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

Recent advances in droplet microfluidics for enzyme and cell factory engineering

Enzymes and cell factories play essential roles in industrial biotechnology for the production of chemicals and fuels. The properties of natural enzymes and cells often cannot meet the requirements of different industrial processes in terms of cost-effectiveness and high durability. To rapidly improve their properties and performances, laboratory evolution equipped with high-throughput screening methods and facilities is commonly used to tailor the desired properties of enzymes and cell factories, addressing the challenges of achieving high titer and the yield of the target products at high/low temperatures or extreme pH, in unnatural environments or in the presence of unconventional media. Droplet microfluidic screening (DMFS) systems have demonstrated great potential for exploring vast genetic diversity in a high-throughput manner (>10⁶/h) for laboratory evolution and have been increasingly used in recent years, contributing to the identification of extraordinary mutants. This review highlights the recent advances in concepts and methods of DMFS for library screening, including the key factors in droplet generation and manipulation, signal sources for sensitive detection and sorting, and a comprehensive summary of success stories of DMFS implementation for engineering enzymes and cell factories during the past decade.

Seaweeds in viticulture: a review focused on grape quality

Cell walls of seaweeds contain a wide number of organic and inorganic constituents, of which polysaccharides have important biological activity. Some researchers suggest that polysaccharides from seaweeds can behave as biotic elicitors in viticulture, triggering the synthesis of phenolic compounds in leaves and grape berries. The mechanism of action of seaweeds after a foliar application to grapevines is not fully understood but it is discussed in this review. An overview of the recent research focused on the effects of seaweeds foliar applications on grapevine productivity, on grape and wine quality is included as well as a short-term future perspective for the research in this field.

Strategies to Modulate Specialized Metabolism in Mediterranean Crops: From Molecular Aspects to Field

Plant specialized metabolites (SMs) play an important role in the interaction with the environment and are part of the plant defense response. These natural products are volatile, semi-volatile and non-volatile compounds produced from common building blocks deriving from primary metabolic pathways and rapidly evolved to allow a better adaptation of plants to environmental cues. Specialized metabolites include terpenes, flavonoids, alkaloids, glucosinolates, tannins, resins, etc. that can be used as phytochemicals, food additives, flavoring agents and pharmaceutical compounds. This review will be focused on Mediterranean crop plants as a source of SMs, with a special attention on the strategies that can be used to modulate their production, including abiotic stresses, interaction with beneficial soil microorganisms and novel genetic approaches.

Effects of Abiotic Elicitors on Expression and Accumulation of Three Candidate Benzophenanthridine Alkaloids in Cultured Greater Celandine Cells

Efforts to develop the necessary biotechnologies in Greater Celandine (Chelidonium majus L.), a leading plant resource for the development of plant-derived medicines, have been hampered by the lack of knowledge about transcriptome and metabolome regulations of its medicinal components. Therefore, this study aimed to examine the effect of abiotic elicitors, methyl jasmonate (MJ) and salicylic acid (SA), at different time courses (12, 24, 48, and 72 h), on expression and metabolome of key benzophenanthridine alkaloids (BPAs) in an optimized in vitro culture. Gene expression analysis indicated the upregulation of CFS (cheilanthifoline synthase) to 2.62, 4.85, and 7.28 times higher than the control at 12, 24, and 48 h respectively, under MJ elicitation. Besides, MJ upregulated the expression of TNMT (tetrahydroprotoberberine N-methyltransferase) to 2.79, 4.75, and 7.21 times at 12, 24, and 48 h respectively, compared to the control. Investigation of BPAs revealed a significant enhancement in the chelidonine content (9.86 µg/mg) after 72 h of MJ elicitation. Additionally, sanguinarine content increased to its highest level (3.42 µg/mg) after 24 h of MJ elicitation; however, no significant enhancement was detected in its content in shorter elicitation time courses. Generally, higher gene expression and BPAs’ level was observed through longer elicitation courses (48 and 72 h). Our findings take part in improving the understanding of transcription and metabolic regulation of BPAs in cultured Greater Celandine cells.

Biotic and Abiotic Elicitors of Stilbenes Production in Vitis vinifera L. Cell Culture

The in vitro cell cultures derived from the grapevine (Vitis vinifera L.) have been used for the production of stilbenes treated with different biotic and abiotic elicitors. The red-grape cultivar Váh has been elicited by natural cellulose from Trichoderma viride, the cell wall homogenate from Fusarium oxysporum and synthetic jasmonates. The sodium-orthovanadate, known as an inhibitor of hypersensitive necrotic response in treated plant cells able to enhance production and release of secondary metabolite into the cultivation medium, was used as an abiotic elicitor. Growth of cells and the content of phenolic compounds trans-resveratrol, trans-piceid, δ-viniferin, and ɛ-viniferin, were analyzed in grapevine cells treated by individual elicitors. The highest accumulation of analyzed individual stilbenes, except of trans-piceid has been observed after treatment with the cell wall homogenate from F. oxysporum. Maximum production of trans-resveratrol, δ- and ɛ-viniferins was triggered by treatment with cellulase from T. viride. The accumulation of trans-piceid in cell cultures elicited by this cellulase revealed exactly the opposite effect, with almost three times higher production of trans-resveratrol than that of trans-piceid. This study suggested that both used fungal elicitors can enhance production more effectively than commonly used jasmonates.

New Insight into Justicidin B Pathway and Production in Linum austriacum

Lignans are the main secondary metabolites synthetized by Linum species as plant defense compounds but they are also valuable for human health, in particular, for novel therapeutics. In this work, Linum austriacum in vitro cultures, cells (Cc), adventitious roots (ARc) and hairy roots (HRc) were developed for the production of justicidin B through elicitation with methyl jasmonate (MeJA) and coronatine (COR). The performances of the cultures were evaluated for their stability, total phenols content and antioxidant ability. NMR was used to identify justicidin B and isojusticidin B and HPLC to quantify the production, highlighting ARc and HRc as the highest productive tissues. MeJA and COR treatments induced the synthesis of justicidin B more than three times and the synthesis of other compounds. RNA-sequencing and a de novo assembly of L. austriacum ARc transcriptome was generated to identify the genes activated by MeJA. Furthermore, for the first time, the intracellular localization of justicidin B in ARc was investigated through microscopic analysis. Then, HRc was chosen for small-scale production in a bioreactor. Altogether, our results improve knowledge on justicidin B pathway and cellular localization in L. austriacum for future scale-up processes.

Recent applications of plant cell culture technology in cosmetics and foods

Plants have been used as the main source of phytochemicals with nutritional, medicinal, cultural and cosmetic applications since times immemorial. Nowadays, achieving sustainable development, global climate change, restricted access to fresh water, limited food supply and growing energy demands are among the critical global challenges faced by humanity. Plant cell culture technology has the potential to address some of these challenges by providing effective tools for sustainable supply of phyto-ingredients with reduced energy, carbon and water footprints. The main aim of this review is to discuss the recent trends in the development of plant cell culture technologies for production of plant-derived substances with application in food products and cosmetic formulations. The specific technological steps and requirements for the final products are discussed in the light of the advances in cultivation technologies used for growing differentiated and undifferentiated plant in vitro systems. Future prospects and existing challenges of the commercialization of plant cell culture-derived products have been outlined through the prism of the authors' point of view. We expect this review will encourage scientists, policymakers and business enterprises to join efforts for speeding-up the mass commercialization and popularization of plant cell culture technology as an eco-friendly alternative method for sustainable production of plant-derived additives with application in food and cosmetic products.

Food ingredients and food made with plant cell and tissue cultures: State-of-the art and future trends

Climate change and an increasing world population means traditional farming methods may not be able to meet the anticipated growth in food demands. Therefore, alternative agricultural strategies should be considered. Here, plant cell and tissue cultures (PCTCs) may present a possible solution, as they allow for controlled, closed and sustainable manufacturing of extracts which have been or are still being used as colorants or health food ingredients today. In this review we would like to highlight developments and the latest trends concerning commercial PCTC extracts and their use as food ingredients or even as food. The commercialization of PCTC-derived products, however, requires not only regulatory approval, but also outstanding product properties or/and a high product titer. If these challenges can be met, PCTCs will become increasingly important for the food sector in coming years.

Application of Plant Growth Regulators Modulates the Profile of Chlorogenic Acids in Cultured Bidens pilosa Cells

Plant cell culture offers an alternative to whole plants for the production of biologically important specialised metabolites. In cultured plant cells, manipulation by auxin and cytokinin plant growth regulators (PGRs) may lead to in vitro organogenesis and metabolome changes. In this study, six different combination ratios of 2,4-dichlorophenoxyacetic acid (2,4-D) and benzylaminopurine (BAP) were investigated with the aim to induce indirect organogenesis from Bidens pilosa callus and to investigate the associated induced changes in the metabolomes of these calli. Phenotypic appearance of the calli and total phenolic contents of hydromethanolic extracts indicated underlying biochemical differences that were investigated using untargeted metabolomics, based on ultra-high-performance liquid chromatography quadrupole time-of-flight mass spectrometry (UHPLC–qTOF–MS), combined with multivariate data analysis. The concentration and combination ratios of PGRs were shown to induce differential metabolic responses and, thus, distinct metabolomic profiles, dominated by chlorogenic acids consisting of caffeoyl- and feruloyl-derivatives of quinic acid. Although organogenesis was not achieved, the results demonstrate that exogenous application PGRs can be used to manipulate the metabolome of B. pilosa for in vitro production of specialised metabolites with purported pharmacological properties.

Responses of Medicinal and Aromatic Plants to Engineered Nanoparticles

Medicinal and aromatic plants have been used by mankind since ancient times. This is primarily due to their healing effects associated with their specific secondary metabolites (some of which are also used as drugs in modern medicine), or their structures, served as a basis for the development of new effective synthetic drugs. One way to increase the production of these secondary metabolites is to use nanoparticles that act as elicitors. However, depending on the specific particle size, composition, concentration, and route of application, nanoparticles may have several other benefits on medicinal and aromatic plants (e.g., increased plant growth, improved photosynthesis, and overall performance). On the other hand, particularly at applications of high concentrations, they are able to damage plants mechanically, adversely affect morphological and biochemical characteristics of plants, and show cytotoxic and genotoxic effects. This paper provides a comprehensive overview of the beneficial and adverse effects of metal-, metalloid-, and carbon-based nanoparticles on the germination, growth, and biochemical characteristics of a wide range of medicinal and aromatic plants, including the corresponding mechanisms of action. The positive impact of nanopriming and application of nanosized fertilizers on medicinal and aromatic plants is emphasized. Special attention is paid to the effects of various nanoparticles on the production of valuable secondary metabolites in these plants cultivated in hydroponic systems, soil, hairy root, or in vitro cultures. The beneficial impact of nanoparticles on the alleviation of abiotic stresses in medicinal and aromatic plants is also discussed.

In Vitro Response of Polyscias filicifolia (Araliaceae) Shoots to Elicitation with Alarmone-Diadenosine Triphosphate, Methyl Jasmonate, and Salicylic Acid

The effectiveness of different elicitation variants in combination with alarmone application was studied in shoot cultures of Polyscias filicifolia. The shoots were elicited with 200 µM methyl jasmonate (MeJA) or 50 µM salicylic acid (SA) alone or in combination, and their activity was compared with those treated with the alarmone diadenosine 5′,5‴-P¹P³-triphosphate (Ap3A), either alone or in combination with SA and/or MeJA. All treatments resulted in significant stimulation of phenolic acid production (chlorogenic and ferulic acids), as well as oleanolic acid (OA) compared to control, with their highest concentration noted under simultaneous elicitation with SA and MeJA. While the maximum content of caffeic acid was detected after treatment with alarmone alone. In each of the culture variants enhanced antioxidant activity was observed, however the level varied according to the treatment. In addition, the SA, Ap3A and Ap3A+SA variants demonstrated additional peroxidase isoforms, as indicated by Native-PAGE, as well as the highest α-tocopherol content. The highest antioxidant capacity of shoot extracts was correlated with the highest abundance of phenolic compounds and OA. The results indicate that ROS induction appears to participate in the signal transduction following Ap3A treatment.

Nano-Elicitation as an Effective and Emerging Strategy for In Vitro Production of Industrially Important Flavonoids

Flavonoids represent a popular class of industrially important bioactive compounds. They possess valuable health-benefiting and disease preventing properties, and therefore they are an important component of the pharmaceutical, nutraceutical, cosmetical and medicinal industries. Moreover, flavonoids possess significant antiallergic, antihepatotoxic, anti-inflammatory, antioxidant, antitumor, antiviral, and antibacterial as well as cardio-protective activities. Due to these properties, there is a rise in global demand for flavonoids, forming a significant part of the world market. However, obtaining flavonoids directly from plants has some limitations, such as low quantity, poor extraction, over-exploitation, time consuming process and loss of flora. Henceforth, there is a shift towards the in vitro production of flavonoids using the plant tissue culture technique to achieve better yields in less time. In order to achieve the productivity of flavonoids at an industrially competitive level, elicitation is a useful tool. The elicitation of in vitro cultures induces stressful conditions to plants, activates the plant defense system and enhances the accumulation of secondary metabolites in higher quantities. In this regard, nanoparticles (NPs) have emerged as novel and effective elicitors for enhancing the in vitro production of industrially important flavonoids. Different classes of NPs, including metallic NPs (silver and copper), metallic oxide NPs (copper oxide, iron oxide, zinc oxide, silicon dioxide) and carbon nanotubes, are widely reported as nano-elicitors of flavonoids discussed herein. Lastly, the mechanisms of NPs as well as knowledge gaps in the area of the nano-elicitation of flavonoids have been highlighted in this review.

Plant in vitro Culture Technologies; A Promise Into Factories of Secondary Metabolites Against COVID-19

The current pandemic has caused chaos throughout the world. While there are few vaccines available now, there is the need for better treatment alternatives in line with preventive measures against COVID-19. Along with synthetic chemical compounds, phytochemicals cannot be overlooked as candidates for drugs against severe respiratory coronavirus 2 (SARS-CoV-2). The important role of secondary metabolites or phytochemical compounds against coronaviruses has been confirmed by studies that reported the anti-coronavirus role of glycyrrhizin from the roots of Glycyrrhiza glabra. The study demonstrated that glycyrrhizin is a very promising phytochemical against SARS-CoV, which caused an outbreak in 2002-2003. Similarly, many phytochemical compounds (apigenin, betulonic acid, reserpine, emodin, etc.) were isolated from different plants such as Isatis indigotica, Lindera aggregate, and Artemisia annua and were employed against SARS-CoV. However, owing to the geographical and seasonal variation, the quality of standard medicinal compounds isolated from plants varies. Furthermore, many of the important medicinal plants are either threatened or on the verge of endangerment because of overharvesting for medicinal purposes. Therefore, plant biotechnology provides a better alternative in the form of in vitro culture technology, including plant cell cultures, adventitious roots cultures, and organ and tissue cultures. In vitro cultures can serve as factories of secondary metabolites/phytochemicals that can be produced in bulk and of uniform quality in the fight against COVID-19, once tested. Similarly, environmental and molecular manipulation of these in vitro cultures could provide engineered drug candidates for testing against COVID-19. The in vitro culture-based phytochemicals have an additional benefit of consistency in terms of yield as well as quality. Nonetheless, as the traditional plant-based compounds might prove toxic in some cases, engineered production of promising phytochemicals can bypass this barrier. Our article focuses on reviewing the potential of the different in vitro plant cultures to produce medicinally important secondary metabolites that could ultimately be helpful in the fight against COVID-19.

From Ethnomedicine to Plant Biotechnology and Machine Learning: The Valorization of the Medicinal Plant Bryophyllum sp

The subgenus Bryophyllum includes about 25 plant species native to Madagascar, and is widely used in traditional medicine worldwide. Different formulations from Bryophyllum have been employed for the treatment of several ailments, including infections, gynecological disorders, and chronic diseases, such as diabetes, neurological and neoplastic diseases. Two major families of secondary metabolites have been reported as responsible for these bioactivities: phenolic compounds and bufadienolides. These compounds are found in limited amounts in plants because they are biosynthesized in response to different biotic and abiotic stresses. Therefore, novel approaches should be undertaken with the aim of achieving the phytochemical valorization of Bryophyllum sp., allowing a sustainable production that prevents from a massive exploitation of wild plant resources. This review focuses on the study of phytoconstituents reported on Bryophyllum sp.; the application of plant tissue culture methodology as a reliable tool for the valorization of bioactive compounds; and the application of machine learning technology to model and optimize the full phytochemical potential of Bryophyllum sp. As a result, Bryophyllum species can be considered as a promising source of plant bioactive compounds, with enormous antioxidant and anticancer potential, which could be used for their large-scale biotechnological exploitation in cosmetic, food, and pharmaceutical industries.

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.

Improvement of stilbene production by mulberry Morus alba root culture via precursor feeding and co-elicitation

Large amounts of Morus alba L. (MA) roots are needed as the source of active stilbenes in the industrial production of traditional medicines and cosmeceuticals. A recent investigation demonstrated resveratrol and its derivatives to be promising anti-COVID-19 agents. However, conventional cultivation of MA does not meet the demand for its stilbenes, and root quality usually varies between crops. This study established the in vitro non-GMO root culture of MA and optimized the root density, precursor feeding, and elicitors for stilbene productivity. A root culture with optimal inoculum density (3 g/flask of 30 mL medium) accumulated mulberroside A, oxyresveratrol, and resveratrol at 18.7 ± 1.00 mg/g, 136 ± 5.05 µg/g, and 41.6 ± 5.84 µg/g dry weight (DW), respectively. The feeding of L-tyrosine shortened the time required to reach the stilbene productive stage. Root cultures co-treated with 200 µM methyl jasmonate and 2 mg/mL yeast extract accumulated the highest contents of mulberroside A (30.3 ± 2.68 mg/g DW), oxyresveratrol (68.6 ± 3.53 µg/g DW), and resveratrol (10.2 ± 0.53 µg/g DW). In summary, root culture is a promising and sustainable source of stilbenes for the development of health products and agents for further investigation as potential anti-COVID-19 agents.

Yeast extract improved biosynthesis of astragalosides in hairy root cultures of Astragalus membranaceus

The dried root of Astragalus membranaceus is a well-known herbal medicine, and it is useful in treating chronic diseases and weakness, as well as for improving overall health and vitality. Astragalosides, which are root quality indicators of A. membranaceus, are natural triterpenoid saponins that are used in the treatment of diabetes and cardiovascular diseases. Currently, there is an urgent need to improve their production because of their low quantity in plants and the difficulty of chemical synthesis. In this study, yeast extract was added to facilitate elicitation in Agrobacterium-mediated hairy root cultures, thereby enhancing astragaloside production in A. membranaceus. Results showed that yeast extract could stimulate astragaloside content effectively in the hairy roots of A. membranaceus. Moreover, astragaloside accumulation was positively correlated with the upregulation of mevalonate biosynthetic gene expression in the presence of yeast extract. Our study demonstrated that pretreatment with yeast extract (3.65 mM) for 72 h serves as an effective strategy to enhance astragaloside levels in A. membranaceus hairy root cultures. Thus, these optimal conditions can provide valuable information for the improvement of astragaloside industrial production in A. membranaceus.

Ectopic Expression of Production of Anthocyanin Pigment 1 (PAP1) Improves the Antioxidant and Anti-Melanogenic Properties of Ginseng (Panax ginseng C.A. Meyer) Hairy Roots

The development of genetically engineered cell cultures has been suggested as a potential approach for the production of target compounds from medicinal plants. In this study, we generated PAP1 (production of anthocyanin pigment 1)-overexpressing ginseng (Panax ginseng C.A. Meyer) hairy roots to improve the production of anthocyanins, as well as the bioactivity (e.g., antioxidant and whitening activities) of ginseng. Based on differentially expressed gene analysis, we found that ectopic expression of PAP1 induced the expression of genes involved in the ‘phenylpropanoid biosynthesis’ (24 genes), and ‘flavonoid biosynthesis’ (17 genes) pathways, resulting in 191- to 341-fold increases in anthocyanin production compared to transgenic control (TC) hairy roots. Additionally, PAP1-overexpressing ginseng hairy roots exhibited an approximately seven-fold higher DPPH-free radical scavenging activity and 10-fold higher ORAC value compared to the TC. In α-melanocyte-stimulating hormone-stimulated B16F10 cells, PAP1-overexpressing ginseng hairy roots strongly inhibited the accumulation of melanin by 50 to 59% compared to mock-control. Furthermore, results obtained by quantitative real-time PCR, western blot, and tyrosinase inhibition assay suggested that the anti-melanogenic activity of PAP1-overexpressing ginseng hairy roots is mediated by tyrosinase activity inhibition. Taken together, our results suggested that the ectopic expression of PAP1 is an effective strategy for the enhancement of anthocyanin production, which improves the biological activities of ginseng root cultures.

Comparative analysis of the effects of chemically and biologically synthesized silver nanoparticles on biomass accumulation and secondary metabolism in callus cultures of Fagonia indica

Biotechnological strategies are needed to produce larger quantities of biomass and phytochemicals. In this study, callus cultures of Fagonia indica were elicited with different concentrations of chemically and biologically synthesized silver nanoparticles (chem- and bioAgNPs) to compare their effects on biomass, total phenolic content (TPC), total flavonoid content (TFC) and antioxidant activity of the extracts from callus. The results revealed that bioAgNPs being more biocompatible produced the highest biomass initially on day 10 (FW = 4.2152 ± 0.13 g; DW = 0.18527 ± 0.01 g) and day 20 (FW = 7.6558 ± 0.10 g; DW = 0.3489 ± 0.01 g) when supplemented in media as 62.5 µg/mL and 250 µg/mL, respectively. Initially, the highest TPC (319.32 ± 8.28 µg GAE/g of DW) was recorded on day 20 in chemAgNPs (31.25 µg/mL) induced callus as compared to TPC = 302.85 ± 3.002 µg GAE/g of DW in bioAgNPs-induced callus. Compared to the highest values of TFC (108.15 ± 2.10 µg QE/g of DW) produced in 15.6 µg/mL chemAgNPs-induced callus on day 20, TFC produced in bioAgNPs (62.5 µg/mL) was 168.61 ± 3.17 µg GAE/g of DW on day 10. Similarly, chemAgNPs-induced callus (62.5 µg/mL) showed the highest free radical scavenging activity (FRSA) i.e. 87.18% on day 20 while bioAgNPs (125 µg/mL) showed 81.69% FRSA on day 20 compared to highest among control callus (63.98% on day 40). The highest total antioxidant capacity of chemAgNPs-(125 µg/mL) induced callus was 330.42 ± 13.65 µg AAE/g of DW on day 20 compared to bioAgNPs-(62.5 µg/mL) induced callus (312.96 ± 1.73 µg AAE/g of DW) on day 10. Conclusively, bioAgNPs are potent elicitors of callus cultures of F. indica.

Hairy root transformation of Brassica rapa with bacterial halogenase genes and regeneration to adult plants to modify production of indolic compounds

During the last years halogenated compounds have drawn a lot of attention. Metabolites with one or more halogen atoms are often more active than their non-halogenated derivatives like indole-3-acetic acid (IAA) and 4-Cl-IAA. Within this work, bacterial flavin-dependent tryptophan halogenase genes were inserted into Brassica rapa ssp. pekinensis (Chinese cabbage) with the aim to produce novel halogenated indole compounds. It was investigated which tryptophan-derived indole metabolites, such as indole glucosinolates or potential degradation products can be synthesized by the transgenic root cultures. In vivo and in vitro activity of halogenases heterologously produced was shown and the production of chlorinated tryptophan in transgenic root lines was confirmed. Furthermore, chlorinated indole-3-acetonitrile (Cl-IAN) was detected. Other tryptophan-derived indole metabolites, such as IAA or indole glucosinolates were not found in the transgenic roots in a chlorinated form. The influence of altered growth conditions on the amount of produced chlorinated compounds was evaluated. We found an increase in Cl-IAN production at low temperatures (8 °C), but otherwise no significant changes were observed. Furthermore, we were able to regenerate the wild type and transgenic root cultures to adult plants, of which the latter still produced chlorinated metabolites. Therefore, we conclude that the genetic information had been stably integrated. The transgenic plants showed a slightly altered phenotype compared to plants grown from seeds since they also still expressed the rol genes. By this approach we were able to generate various stably transformed plant materials from which it was possible to isolate chlorinated tryptophan and Cl-IAN.

Enhanced Production of Bryonolic Acid in Trichosanthes cucumerina L. (Thai Cultivar) Cell Cultures by Elicitors and Their Biological Activities

Bryonolic acid is a triterpenoid compound found in cucurbitaceous roots. Due to its biological activities, this compound gets more attention to improve production. Herein, we carried out efficient ways with high bryonolic acid productions from Trichosanthes cucumerina L., a Thai medicinal plant utilizing plant cell cultures. The results showed that calli (24.65 ± 1.97 mg/g dry weight) and cell suspensions (15.69 ± 0.78 mg/g dry weight) exhibited the highest bryonolic acid productions compared with natural roots (approximately 2 mg/g dry weight). In the presence of three elicitors (methyl jasmonate, yeast extract, and chitosan), cell suspensions treated with 1 mg/mL of chitosan for eight days led to higher bryonolic acid contents (23.56 ± 1.68 mg/g dry weight). Interestingly, cell culture and root extracts with high bryonolic acid contents resulted in significantly higher percent cell viabilities than those observed under control (1% v/v DMSO) treatment in Saos-2 and MCF-7 cells. The present study indicated that T. cucumerina L. cell cultures are alternative and efficient to produce the biologically important secondary metabolite.

Plant tissue culture as a perpetual source for production of industrially important bioactive compounds

Plants have been used throughout the world for its medicinal powers since ancient time. The pharmacological properties of plants are based on their phytochemical components especially the secondary metabolites which are outstanding sources of value added bioactive compounds. Secondary metabolites have complex chemical composition and are produced in response to various forms of stress to perform different physiological tasks in plants. They are used in pharmaceutical industries, cosmetics, dietary supplements, fragrances, flavors, dyes, etc. Extended use of these metabolites in various industrial sectors has initiated a need to focus research on increasing the production by employing plant tissue culture (PTC) techniques and optimizing their large scale production using bioreactors. PTC techniques being independent of climatic and geographical conditions will provide an incessant, sustainable, economical and viable production of secondary metabolites. This review article intends to assess the advantages of using plant tissue culture, distribution of important secondary metabolites in plant families, strategies involved for optimal metabolite production and the industrial importance of selected secondary metabolites.

Elicitation and enhancement of bacoside production using suspension cultures of Bacopa monnieri (L.) Wettst

The effect of different elicitors [jasmonic acid, salicylic acid] and precursors [calcium pantothenate, cholesterol, sodium nitroprusside] on the stimulation of biomass and secondary metabolite production in suspension cultures of Bacopa monnieri was studied. Induction of primary callus cultures was successfully carried out on the Gamborg's B5 (B5) medium fortified with 2, 4-D (1.0 mg l-1) using Bacopa monnieri leaves as explants. The friable fine suspension cell culture was raised on parent B5 media without agar. The elicitation using different elicitors and precursors at varying concentrations was carried out over a period of 3, 6, 9, 15 days. Elicitor treated cultures showed marked increase in biomass and bacoside production around 6th-9th day (0.98 GI DW). In the present study, salicylic acid at 1.0 mg l-1 induced a maximum elicitation in bacoside content (6.58 mg g-1 DW). The present study provides favorable evidence on the potential of bacoside production using suspension cultures of B. monnieri. The study results also indicate the beneficial effects of elicitation on metabolite production in in vitro suspension cultures of B. monnieri plant known for its cognitive improving properties.

Effect of Elicitation on Polyphenol and Carotenoid Metabolism in Butterhead Lettuce (Lactuca sativa var. capitata)

The effect of elicitation in butterhead lettuce on carotenoid and polyphenol metabolism was evaluated. Different concentrations of arachidonic acid (AA), salicylic acid (SA), methyl jasmonate (MJ) (15, 45, and 90 μM) and Harpin protein (HP) (30, 60, and 120 mg/L) were applied on red and green butterhead lettuces. Total phenolic and flavonoid content were incremented by MJ (90 μM) in green and red lettuce. Carotenoids were increased in red lettuce (AA; 45 μM). Green lettuce modifies their phenolic acid profile after elicitation with AA and MJ; meanwhile, red lettuce incremented mainly in hydroxycinnamic acids and flavonols, MJ being the elicitor with the highest effect. There was an impact on secondary metabolite enzyme gene transcript concentration. Phenylalanine ammonia-lyase (PAL) and lycopene beta cyclase (LBC) increased in both varieties after elicitation. A relationship between phytochemical increase and the activation of the metabolic pathways after elicitation in butterhead lettuce was observed.

Salicylic acid increases flavonolignans accumulation in the fruits of hydroponically cultured Silybum marianum

Silybum marianum (L.) Gaertn. (Asteraceae) was hydroponically cultured using a nutrient film technique system. Silibinin, isosilibinin and silychristin were detected in the fruits of the cultured plants. The effect of salicylic acid on the improvement of flavonolignans production by the fruits of the hydroponically cultured S. marianum was investigated. Salicylic acid was added to the nutrient solution at different concentrations (100, 200 and 400 µM) and the mature fruits of the plant were collected five days after elicitor addition. The fruits were then analyzed for their total flavonolignans contents and individual components using quantitative proton nuclear magnetic resonance spectroscopy (qHNMR) and high-performance liquid chromatography (HPLC). The results showed that elicitation with salicylic acid at 200 µM for five days increased production of total flavonolignans (1.7-fold by qHNMR and 1.6-fold by HPLC) higher than the control cultures and (1.4-fold by qHNMR and 1.1-fold by HPLC) higher than the cultivated plants. Silychristin was the major flavonolignan produced by the cultured plant. Elicitation by 200 µM salicylic acid increased silychristin production (1.6-fold by qHNMR and HPLC) higher than the control cultures and (1.3-fold by qHNMR and 1.0-fold by HPLC) higher than the cultivated plants. The present study provides a chance to improve secondary metabolite yield, serves as a useful tool for studying the biosynthesis of these medicinally valuable compounds and its regulation in plant and spots more light on hydroponic system as an important agricultural technique.

Panax quinquefolium L. Ginsenosides from Hairy Root Cultures and Their Clones Exert Cytotoxic, Genotoxic and Pro-Apoptotic Activity towards Human Colon Adenocarcinoma Cell Line Caco-2

American ginseng, Panax quinquefolium (L.), is traditionally used in folk medicine. It exhibits a range of anti-inflammatory, hepatoprotective, anti-diabetic, anti-obesity, anti-hyperlipidemic and anti-carcinogenic effects. Its main components are ginsenosides, also known as panaxosides or triterpene saponins. In order to obtain high yields of ginsenosides, different methods of controlled production are involved, i.e., with hairy root cultures. However, they are still employed under in vitro conditions. Our studies revealed that hairy root cultures subjected to an elicitation process can be considered as a potent source of ginsenosides. The present study examines the biological activity of ginseng hairy root cultures against the Caco-2 human adenocarcinoma cell line. Among our six different clones of P. quinquefolium hairy roots, extracts B and Be (treated with elicitor) were the strongest inhibitors of the cellular metabolic activity. While all extracts induced DNA damage, B and Be also generated reactive oxygen species (ROS) in a concentration-dependent manner, which was correlated with the depletion of the mitochondrial membrane potential and induction of apoptosis. These findings indicate that further research concerning P. quinquefolium hairy root cultures should focus on the activity of rare ginsenosides and other biologically active compound profiles (i.e., phenolic compounds).

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.

A Smart Strategy to Improve t-Resveratrol Production in Grapevine Cells Treated with Cyclodextrin Polymers Coated with Magnetic Nanoparticles

One of the most successfully procedures used to increase the production of t-resveratrol in Vitis vinifera suspension-cultured cells is the application of cyclodextrins (CDs) and methyl jasmonate (MJ) as elicitors. In particular, β-CDs are characterized by their chemical structure which makes them special, not only by acting as elicitors, but also because they are compounds capable of trapping high added-value hydrophobic molecules such as t-resveratrol. However, the use of β-CDs as elicitors increases the production costs of this compound, making their industrial exploitation economically unfeasible. Therefore, the development of β-CDs recovery strategies is necessary to provide a viable solution to their industrial use. In this work, carboxymethylated and hydroxypropylated β-CDs have been used to form polymers using epichlorohydrin (EPI) as a cross-linking agent. The polymers were coated to Fe₃O₄ nanoparticles and were jointly used with MJ to elicit V. vinifera suspension-cultured cells. Once elicitation experiments were finished, a magnet easily allowed the recovery of polymers, and t-resveratrol was extracted from them by using ethyl acetate. The results indicated that the production of t-resveratrol in the presence of free carboxymethyl-β-CDs was much lower than that found in the presence of carboxymethyl-β-cyclodextrins-EPI polymer coated magnetic nanoparticles. In addition, the maximal levels of t-resveratrol were found at 168 h of elicitation in the presence of 15 g/L hydroxypropyl-β-CDs polymer coated magnetic nanoparticles and MJ, and non-t-resveratrol was found in the extracellular medium, indicating that all the t-resveratrol produced by the cells and secreted into the culture medium was trapped by the polymer and extracted from it. This work also showed that polymers can be regenerated and reused during three cycles of continuous elicitation since the induction and adsorption capacity of hydroxypropyl-β-CDs polymer-coated magnetic nanoparticles after these cycles of elicitation remained high, allowing high concentrations of t-resveratrol to be obtained.

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.

Effects of addition of elicitors on rimocidin biosynthesis in Streptomyces rimosus M527

The polyene macrolide rimocidin, produced by Streptomyces rimosus M527, is highly effective against a broad range of fungal plant pathogens, but at low yields. Elicitation is an effective method of stimulating the yield of bioactive secondary metabolites. In this study, the biomass and filtrate of a culture broth of Escherichia coli JM109, Bacillus subtilis WB600, Saccharomyces cerevisiae, and Fusarium oxysporum f. sp. cucumerinum were employed as elicitors to promote rimocidin production in S. rimosus M527. Adding culture broth and biomass of S. cerevisiae (A3) and F. oxysporum f. sp. cucumerinum (B4) resulted in an increase of rimocidin production by 51.2% and 68.3% respectively compared with the production under normal conditions in 5-l fermentor. In addition, quantitative RT-PCR analysis revealed that the transcriptions of ten genes (rimA to rimK) located in the gene cluster involved in rimocidin biosynthesis in A3 or B4 elicitation experimental group were all higher than those of a control group. Using a β-glucuronidase (GUS) reporter system, GUS enzyme activity assay, and Western blot analysis, we discovered that elicitation of A3 or B4 increased protein synthesis in S. rimosus M527. These results demonstrate that the addition of elicitors is a useful approach to improve rimocidin production.Key Points • An effective strategy for enhancing rimocidin production in S. rimosus M527 is demonstrated. • Overproduction of rimocidin is a result of higher expressed structural genes followed by an increase in protein synthesis.

Fungal Cell Wall and Methyl-β-Cyclodextrin Synergistically Enhance Paclitaxel Biosynthesis and Secretion in Corylus avellana Cell Suspension Culture

Paclitaxel is the top-selling chemotherapeutic drug used for the treatment of lung, ovarian and breast cancer as well as Kaposi's sarcoma. Cell suspension culture (CSC) of Corylus avellana has been addressed as a promising alternative for producing paclitaxel. In this study, endophytic fungus strain YEF33 was isolated from Taxus baccata and identified as Coniothyrium palmarum. The effects of the elicitors derived from this fungus including cell extract, culture filtrate and cell wall (CW) and also chitin, alone or in combination with Methyl-β-Cyclodextrin (MBCD), on paclitaxel biosynthesis in C. avellana CSC were assayed for the first time. CW of C. palmarum was the most efficient fungal elicitor for paclitaxel biosynthesis in C. avellana CSC. The results revealed that MBCD affected paclitaxel biosynthesis differently depending on fungal elicitor type and vice versa. MBCD, either alone or in combination with fungal elicitors, induced a high secretion of paclitaxel, suggesting the decrement of toxicity and retro-inhibition processes of paclitaxel for cells. The joint effects of C. palmarum CW (2.5% (v/v) on 17th day) and 50 mM MBCD synergistically enhanced paclitaxel biosynthesis (402.4 µg l-1; 5.8-fold), 78.6% of which (316.5 µg l-1) were secreted into culture medium, a level 146% higher than that in control.

Isatis tinctoria L. (Woad): A Review of its Botany, Ethnobotanical Uses, Phytochemistry, Biological Activities, and Biotechnological Studies

Isatis tinctoria L. (Brassicaceae), which is commonly known as woad, is a species with an ancient and well-documented history as an indigo dye and medicinal plant. Currently, I. tinctoria is utilized more often as medicinal remedy and also as a cosmetic ingredient. In 2011, I. tinctoria root was accepted in the official European phytotherapy by introducing its monograph in the European Pharmacopoeia. The biological properties of raw material have been known from Traditional Chinese Medicine (TCM). Over recent decades, I. tinctoria has been investigated both from a phytochemical and a biological point of view. The modern in vitro and in vivo scientific studies proved anti-inflammatory, anti-tumour, antimicrobial, antiviral, analgesic, and antioxidant activities. The phytochemical composition of I. tinctoria has been thoroughly investigated and the plant was proven to contain many valuable biologically active compounds, including several alkaloids, among which tryptanthrin, indirubin, indolinone, phenolic compounds, and polysaccharides as well as glucosinolates, carotenoids, volatile constituents, and fatty acids. This article provides a general botanical and ethnobotanical overview that summarizes the up-to-date knowledge on the phytochemistry and biological properties of this valuable plant in order to support its therapeutic potential. Moreover, the biotechnological studies on I. tinctoria, which mainly focused on hairy root cultures for the enhanced production of flavonoids and alkaloids as well as on the establishment of shoot cultures and micropropagation protocols, were reviewed. They provide input for future research prospects.

Antigenotoxic, Anti-photogenotoxic, and Antioxidant Properties of Polyscias filicifolia Shoots Cultivated In Vitro

Traditional medicinal plants are an important source of active compounds with potential antimutagenic activity. Polyscias filicifolia Bailey (Araliaceae) is a South Asian traditional herb used as an adaptogenic and cardiac drug. Extracts of P. filicifolia contain a wide range of biologically active compounds like phenolic acids and triterpenoid saponins. In the present study. antigenotoxic potential of three naturally occurring phenolic acids and extracts of P. filicifolia growing in vitro with the addition of elicitors was evaluated against direct (4-nitroquinoline-N-oxide (4NQO) and mitomycin C (MMC)) and indirect mutagens (2-aminoanthracene (2AA)). The evaluation was made using a bacterial umu-test. Moreover, the ability to prevent photogenotoxicity induced by chlorpromazine (CPZ) under UVA irradiation was measured. The phytochemical profiling of examined extracts revealed the presence of numerous compounds with the prevelance of chlorogenic, caffeic, and ferulic acid derivatives; however, saponin fractions were also determined. The antioxidant potential of extracts strictly correlated with their composition. The tested extracts exhibited high antigenotoxic activity if the assay was performed with 2AA and metabolic activation. Moreover, the extracts slightly decreased the MMC-induced genotoxicity. However, an increase of the genotoxic effect was observed in the assay performed with 4NQO. In addition, photo-antigenotoxic activity was observed. In our study, phenolic acids exhibited lower activity than the extracts.

Spectral quality as an elicitor of bioactive compound production in Solanum aculeatissimum JACQ cell suspension

Solanum aculeatissimum Jacq. is a common plant in much of Brazil. Despite containing metabolites with a wide range of pharmacological applications, there are few tissue culture reports for this plant. The possibility of large-scale in vitro production of this material has significant biotechnological potential. Therefore, the objective of this study was to investigate the effect of light conditions on the growth of cells in suspension, observing the production and yield of biomass and bioactive compounds and the enzymatic behavior. Calli obtained from leaf segments were cultured in solid medium supplemented with 1 mg L^-1 of 2,4-D, 2.5 mg L^-1 kinetin, pH 5.7, in the dark. After 110 days of subculture, the calli were transferred to liquid medium. Cells were kept in the dark under agitation at 110 rpm and 25 °C and subcultured every 30 days. After 90 days of culture, 20 mL aliquots of cell suspension were added to flasks containing approximately 20 mL of medium (1:1) and cultured at different wavelengths (white, green, blue, red, and blue/red) under a photoperiod of 16 h with irradiance of 50 μmol m^-2 s^-1) and in the absence of light. The experiment was performed in a 6 × 6 factorial design (light condition × culture time). The cell cultures showed viability throughout the entire cycle, and chlorogenic and ferulic acids, orientin, quercitrin and, in higher amounts, quercetin, were detected in the first 7 days of culture. There was an increase in superoxide dismutase and catalase and a decrease in ascorbate peroxidase after exposure to different light conditions; for phenylalanine ammonia lyase, no differences were observed. The different light conditions were not sufficient to trigger responses in the concentrations of bioactive compounds, despite the detection of increased levels of the enzymes involved in cellular homeostasis.

Time-dependent behavior of phenylpropanoid pathway in response to methyl jasmonate in Scrophularia striata cell cultures

MeJA triggers a time-dependent behavior of the phenylpropanoid compounds. Plant cells produce a large number of metabolites in response to environmental factors. The cellular responses to environmental changes are orchestrated by signaling molecules, such as methyl jasmonate (MeJA). To understand how the MeJA changes the behavior of amino acids, carbohydrates, and phenylpropanoid compounds such as phenolic acids, phenylethanoid-glycosides, and flavonoids in Scrophularia striata cells; we monitored the metabolic responses for different times of exposure. In this study, we performed a time course analysis of metabolites and enzymes in S. striata cells exposed to MeJA (100 µM) and evaluated the metabolic flux towards carbon-rich secondary metabolites production. Moreover, we calculated the biosynthetic energy cost for free amino acids. Our results indicated that MeJA accelerates the sucrose degradation and directs the metabolic fluxes towards a pool of flavonoids and phenylethanoid glycosides through a change in enzyme behavior in the entry point and center of the phenylpropanoid pathway. MeJA also decreased and then raised the amino acid biosynthesis cost in S. striata cells in a time-dependent manner, indicating the cells evolve to utilize amino acids more economically by reducing cell growth. Finally, we classified the marked changes in the metabolites level and enzyme activities into three groups including early-, late-, and oscillatory-response groups to MeJA and summarized our findings as a model depicting pathway interactions during MeJA elicitation. Determination of metabolic levels in response to MeJA suggests that the changes in metabolic responses are time-dependent.

In Vitro Regeneration and ISSR-Based Genetic Fidelity Analysis of Orthosiphon stamineus Benth

Orthosiphon stamineus has been widely used as traditional remedy for various illnesses and diseases, such as cardiovascular diseases and epileptic seizures. In this study, direct regeneration through nodal segment of this species was attempted using Kinetin (6-Furfurylaminopurine) and IAA (indole-3-acetic acid). Optimum regeneration media was identified as MS media supplemented with 2.0 mg L−1 Kin plus 0.5 mg L−1 IAA. This yielded the highest number of shoots (5.57 ± 0.42) and leaves (20.53 ± 1.91) per explant. Acclimatization of the resulting in vitro regenerants was successful in all potting mixtures tested. However, potting mixture PF (1:1:1 ratio of black soil/red soil/compost) was identified as the best medium for acclimatization of this species, as it yielded 100% survival percentage after 90 days of acclimatization. Ten in vitro regenerants of O. stamineus were randomly collected after the third subculture and subjected to genetic variation analysis using inter-simple sequence repeat (ISSR) markers. Out of 20 ISSR markers tested, 10 working primers were observed to produce satisfactory amplification of bands, with an average of 7.11 bands per primer. A total of 610 bands were produced by the 10 primers. The percentage of polymorphism was observed to be very low, yielding only 7.32% polymorphism among all samples. Jaccard dissimilarity analysis was also conducted and very low genetic distance (about 0.1) was found among the in vitro regenerants and between the regenerants with the mother plant, thus ascertaining the clonal nature of the plantlets produced in this study.

Chitosan Upregulates the Genes of the ROS Pathway and Enhances the Antioxidant Potential of Grape (Vitis vinifera L. 'Touriga Franca' and 'Tinto Cão') Tissues

Chitosan is an environmentally-friendly active molecule that has been explored for numerous agricultural uses. Its use in crop protection is well-known, however, other properties, such as bioactivity, deserve attention. Moreover, the modes of actions of chitosan remain to be elucidated. The present study assessed the levels of total phenolic compounds, the antioxidant potential, and the expression of reactive oxygen species (ROS) scavenging genes in the berries (skins and seeds), leaves, cluster stems, and shoots upon chitosan application on two red grapevine varieties (Touriga Franca and Tinto Cão). The application of chitosan on the whole vine before and after veraison led to the increased levels of polyphenols, anthocyanins, and tannins in Tinto Cão berries, and polyphenols and tannins in Touriga Franca berries, respectively. CUPric Reducing Antioxidant Capacity (CUPRAC) and Ferric Reducing Antioxidant Power (FRAP) assays indicated an increase in the antioxidant potential of berries. With the exception of ascorbate peroxidase (APX), all the ROS pathway genes tested, i.e., iron-superoxide dismutase (Fe-SOD), copper-zinc-superoxide dismutase (Cu/Zn-SOD), catalase (CAT), glutathione reductase (GR), glutaredoxin (Grx), respiratory burst oxidase (Rboh), amine oxidase (AO), peroxidase (POD) and polyphenol oxidase (PPO), were found up-regulated in chitosan-treated berries. Results from the analyses of leaves, stems, and shoots revealed that chitosan not only induced the synthesis of phenolic compounds but also acted as a facilitator for the transfer of polyphenols from the leaves to the berries.

Plant triterpenoid saponins: biosynthesis, in vitro production, and pharmacological relevance

The saponins are a diverse class of natural products, with a broad scale distribution across different plant species. Chemically characterized as triterpenoid glycosides, they posses a 30C oxidosqualene precursor-based aglycone moiety (sapogenin), to which glycosyl residues are subsequently attached to yield the corresponding saponin. Based on the chemically distinct aglycone moieties, broadly, they are divided into triterpenoid saponins (dammaranes, ursanes, oleananes, lupanes, hopanes, etc.) and the sterol glycosides. This review aims to present in detail the biosynthesis patterns of the different aglycones from a common precursor and their glycosylation patterns to yield the functionally active glycoside. The review also presents recent advances in the pharmacological activities of these saponins, particularly as potent anti-neoplastic pharmacophores, antioxidants, or anti-viral/antibacterial agents. Since alternate production pedestals for these pharmacologically important triterpenes via cell and tissue cultures are an attractive option for their sustainable production, recent trends in the variety and scale of in vitro production of plant triterpenoids have also been discussed.

Cyclodextrin-Elicited Bryophyllum Suspension Cultured Cells: Enhancement of the Production of Bioactive Compounds

The rates of production of secondary metabolites obtained by employing conventional plant breeding may be low for practical purposes. Thus, innovative approaches for increasing their rates of production are being developed. Here, we propose the use of elicited plant suspension cultured cells (PSCC) with cyclodextrins (CDs) as an alternative method for the production of bioactive compounds from Bryophyllum species. For this purpose, we analyzed the effects of methyl-β-cyclodextrin and 2-hydroxypropyl-β-cyclodextrin on cell culture growth and on the intra- and extracellular production of phenols and flavonoids. Results clearly show that CDs enhance the biosynthesis of polyphenols by PSCC favoring their accumulation outside the cells. CDs shift the homeostatic equilibrium by complexing extracellular phenolics, causing stress in cells that respond by increasing the production of intracellular phenolics. We also analyzed the radical scavenging activity of the culture medium extracts against 2,2-diphenyl-1-pycrilhydrazyl (DPPH) radical, which increased with respect to the control samples (no added CDs). Our results suggest that both the increase in the production of polyphenols and their radical scavenging activity are a consequence of their inclusion in the CD cavities. Overall, based on our findings, CDs can be employed as hosts for increasing the production of polyphenols from Bryophyllum species.

Improvement of phytochemical production by plant cells and organ culture and by genetic engineering

Plants display an amazing ability to synthesize a vast array of secondary metabolites that are an inexhaustible source of phytochemicals, bioactive molecules some of which impact the human health. Phytochemicals present in medicinal herbs and spices have long been used as natural remedies against illness. Plant tissue culture represents an alternative to whole plants as a source of phytochemicals. This approach spares agricultural land that can be used for producing food and other raw materials, thus favoring standardized phytochemical production regardless of climatic adversities and political events. Over the past 20 years, different strategies have been developed to increase the synthesis and the extraction of phytochemicals from tissue culture often obtaining remarkable results. Moreover, the availability of genomics and metabolomics tools, along with improved recombinant methods related to the ability to overexpress, silence or disrupt one or more genes of the pathway of interest promise to open new exciting possibilities of metabolic engineering. This review provides a general framework of the cellular and molecular tools developed so far to enhance the yield of phytochemicals. Additionally, some emerging topics such as the culture of cambial meristemoid cells, the selection of plant cell following the expression of genes encoding human target proteins, and the bioextraction of phytochemicals from plant material have been addressed. Altogether, the herein described techniques and results are expected to improve metabolic engineering tools aiming at improving the production of phytochemicals of pharmaceutical and nutraceutical interest.

Biotechnological production of ruscogenins in plant cell and organ cultures of Ruscus aculeatus

Ruscus aculeatus is a threatened medicinal plant whose main bioactive components, the ruscogenins, have long been used in the treatment of hemorrhoids and varicose veins, but recently demonstrated activity against some types of cancer. Plant cell biofactories could constitute an alternative to the whole plant as a source of ruscogenins. In this pipeline, despite the in vitro recalcitrance of R. aculeatus, after many attempts we developed friable calli and derived plant cell suspensions, and their ruscogenin production was compared with that of organized in vitro plantlet and root-rhizome cultures. Root-rhizomes showed a higher capacity for biomass and ruscogenin production than the cell suspensions and the yields were greatly improved by elicitation with coronatine. Although ruscogenins accumulate in plants mainly in the root-rhizome, it was demonstrated that the aerial part could play an important role in their biosynthesis, as production was higher in the whole plant than in the root-rhizome cultures.

Small-Scale Bioreactor for Sterile Hydroponics and Hairy Roots: Metabolic Diversity and Salicylic Acid Exudation by Hairy Roots of Hyoscyamus niger

The volume and complexity of commercial bioreactors for sterile hydroponics and hairy roots are too large for comparative analysis of many cultures. Here a small-scale bioreactor fabricated from standard glass materials and suitable for both airlift and bubble aeration mode is described. The performance of the bioreactor was tested by growing oilseed rape (Brassica napus L.) and rose plants (Rosa canina L.) in sterile hydroponics and by cultivating hairy roots of henbane (Hyoscyamus niger L.) and sesame (Hyoscyamus niger L.). Plants grown in hydroponics for up to six weeks did not show chloroses or necroses. Hairy roots grew faster or comparably fast in bioreactors as compared to shaking flasks. Root exudates of roses and exudates of hairy roots of henbane were subjected to targeted and nontargeted analysis by HPLC coupled with optical and mass spectrometric detectors. The diversity and concentration of hairy root exudates were higher in bioreactors than in shaking flasks. The composition of hairy root exudates of three accessions of H. niger did not match the genetic relatedness among the accessions. Hairy roots of Hyoscyamus niger exuded salicylic acid in amounts varying among plant accessions and between bioreactors and shaking flask cultures.

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.

Chitosan promoting formononetin and calycosin accumulation in Astragalus membranaceus hairy root cultures via mitogen-activated protein kinase signaling cascades

Chitosan, behaving as a potent biotic elicitor, can induce plant defense response with the consequent enhancement in phytoalexin accumulation. Accordingly, chitosan elicitation was conducted to promote the production of two phytoalexins, i.e. formononetin and calycosin (also known as health-promoting isoflavones), in Astragalus membranaceus hairy root cultures (AMHRCs). Compared with control, 12.45- and 6.17-fold increases in the yields of formononetin (764.19 ± 50.81 μg/g DW) and calycosin (611.53 ± 42.22 μg/g DW) were obtained in 34 day-old AMHRCs treated by 100 mg/L of chitosan for 24 h, respectively. Moreover, chitosan elicitation could cause oxidative burst that would induce the expression of genes (MPK3 and MPK6) related to mitogen-activated protein kinase signaling (MAPK) cascades, which contributed to the transcriptional activation of pathogenesis-related genes (β-1,3-glucanase, Chitinase, and PR-1) and eight biosynthesis genes involved in the calycosin and formononetin pathway. Overall, the findings in this work not only highlight a feasible chitosan elicitation practice to enhance the in vitro production of two bioactive isoflavones for nutraceutical and food applications, but also contribute to understanding the phytoalexin biosynthesis in response to chitosan elicitation.

Regulation of terpenoid biosynthesis by miRNA in Persicaria minor induced by Fusarium oxysporum

Background

Persicaria minor (kesum) is an herbaceous plant with a high level of secondary metabolite compounds, particularly terpenoids. These terpenoid compounds have well-established roles in the pharmaceutical and food industries. Although the terpenoids of P. minor have been studied thoroughly, the involvement of microRNA (miRNA) in terpenoid regulation remains poorly understood and needs to be explored. In this study, P. minor plants were inoculated with the pathogenic fungus Fusarium oxysporum for terpenoid induction.

Result

SPME GC-MS analysis showed the highest terpenoid accumulation on the 6th day post-inoculation (dpi) compared to the other treatment time points (0 dpi, 3 dpi, and 9 dpi). Among the increased terpenoid compounds, α-cedrene, valencene and β-bisabolene were prominent. P. minor inoculated for 6 days was selected for miRNA library construction using next generation sequencing. Differential gene expression analysis showed that 58 miRNAs belonging to 30 families had significantly altered regulation. Among these 58 differentially expressed genes (DEGs), 33 miRNAs were upregulated, whereas 25 miRNAs were downregulated. Two putative novel pre-miRNAs were identified and validated through reverse transcriptase PCR. Prediction of target transcripts potentially involved in the mevalonate pathway (MVA) was carried out by psRobot software, resulting in four miRNAs: pmi-miR530, pmi-miR6173, pmi-miR6300 and a novel miRNA, pmi-Nov_13. In addition, two miRNAs, miR396a and miR398f/g, were predicted to have their target transcripts in the non-mevalonate pathway (MEP). In addition, a novel miRNA, pmi-Nov_12, was identified to have a target gene involved in green leaf volatile (GLV) biosynthesis. RT-qPCR analysis showed that pmi-miR6173, pmi-miR6300 and pmi-nov_13 were downregulated, while miR396a and miR398f/g were upregulated. Pmi-miR530 showed upregulation at 9 dpi, and dynamic expression was observed for pmi-nov_12. Pmi-6300 and pmi-miR396a cleavage sites were detected through degradome sequence analysis. Furthermore, the relationship between miRNA metabolites and mRNA metabolites was validated using correlation analysis.

Conclusion

Our findings suggest that six studied miRNAs post-transcriptionally regulate terpenoid biosynthesis in P. minor. This regulatory behaviour of miRNAs has potential as a genetic tool to regulate terpenoid biosynthesis in P. minor.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5954-0) contains supplementary material, which is available to authorized users.