Virulence of different Agrobacterium strains on hairy root formation of Hyoscyamus muticus

Effect of silver nanoparticles on tropane alkaloid production of transgenic hairy root cultures of Hyoscyamus muticus L. and their antimicrobial activity

The utilization of nanotechnology and biotechnology for enhancing the synthesis of plant bioactive chemicals is becoming increasingly common. The hairy root culture technique can be used to increase secondary metabolites such as tropane alkaloids. Agrobacterium was used to induce hairy roots from various explants of Hyoscyamus muticus. The effect of nano-silver particles (AgNPs) at concentrations of 0, 25, 50, 100, and 200 mg/L on tropane alkaloids synthesis, particularly hyoscyamine and scopolamine, was studied in transgenic hairy root cultures. Different types of explants obtained from 10-day-old seedlings of H. muticus were inoculated with two strains of Agrobacterium rhizogenes (15,834 and A4). The antimicrobial activity of an ethanolic extract of AgNPs-induced hairy root cultures of H. muticus was tested. The frequency of hairy roots was higher in hypocotyl, root, leaf, and stem explants treated with A. rhizogenes strain A4 compared to those treated with strain 15,834. In transgenic hairy root cultures, AgNPs application at a concentration of 100 mg/L resulted in the highest total tropane alkaloid production, which exhibited broad-spectrum antimicrobial activity. The study demonstrated the potential of nano-silver as an elicitor for promoting the production of target alkaloids in Hyoscyamus muticus hairy root cultures, which exhibit high biological activity.

Critical points for the design and application of RNA silencing constructs for plant virus resistance

Control of plant virus diseases is a big challenge in agriculture as is resistance in plant lines to infection by viruses. Recent progress using advanced technologies has provided fast and durable alternatives. One of the most promising techniques against plant viruses that is cost-effective and environmentally safe is RNA silencing or RNA interference (RNAi), a technology that could be used alone or along with other control methods. To achieve the goals of fast and durable resistance, the expressed and target RNAs have been examined in many studies, with regard to the variability in silencing efficiency, which is regulated by various factors such as target sequences, target accessibility, RNA secondary structures, sequence variation in matching positions, and other intrinsic characteristics of various small RNAs. Developing a comprehensive and applicable toolbox for the prediction and construction of RNAi helps researchers to achieve the acceptable performance level of silencing elements. Although the attainment of complete prediction of RNAi robustness is not possible, as it also depends on the cellular genetic background and the nature of the target sequences, some important critical points have been discerned. Thus, the efficiency and robustness of RNA silencing against viruses can be improved by considering the various parameters of the target sequence and the construct design. In this review, we provide a comprehensive treatise regarding past, present and future prospective developments toward designing and applying RNAi constructs for resistance to plant viruses.

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.

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.

Establishment of hairy root cultures of Salvia bulleyana Diels for production of polyphenolic compounds

This study was to obtain stable transformed roots of Salvia bulleyana using A. rhizogenes strain A4 and then evaluate their phytochemical profile and selected the most productive clone. Our results indicated that the type of explant and medium used for bacterium and explant incubation had an influence on the frequency of hairy root formation. The best response was obtained on leaves infected with bacteria cultivated on YMB medium supplemented with acetosyringone. Of the four selected transformed root clones, after five-week cultivation in Woody Plant (WP) medium, the highest growth indexes were demonstrated for line C1: i.e. 13 for fresh and 15 for dry weight (81.4 and 8.2 g/l fresh and dry weight, respectively). The qualitative analysis of hydromethanolic extracts of hairy roots of S. bulleyana using UPLC-PDA-ESI-MS/MS method showed the presence of 10 polyphenolic compounds including predominant rosmarinic acid (RA), its derivatives (hexoside and methyl rosmarinate), caffeic acid, its derivatives and several salvianolic acids: K, E and F. Their production varied among the four root clones studied; the highest RA (39.6 mg/g dry weight) and total polyphenol (48.9 mg/g dry weight) level were found in the roots of C4 clone. These values were significantly higher than those of the roots of plants grown for several years under field conditions. The transformation of the obtained root cultures was confirmed by polymerase chain reaction using aux1, aux2, rolB, rolC and rolD primers.

Establishment of hairy root cultures by Agrobacterium rhizogenes mediated transformation of Trachyspermum ammi L. for the efficient production of thymol

Trachyspermum ammi is an important medicinal plant that contains a bioactive compound namely thymol. In the study, T. ammi was transformed by Agrobacterium rhizogenes strains. Seedling stem explants were inoculated with A. rhizogenes strains A4, LBA 9402, ATCC 15834, and the effect of different co-cultivation media along with incorporation of acetosyringone (100 µM) was evaluated comparatively on the frequency of hairy root induction. The polymerase chain reaction using rolB and virD specific primers was served to confirm the putative transformed hairy roots. All strains established hairy root with various frequencies, among which strain ATCC 15834 was significantly the most efficient strain for hairy root induction (84.3%). Half-strength B5 medium and incorporation of acetosiryngone (100 µM) were also significantly optimal for hairy root induction. Hairy roots culture induced by ATCC 15834 using half-strength B5 liquid medium supplemented with 30 g L^-1 sucrose indicated the highest accumulation of biomass (99.05 g L^-1 FW and 10.95 g L^-1 DW) and thymol content (11.30 mg g^-1 DM) at 20 days. Nearly 4.9-fold and 5.3-fold increment of biomass and thymol accumulation was observed, respectively, at 20 days in comparison with the untransformed control roots. The results showed the high potential of T. ammi hairy roots for the biosynthesis of thymol.

Comparison of Different Strains of Agrobacterium rhizogenes for Hairy Root Induction and Betulin and Betulinic Acid Production in Morus alba

Three Agrobacterium rhizogenes strains were tested for their ability to transform the plant Morus alba L. and to induce production of the secondary metabolites betulin and betulinic acid. All the tested strains of A. rhizogenes (R1601, LBA9402 and R1000) were able to induce hairy root formation in leaf tissue explants. Strain LBA9402 had the highest rate of infection (92.7% ± 8.8%), whereas strain R1601 had the lowest rate (87.4% ± 9.3%). The highest number of hairy roots per explant (5.6 ± 0.5) and the greatest root length (2.4 ± 0.2 mm) were obtained with strain LBA9402. We also evaluated dry weight (a measure of growth) and betulin and betulinic acid production in hairy roots and found that the highest growth (167.8 ± 14.5 mg/flask) occurred after infection with strain LBA9402. Furthermore the highest production of betulin (5.4 ± 0.4 mg/g dry weight) and betulinic acid (2.3 ± 0.2 mg/g dry weight) was noted using strain LBA9402. Among three elicitors, yeast extract showed the highest induction of betulin production (8.7 ± 0.4 mg/g) and silver nitrate induced the highest yield of betulinic acid (4.1 ± 0.2 mg/g). Our study showed that A. rhizogenes strain LBA9402 was the most effective of the three tested strains for production of transformed root cultures and betulin and betulinic acid.

Establishment of transgenic Rhazya stricta hairy roots to modulate terpenoid indole alkaloid production

Transgenic hairy roots of R. stricta were developed for investigation of alkaloid accumulations. The contents of five identified alkaloids, including serpentine as a new compound, increased compared to non-transformed roots. Rhazya stricta Decne. is a rich source of pharmacologically active terpenoid indole alkaloids (TIAs). In order to study TIA production and enable metabolic engineering, we established hairy root cultures of R. stricta by co-cultivating cotyledon, hypocotyl, leaf, and shoot explants with wild-type Agrobacterium rhizogenes strain LBA 9402 and A. rhizogenes carrying the pK2WG7-gusA binary vector. Hairy roots initiated from the leaf explants 2 to 8 weeks. Transformation was confirmed by polymerase chain reaction and in case of GUS clones with GUS staining assay. Transformation efficiency was 74 and 83% for wild-type and GUS hairy root clones, respectively. Alkaloid accumulation was monitored by HPLC, and identification was achieved by UPLC-MS analysis. The influence of light (16 h photoperiod versus total darkness) and media composition (modified Gamborg B5 medium versus Woody Plant Medium) on the production of TIAs were investigated. Compared to non-transformed roots, wild-type hairy roots accumulated significantly higher amounts of five alkaloids. GUS hairy roots contained higher amounts two of alkaloids compared to non-transformed roots. Light conditions had a marked effect on the accumulation of five alkaloids whereas the composition of media only affected the accumulation of two alkaloids. By successfully establishing R. stricta hairy root clones, the potential of transgenic hairy root systems in modulating TIA production was confirmed.

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.

An efficient protocol for genetic transformation of Platycodon grandiflorum with Agrobacterium rhizogenes

The balloon flower (Platycodon grandiflorum) is a popular traditional medicinal plant used in Korea to treat conditions such as bronchitis, asthma, tuberculosis, diabetes, and inflammatory diseases. Recently, immunopharmacological research identified triterpenoid and saponin as important active compounds in P. grandiflorum. To study and extract these compounds and other metabolites from P. grandiflorum, a technique was developed for producing hairy root cultures, which are a reliable source of plant compounds. To achieve this, the activity of Agrobacterium rhizogenes was exploited, which can transfer DNA segments into plant genomes after infecting them. In this study, the A. rhizogenes strain R1000 was determined that had the highest infection frequency (87.5%) and induced the most hairy roots per plant, and the concentration of antibiotics (75 mg/l kanamycin) was elucidated for selection after transformation. Wild-type and transgenic hairy roots contained various phenolic compounds, although both of them had similar concentrations of phenolic compounds. In the future, the protocols described here should be useful for studying and extracting valuable metabolites such as phenolic compounds from P. grandiflorum hairy root cultures.

Green fluorescent protein as an efficient selection marker for Agrobacterium rhizogenes mediated carrot transformation

Agrobacterium rhizogenes mediated transformation combined with a visual selection for green fluorescent protein (GFP) has been applied effectively in carrot (Daucus carota L.) transformation. Carrot root discs were inoculated with A4, A4T, LBA1334 and LBA9402 strains, all bearing gfp gene in pBIN-m-gfp5-ER. The results indicate that transformed adventitious roots can be visually selected solely based on GFP fluorescence with a very high accuracy. The method requires no selection agents like antibiotics or herbicides and enables a reduction of labour and time necessary for tissue culture. Moreover, individual transformants can be easily excised from the host tissue and cultured separately. All of the 12 used carrot cultivars produced transformed adventitious roots and the frequency of discs producing GFP expressing adventitious roots varied from 13 to 85%. The highest transformation rate was found for A4T and LBA1334 strains possessing chromosomal background of A. tumefaciens C58. The results encourage that visual selection of transformed, fluorescing adventitious roots can be highly effective and applied routinely for the production of carrot transgenic plants.

Simultaneous determination of scopolamine, hyoscyamine and littorine in plants and different hairy root clones of Hyoscyamus muticus by micellar electrokinetic chromatography

Hyoscyamus muticus hairy root clones were established following infection with Agrobacterium rhizogenes strains A4, LBA-9402 and 15834 and with A. tumefaciens strain C58C1pRTGus104. The accumulation of tropane alkaloids hyoscyamine, littorine and scopolamine was evaluated by micellar electrokinetic capillary electrophoresis. Littorine was reported for the first time in these clones as well as in the roots of the intact plant and confirmed by collision induced dissociation-mass spectrometry. Tropane alkaloid content in hairy roots was compared with leaves and roots of normal plants at two vegetative stages. Significant differences appeared between the alkaloid contents of the different clones. In particular, all the hairy root clones and the roots of the intact plant produced 1.5-3 and 4.5-9 times more littorine than scopolamine, respectively. The only exception was clone KB7, carrying the h6h gene, which overproduced scopolamine. The aerial parts of H. muticus plants did not contain any littorine, thus indicating different transportation or translocation mechanisms of the various tropane alkaloids.

Transgenic hairy roots

Agrobacterium rhizogenes causes hairy root disease in plants. The neoplastic roots produced by A. rhizogenes infection is characterized by high growth rate and genetic stability. These genetically transformed root cultures can produce higher levels of secondary metabolites or amounts comparable to that of intact plants. Hairy root cultures offer promise for production of valuable secondary metabolites in many plants. The main constraint for commercial exploitation of hairy root cultures is their scaling up, as there is a need for developing a specially designed bioreactor that permits the growth of interconnected tissues unevenly distributed throughout the vessel. Rheological characteristics of heterogeneous system should also be taken into consideration during mass scale culturing of hairy roots. Development of bioreactor models for hairy root cultures is still a recent phenomenon. It is also necessary to develop computer-aided models for different parameters such as oxygen consumption and excretion of product to the medium. Further, transformed roots are able to regenerate genetically stable plants as transgenics or clones. This property of rapid growth and high plantlet regeneration frequency allows clonal propagation of elite plants. In addition, the altered phenotype of hairy root regenerants (hairy root syndrome) is useful in plant breeding programs with plants of ornamental interest. In vitro transformation and regeneration from hairy roots facilitates application of biotechnology to tree species. The ability to manipulate trees at a cellular and molecular level shows great potential for clonal propagation and genetic improvement. Transgenic root system offers tremendous potential for introducing additional genes along with the Ri T-DNA genes for alteration of metabolic pathways and production of useful metabolites or compounds of interest. This article discusses various applications and perspectives of hairy root cultures and the recent progress achieved with respect to transformation of plants using A. rhizogenes.

Chemicals from roots, hairy roots, and their application

Plants produce thousands of different compounds through the secondary metabolism pathways. Since many of these products are obtained by direct extraction from plants that are cultivated in the field or some times even collected in their original habitat several factors can alter their yield. The use of plant cell cultures has overcome several inconveniences for the production of secondary metabolites. Organized cultures, and especially root cultures, can make a significant contribution to our understanding of secondary metabolism. Furthermore, a new alternative has arisen: transformed root cultures. Until now, hairy roots have been obtained from more than 100 different species. The products that they are able to produce range from alkaloids to aromatic compounds and dyes. These kinds of cultures have turned out to be an invaluable tool to study the biochemistry and the gene expression of the metabolic pathways in order to elucidate the intermediaries and enzymes involved in the biosynthesis of secondary metabolites.