Hairy root induction and plant regeneration of medicinal plant Dracocephalum kotschyi

The History of Agrobacterium Rhizogenes: From Pathogen to a Multitasking Platform for Biotechnology

Agrobacterium's journey has been a roller coaster, from being a pathogen to becoming a powerful biotechnological tool. While A. tumefaciens has provided the scientific community with a versatile tool for plant transformation, Agrobacterium rhizogenes has given researchers a Swiss army knife for developing many applications. These applications range from a methodology to regenerate plants, often recalcitrant, to establish bioremediation protocols to a valuable system to produce secondary metabolites. This chapter reviews its discovery, biology, controversies over its nomenclature, and some of the multiple applications developed using A. rhizogenes as a platform.

Induction and metabolomic analysis of hairy roots of Atractylodes lancea

Atractylodes lancea is an important source of traditional Chinese medicines. Sesquiterpenoids are the key active compounds in A. lancea, and their presence determines the quality of the material. Hairy hoot (HR) culture is a potential method to produce medicinally active compounds industrially; however, the induction and metabolic profiling of A. lancea HR have not been reported. We found that optimal induction of A. lancea HR was achieved by Agrobacterium rhizogenes strain C58C1 using the young leaves of tissue culture seedlings in the rooting stage as explants. Ultra-performance liquid chromatography-tandem mass spectrometric analyses of the chemical compositions of HR and normal root (NR) led to the annotation of 1046 metabolites. Over 200 differentially accumulated metabolites were identified, with 41 found to be up-regulated in HR relative to NR and 179 down-regulated in HR. Specifically, atractylodin levels were higher in HR, while the levels of β-eudesmol and hinesol were higher in NR. Metabolic pathway analyses showed a significant difference in metabolites of the shikimate acid pathway between HR and NR. Five A. lancea compounds are potential biomarkers for evaluation of HR and NR quality. This study provides an important reference for the application of HR for the production of medicinally active compounds. KEY POINTS: • We established an efficient protocol for the induction of HR in A. lancea • HR was found to have a significantly higher amount of atractylodin than did NRs • Metabolic pathway analyses showed a significant difference in metabolites of the shikimate acid pathway between HR and NR.

ZnO nanoparticles efficiently enhance drought tolerance in Dracocephalum kotschyi through altering physiological, biochemical and elemental contents

Using nanofertilizers in certain concentrations can be a novel method to alleviate drought stress effects in plants as a global climate problem. We aimed to determine the impacts of zinc nanoparticles (ZnO-N) and zinc sulfate (ZnSO₄) fertilizers on the improvement of drought tolerance in Dracocephalum kotschyi as a medicinal-ornamental plant. Plants were treated with three doses of ZnO-N and ZnSO₄ (0, 10, and 20 mg/l) under two levels of drought stress [50% and 100% field capacity (FC)]. Relative water content (RWC), electrolyte conductivity (EC), chlorophyll, sugar, proline, protein, superoxide dismutase (SOD), polyphenol oxidase (PPO) and, guaiacol peroxidase (GPO) were measured. Moreover, the concentration of some elements interacting with Zn was reported using the SEM-EDX method. Results indicated that foliar fertilization of D. kotschyi under drought stress with ZnO-N decreased EC, while ZnSO₄ application was less effective. Moreover, sugar and proline content as well as activity of SOD and GPO (and to some extent PPO) in treated plants by 50% FC, increased under the influence of ZnO-N. ZnSO₄ application could increase chlorophyll and protein content and PPO activity in this plant under drought stress. Based on the results, ZnO-N and then ZnSO₄ improved the drought tolerance of D. kotschyi through their positive effects on physiological and biochemical attributes changing the concentration of Zn, P, Cu, and Fe. Accordingly, due to the increased sugar and proline content and also antioxidant enzyme activity (SOD, GPO, and to some extent PPO) on enhancing drought tolerance in this plant, ZnO-N fertilization is advisable.

Inductive effect of titanium dioxide nanoparticles on the anticancer compounds production and expression of rosmarinic acid biosynthesis genes in Dracocephalum kotschyi transformed roots

Methoxylated flavonoids, mainly xanthomicrol and cirsimaritin that can be extracted from Dracocephalum kotschyi Boiss, have anticancer, antispasmodic and antiplatelet effects. The production of these valuable pharmaceutical compounds is one of the major goals of biotechnology studies. In this work, induced transformed roots were influenced by various concentrations of titanium dioxide nanoparticles (TiO2 NPs) at 24 or 48 h exposure time. The effects of TiO2 NPs were assessed on growth rate, activity of antioxidant enzymes, total phenol and flavonoid content (TPC and TFC) and rosmarinic acid (RA) and some flavonoids accumulation. The gene expression level of phenylalanine ammonia-lyase (pal) and rosmarinic acid synthase (ras) genes were assessed by real time PCR analysis. The transformed roots biomass was substantially increased in elicited roots in comparison with the control. The TPC, TFC and antioxidant enzymes activitywere affected by TiO2 NPs concentration and exposure time. Valuable flavonoids with anticancer characteristics along with xanthomicrol, cirsimaritin and isokaempferide exhibited an increase (70, 34.28 and 7.81-fold, respectively) versus the control. The maximum content of RA (530.5 μg g-1 FW), which was 4.30 times as great as that of control was detected in samples treated with TiO2 NPs (50 mg L-1) 24 h after elicitation. Real-time PCR analysis revealed a considerable increase in pal and ras expression rate engaged by TiO2 NPs levels and exposure time. Overall D. kotschyi transformed roots elicitation by TiO2 NPs led to a massive increment in the production of valuable anticancer flavonoids such as xanthomicrol, cirsimaritin and RA as polyphenol.

Agrobacterium rhizogenes-mediated transformation of grain (Amaranthus hypochondriacus) and leafy (A. hybridus) amaranths

Transgenic A. hypochondriacus and A. hybridus roots were generated. Further, a distinct plant regeneration program via somatic embryos produced from hairy roots was established. Work was implemented to develop an optimized protocol for root genetic transformation of the three grain amaranth species and A. hybridus, their presumed ancestor. Transformation efficiency was species-specific, being higher in A. hypochondriacus and followed by A. hybridus. Amaranthus cruentus and A. caudatus remained recalcitrant. A reliable and efficient Agrobacteruim rhizogenes-mediated transformation of these species was established using cotyledon explants infected with the previously untested BVG strain. Optimal OD₆₀₀ bacterial cell densities were 0.4 and 0.8 for A. hypochondriacus and A. hybridus, respectively. Hairy roots of both amaranth species were validated by the amplification of appropriate marker genes and, when pertinent, by monitoring green fluorescent protein emission or β-glucuronidase activity. Embryogenic calli were generated from A. hypochondriacus rhizoclones. Subsequent somatic embryo maturation and germination required the activation of cytokinin signaling, osmotic stress, red light, and calcium incorporation. A crucial step to ensure the differentiation of germinating somatic embryos into plantlets was their individualization and subcultivation in 5/5 media containing 5% sucrose, 5 g/L gelrite, and 0.2 mg/L 2-isopentenyladenine (2iP) previously acidified to pH 4.0 with phosphoric acid, followed by their transfer to 5/5 + 2iP media supplemented with 100 mg/L CaCl₂. These steps were strictly red light dependent. This process represents a viable protocol for plant regeneration via somatic embryo germination from grain amaranth transgenic hairy roots. Its capacity to overcome the recalcitrance to genetic transformation characteristic of grain amaranth has the potential to significantly advance the knowledge of several unresolved biological aspects of grain amaranths.

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 flavonoid production in hairy root cultures of Scutellaria bornmuelleri by elicitor induced over-expression of MYB7 and FNSП2 genes

For the purpose of the current study, hairy root induction in S. bornmuelleri, which is an important medicinal plant, was examined using a particular protocol. Accordingly, some factors such as four strain types of Agrobacterium rhizogenes (A4, A13, MSU440 and ATCC15834), three different explants, namely stem, petiole and leaf, two co-cultivation media, i.e. full and half-MS were studied. Besides, two inoculation methods including injection and immersion as well as three inoculation times (5, 7 and 10 min) were closely taken into account. Utilizing injection method by MSU440 strain, hairy root induction took place in stem explants, and a remarkable increase in transformation frequency (100%) was observed in half-strength MS medium. Methyl jasmonate (MeJA, 100 μM), methyl-b-cyclodextrin (b-CD, 0.7, 7 and 14 mM) and Chitosan (Chi, 50, 100 and 200 mg/l) were used either individually or in a combined way to elicitation. Based on the HPLC results, production of chrysin, wogonin and baicalein increased 9.15, 10.56 and 13.25 times after elicitation of hairy roots by MeJA + Chi. In addition, transcripts of FNSП2 and MYB7, two important genes involved in the flavonoid biosynthesis pathway, were studies. By applying Chi and MeJA + Chi elicitor, the expression of both genes increased noticeably. It can be concluded that the mentioned hairy root culture system of S. bornmuelleri can be an alternative to flavonoids production. Moreover, there is a direct and positive relationship between the expression of FNSП2 and MYB7 genes as well as the level of three flavonoids.

Efficient Generation of CRISPR/Cas9-Mediated Homozygous/Biallelic Medicago truncatula Mutants Using a Hairy Root System

In the process of acquiring mutants mediated by CRISPR/Cas9, plantlets are often regenerated from both mutated and non-mutated cells in a random manner, which increase the odds of chimeric mutated plant. In general, it's necessary to infect more explants or grow to next generation for the need of generating more biallelic or homozygous mutants. In present study, an efficient way of obtaining biallelic or homozygous mutated lines via fast-growing hairy root system without increasing numbers of infected explants or prolonging sexual propagation generation is reported. The fast growing lateral branches of hair roots are originated deep within the parental root from a small number of founder cells at the periphery, and therefore were employed as a library that classify different editing types in different lateral branches in which the homozygous or biallelic lines were screened. Here, MtPDS was employed in a proof-of-concept experiment to evaluate the efficiency of genome editing with our hairy root system. Homozygous/biallelic mutations were found only 1 of the 20 lines in the 1^st generation hairy roots, and 8 lines randomly selected were cultured to obtain their branch roots, homozygous/biallelic mutations were found in 6 of the 8 lines in their branch roots. We also tested the method with MtCOMT gene and got the same result. All of the seedlings regenerated from the homozygous/biallelic hairy root mutation lines of MtPDS displayed albino phenotypes. The entire process from vector design to the recovery of plantlets with homozygous/biallelic mutations took approximately 4.5-6.5 months. The whole process could bring inspiration for efficiently generating homozygous/biallelic mutants through CRISPR/Cas9 system from the hairy root or root system of a chimeric mutated transformants, especially for the rare and endangered plants whose explants sources are very limited or the plants that lack of tissue culture and rapid propagation system.

Iron oxide nanoparticles: a novel elicitor to enhance anticancer flavonoid production and gene expression in Dracocephalum kotschyi hairy-root cultures

BACKGROUND

Dracocephalum kotschyi Boiss. is a valuable source of rosmarinic acid (RA) and methoxylated hydroxyflavones (such as xanthomicrol and cirsimaritin) with antioxidative and antiplatelet effects and with antiproliferative potential against various cancer cells. The extensive application of nanotechnology in hairy root cultures is a new sustainable production platform for producing these active constituents. In the present study, hairy roots derived from 4-week-old leaves and Agrobacterium rhizogenes strain ATCC15834 were used to investigate the impact of various concentrations of iron oxide nanoparticles (Fe NPs) in two elicitation time exposures (24 and 48 h) on growth, antioxidant enzyme activity, total phenolic and flavonoid content (TPC and TFC), and some polyphenols. Gene expression levels of phenylalanine ammonia-lyase (pal) and rosmarinic acid synthase (ras) were also analyzed.

RESULTS

Iron nanoparticles enhanced biomass accumulation in hairy roots. The treatment time and Fe NP dosage largely improved the activity of antioxidant enzymes, TPC and TFC. The highest RA (1194 μg g^-1 FW) content (9.7-fold), compared to controls, was detected with 24 h of exposure to 75 mg L^-1 Fe NP, which was consistent with the expression of pal and ras genes under the influence of elicitation. The xanthomicrol, cirsimaritin, and isokaempferide content was increased 11.87, 3.85, and 2.27-fold, respectively.

CONCLUSION

Stimulation of D. kotschyi hairy roots by Fe NPs led to a significant increase in the induction and production of important pharmaceutical compounds such as rosmarinic acid and xanthomicrol. © 2019 Society of Chemical Industry.

Hairy root induction and Farnesiferol B production of endemic medicinal plant Ferula pseudalliacea

The effects of medium, gibberellic acid (GA₃) and stratification treatments on the seed germination of Ferula pseudalliacea were evaluated. Filter paper medium, 500 micro molar GA₃ and 8 week chilling treatment were resulted in significantly more seed germination than others. F. pseudalliacea was also transformed by Agrobacterium rhizogenes. Explants from young leaves, stems, cotyledon, and embryo were inoculated with A. rhizogenes strains ATCC 15834, 1724, A4, LB9402 and Ar318. Hairy roots were induced only from 10 to 12-days embryo explants using strains ATCC 15824 and 1724. Although, the transformation efficiency of ATCC 15834 (4%) strain was higher than 1724 (2%). Maximum hairy root transformation frequency (25%) was obtained in infection time of 10 min compared to that of 20 (20%) and 30 (5%) min. In addition, the transformation rate was significantly higher at the inoculation time of 72 h (29%) compared to that of 48 h (22%) and 24 h (6%). Transgenic hairy root lines were confirmed by PCR amplification of rolB gene. Hairy root lines were produced higher biomass in half B5 medium compared to that of half MS medium. Hairy roots lines from the strain ATCC 15834 produced more hairy root numbers and fresh and dried biomass compared to that of the strain 1724. Analyses of transgenic hairy root and natural roots extracts using HPLC showed that all the hairy root lines produced farnesiferol B.

Elimination of macro elements from inoculation and co-cultivation media enhances the efficiency of Agrobacterium-mediated transformation in Petunia

In order to evaluate the effect of inoculation and co-cultivation media elements on transformation frequency in Petunia hybrida, modified MS media with different elements were tested on Alvan and Large Flower Alvan (LF Alvan), two local cultivars. Leaf explants of both cultivars were inoculated with Agrobacterium tumefaciens strain LBA4404 (pBI121) containing neomycin phosphotransferase (nptII) and an intron-containing β-glucuronidase (gus) genes. When medium lacking KH2PO4, NH4NO3, KNO3, and CaCl2 was used as inoculation and co-cultivation medium, a higher frequency of transformation for Alvan (22%) and LF Alvan (16%) was obtained. Kanamycin resistant plantlets were stained blue by GUS assay. Furthermore, polymerase chain reaction (PCR) analysis revealed the presence of both gus and nptII genes in all putative transformants. Finally, southern blot hybridization confirmed insertion of 1-4 copies of gus gene in transgenic plants.

Enhanced production of hyoscyamine and scopolamine from genetically transformed root culture of Hyoscyamus reticulatus L. elicited by iron oxide nanoparticles

The medicinal plant Hyoscyamus reticulatus L. is a rich source of hyoscyamine and scopolamine, the tropane alkaloids. The use of hairy root cultures has focused significant attention on production of important metabolites such as stable tropane alkaloid production. Elicitation is an effective approach to induce secondary metabolite biosynthetic pathways. Hairy roots were derived from cotyledon explants inoculated with Agrobacterium rhizogenes and elicited by iron oxide nanoparticles (FeNPs) at different concentrations (0, 450, 900, 1800, and 3600 mg L-1) for different exposure times (24, 48, and 72 h). The highest hairy root fresh and dry weights were found in the medium supplemented with 900 mg L-1 FeNPs. Antioxidant enzyme activity was significantly increased in induced hairy roots compared to non-transgenic roots. The highest hyoscyamine and scopolamine production (about fivefold increase over the control) was achieved with 900 and 450 mg L-1 FeNPs at 24 and 48 h of exposure time, respectively. This is the first report of the effect of FeNP elicitor on hairy root cultures of a medicinal plant. We suggest that FeNPs could be an effective elicitor in hairy root cultures in order to increase tropane alkaloid production.

Efficient genetic transformation and regeneration system from hairy root of Origanum vulgare

Origanum vulgare L is commonly known as a wild marjoram and winter sweet which has been used in the traditional medicine due to its therapeutic effects as stimulant, anticancer, antioxidant, antibacterial, anti-inflammatory and many other diseases. A reliable gene transfer system via Agrobacterium rhizogenes and plant regeneration via hairy roots was established in O. vulgare for the first time. The frequency of induced hairy roots was different by modification of the co-cultivation medium elements after infection by Agrobacterium rhizogenes strains K599 and ATCC15834. High transformation frequency (91.3 %) was achieved by co-cultivation of explants with A. rhizogenes on modified (MS) medium. The frequency of calli induction with an 81.5 % was achieved from hairy roots on MS medium with 0.25 mg/L(-1) 2,4-D. For shoot induction, initiated calli was transferred into a medium containing various concentrations of BA (0.1, 0.25, 0.5, 0.75 and 1 mg/L(-1)). The frequency of shoot generation (85.18 %) was achieved in medium fortified with 0.25 mg/L(-1) of BA. Shoots were placed on MS medium with 0.25 mg/l IBA for root induction. Roots appeared and induction rate was achieved after 15 days.

Efficient genetic transformation and regeneration system from hairy root of Origanum vulgare

Origanum vulgare L is commonly known as a wild marjoram and winter sweet which has been used in the traditional medicine due to its therapeutic effects as stimulant, anticancer, antioxidant, antibacterial, anti-inflammatory and many other diseases. A reliable gene transfer system via Agrobacterium rhizogenes and plant regeneration via hairy roots was established in O. vulgare for the first time. The frequency of induced hairy roots was different by modification of the co-cultivation medium elements after infection by Agrobacterium rhizogenes strains K599 and ATCC15834. High transformation frequency (91.3 %) was achieved by co-cultivation of explants with A. rhizogenes on modified (MS) medium. The frequency of calli induction with an 81.5 % was achieved from hairy roots on MS medium with 0.25 mg/L(-1) 2,4-D. For shoot induction, initiated calli was transferred into a medium containing various concentrations of BA (0.1, 0.25, 0.5, 0.75 and 1 mg/L(-1)). The frequency of shoot generation (85.18 %) was achieved in medium fortified with 0.25 mg/L(-1) of BA. Shoots were placed on MS medium with 0.25 mg/l IBA for root induction. Roots appeared and induction rate was achieved after 15 days.

In vitro regeneration and Agrobacterium mediated genetic transformation of Artemisia aucheri Boiss

In the present study, we developed an efficient protocol for in vitro plant regeneration and genetically transformed root induction in medicinal plant Artemisia aucheri Boiss. Leaf explants were cultivated in MS medium supplemented by combination of plant growth regulators including α-naphthalene-acetic acid, 6-benzyl-aminopurine, indole-3-acetic acid and 2, 4-dichlorophenoxyaceticacid. The highest frequency of shoot organogenesis occurred on MS medium supplemented with 0.05 mg/l NAA plus 2 mg/l BA (96.3 %) and MS medium supplemented with 0.5 mg/l IAA plus 2 mg/l BA (88.3 %). Root induction was obtained on MS medium supplemented with 0.5 mg/l IBA. This is a simple, reliable, rapid and high efficient regeneration system for A. aucheri Boiss in short period via adventitious shoot induction approach. Also, an efficient genetically transformed root induction for A. aucheri was developed through Agrobacterium rhizogenes-mediated transformation by four bacterial strains, A4, ATCC15834, MSU440, and A13 (MAFF-02-10266). The maximum frequency of hairy root induction was obtained using MSU440 (93 %) and ATCC15834 (89 %) bacterial strains. Hairy root lines were confirmed by PCR using the rolB gene specific primers and Southern blot analysis.

A reliable and efficient protocol for inducing genetically transformed roots in medicinal plant Nepeta pogonosperma

Nepeta pogonosperma is an important medicinal plant with anti-inflammatory effects. An efficient and reliable transformation system for this plant was developed through optimization of several factors which affected the rate of Agrobacterium rhizogenes mediated transformation. Five bacterial strains, A4, ATCC15834, LBA9402, MSU440 and A13, two explant types, leaves and stems, and several co-cultivation media were examined. The maximum rate of hairy root induction was obtained from stem explants using MSU440 and ATCC15834 bacterial strains. A drastic increase in the frequency of transformation (91 %) was observed when MS medium lacking NH4NO3, KH2PO4, KNO3 and CaCl2. Hairy root lines were confirmed by polymerase chain reaction (PCR) using primers of the rolB gene. According to Southern blot analysis, one T-DNA copy was inserted into each of the hairy root lines. In the present study, transgenic hairy roots have been obtained trough genetic transformation by A. rhizogenes harbouring two plasmids, the Ri plasmid and pBI121 binary vector harbouring gus reporter gene. Expression of the gus gene in transgenic hairy root was confirmed by histochemical GUS assay.