Spontaneous plant regeneration in transformed roots and calli from Tylophora indica: Changes in morphological phenotype and tylophorine accumulation associated with transformation by Agrobacterium rhizogenes

Effect of Light Conditions on Polyphenol Production in Transformed Shoot Culture of Salvia bulleyana Diels

Various strategies have been used to increase the efficiency of secondary metabolite production in Salvia plants. This report is the first to examine the spontaneous development of Salvia bulleyana shoots transformed by Agrobacterium rhizogenes on hairy roots and the influence of light conditions on the phytochemical profile of this shoot culture. The transformed shoots were cultivated on solid MS medium with 0.1 mg/L of IAA (indole-3-acetic acid) and 1 mg/L of m-Top (meta-topolin), and their transgenic characteristic was confirmed by PCR-based detection of the rolB and rolC genes in the target plant genome. This study assessed the phytochemical, morphological, and physiological responses of the shoot culture under stimulation by light-emitting diodes (LEDs) with different wavelengths (white, WL; blue, B; red, RL; and red/blue, ML) and under fluorescent lamps (FL, control). Eleven polyphenols identified as phenolic acids and their derivatives were detected via ultrahigh-performance liquid chromatography with diode-array detection coupled to electrospray ionization tandem mass spectrometry (UPLC-DAD/ESI-MS) in the plant material, and their content was determined using high-performance liquid chromatography (HPLC). Rosmarinic acid was the predominant compound in the analyzed extracts. The mixed red and blue LEDs gave the highest levels of polyphenol and rosmarinic acid accumulation (respectively, 24.3 mg/g of DW and 20.0 mg/g of DW), reaching two times greater concentrations of polyphenols and three times greater rosmarinic acid levels compared to the aerial parts of two-year-old intact plants. Similar to WL, ML also stimulated regeneration ability and biomass accumulation effectively. However, the highest total photosynthetic pigment production (1.13 mg/g of DW for total chlorophyll and 0.231 mg/g of DW for carotenoids) was found in the shoots cultivated under RL followed by BL, while the culture exposed to BL was characterized as having the highest antioxidant enzyme activities.

Spontaneous Regeneration of Plantlets Derived from Hairy Root Cultures of Lopezia racemosa and the Cytotoxic Activity of Their Organic Extracts

A histological analysis was performed with the aim of elucidating the spontaneous regeneration process of the hairy root lines LRT 2.3 and LRT 6.4, derived from Lopezia racemosa leaf explants and genetically transformed with the Agrobacterium rhizogenes strain ATCC15834/pTDT. The analysis showed both lines regenerate via indirect somatic embryogenesis; LRT 6.4 also regenerated by direct organogenesis. The morphogenic characteristics of the regenerated plantlets from both lines showed the typical characteristics, described previously, including a higher number of axillary shoot formation, short internodes, and plagiotropic roots compared with wild-type seedlings. The regeneration process occurred without the addition of plant growth regulators and was linked to the sucrose concentration in the culture medium. Reducing the sucrose concentration from 3% to 2%, 1%, and 0.5% increased the regeneration rate in LRT 6.4; the effect was less pronounced in LRT 2.3. The cytotoxic activity of different organic extracts obtained from roots and shoots were evaluated in the cancer cell lines HeLa (cervical carcinoma), HCT-15 (colon adenocarcinoma), and OVCAR (ovary carcinoma). The hexane and dichloromethane extracts from roots of both lines showed cytotoxic activity against the HeLa cell line. Only the dichloromethane extract from the roots of PLRT 2.3 showed cytotoxic activity against the OVCAR cell line. None of the methanol extracts showed cytotoxic activity, nor the shoot extracts from any solvent.

Poison ivy hairy root cultures enable a stable transformation system suitable for detailed investigation of urushiol metabolism

Poison ivy (Toxicodendron radicans) is best known for causing exasperating allergenic delayed-contact dermatitis symptoms that last for weeks on persons who have contacted the plant. Urushiols are alkylcatechols produced by poison ivy responsible for causing this dermatitis. While urushiol chemical structures are well known, the metabolic intermediates and genes responsible for their biosynthesis have not been experimentally validated. A molecular genetic characterization of urushiol biosynthesis in poison ivy will require stable genetic transformation and subsequent regeneration of organs that retain the capacity synthesize urushiol. To this end, Agrobacterium rhizogenes was used to generate hormone-independent poison ivy hairy root cultures. Optimal conditions for hairy root formation were skotomorphic poison ivy hypocotyls prick-inoculated with A. rhizogenes, and preferential propagation of cultures with an atypical clumpy hairy root growth habit. The origin of the poison ivy accession used for A. rhizogenes prick-inoculation did not affect the initial formation of calli/hairy root primordia, but rather significantly influenced the establishment of long-term hormone-independent hairy root growth. A. rhizogenes harboring a recombinant T-DNA binary plasmid with an intron-containing Firefly Luciferase gene produced stable transgenic hairy root lines expressing luciferase activity at high frequency. Poison ivy hairy root lines produced significantly lower steady-state urushiol levels relative to wild-type roots, but higher urushiol levels than a poison ivy undifferentiated callus line with undetectable urushiol levels, suggesting that urushiol biosynthesis requires intact poison ivy organs. The lower urushiol levels in poison ivy hairy root lines facilitated the first identification of anacardic acid metabolites initially in hairy roots, and subsequently in wild-type roots as well. This study establishes a transformation hairy root regeneration protocol for poison ivy that can serve as a platform for future reverse-genetic studies of urushiol biosynthesis in poison ivy hairy roots.

Engineering Tropane Alkaloid Production Based on Metabolic Characterization of Ornithine Decarboxylase in Atropa belladonna

Ornithine decarboxylase (ODC) plays an important role in various biological processes; however, its role in plant secondary metabolism, especially in the biosynthesis of tropane alkaloids (TAs) such as pharmaceutical hyoscyamine, anisodamine, and scopolamine, remains largely unknown. In this study, we characterized the physiological and metabolic functions of the ODC gene of Atropa belladonna (AbODC) and determined its role in TA production using metabolic engineering approaches. Feeding assays with enzyme inhibitors indicated that ODC, rather than arginine decarboxylase (ADC), plays a major role in TA biosynthesis. Tissue-specific AbODC expression analysis and β-glucuronidase (GUS) staining assays showed that AbODC was highly expressed in secondary roots, especially in the cylinder tissue. Enzymatic assays indicated that AbODC was able to convert ornithine to putrescine, with the highest activity at pH 8.0 and 30 °C. Additionally, AbODC showed higher catalytic efficiency than other plant ODCs, as evident from the K_m, V_max, and K_cat values of AbODC using ornithine as the substrate. In A. belladonna root cultures, suppression of AbODC greatly reduced the production of putrescine, N-methylputrescine, and TAs, whereas overexpression of AbODC significantly increased the biosynthesis of putrescine, N-methylputrescine, hyoscyamine, and anisodamine. Moreover, transgenic A. belladonna plants overexpressing AbODC showed a significantly higher production of hyoscyamine and anisodamine compared with control plants. These findings indicate that AbODC plays a key role in TA biosynthesis and therefore is a valuable candidate for increasing TA production in A. belladonna.

Rhizogenic agrobacteria as an innovative tool for plant breeding: current achievements and limitations

Compact plant growth is an economically important trait for many crops. In practice, compactness is frequently obtained by applying chemical plant growth regulators. In view of sustainable and environmental-friendly plant production, the search for viable alternatives is a priority for breeders. Co-cultivation and natural transformation using rhizogenic agrobacteria result in morphological alterations which together compose the Ri phenotype. This phenotype is known to exhibit a more compact plant habit, besides other features. In this review, we highlight the use of rhizogenic agrobacteria and the Ri phenotype with regard to sustainable plant production and plant breeding. An overview of described Ri lines and current breeding applications is presented. The potential of Ri lines as pre-breeding material is discussed from both a practical and legal point of view.

The effect of purine-type cytokinin on the proliferation and production of phenolic compounds in transformed shoots of Dracocephalum forrestii

Dracocephalum forrestii is a perennial, endemic to China plant with a number of pharmaceutical properties. Transformed shoots of the species spontaneously regenerated from hairy roots induced by Agrobacterium rhizogenes. The transgenic nature of the shoots was confirmed by polymerase chain reaction (PCR). The shoot culture was multiplied on Murashige and Skoog (MS) medium with 0.2 mg/l IAA and 0.2, 0.5, 1.0, 2.0 or 5.0 mg/l purine-type cytokinins (mT, BAR, BPA or BAP). The highest multiplication rate (about thirteen shoot or buds per explant) was obtained on MS medium with 0.2 mg/l mT after four weeks of culture. The phenolic compounds present in the hydromethanolic extracts from the D. forrestii transgenic shoots were characterized using UPLC-PDA-ESI-MS. The shoots were found to biosynthesize three phenolic acids and five flavonoid glycosides. UHPLC analysis of the hydromethanolic extracts found the predominant phenolic acid to be rosmarinic acid, with its highest content observed in shoots cultivated with 5.0 mg/l BPA. In contrast, the greatest production of flavonoid derivatives (especially acacetin derivatives) was observed in the medium supplemented with 2 mg/l BPA.

Datura innoxia plants hydroponically-inoculated with Agrobacterium rhizogenes display an enhanced growth and alkaloid metabolism

BACKGROUND

The production of secondary metabolites through the culture of entire plants is of great interest. Soilless culture, such as hydroponics, enables the control of plant growth and metabolism. Specific environmental conditions must be developed to maximize the productivity of medicinal plants used as efficient natural bioreactors.

METHODS

The nutrient solution of newly established hydroponic cultures ofDatura innoxia Mill. were inoculated with Agrobacterium rhizogenes (A.r.) wild strains (TR7, TR107, 11325 or 15834). Growth and the alkaloid contents of roots and aerial parts were analyzed. Axenic cultures were also performed with modified TR7 strains containing the egfp or gus reporter gene. In vitro isolated root cultures enabled the phenological and molecular demonstration of gene transfer.

RESULTS

A.r.TR 7 led to a greater improvement in plant secondary metabolism and growth. Positive expression of the reporter genes occurred. Isolation and subculture of some of the roots of these plants showed a hairy root phenotype; molecular tests proved the transfer of bacterial genes into the roots isolated from the plants.

CONCLUSIONS

Hyoscyamine and scopolamine productivity is enhanced after A.r. inoculation in the nutrient solution of hydroponic plants. Transformation events occur in the original roots of the plants. This leads to chimeric plants with a part of their roots harboring a hairy root phenotype. Such semi-composite plants could be used for successful specialized metabolite bioproduction in greenhouses.

Neoteric trends in tissue culture-mediated biotechnology of Indian ipecac [Tylophora indica (Burm. f.) Merrill]

Tylophora indica (Burm. f.) Merrill, an ethno-pharmacologically important perennial climber of Asclepiadaceae, is commonly known as Antamul or Indian ipecac. It is essentially accredited for its medicinal properties owing to its wide range of alkaloids in the form of bioactive secondary metabolites, such as tylophorine, tylophorinine, and tylophorinidine. Accelerated mass propagation of Tylophora is challenging because of its reduced seed germination frequency that consequently headed the pursuit for efficient protocols on in vitro propagation for the large-scale regeneration, conservation as well as sustainable supply of quality propagules. Ample tissue culture-mediated biotechnological investigations have been carried out on this medicinal plant till date and several micropropagation protocols have been standardized as well. The present review compares between several typical methods as well as factors, involving on direct and indirect organogenesis of Tylophora along with various up-to-date and modified techniques such as somatic embryogenesis, protoplast culture, synthetic seed production, genetic transformation, and in vitro interventions for the secondary metabolite production that have been reported in last two decades. This compilation will allow assessing the achievements and trends of Tylophora research so far, as well as will advance the research more rapidly, since many aspects, basic and applied, have yet to be explored.

FRET-based nanobiosensor for detection of scopolamine in hairy root extraction of Atropa belladonna

A simple, sensitive, selective, and rapid optical nanobiosensor based on FRET was designed to detect tropane alkaloids as anti-cholinergic agents in natural and transgenic hairy roots extracts of Atropa belladonna. To achieve that, conjugation of tioglycolyic acid capped cadmium telluride quantum Dots, M₂ muscarinic receptor (Cd/Te QDs-M₂R) and conjugation of scopolamine-rhodamine123 (Sc-Rho123) were performed. More specifically, proportional amounts of M₂ muscarinic receptor and quantum dots (QDs) were conjugated while scopolamine (as a tropane alkaloid) and rhodamine123 were also combined and these moieties functioned as donor and acceptor pairs, respectively. The system response was linear over the range of 0.01-4µmolL^-1 of scopolamine hydrochloride concentration with a detection limit of 0.001µmolL^-1. The developed nanobiosensor was successfully used for in vitro recognition of scopolamine as an anti-cholinergic agent in the investigated plant extracts. In addition, Agrobacterium rhizogenesis mediated gene transfer technique was employed to generate hairy roots and to enhance the production of tropane alkaloids in the studied medicinal plant.

Micropropagation and genetic transformation of Tylophora indica (Burm. f.) Merr.: a review

This review provides an in-depth and comprehensive overview of the in vitro culture of Tylophora species, which have medicinal properties. Tylophora indica (Burm. f.) Merr. is a climbing perennial vine with medicinal properties. The tissue culture and genetic transformation of T. indica, which has been extensively studied, is reviewed. Micropropagation using nodal explants has been reported in 25 % of all publications. Leaf explants from field-grown plants has been the explant of choice of independent research groups, which reported direct and callus-mediated organogenesis as well as callus-mediated somatic embryogenesis. Protoplast-mediated regeneration and callus-mediated shoot organogenesis has also been reported from stem explants, and to a lesser degree from root explants of micropropagated plants in vitro. Recent studies that used HPLC confirmed the potential of micropropagated plants to synthesize the major T. indica alkaloid tylophorine prior to and after transfer to field conditions. The genetic integrity of callus-regenerated plants was confirmed by RAPD in a few reports. Tissue culture is an essential base for genetic transformation studies. Hairy roots and transgenic T. indica plants have been shown to accumulate tylophorine suggesting that in vitro biology and transgenic methods are viable ways of clonally producing valuable germplasm and mass producing compounds of commercial value. Further studies that investigate the factors affecting the biosynthesis of Tylophora alkaloids and other secondary metabolites need to be conducted using non-transformed as well as transformed cell and organ cultures.

The Fate of Integrated Ri T-DNA rol Genes during Regeneration via Somatic Embryogenesis in Tylophora indica

The fate of integrated Ri T-DNA rol genes during regeneration via indirect somatic embryogenesis and stability of its effect on morphology and tylophorine content of Ri-transformed plants have been studied in Tylophora indica. Integration and expression of Ri T-DNA genes in transformed embryogenic callus lines derived from transformed root lines, 300 Ri-transformed somatic embryos, and 23 Ri-transformed plant lines were analysed. Fifty root lines studied showed integration and expression of four rol genes of TL-DNA. Spontaneous regeneration via indirect somatic embryogenesis was obtained from root lines that were TL+/TR−. Stable integration and expression of rol genes were observed in root lines, embryogenic callus lines, and the spontaneously induced somatic embryos. Nineteen out of the 23 Ri-transformed plant lines and their clones showed phenotypic and genetic stability over the period of 3 years. Four Ri-transformed plants were morphologically similar to nontransformed plants but showed variation with the integration and expression of the rolA gene and absence of other rol genes. Variant Ri-transformed plant line A428#1-V showed highest tylophorine content (2.93±0.03 mg gDW−1) among plant lines studied. The effects of T-DNA genes on growth, morphology, and tylophorine content of the Ri-transformed plants were stable in the long term culture.

Production of triterpenoid anti-cancer compound taraxerol in Agrobacterium-transformed root cultures of butterfly pea (Clitoria ternatea L.)

Independent transformed root somaclones (rhizoclones) of butterfly pea (Clitoria ternatea L.) were established using explant co-cultivation with Agrobacterium rhizogenes. Rhizoclones capable of sustained growth were maintained under low illumination in auxin-free agar-solidified MS medium through subcultures at periodic intervals. Integration of T(L)-DNA rolB gene in the transformed rhizoclone genome was verified by Southern blot hybridization, and the transcript expression of T(R)-DNA ags and man2 genes was ascertained by reverse transcription polymerase chain reaction analysis. The major compound isolated and purified from the transformed root extracts was identified as the pentacyclic triterpenoid compound taraxerol using IR, (1)H-NMR, and (13)C-NMR spectroscopy. The taraxerol yield in cultured hairy roots, as quantified by HPTLC analysis, was up to 4-fold on dry weight basis compared to that in natural roots. Scanning of bands from cultured transformed roots and natural roots gave super-imposable spectra with standard taraxerol, suggesting a remarkable homology in composition. To date, this is the first report claiming production of the cancer therapeutic phytochemical taraxerol in genetically transformed root cultures as a viable alternative to in vivo roots of naturally occurring plant species.

Use of the cryptogein gene to stimulate the accumulation of Bacopa saponins in transgenic Bacopa monnieri plants

Genetic transformation of the Indian medicinal plant, Bacopa monnieri, using a gene encoding cryptogein, a proteinaceous elicitor, via Ri and Ti plasmids, were established and induced bioproduction of bacopa saponins in crypt-transgenic plants were obtained. Transformed roots obtained with A. rhizogenes strain LBA 9402 crypt on selection medium containing kanamycin (100 mg l(-1)) dedifferentiated forming callus and redifferentiated to roots which, spontaneously showed shoot bud induction. Ri crypt-transformed plants thus obtained showed integration and expression of rol genes as well as crypt gene. Ti crypt-transformed B. monnieri plants were established following transformation with disarmed A. tumefaciens strain harboring crypt. Transgenic plants showed significant enhancement in growth and bacopa saponin content. Bacopasaponin D (1.4-1.69 %) was maximally enhanced in transgenic plants containing crypt. In comparison to Ri-transformed plants, Ri crypt-transformed plants showed significantly (p ≤ 0.05) enhanced accumulation of bacoside A(3), bacopasaponin D, bacopaside II, bacopaside III and bacopaside V. Produced transgenic lines can be used for further research on elicitation in crypt-transgenic plants as well as for large scale production of saponins. Key message The cryptogein gene, which encodes a proteinaceous elicitor is associated with increase in secondary metabolite accumulation-either alone or in addition to the increases associated with transformation by A. rhizogenes.

Genetic transformation of Bacopa monnieri by wild type strains of Agrobacterium rhizogenes stimulates production of bacopa saponins in transformed calli and plants

We have developed an efficient transformation system for Bacopa monnieri, an important Indian medicinal plant, using Agrobacterium rhizogenes strains LBA 9402 and A4. Transformed roots induced by strain LBA 9402 spontaneously dedifferentiated to callus while excised roots induced by strain A4 spontaneously showed induction of shoot buds within 10 days. PCR and RT-PCR analysis revealed the presence and expression of the rolAB and rolC genes at the transcription level in pRi A4 transformed cultures indicating that the TL-DNA was integrated retained and expressed in the A4-Ri transformed shoots. Transformed calli showed the presence of rolAB or rol A, TR and ags genes. Transformed plants showed morphological features typically seen in transgenic plants produced by A. rhizogenes. Growth and biomass accumulation was significantly higher in the transformed shoots (twofold) and roots (fourfold) than in the non-transformed (WT) plants. In pRi A4-transformed plants, the content of bacopasaponin D, bacopasaponin F, bacopaside II and bacopaside V was enhanced significantly as compared to WT plants of similar age while bacoside A3 and bacopasaponin C content was comparable with that of WT plants. Significant increase in content of five bacopa saponins could be detected in pRi 9402-transformed callus cultures. There is an overall stimulatory effect on accumulation of bacopa saponins in transformed plants and cells of B. monnieri establishing the role of endogenous elicitation by Ri T-DNA of A. rhizogenes.

Transformation of Kalanchoe blossfeldiana with rol-genes is useful in molecular breeding towards compact growth

Dwarf genotypes of the economically important flowering potted plant Kalanchoe blossfeldiana were developed by molecular breeding. Root inducing (Ri)-lines were regenerated by applying CPPU to the hairy roots, which were produced by inoculating leaf explants with a wild-type Agrobacterium rhizogenes strain ATCC15834. Amplification by polymerase chain reaction (PCR) and Southern blot analysis confirmed the presence of T-DNA in the Ri-lines. Six Ri-lines were characterised in a greenhouse trial revealing that several morphological traits changed with respect to ornamental value such as plant height, number of lateral shoots, leaf size, leaf number, flower size and number of flowers. The Ri-lines differed in their degree of Ri-phenotype, and the internodes of the Ri-lines were clearly shorter, giving a compact growth habit compared to control plants. Time to anthesis was the same in Ri-line 331 as in control plants and delayed by only 3 days in Ri-line 306 as compared to control plants. A compact plant without delayed flowering can be assumed to be valuable for further breeding.