructing gs-silenced strains and adding 1 mM GS inhibitor to inhibit GS activity, we found that a decrease in GS activity led to a decrease in ganoderic acid biosynthesis. The transcription of gs increased approximately five fold under nitrate conditions compared with that under ammonia. Electrophoretic mobility shift and yeast one-hybrid assay showed that gs was transcriptionally regulated by AreA. Although both gs expression and GS protein content increased under nitrate conditions, the GS activity still decreased. Treatment of recombinant GS with SIN-1 (protein nitration donor) resulted in a strengthened nitration accompanied by a 71% decrease in recombinant GS activity. Furthermore, intracellular GS could be nitrated from mycelia cultivated under nitrate conditions. These results indicated that GS activity could be inhibited by NO-mediated protein nitration. Our findings provide the first insight into the role of transcriptional and posttranslational regulation of GS activity in regulating secondary metabolism in fungi.

Physio-chemical responses of exogenous calcium nanoparticle and putrescine polyamine in Saffron (Crocus sativus L.)

The aim of this study was to investigate the effect of calcium nanoparticles (CaNP) and putrescine polyamine on some physiological and biochemical properties of saffron (Crocus sativus L.) under the control condition. Saffron corm was treated by different concentrations of putrescine (0, 0.25, 0.5, 1, 2 mM) and CaNP (0, 0.25, 0.5, 1, 1.5 g/l). The treatment of corm with putrescine and CaNP separately caused a significant increase in morphological parameters. Changes in biochemical parameters were also significant. Compared to other concentrations, the highest concentration of putrescine (1 mM) and CaNP (1 g/l) treatment in the plant showed the greatest effect. The combined effect of putrescine and CaNP treatment on morphological parameters was significant. The results of HPLC analysis showed that CaNP treatment alone is more effective on crocin, picrocrocin, and safranal content than the combined effect of CaNP and putrescine. The present study reported the functional potential of CaNP and putrescine combination to increase growth and phytochemical properties in Crocus sativus.

An oxidatively stressful situation: a case of Artemisia annua L

Artemisinin (ART) is an antimalarial compound that possesses a variety of novel biological activities. Due to the low abundance of ART in natural sources, agricultural supply has been erratic, and prices are highly volatile. While heterologous biosynthesis and semi-synthesis are advantageous in certain aspects, these approaches remained disadvantageous in terms of productivity and cost-effectiveness. Therefore, further improvement in ART production calls for approaches that should supplement the agricultural production gap, while reducing production costs and stabilising supply. The present review offers a discussion on the elicitation of plants and/or in vitro cultures as an economically feasible yield enhancement strategy to address the global problem of access to affordable ART. Deemed critical for the manipulation of biosynthetic potential, the mechanism of ART biosynthesis is reviewed. It includes a discussion on the current biotechnological solutions to ART production, focusing on semi-synthesis and elicitation. A brief commentary on the possible aspects that influence elicitation efficiency and how oxidative stress modulates ART synthesis is also presented. Based on the critical analysis of current literature, a hypothesis is put forward to explain the possible involvement of enzymes in assisting the final non-enzymatic transformation step leading to ART formation. This review highlights the critical factors limiting the success of elicitor-induced modulation of ART metabolism, that will help inform strategies for future improvement of ART production. Additionally, new avenues for future research based on the proposed hypothesis will lead to exciting perspectives in this research area and continue to enhance our understanding of this intricate metabolic process.

Nitric Oxide and Hydrogen Peroxide Signaling in Extractive Shiraia Fermentation by Triton X-100 for Hypocrellin A Production

Shiraia mycelial culture is a promising biotechnological alternative for the production of hypocrellin A (HA), a new photosensitizer for anticancer photodynamic therapy (PDT). The extractive fermentation of intracellular HA in the nonionic surfactant Triton X-100 (TX100) aqueous solution was studied in the present work. The addition of 25 g/L TX100 at 36 h of the fermentation not only enhanced HA exudation to the broth by 15.6-fold, but stimulated HA content in mycelia by 5.1-fold, leading to the higher production 206.2 mg/L, a 5.4-fold of the control on day 9. After the induced cell membrane permeabilization by TX100 addition, a rapid generation of nitric oxide (NO) and hydrogen peroxide (H₂O₂) was observed. The increase of NO level was suppressed by the scavenger vitamin C (VC) of reactive oxygen species (ROS), whereas the induced H₂O₂ production could not be prevented by the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO), suggesting that NO production may occur downstream of ROS in the extractive fermentation. Both NO and H₂O₂ were proved to be involved in the expressions of HA biosynthetic genes (Mono, PKS and Omef) and HA production. NO was found to be able to up-regulate the expression of transporter genes (MFS and ABC) for HA exudation. Our results indicated the integrated role of NO and ROS in the extractive fermentation and provided a practical biotechnological process for HA production.

Elicitation: A biotechnological tool for enhanced production of secondary metabolites in hairy root cultures

Elicitation is a possible aid to overcome various difficulties associated with the large-scale production of most commercially important bioactive secondary metabolites from wild and cultivated plants, undifferentiated or differentiated cultures. Secondary metabolite accumulation in vitro or their efflux in culture medium has been elicited in the undifferentiated or differentiated tissue cultures of several plant species by the application of a low concentration of biotic and abiotic elicitors in the last three decades. Hairy root cultures are preferred for the application of elicitation due to their genetic and biosynthetic stability, high growth rate in growth regulator-free media, and production consistence in response to elicitor treatment. Elicitors act as signal, recognized by elicitor-specific receptors on the plant cell membrane and stimulate defense responses during elicitation resulting in increased synthesis and accumulation of secondary metabolites. Optimization of various parameters, such as elicitor type, concentration, duration of exposure, and treatment schedule is essential for the effectiveness of the elicitation strategies. Combined application of different elicitors, integration of precursor feeding, or replenishment of medium or in situ product recovery from the roots/liquid medium with the elicitor treatment have showed improved accumulation of secondary metabolites due to their synergistic effect. This is a comprehensive review about the progress in the elicitation approach to hairy root cultures from 2010 to 2019 and the information provided is valuable and will be of interest for scientists working in this area of plant biotechnology.

Emerging Roles of Sphingolipid Signaling in Plant Response to Biotic and Abiotic Stresses

Plant sphingolipids are not only structural components of the plasma membrane and other endomembrane systems but also act as signaling molecules during biotic and abiotic stresses. However, the roles of sphingolipids in plant signal transduction in response to environmental cues are yet to be investigated in detail. In this review, we discuss the signaling roles of sphingolipid metabolites with a focus on plant sphingolipids. We also mention some microbial sphingolipids that initiate signals during their interaction with plants, because of the limited literatures on their plant analogs. The equilibrium of nonphosphorylated and phosphorylated sphingolipid species determine the destiny of plant cells, whereas molecular connections among the enzymes responsible for this equilibrium in a coordinated signaling network are poorly understood. A mechanistic link between the phytohormone-sphingolipid interplay has also not yet been fully understood and many key participants involved in this complex interaction operating under stress conditions await to be identified. Future research is needed to fill these gaps and to better understand the signal pathways of plant sphingolipids and their interplay with other signals in response to environmental stresses.

Endophyte Chaetomium globosum D38 Promotes Bioactive Constituents Accumulation and Root Production in Salvia miltiorrhiza

Salvia miltiorrhiza is known for tanshinones and salvianolic acids, which have been shown to have a protective effect against ROS, especially for cardiovascular diseases and other various ailments of human organs. Due to the low yield of tanshinones and their analogs in S. miltiorrhiza, multiple stimulation strategies have been developed to improve tanshinones production in plant tissue cultures. Endophytic fungi have been reported to form different relationships with their host plants, including symbiotic, mutualistic, commensalistic, and parasitic interactions. Thus we take the assumption that endophytic fungi may be a potential microbial tool for secondary metabolism promotion in medicinal plants. We recently isolated Chaetomium globosum D38 from the roots of S. miltiorrhiza and our study aimed to examine the effects of this live endophytic fungus D38 and its elicitor on the accumulation of tanshinones in the hairy root cultures of S. miltiorrhiza. Our results revealed that C. globosum D38 mainly colonized in the intercellular gap of xylem parenchyma cells of S. miltiorrhiza hairy roots during the long term co-existence without any toxicity. Moreover, both of the live fungus and its mycelia extract could increase the production of tanshinones, especially for dihydrotanshinone I and cryptotanshinone. The effect of the mycelia extract was much stronger than that of the live fungus on tanshinones synthesis, which significantly increased the transcriptional activity of those key genes in tanshinone biosynthetic pathway. Furthermore, the live C. globosum D38 could also be made into biotic fertilizer used for S. miltiorrhiza seedlings culture, which not only significantly promoted the growth of the host plant, but also notably enhanced the accumulation of tanshinones and salvianolic acids. We thus speculated that, in the soil environment D38 could form bitrophic and mutual beneficial interactions with the host and enhance the plant growth and its secondary metabolism on the whole so as to have facilitative effects on both tanshinones and salvianolic acids accumulation. In conclusion, Chaetomium globosum D38 was a highly beneficial endophytic fungus for the growth and metabolism of S. miltiorrhiza.

Strategies to enhance biologically active-secondary metabolites in cell cultures of Artemisia - current trends

The genus Artemisia has been utilized worldwide due to its immense potential for protection against various diseases, especially malaria. Artemisia absinthium, previously renowned for its utilization in the popular beverage absinthe, is gaining resurgence due to its extensive pharmacological activities. Like A. annua, this species exhibits strong biological activities like antimalarial, anticancer and antioxidant. Although artemisinin was found to be the major metabolite for its antimalarial effects, several flavonoids and terpenoids are considered to possess biological activities when used alone and also to synergistically boost the bioavailability of artemisinin. However, due to the limited quantities of these metabolites in wild plants, in vitro cultures were established and strategies have been adopted to enhance medicinally important secondary metabolites in these cultures. This review elaborates on the traditional medicinal uses of Artemisia species and explains current trends to establish cell cultures of A. annua and A. absinthium for enhanced production of medicinally important secondary metabolites.

Antioxidant and DNA Damage Protecting Activity of Exopolysaccharides from the Endophytic Bacterium Bacillus cereus SZ1

An endophytic bacterium was isolated from the Chinese medicinal plant Artemisia annua L. The phylogenetic and physiological characterization indicated that the isolate, strain SZ-1, was Bacillus cereus. The endophyte could produce an exopolysaccharide (EPS) at 46 mg/L. The 1,1-diphenyl-2-picrylhydracyl (DPPH) radical scavenging activity of the EPS reached more than 50% at 3-5 mg/mL. The EPS was also effective in scavenging superoxide radical in a concentration dependent fashion with an EC50 value of 2.6 mg/mL. The corresponding EC50 for scavenging hydroxyl radical was 3.1 mg/mL. Moreover, phenanthroline-copper complex-mediated chemiluminescent emission of DNA damage was both inhibited and delayed by EPS. The EPS at 0.7-1.7 mg/mL also protected supercoiled DNA strands in plasmid pBR322 against scission induced by Fenton-mediated hydroxyl radical. The preincubation of PC12 cells with the EPS prior to H₂O₂ exposure increased the cell survival and glutathione (GSH) level and catalase (CAT) activities, and decreased the level of malondialdehyde (MDA) and lactate dehydrogenase (LDH) activity in a dose-dependent manner, suggesting a pronounced protective effect against H₂O₂-induced cytotoxicity. Our study indicated that the EPS could be useful for preventing oxidative DNA damage and cellular oxidation in pharmaceutical and food industries.

Updates on artemisinin: an insight to mode of actions and strategies for enhanced global production

Application of traditional Chinese drug, artemisinin, originally derived from Artemisia annua L., in malaria therapy has now been globally accepted. Artemisinin and its derivatives, with their established safety records, form the first line of malaria treatment via artemisinin combination therapies (ACTs). In addition to its antimalarial effects, artemisinin has recently been evaluated in terms of its antitumour, antibacterial, antiviral, antileishmanial, antischistosomiatic, herbicidal and other properties. However, low levels of artemisinin in plants have emerged various conventional, transgenic and nontransgenic approaches for enhanced production of the drug. According to WHO (2014), approximately 3.2 billion people are at risk of this disease. However, unfortunately, artemisinin availability is still facing its short supply. To fulfil artemisinin's global demand, no single method alone is reliable, and there is a need to collectively use conventional and advanced approaches for its higher production. Further, it is the unique structure of artemisinin that makes it a potential drug not only against malaria but to other diseases as well. Execution of its action through multiple mechanisms is probably the reason behind its wide spectrum of action. Unfortunately, due to clues for developing artemisinin resistance in malaria parasites, it has become desirable to explore all possible modes of action of artemisinin so that new generation antimalarial drugs can be developed in future. The present review provides a comprehensive updates on artemisinin modes of action and strategies for enhanced artemisinin production at global level.

Transcriptome responses involved in artemisinin production in Artemisia annua L. under UV-B radiation

Artemisinin, an endoperoxide sesquiterpene lactone, is an effective antimalarial drug isolated from Artemisia annua L. In this study, a low dose (1.44 kJm(-2)d(-1)) of UV-B radiation (280-320 nm) for short-term (1h per day for 10 days) was applied to A. annua seedlings to stimulate artemisinin production. UV-B treatment not only induced the generation of reactive oxygen species (ROS), enhanced peroxidase activity and endogenous content of abscisic acid (ABA), but stimulated the biosynthesis of artemisinin in the seedlings. Here, transcriptomic changes during UV-B radiation in A. annua were detected using an Agilent GeneChip with 43,692 probe sets. In total, 358 transcripts were identified as differentially expressed under UV-B stress, of which 172 transcripts increased and 186 transcripts decreased in abundance. In terms of biological processes, gene ontology (GO) terms including primary carbohydrate and nitrogen compound metabolic processes were enriched in UV-B-repressed genes. The up-regulated genes were enriched in response to stress, ROS generation, hormone (ethylene, ABA) stimulus and cell cycle control. The expression of key enzymes such as amorpha-4,11-diene synthase (ADS) and cytochrome P450 dependent monooxygenase/hydroxylase (CYP71AV1), and related WRKY transcription factors was up-regulated significantly for artemisinin biosynthesis. This profile of global gene expression patterns during UV-B stress will be valuable for further identification of the enzymes involved in artemisinin biosynthesis.

Cerebroside C increases tolerance to chilling injury and alters lipid composition in wheat roots

Chilling tolerance was increased in seed germination and root growth of wheat seedlings grown in media containing 20 µg/mL cerebroside C (CC), isolated from the endophytic Phyllosticta sp. TG78. Seeds treated with 20 µg/mL CC at 4 °C expressed the higher germination rate (77.78%), potential (23.46%), index (3.44) and the shorter germination time (6.19 d); root growth was also significantly improved by 13.76% in length, 13.44% in fresh weight and 6.88% in dry mass compared to controls. During the cultivation process at 4 °C for three days and the followed 24 h at 25 °C, lipid peroxidation, expressed by malondialdehyde (MDA) content and relative membrane permeability (RMP) was significantly reduced in CC-treated roots; activities of lipoxygenase (LOX), phospholipid C (PLC) and phospholipid D (PLD) were inhibited by 13.62-62.26%, 13.54-63.93% and 13.90-61.17%, respectively; unsaturation degree of fatty acids was enhanced through detecting the contents of CC-induced linoleic acid, linolenic acid, palmitic acid and stearic acid using GC-MS; capacities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GSH-Px) were individually increased by 7.69-46.06%, 3.37-37.96%, and -7.00-178.07%. These results suggest that increased chilling tolerance may be due, in part, to the reduction of lipid peroxidation and alternation of lipid composition of roots in the presence of CC.

Nitric oxide-sphingolipid interplays in plant signalling: a new enigma from the Sphinx?

Nitric oxide (NO) emerged as one of the major signaling molecules operating during plant development and plant responses to its environment. Beyond the identification of the direct molecular targets of NO, a series of studies considered its interplay with other actors of signal transduction and the integration of NO into complex signaling networks. Beside the close relationships between NO and calcium or phosphatidic acid signaling pathways that are now well-established, recent reports paved the way for interplays between NO and sphingolipids (SLs). This mini-review summarizes our current knowledge of the influence NO and SLs might exert on each other in plant physiology. Based on comparisons with examples from the animal field, it further indicates that, although SL-NO interplays are common features in signaling networks of eukaryotic cells, the underlying mechanisms and molecular targets significantly differ.

Effective elicitors and process strategies for enhancement of secondary metabolite production in hairy root cultures

This chapter reviews the various biotic and abiotic elicitors applied to hairy root cultures and their stimulating effects on the accumulation of secondary metabolites. Elicitors generally refer to the agents that stimulate the defense responses of plants. As a major response of plants to biotic and abiotic stress, the accumulation of secondary metabolites in plant tissue cultures can be stimulated by the elicitors. Among the many elicitors applied to hairy root cultures as well as plant cell suspension cultures, the most common and effective elicitors are fungal cell extracts, polysaccharides from fungal and plant cells, and heavy metal salts. With the crude fungal cell extracts, it is essential to observe the preparation conditions carefully for achieving reproducible effects. In addition to the chemical agents, UV-radiation, hyperosmotic stress and temperature shift have been shown effective for some plant species/metabolites. Elicitor type, dose, and treatment schedule are major factors determining the effects on the secondary metabolite production. In addition to the accumulation of products in roots, elicitor treatments often stimulate the release of intracellular products. Although elicitation is mainly effective to increase specific product yield on per unit mass of roots, the incorporation of nutrient feeding strategies can be applied to enhance the volumetric product yield. The integration of in situ product recovery from the roots/liquid medium is another synergistic strategy with the elicitor treatment to improve the process.

An endophytic Pseudonocardia species induces the production of artemisinin in Artemisia annua

Endophytic actinobacteria colonize internal tissues of their host plants and are considered as a rich and reliable source of diverse species and functional microorganisms. In this study, endophytic actinobacterial strain YIM 63111 was isolated from surface-sterilized tissue of the medicinal plant Artemisia annua. We identified strain YIM 63111 as a member of the genus Pseudonocardia. A. annua seedlings grown under both sterile and greenhouse conditions were inoculated with strain YIM 63111. The growth of A. annua seedlings was strongly reduced when YIM 63111 was inoculated at higher concentrations under sterile conditions. However, no growth inhibition was observed when A. annua was grown under greenhouse conditions. Using an enhanced green fluorescent protein (EGFP) expressing YIM 63111 strain, we also observed the endophytic colonization of A. annua seedling using confocal laser-scanning microscopy. The transcription levels of the key genes involved in artemisinin biosynthesis were investigated using real time RT-PCR, revealing that cytochrome P450 monooxygenase (CYP71AV1) and cytochrome P450 oxidoreductase (CPR) expression were up-regulated in A. annua upon inoculation with strain YIM 63111 under certain conditions. The up-regulation of these genes was associated with the increased accumulation of artemisinin. These results suggest that endophytic actinobacteria effectively stimulate certain plant defense responses. Our data also demonstrate the use of Pseudonocardia sp. strain YIM 63111 as a promising means to enhance artemisinin production in plants.

Exogenous nitric oxide donor protects Artemisia annua from oxidative stress generated by boron and aluminium toxicity

Nitric oxide (NO) is an important signal molecule modulating the response of plants to environmental stress. Here we report the effects of boron (B) and aluminium (Al) contamination in soil, carried out with or without application of exogenous SNP (NO donor), on various plant processes in Artemisia annua, including changes in artemisinin content. The addition of B or Al to soil medium significantly reduced the yield and growth of plants and lowered the values of net photosynthetic rate, stomatal conductance, internal CO(2) concentration and total chlorophyll content. The follow-up treatment of NO donor favoured growth and improved the photosynthetic efficiency in stressed as well as non-stressed plants. Artemisinin content was enhanced by 24.6% and 43.8% at 1mmole of soil-applied B or Al. When SNP was applied at 2mmole concentration together with either 1mmole of B and/or Al, it further stimulated artemisinin biosynthesis compared to the control. Application of B+Al+SNP proved to be the best treatment combination for the artemisinin content in Artemisia annua leaves.

Roles of reactive oxygen species in methyl jasmonate and nitric oxide-induced tanshinone production in Salvia miltiorrhiza hairy roots

Salvia miltiorrhiza is one of the most popular traditional Chinese medicinal plants for treatment of coronary heart disease. Tanshinones are the main biological active compounds in S. miltiorrhiza. In this study, effects of exogenous methyl jasmonate (MJ) and nitric oxide (NO) on tanshinone production in S. miltiorrhiza hairy roots were investigated and the roles of reactive oxygen species (ROS) in MJ and NO-induced tanshinone production were elucidated further. The results showed that contents of four tanshinone compounds were significantly increased by 100 μM MJ when compared to the control. Application of 100 μM sodium nitroprusside (SNP), a donor of NO, also resulted in a significant increase of tanshinone production. Expression of two key genes encoding 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR) and 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR) was up-regulated by MJ and SNP. Generations of O(2)(-) and H(2)O(2) were triggered by MJ, but not by SNP. The increase of tanshinone production and up-regulation of HMGR and DXR expression induced by MJ were significantly inhibited by ROS scavengers, superoxide dismutase (SOD) and catalase (CAT). However, neither SOD nor CAT was able to suppress the SNP-induced increase of tanshinone production and expression of HMGR and DXR gene. In conclusion, tanshinone production was significantly stimulated by MJ and SNP. Of four tanshinone compounds, cryptotanshinone accumulation was most affected by MJ elicitation, while cryptotanshinone and tanshinone IIA accumulation was more affected by SNP elicitation. ROS mediated MJ-induced tanshinone production, but SNP-induced tanshinone production was ROS independent.

Exudation: an expanding technique for continuous production and release of secondary metabolites from plant cell suspension and hairy root cultures

This review addresses methods of obtaining secondary metabolites from plant cell suspension and hairy root cultures and their exudates, particularly the physiological mechanisms of secondary metabolites release and trafficking. The efficiency for product recovery of metabolites can be increased by various methods, based on the principle of continuous product release into the cultivation medium. The most common methods for metabolite recovery are elicitation, influencing membrane permeability, and in situ product removal. The biosynthetic pathways can be influenced by cultivation conditions, transformation, or application of elicitors. The membrane permeability can be altered through the application of chemical or physical treatments. Product removal can be greatly increased through a two-phase system and the introduction of absorbents into the cultivation medium. In this review, we describe some improved approaches that have proven useful in these efforts.

Nitric oxide elicitation for secondary metabolite production in cultured plant cells

Nitric oxide (NO) is an important signal molecule in stress responses. Accumulation of secondary metabolites often occurs in plants subjected to stresses including various elicitors or signal molecules. NO has been reported to play important roles in elicitor-induced secondary metabolite production in tissue and cell cultures of medicinal plants. Better understanding of NO role in the biosynthesis of such metabolites is very important for optimizing the commercial production of those pharmaceutically significant secondary metabolites. This paper summarizes progress made on several aspects of NO signal leading to the production of plant secondary metabolites, including various abiotic and biotic elicitors that induce NO production, elicitor-triggered NO generation cascades, the impact of NO on growth development and programmed cell death in medicinal plants, and NO-mediated regulation of the biosynthetic pathways of such metabolites. Cross-talks among NO signaling and reactive oxygen species, salicylic acid, and jasmonic acid are discussed. Some perspectives on the application of NO donors for induction of the secondary metabolite accumulation in plant cultures are also presented.

β-Cyclodextrins enhance artemisinin production in Artemisia annua suspension cell cultures

Artemisinin is a sesquiterpene antimalarial compound produced, though at low levels (0.1-1% dry weight), in Artemisia annua in which it accumulates in the glandular trichomes of the plant. Due to its antimalarial properties and short supply, efforts are being made to improve our understanding of artemisinin biosynthesis and its production. Native β-cyclodextrins, as well as the chemically modified heptakis(2,6-di-O-methyl)-β-cyclodextrin (DIMEB) and 2-hydroxypropyl-β-cyclodextrins, were added to the culture medium of A. annua suspension cultures, and their effects on artemisinin production were analysed. The effects of a joint cyclodextrin and methyl jasmonate treatment were also investigated. Fifty millimolar DIMEB, as well as a combination of 50 mM DIMEB and 100 μM methyl jasmonate, was highly effective in increasing the artemisinin levels in the culture medium. The observed artemisinin level (27 μmol g(-1) dry weight) was about 300-fold higher than that observed in untreated suspensions. The influence of β-cyclodextrins and methyl jasmonate on the expression of artemisinin biosynthetic genes was also investigated.

Pitfalls in new artemisinin-containing antimalarial drug development

Artemisinin combination therapy (ACT) paves the way for new opportunities to eliminate malaria in the tropics. However, the huge increase of ACT consumption raises major concerns about their availability over the next few years. At the same time a decrease in their efficacy has already been reported. Alongside the deployment of multifocal control programs, the process ranging from artemisia crop production to accreditation of new ACT combinations urgently needs to be strengthened to supply sufficient quantities of high-quality drugs. New suppliers will have the opportunity to enter this market to develop new formulations, and bioequivalence studies are required to validate these new formulations. It is thus crucial for national malaria control teams to be able to better scrutinize the dossier of these new formulations.