Hairy root cultures: A suitable biological system for studying secondary metabolic pathways in plants: Hairy root cultures for studying secondary metabolic pathway elucidation

Agrobacterium rhizogenes: paving the road to research and breeding for woody plants

Woody plants play a vital role in global ecosystems and serve as valuable resources for various industries and human needs. While many woody plant genomes have been fully sequenced, gene function research and biotechnological breeding advances have lagged behind. As a result, only a limited number of genes have been elucidated, making it difficult to use newer tools such as CRISPR-Cas9 for biotechnological breeding purposes. The use of Agrobacterium rhizogenes as a transformative tool in plant biotechnology has received considerable attention in recent years, particularly in the research field on woody plants. Over the past three decades, numerous woody plants have been effectively transformed using A. rhizogenes-mediated techniques. Some of these transformed plants have successfully regenerated. Recent research on A. rhizogenes-mediated transformation of woody plants has demonstrated its potential for various applications, including gene function analysis, gene expression profiling, gene interaction studies, and gene regulation analysis. The introduction of the Ri plasmid has resulted in the emergence of several Ri phenotypes, such as compact plant types, which can be exploited for Ri breeding purposes. This review paper presents recent advances in A. rhizogenes-mediated basic research and Ri breeding in woody plants. This study highlights various aspects of A. rhizogenes-mediated transformation, its multiple applications in gene function analysis, and the potential of Ri lines as valuable breeding materials.

Identification and Functional Characterization of UDP-Glycosyltransferases Involved in Isoflavone Biosynthesis in Astragalus membranaceus

Isoflavones are rich natural compounds present in legumes and are essential for plant growth and development. Moreover, they are beneficial for animals and humans. Isoflavones are primarily found as glycoconjugates, including calycosin-7-O-β-d-glucoside (CG) in Astragalus membranaceus, a legume. However, the glycosylation mechanism of isoflavones in A. membranaceus remains unclear. In the present study, three uridine diphosphate (UDP)-glycosyltransferases (UGTs) that may be involved in the biosynthesis of isoflavone were identified in the transcriptome of A. membranaceus. Enzymatic analysis revealed that AmUGT88E29 and AmUGT88E30 had high catalytic activity toward isoflavones in vitro. In addition, AmUGT88E29 and AmUGT88E30 could accept various flavones, flavanones, flavonols, dihydroflavonols, and dihydrochalcones as substrates. AmUGT71G10 was only active against phloretin and dihydroresveratrol. Overexpression of AmUGT88E29 significantly increased the contents of CG, an isoflavone glucoside, in the hairy roots of A. membranaceus. This study provided candidate AmUGT genes for the potential metabolic engineering of flavonoid compounds in plants and a valuable resource for studying the calycosin glycosides biosynthesis pathway.

Biotechnological Approaches to Producing Natural Antioxidants: Anti-Ageing and Skin Longevity Prospects

Plants are the main source of bioactive compounds that can be used for the formulation of cosmetic products. Plant extracts have numerous proven health benefits, among which are anti-ageing and skin-care properties. However, with the increased demand for plant-derived cosmetic products, there is a crucial prerequisite for establishing alternative approaches to conventional methods to ensure sufficient biomass for sustainable production. Plant tissue culture techniques, such as in vitro root cultures, micropropagation, or callogenesis, offer the possibility to produce considerable amounts of bioactive compounds independent of external factors that may influence their production. This production can also be significantly increased with the implementation of other biotechnological approaches such as elicitation, metabolic engineering, precursor and/or nutrient feeding, immobilization, and permeabilization. This work aimed to evaluate the potential of biotechnological tools for producing bioactive compounds, with a focus on bioactive compounds with anti-ageing properties, which can be used for the development of green-label cosmeceutical products. In addition, some examples demonstrating the use of plant tissue culture techniques to produce high-value bioactive ingredients for cosmeceutical applications are also addressed, showing the importance of these tools and approaches for the sustainable production of plant-derived cosmetic products.

Collection of Hairy Roots as a Basis for Fundamental and Applied Research

Due to population growth, instability of climatic conditions, and reduction of the areas of natural ecosystems, it becomes necessary to involve modern biotechnological approaches to obtain highly productive plant material. This statement applies both to the creation of plant varieties and the production of new pharmaceutical raw materials. Genetic transformation of valuable medicinal plants using Agrobacterium rhizogenes ensures the production of stable and rapidly growing hairy roots cultures that have a number of advantages compared with cell culture and, above all, can synthesize root-specific substances at the level of the roots of the intact plant. In this regard, special attention should be paid to the collection of hairy roots of the Institute of Plant Physiology RAS, Russian Academy of Sciences, the founder of which was Dr. Kuzovkina I.N. Currently, the collection contains 38 hairy roots lines of valuable medicinal and forage plants. The review discusses the prospects of creating a hairy roots collection as a basis for fundamental research and commercial purposes.

Metabolic engineering of the diosgenin biosynthesis pathway in Trigonella foenum-graceum hairy root cultures

Diosgenin as a triterpene with numbers of pharmaceutical applications has been identified in Trigonella foenum-graceum. In this survey, in order to scale up the amount of diosgenin in Fenugreek as a promising alternative of yam, ∆²⁴-reductase as a rate limiting enzyme in diosgenin biosynthesis pathway has been overexpressed by utilizing pBI121 expression plasmid in hairy roots culture platform. The recombinant binary vector pBI121-∆²⁴-reductase was transformed into R. rhizogenes strain ATCC 15834 to induce transgenic hairy roots in "Hamedan" as a low-diosgenin production genotype. In the transgenic hairy roots, the ∆²⁴-reductase expression level was significantly 8.15 times overexpressed comparing to the non-transgenic hairy roots, Nonetheless the Sterol-methyltransferase, as a competitive enzyme, was 6 times downregulated. Furthermore, the expression rate of Squalene synthase, Cycloartenol synthase, C26-Hydroxylase were also increased 1.5, 1.7, 2.9 times higher than those of the non-transgenic hairy roots, respectively. The diosgenin content in the transgenic hairy root was raised 3 times up comparing to the non-transgenic hairy roots, besides it was scaled up 25-fold comparing to the diosgenin amount in "Hamedan" Leaf. As a result, the first metabolic engineering on this pathway was clearly revealed the impact of ∆²⁴ -reductase gene in diosgenin content enhancement.

Biotic Elicitors in Adventitious and Hairy Root Cultures: A Review from 2010 to 2022

One of the aims of plant in vitro culture is to produce secondary plant metabolites using plant cells and organ cultures, such as cell suspensions, adventitious, and hairy roots (among others). In cases where the biosynthesis of a compound in the plant is restricted to a specific organ, unorganized systems, such as plant cell cultures, are sometimes unsuitable for biosynthesis. Then, its production is based on the establishment of organ cultures such as roots or aerial shoots. To increase the production in these biotechnological systems, elicitors have been used for years as a useful tool since they activate secondary biosynthetic pathways that control the flow of carbon to obtain different plant compounds. One important biotechnological system for the production of plant secondary metabolites or phytochemicals is root culture. Plant roots have a very active metabolism and can biosynthesize a large number of secondary compounds in an exclusive way. Some of these compounds, such as tropane alkaloids, ajmalicine, ginsenosides, etc., can also be biosynthesized in undifferentiated systems, such as cell cultures. In some cases, cell differentiation and organ formation is necessary to produce the bioactive compounds. This review analyses the biotic elicitors most frequently used in adventitious and hairy root cultures from 2010 to 2022, focusing on the plant species, the target secondary metabolite, the elicitor and its concentration, and the yield/productivity of the target compounds obtained. With this overview, it may be easier to work with elicitors in in vitro root cultures and help understand why some are more effective than others.

Modifying Anthocyanins Biosynthesis in Tomato Hairy Roots: A Test Bed for Plant Resistance to Ionizing Radiation and Antioxidant Properties in Space

Gene expression manipulation of specific metabolic pathways can be used to obtain bioaccumulation of valuable molecules and desired quality traits in plants. A single-gene approach to impact different traits would be greatly desirable in agrospace applications, where several aspects of plant physiology can be affected, influencing growth. In this work, MicroTom hairy root cultures expressing a MYB-like transcription factor that regulates the biosynthesis of anthocyanins in Petunia hybrida (PhAN4), were considered as a testbed for bio-fortified tomato whole plants aimed at agrospace applications. Ectopic expression of PhAN4 promoted biosynthesis of anthocyanins, allowing to profile 5 major derivatives of delphinidin and petunidin together with pelargonidin and malvidin-based anthocyanins, unusual in tomato. Consistent with PhAN4 features, transcriptomic profiling indicated upregulation of genes correlated to anthocyanin biosynthesis. Interestingly, a transcriptome reprogramming oriented to positive regulation of cell response to biotic, abiotic, and redox stimuli was evidenced. PhAN4 hairy root cultures showed the significant capability to counteract reactive oxygen species (ROS) accumulation and protein misfolding upon high-dose gamma irradiation, which is among the most potent pro-oxidant stress that can be encountered in space. These results may have significance in the engineering of whole tomato plants that can benefit space agriculture.

Effect of Ethylene and Abscisic Acid on Steroid and Triterpenoid Synthesis in Calendula officinalis Hairy Roots and Saponin Release to the Culture Medium

Phytohormones (plant growth regulators) can be applied as efficient elicitors to enhance the productivity of plant in vitro cultures, due to their significance in regulating the plant metabolism and strong influence on plant defense responses. In the present study, the effects of exogenous ethylene (ETY, applied in the form of ethephon as an ethylene-generating agent) and abscisic acid (ABA) on the synthesis of triterpenoids and steroids in Calendula officinalis hairy roots were investigated. ABA appeared to be an efficient elicitor of the biosynthesis of triterpenoid oleanolic acid (almost two-fold) and the release of its glycosides (saponins) to the culture medium (up to 6.6-fold). ETY had only a slight effect on triterpenoid metabolism; instead, it strongly influenced steroid metabolism, leading to profound modifications of the quantitative profiles of these compounds, particularly the ratio of stigmasterol to sitosterol. Both the applied phytohormones influenced the interplay between steroid and triterpenoid biosynthetic pathways, revealing the symptoms of their competition.

Effects of various Agrobacterium rhizogenes strains on hairy root induction and analyses of primary and secondary metabolites in Ocimum basilicum

The hairy root (HR) culture system is an excellent alternative strategy to the whole plant system for producing valuable compounds. However, selection of suitable Agrobacterium strain for the successful induction of HR is an essential step for enhanced production of beneficial secondary metabolites. In this study, we examined the transformation efficiency of various A. rhizogenes strains (ATCC 13333, ATCC 15834, A4, R1000, R1200, and R1601) for transgenic HRs induction in Ocimum basilicum. Among the tested strains, the R1601 was found to be one of the most promising strain for mass production of HR in terms of transformation efficiency (94%) and the number and length of HR (8.4 ± 0.52 and 1.68 ± 0.14 cm). The HR induced by the same strain exhibited highest levels of rosmarinic acid level (62.05 ± 4.94 µg/g DW) and total phenolic content (62.3 ± 4.95 µg/g DW). A total of 55 metabolites were identified using high-performance liquid chromatography (HPLC) and gas chromatography-time-of-flight mass spectrometry (GC-TOFMS). The PCA and PLS-DA plot of the identified metabolites showed that HR induced by A4 and ATCC 15834 displayed variation in primary and secondary metabolite contents. Analysis of the metabolic pathway identified a total of 56 pathways, among which 35 were found to be impacted. A heat map and hierarchical clustering analysis indicated that HR induced by different Agrobacterium strains exhibited differential metabolites profiles. In conclusion, Agrobacterium strains R1601 is one of the best and most promising strains for inducing mass HR production and enhanced levels of secondary metabolites in O. basilicum.

Polyscias filicifolia (Araliaceae) Hairy Roots with Antigenotoxic and Anti-Photogenotoxic Activity

Hairy root cultures are considered as a valuable source of bioactive phytoconstituents with expanding applicability for their production. In the present study, hairy root cultures of Polyscias filicifolia (Araliaceae), a traditional Southeast Asian medicinal plant, were established. The transformation with Agrobacterium rhizogenes ATCC 15834 allowed to obtain 15 root lines. The K-1 line, demonstrating the highest growth capabilities, was subjected to further investigations. To enhance the biosynthetic potential of hairy roots, methyl jasmonate elicitation approach was applied (MeJA; at different doses and exposure time), with subsequent transfer of elicited roots to control medium. This strategy resulted in chlorogenic acid production up to 1.59 mg/g dry weight. HPLC-PDA-ESI-MS analysis demonstrated variation in extracts composition and allowed to identify different caffeic and ferulic acid derivatives. Next, cytotoxic, antigenotoxic, and anti-photogenotoxic properties of hairy roots extracts were determined. None of the tested extracts were cytotoxic. In addition, they demonstrated significant antigenotoxic activity with the highest protective potential; up to 52% and 49% of inhibition of induction ratio (IR) induced by the 2-aminoanthracene was revealed for extracts derived from hairy roots elicited for 3 days with 50 µM MeJA and roots elicited for 7 days with 100 µM MeJA and then transferred for 30 days to control medium, respectively. These same extracts exhibited the highest anti-photogenotoxic potential, up to 36% of inhibition of chloropromazine-induced genotoxicity.

Enhancement of Phytosterol and Triterpenoid Production in Plant Hairy Root Cultures-Simultaneous Stimulation or Competition?

Plant in vitro cultures, including hairy roots, can be applied for controlled production of valuable natural products, such as triterpenoids and sterols. These compounds originate from the common precursor squalene. Sterols and triterpenoids distinctly differ in their functions, and the 2,3-oxidosqualene cyclization step is often regarded as a branch point between primary and secondary (more aptly: general and specialized) metabolism. Considering the crucial role of phytosterols as membrane constituents, it has been postulated that unconstrained biosynthesis of triterpenoids can occur when sterol formation is already satisfied, and these compounds are no longer needed for cell growth and division. This hypothesis seems to follow directly the growth-defense trade-off plant dilemma. In this review, we present some examples illustrating the specific interplay between the two divergent pathways for sterol and triterpenoid biosynthesis appearing in root cultures. These studies were significant for revealing the steps of the biosynthetic pathway, understanding the role of particular enzymes, and discovering the possibility of gene regulation. Currently, hairy roots of many plant species can be considered not only as an efficient tool for production of phytochemicals, but also as suitable experimental models for investigations on regulatory mechanisms of plant metabolism.

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.

Preliminary Phytochemical Analysis and Evaluation of the Biological Activity of Leonotis nepetifolia (L.) R. Br Transformed Roots Extracts Obtained through Rhizobium rhizogenes-Mediated Transformation

According to the present knowledge, this is the first report on establishing transformed root cultures of Leonotis nepetifolia after Rhizobium rhizogenes-mediated transformation. The preliminary phytochemical analysis showed differences in the content of phenols and flavonoids in transformed and nontransformed roots. The dominant compounds in the analyzed extracts were (+)-catechin (5464 and 6808 µg/g DW), p-coumaric acid (2549 and 4907 µg/g DW), m-coumaric acid (1508 and 2048 µg/g DW) and rosmarinic acid (1844 and 2643 µg/g DW) for nontransformed (LNNR) and transformed (LNTR4) roots, respectively. Initial biological studies carried out on LNNR, and LNTR4 extracts showed a cytotoxic effect on the A549 lung, HCC1937 breast and leukemia NALM-6 cell lines, antioxidants, as well as repair and protection against DNA damage induced by H₂O₂ in HUVEC cells. Due to the stronger effect of the LNTR4 root extract, which can be a relatively efficient and cheap source of bioactive secondary metabolites, further biological analyses are needed to discover in detail their potentially valuable biological 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.

Piriformospora indica based elicitation for overproduction of phenolic compounds by hairy root cultures of Ficus carica

Ficus carica L. is an important source of phenolic and flavonoid compounds with valuable pharmaceutical application across various diseases. The current study was carried out to investigate the influence of Piriformospora indica elicitation on growth, production of phenolic compounds, antioxidant capacity, and expression level of flavonoid biosynthetic pathway genes in hairy root (HR) cultures of F. carica. The maximum improvement in accumulation of phenolic compounds was observed when HR culture of Ficus carica L. was exposed to 2% culture filtrate of P. indica for 72 h: gallic acid (80.5- fold), caffeic acid (26.2-fold), coumaric acid (4.5-fold), and cinnamic acid (60.1-fold), apigenin (27.6-fold) and rutin (5.7-fold). While the highest levels of chlorogenic acid (4.9-fold) and quercetin flavonoid (8.8-fold) were obtained after 48 h elicitation with culture filtrate and cell extract of P. indica at 6% (v/v), respectively. The analysis of biosynthetic genes revealed that the exposure to fungal elicitors resulted in up-regulation of phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), UDP-glucose flavonoid 3-O-glucosyltransferase (UFGT) and MYB3 transcription factor. This study shows the potential of P. indica as an efficacious elicitor for enhancing the secondary metabolites production by F. carica HRs.

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

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

Production of rosmarinic acid and correlated gene expression in hairy root cultures of green and purple basil (Ocimum basilicum L.)

Rosmarinic acid (RA) is an active constituent of Ocimum basilicum. It has been shown that hairy root production (measured as dry weight) improves when green basil (O. basilicum "Cinnamon") is cultured under the light. In contrast, purple basil (O. basilicum "Purpurascens") shows greater hairy root production when cultured under dark conditions. The level of gene expression was highest in hairy roots of green basil under dark conditions for up to 1 week. Transcript levels were highest in hairy roots of purple basil under both dark and light conditions after 2 weeks of culturing. After 3 weeks of culture under light conditions, green basil had accumulated 1.9-fold higher RA content than that of purple basil, which in turn was fivefold higher than that of the natural roots (42.86 µg/mg). Tyrosine aminotransferase showed a higher transcript level when compared to the other phenylpropanoid pathway genes (phenylalanine ammonia-lyase, cinnamate 4-hydroxylase, and coenzyme-A ligase) in both dark and light conditions and in all-time regimens. RA accumulation was higher in the cultured hairy roots of green basil than those of purple basil under both light and dark conditions.

Toward alternative sources of milk coagulants for cheese manufacturing: establishment of hairy roots culture and protease characterization from Cynara cardunculus L

Extracts from hairy root cultures of Cynara cardunculus L. contain proteases and show milk-clotting activity. Cynara cardunculus L. or cardoon is often used as rennet in traditional cheese manufacturing, due to the presence of specific proteases in the flower. However, the flower extracts are variable depending on the provenance and quality of the flowers as well as high genetic variability among cardoon populations, and this affects the quality of the final product. In search for alternative sources of milk-clotting enzymes, hairy root cultures from cardoon were obtained and characterized regarding their protease content and proteolytic activity toward milk proteins. Aspartic, serine and cysteine proteases were identified in hairy roots by mass spectrometry analysis and an azocasein assay combined with specific inhibitors. RT-PCR analysis revealed the expression of cardosin A and D, and immunoblotting analysis suggested the presence of cardosin A or cardosin A-like enzyme in its mature form, supporting this system as an alternative source of cardosins. Hairy root protein extracts showed activity over caseins, supporting its use as milk coagulant, which was further tested by milk-clotting assays. This is also the first report on the establishment of hairy root cultures from cardoon, which paves the way for future work on controlled platforms for production of valuable metabolites which are known to be present in this species.

Strategic enhancement of genetic gain for nutraceutical development in buckwheat: A genomics-driven perspective

Buckwheat (Fagopyrum spp.) under the family Polygonaceae is an ancient pseudocereal with stupendous but less studied nutraceutical properties. The gluten free nature of protein, balanced amino acid profile and health promoting bioactive flavonoids make it a golden crop of future. Besides a scanty basic research, not much attention has been paid to the improvement of plant type and breeding of nutraceutical traits. Scanning of scientific literature indicates that adequate genetic variation exists for agronomic and nutritional traits in mainstream and wild gene pool of buckwheat. However, the currently employed conventional approaches together with poorly understood genetic mechanisms restrict effective utilization of the existing genetic variation in nutraceutical breeding of buckwheat. The latest trends in buckwheat genomics, particularly avalilabity of draft genome sequences for both the cultivated species (F. esculentum and F.tataricum) hold immense potential to overcome these limitations. Utilizing the transgenic hairy rot cultures, role of various transcription factors and gene families have been deduced in production and biosynthesis of bioactive flavonoids. Further, the acquisition of high-density genomics data coupled with the next-generation phenotyping will certainly improve our understanding of underlying genetic regulation of nutraceutical traits. The present paper highlights the application of multilayered omics interventions for tailoring a nutrient rich buckwheat cultivar and nutraceutical product development.

Efficient Genome Editing Using CRISPR/Cas9 Technology in Chicory

CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR associated with protein CAS9) is a genome-editing tool that has been extensively used in the last five years because of its novelty, affordability, and feasibility. This technology has been developed in many plant species for gene function analysis and crop improvement but has never been used in chicory (Cichorium intybus L.). In this study, we successfully applied CRISPR/Cas9-mediated targeted mutagenesis to chicory using Agrobacterium rhizogenes-mediated transformation and protoplast transfection methods. A U6 promoter (CiU6-1p) among eight predicted U6 promoters in chicory was selected to drive sgRNA expression. A binary vector designed to induce targeted mutations in the fifth exon of the chicory phytoene desaturase gene (CiPDS) was then constructed and used to transform chicory. The mutation frequency was 4.5% with the protoplast transient expression system and 31.25% with A. rhizogenes-mediated stable transformation. Biallelic mutations were detected in all the mutant plants. The use of A. rhizogenes-mediated transformation seems preferable as the regeneration of plants is faster and the mutation frequency was shown to be higher. With both transformation methods, foreign DNA was integrated in the plant genome. Hence, selection of vector (transgene)-free segregants is required. Our results showed that genome editing with CRISPR/Cas9 system can be efficiently used with chicory, which should facilitate and accelerate genetic improvement and functional biology.

Agrobacterium rhizogenes-mediated hairy roots transformation as a tool for exploring aluminum-responsive genes function

AIM

To develop a useful alternative approach to evaluate the gene function in hairy roots.

METHODS

Arabidopsis and tobacco (wild-type or mutant) were a host for Agrobacterium rhizogenes transformation.

RESULTS

The hairy roots formation efficiency ranged from 53 to 98% in tobacco and 53 to 66% in Arabidopsis. Hairy and intact roots showed similar gene expression pattern in response to salt and aluminum stress. Genomic polymerase chain reaction and fluorescent images showed high rate (>80%) of co-integration of T-DNAs and uniform cell transformation without use of any antibiotic selection. Whole processes of hairy roots were completed within 1 month after the infection of Agrobacterium.

CONCLUSION

Aluminum-responsive orthologous gene function could be evaluated by NtSTOP1-KD and Atstop1 as a host for hairy roots transformation.

Plant cell culture technology in the cosmetics and food industries: current state and future trends

The production of drugs, cosmetics, and food which are derived from plant cell and tissue cultures has a long tradition. The emerging trend of manufacturing cosmetics and food products in a natural and sustainable manner has brought a new wave in plant cell culture technology over the past 10 years. More than 50 products based on extracts from plant cell cultures have made their way into the cosmetics industry during this time, whereby the majority is produced with plant cell suspension cultures. In addition, the first plant cell culture-based food supplement ingredients, such as Echigena Plus and Teoside 10, are now produced at production scale. In this mini review, we discuss the reasons for and the characteristics as well as the challenges of plant cell culture-based productions for the cosmetics and food industries. It focuses on the current state of the art in this field. In addition, two examples of the latest developments in plant cell culture-based food production are presented, that is, superfood which boosts health and food that can be produced in the lab or at home.

Hairy root induction and benzylisoquinoline alkaloid production in Macleaya cordata

Sanguinarine is currently widely used to replace antibiotic growth promoters in animal feeding and has demonstrated useful anticancer activity. Currently, the main source of sanguinarine is from an important medicinal plant, Macleaya cordata. To obtain a new source of sanguinarine production, we established hairy root cultures of M. cordata by co-cultivating leaf and stem explants with Agrobacterium rhizogenes. Except the co-cultivation medium, all growth media contained 200 mg/L timentin to eliminate A. rhizogenes. Through comparing the metabolic profiles and gene expression of hairy roots and wild-type roots sampled at five time points, we found that the sanguinarine and dihydrosanguinarine contents of hairy roots were far higher than those of wild-type roots, and we revealed the molecular mechanism that causes these metabolites to increase. Consequently, this study demonstrated that the hairy root system has further potential for bioengineering and sustainable production of sanguinarine on a commercial scale. To the best of our knowledge, this is the first efficient protocol reported for the establishment of hairy root cultures in M. cordata using A. rhizogenes.

Hairy root induction and benzylisoquinoline alkaloid production in Macleaya cordata

Sanguinarine is currently widely used to replace antibiotic growth promoters in animal feeding and has demonstrated useful anticancer activity. Currently, the main source of sanguinarine is from an important medicinal plant, Macleaya cordata. To obtain a new source of sanguinarine production, we established hairy root cultures of M. cordata by co-cultivating leaf and stem explants with Agrobacterium rhizogenes. Except the co-cultivation medium, all growth media contained 200 mg/L timentin to eliminate A. rhizogenes. Through comparing the metabolic profiles and gene expression of hairy roots and wild-type roots sampled at five time points, we found that the sanguinarine and dihydrosanguinarine contents of hairy roots were far higher than those of wild-type roots, and we revealed the molecular mechanism that causes these metabolites to increase. Consequently, this study demonstrated that the hairy root system has further potential for bioengineering and sustainable production of sanguinarine on a commercial scale. To the best of our knowledge, this is the first efficient protocol reported for the establishment of hairy root cultures in M. cordata using A. rhizogenes.

Biotechnological approaches for artemisinin production in Artemisia

Abstract

Artemisinin and its analogues are naturally occurring most effective antimalarial secondary metabolites. These compounds also possess activity against various types of cancer cells, schistosomiasis, and some viral diseases. Artemisinin and its derivatives (A&D) are found in very low amounts in the only natural source i.e. Artemisia plant. To meet the global needs, plant sources have been exploited for the enhanced production of these natural products because their chemical synthesis is not profitable. The generally adopted approaches include non-transgenic (tissue and cell cultures) and transgenic together with the cell, tissue, and whole transgenic plant cultures. The genes targeted for the overproduction of A&D include the biosynthetic pathway genes, trichome development genes and rol genes, etc. Artemisinin is naturally produced in trichomes of leaves. At the same time, transgenic hairy roots are considered a good source to harvest artemisinin. However, the absence of trichomes in hairy roots suggests that artemisinin biosynthesis is not limited to trichomes. Moreover, the expression of the gene involved in trichome development and sesquiterpenoid biosynthesis (TFAR1) in transgenic and non-transgenic roots provokes researchers to look for new insight of artemisinin biosynthesis. Here we discuss and review precisely the various biotechnological approaches for the enhanced biosynthesis of A&D.

Graphical Abstract

Larvicidal activity and in vitro regulation of rotenoids from Cassia tora L

The search for new insecticidal natural products is very important viewing the global incidence of malaria. In the present study, rotenoids viz., sumatrol, rotenone, tephrosin, rotenol, deguelin, and elliptone were identified from the plant parts and callus culture of Cassia tora L. Maximum content of rotenoids was observed in roots (1.96% ± 0.03) and minimum in the stem (0.52% ± 0.02). Rotenoid showed larvicidal activity against Anopheles stephensi larvae (LC₅₀-120.61 ppm; P < 0.05). To enhance the production of rotenoids in vitro, the callus culture of C. tora was supplemented with different concentrations of precursors (phenylalanine and methionine). More than onefold increase in the rotenoid content was observed as compared to the control. The present study highlights the insecticidal potential of rotenoids from C. tora. Moreover, the enhanced production of rotenoids using precursors can be exploited commercially.

A MDR transporter contributes to the different extracellular production of sesquiterpene pyridine alkaloids between adventitious root and hairy root liquid cultures of Tripterygium wilfordii Hook.f

TwMDR1 transports sesquiterpene pyridine alkaloids, wilforine and wilforgine, into the hairy roots of T. wilfordii Hook.f. resulting in low secretion ratio of alkaloids. Hairy roots (HRs) exhibit high growth rate and biochemical and genetic stability. However, varying secondary metabolites in HR liquid cultures mainly remain in root tissues, and this condition may affect cell growth and cause inconvenience in downstream extraction. Studies pay less attention to adventitious root (AR) liquid cultures though release ratio of some metabolites in AR liquid cultures is significantly higher than that of HR. In Tripterygium wilfordii Hook.f., release ratio of wilforine in AR liquid cultures reached 92.75 and 13.32% in HR on day 15 of culture. To explore potential roles of transporters in this phenomenon, we cloned and functionally identified a multidrug resistance (MDR) transporter, TwMDR1, which shows high expression levels in HRs and is correlated to transmembrane transportation of alkaloids. Nicotiana tabacum cells with overexpressed TwMDR1 efficiently transported wilforine and wilforgine in an inward direction. To further prove the feasibility of genetically engineered TwMDR1 and improve alkaloid production, we performed a transient RNAi experiment on TwMDR1 in T. wilfordii Hook.f. suspension cells. Results indicated that release ratios of wilforine and wilforgine increased by 1.94- and 1.64-folds compared with that of the control group, respectively. This study provides bases for future studies that aim at increasing secretion ratios of alkaloids in root liquid cultures in vitro.

A Cytotoxic and Anti-inflammatory Campesterol Derivative from Genetically Transformed Hairy Roots of Lopezia racemosa Cav. (Onagraceae)

The genetically transformed hairy root line LRT 7.31 obtained by infecting leaf explants of Lopezia racemosa Cav with the Agrobacterium rhizogenes strain ATCC15834/pTDT, was evaluated to identify the anti-inflammatory and cytotoxic compounds reported previously for the wild plant. After several subcultures of the LRT 7.31 line, the bio-guided fractionation of the dichloromethane-methanol (1:1) extract obtained from dry biomass afforded a fraction that showed important in vivo anti-inflammatory, and in vitro cytotoxic activities. Chemical separation of the active fraction allowed us to identify the triterpenes ursolic (1) and oleanolic (2) acids, and (23R)-2α,3β,23,28-tetrahydroxy-14,15-dehydrocampesterol (3) as the anti-inflammatory principles of the active fraction. A new molecule 3 was characterized by spectroscopic analysis of its tetraacetate derivative 3a. This compound was not described in previous reports of callus cultures, in vitro germinated seedlings and wild plant extracts of whole L. racemosa plants. The anti-inflammatory and cytotoxic activities displayed by the fraction are associated to the presence of compounds 1-3. The present study reports the obtaining of the transformed hairy roots, the bioguided isolation of the new molecule 3, and its structure characterization.

Isolation of protein complexes from the model legume Medicago truncatula by tandem affinity purification in hairy root cultures

Tandem affinity purification coupled to mass spectrometry (TAP-MS) is one of the most powerful techniques to isolate protein complexes and elucidate protein interaction networks. Here, we describe the development of a TAP-MS strategy for the model legume Medicago truncatula, which is widely studied for its ability to produce valuable natural products and to engage in endosymbiotic interactions. As biological material, transgenic hairy roots, generated through Agrobacterium rhizogenes-mediated transformation of M. truncatula seedlings, were used. As proof of concept, proteins involved in the cell cycle, transcript processing and jasmonate signalling were chosen as bait proteins, resulting in a list of putative interactors, many of which confirm the interologue concept of protein interactions, and which can contribute to biological information about the functioning of these bait proteins in planta. Subsequently, binary protein-protein interactions among baits and preys, and among preys were confirmed by a systematic yeast two-hybrid screen. Together, by establishing a M. truncatula TAP-MS platform, we extended the molecular toolbox of this model species.

Exploring the Metabolic Stability of Engineered Hairy Roots after 16 Years Maintenance

Plants remain a major source of new drugs, leads and fine chemicals. Cell cultures deriving from plants offer a fascinating tool to study plant metabolic pathways and offer large scale production systems for valuable compounds - commercial examples include compounds such as paclitaxel. The major constraint with undifferentiated cell cultures is that they are generally considered to be genetically unstable and cultured cells tend to produce low yields of secondary metabolites especially over time. Hairy roots, a tumor tissue caused by infection of Agrobacterium rhizogenes is a relevant alternative for plant secondary metabolite production for being fast growing, able to grow without phytohormones, and displaying higher stability than undifferentiated cells. Although genetic and metabolic stability has often been connected to transgenic hairy roots, there are only few reports on how a very long-term subculturing effects on the production capacity of hairy roots. In this study, hairy roots producing high tropane alkaloid levels were subjected to 16-year follow-up in relation to genetic and metabolic stability. Cryopreservation method for hairy roots of Hyoscyamus muticus was developed to replace laborious subculturing, and although the post-thaw recovery rates remained low, the expression of transgene remained unaltered in cryopreserved roots. It was shown that although displaying some fluctuation in the metabolite yields, even an exceedingly long-term subculturing was successfully applied without significant loss of metabolic activity.

Effect of Different Agrobacterium rhizogenes Strains on Hairy Root Induction and Phenylpropanoid Biosynthesis in Tartary Buckwheat (Fagopyrum tataricum Gaertn)

The development of an efficient protocol for successful hairy root induction by Agrobacterium rhizogenes is the key step toward an in vitro culturing method for the mass production of secondary metabolites. The selection of an effective Agrobacterium strain for the production of hairy roots is highly plant species dependent and must be determined empirically. Therefore, our goal was to investigate the transformation efficiency of different A. rhizogenes strains for the induction of transgenic hairy roots in Fagopyrum tataricum ‘Hokkai T10’ cultivar; to determine the expression levels of the polypropanoid biosynthetic pathway genes, such as ftpAL, FtC4H, Ft4CL, FrCHS, FrCH1, FrF3H, FtFLS1, FtFLS2, FtF3^, H1, FtF3′H2, FtANS, and FtDFR; and to quantify the in vitro synthesis of phenolic compounds and anthocyanins. Among different strains, R1000 was the most promising candidate for hairy root stimulation because it induced the highest growth rate, root number, root length, transformation efficiency, and total anthocyanin and rutin content. The R1000, 15834, and A4 strains provided higher transcript levels for most metabolic pathway genes for the synthesis of rutin (22.31, 15.48, and 13.04 μg/mg DW, respectively), cyanidin 3-O-glucoside (800, 750, and 650 μg/g DW, respectively), and cyanidin 3-O-rutinoside (2410, 1530, and 1170 μg/g DW, respectively). A suitable A. rhizogenes strain could play a vital role in the fast growth of the bulk amount of hairy roots and secondary metabolites. Overall, R1000 was the most promising strain for hairy root induction in buckwheat.

Ultraviolet Radiation-Elicited Enhancement of Isoflavonoid Accumulation, Biosynthetic Gene Expression, and Antioxidant Activity in Astragalus membranaceus Hairy Root Cultures

In this work, Astragalus membranaceus hairy root cultures (AMHRCs) were exposed to ultraviolet radiation (UV-A, UV-B, and UV-C) for promoting isoflavonoid accumulation. The optimum enhancement for isoflavonoid production was achieved in 34-day-old AMHRCs elicited by 86.4 kJ/m(2) of UV-B. The resulting isoflavonoid yield was 533.54 ± 13.61 μg/g dry weight (DW), which was 2.29-fold higher relative to control (232.93 ± 3.08 μg/g DW). UV-B up-regulated the transcriptional expressions of all investigated genes involved in isoflavonoid biosynthetic pathway. PAL and C4H were found to be two potential key genes that controlled isoflavonoid biosynthesis. Moreover, a significant increase was noted in antioxidant activity of extracts from UV-B-elicited AMHRCs (IC50 values = 0.85 and 1.08 mg/mL) in comparison with control (1.38 and 1.71 mg/mL). Overall, this study offered a feasible elicitation strategy to enhance isoflavonoid accumulation in AMHRCs and also provided a basis for metabolic engineering of isoflavonoid biosynthesis in the future.

Hairy root induction and phytoremediation of textile dye, Reactive green 19A-HE4BD, in a halophyte, Sesuvium portulacastrum (L.) L

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Hairy roots induction from A. rhizogenes NCIM 5140 strain in Sesuvium.

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Textile dye degradation and color removal using hairy roots.

In this study, we report phytoremediation of textile dyes using hairy roots derived through Agrobacterium rhizogenes (NCIM 5140) infection of in vitro leaf and stem explants of a halophyte Sesuvium portulacastrum (L.) L. Leaf explants showed higher frequency of hairy root induction (70%) than stem explants (30%), and maximum number of roots (leaf 42.3 ± 2.4 and stem 50.3 ± 1.7). Transformed nature of hairy roots was ascertained by amplifying 970 bp region of T-DNA of Ri plasmid. Hairy roots were screened for phytoremediation of various textile dyes and results showed that HRs were able to degrade Reactive green 19A HE4BD upto 98% within 5 days of incubation. Spectrophotometric analysis showed decrease in dye concentration while HPLC and FTIR analysis confirmed its degradation. Seed germination assay demonstrated non-toxic nature of the extracted metabolites. This is the first report on induction of hairy root culture in Sesuvium portulacastrum and phytoremediation of textile dyes.

Plant growth promoting rhizobia: challenges and opportunities

Modern agriculture faces challenges, such as loss of soil fertility, fluctuating climatic factors and increasing pathogen and pest attacks. Sustainability and environmental safety of agricultural production relies on eco-friendly approaches like biofertilizers, biopesticides and crop residue return. The multiplicity of beneficial effects of microbial inoculants, particularly plant growth promoters (PGP), emphasizes the need for further strengthening the research and their use in modern agriculture. PGP inhabit the rhizosphere for nutrients from plant root exudates. By reaction, they help in (1) increased plant growth through soil nutrient enrichment by nitrogen fixation, phosphate solubilization, siderophore production and phytohormones production (2) increased plant protection by influencing cellulase, protease, lipase and β-1,3 glucanase productions and enhance plant defense by triggering induced systemic resistance through lipopolysaccharides, flagella, homoserine lactones, acetoin and butanediol against pests and pathogens. In addition, the PGP microbes contain useful variation for tolerating abiotic stresses like extremes of temperature, pH, salinity and drought; heavy metal and pesticide pollution. Seeking such tolerant PGP microbes is expected to offer enhanced plant growth and yield even under a combination of stresses. This review summarizes the PGP related research and its benefits, and highlights the benefits of PGP rhizobia belonging to the family Rhizobiaceae, Phyllobacteriaceae and Bradyrhizobiaceae.

Efficient production of isoflavonoids by Astragalus membranaceus hairy root cultures and evaluation of antioxidant activities of extracts

In this study, Astragalus membranaceus hairy root cultures (AMHRCs) were established as an attractive alternative source for the efficient production of isoflavonoids (IF). A. membranaceus hairy root line II was screened as the most efficient line and was confirmed by PCR amplification of rolB, rolC and aux1 genes. Culture parameters of AMHRCs were systematically optimized, and five main IF constituents were quali-quantitatively determined by LC-MS/MS. Under optimal conditions, the total IF accumulation of 34 day old AMHRCs was 234.77 μg/g dry weight (DW). This yield was significantly higher compared to that of 3 year old field grown roots (187.38 μg/g DW). Additionally, in vitro antioxidant assays demonstrated that AMHRC extracts exhibited antioxidant activities with lower IC50 values (1.40 and 1.73 mg/mL) as compared to those of field grown roots (1.96 and 2.17 mg/mL). Overall, AMHRCs may offer a promising and continuous product platform for naturally derived, high quality and valuable nutraceuticals.

Enhancement of ginsenoside biosynthesis and secretion by Tween 80 in Panax ginseng hairy roots

We evaluated the effect of Tween 80 permeabilization on ginsenoside secretion in Panax ginseng hairy roots. Tween 80 (1.2%, w/v) had no significant effect on hairy root vitality. After a 25-day treatment with Tween 80, approximately 76% of the total ginsenosides was released into the surrounding medium. In the case of control, the ginsenosides secreted into the medium were negligible. Furthermore, when compared with control, the level of total ginsenosides was enhanced by approximately threefold under Tween treatment. Additionally, secretion of the typical ginsenoside monomers including Rb1 , Rg1 , and Re was analyzed, indicating that the most of them were released into the medium. Moreover, it was observed that dammarenediol synthase, a key enzyme involved in ginsenoside biosynthesis, was upregulated at both gene expression and enzyme activity levels. The expression of genes CYP716A47 and CYP716A53v2 encoding Cyt P450 enzymes catalyzing the formation of protopanaxadiol from dammarenediol and protopanaxatriol from protopanaxadiol, respectively, was slightly upregulated. These results clearly demonstrated that Tween 80 could act not only as an efficient permeabilizer to enhance ginsenoside secretion from the hairy roots, but also as an elicitor to promote the biosynthesis of ginsenoside.

Enhancement of chlorogenic acid production in hairy roots of Platycodon grandiflorum by over-expression of an Arabidopsis thaliana transcription factor AtPAP1

To improve the production of chlorogenic acid (CGA) in hairy roots of Platycodon grandiflorum, we induced over-expression of Arabidopsis thaliana transcription factor production of anthocyanin pigment (AtPAP1) using an Agrobacterium rhizogenes-mediated transformation system. Twelve hairy root lines showing over-expression of AtPAP1 were generated. In order to investigate the regulation of AtPAP1 on the activities of CGA biosynthetic genes, the expression levels of seven P. grandiflorum CGA biosynthetic genes were analyzed in the hairy root line that had the greatest accumulation of AtPAP1 transcript, OxPAP1-1. The introduction of AtPAP1 increased the mRNA levels of all examined CGA biosynthetic genes and resulted in a 900% up-regulation of CGA accumulation in OxPAP1-1 hairy roots relative to controls. This suggests that P. grandiflorum hairy roots that over-express the AtPAP1 gene are a potential alternative source of roots for the production of CGA.

Threats and opportunities of plant pathogenic bacteria

Plant pathogenic bacteria can have devastating effects on plant productivity and yield. Nevertheless, because these often soil-dwelling bacteria have evolved to interact with eukaryotes, they generally exhibit a strong adaptivity, a versatile metabolism, and ingenious mechanisms tailored to modify the development of their hosts. Consequently, besides being a threat for agricultural practices, phytopathogens may also represent opportunities for plant production or be useful for specific biotechnological applications. Here, we illustrate this idea by reviewing the pathogenic strategies and the (potential) uses of five very different (hemi)biotrophic plant pathogenic bacteria: Agrobacterium tumefaciens, A. rhizogenes, Rhodococcus fascians, scab-inducing Streptomyces spp., and Pseudomonas syringae.