Olive (Olea europaea L.) Genetic Transformation: Current Status and Future Prospects

Olive (Olea europaea L.) is the most characteristic and important oil crop of the Mediterranean region. Traditional olive cultivation is based on few tens cultivars of ancient origin. To improve this crop, novel selections with higher tolerance to biotic and abiotic stress, adaptable to high-density planting systems and resilient to climate change are needed; however, breeding programs are hindered by the long juvenile period of this species and few improved genotypes have been released so far. Genetic transformation could be of great value, in the near future, to develop new varieties or rootstocks in a shorter time; in addition, it has currently become an essential tool for functional genomic studies. The recalcitrance of olive tissues to their in vitro manipulation has been the main bottleneck in the development of genetic transformation procedures in this species; however, some important traits such as fungal resistance, flowering or lipid composition have successfully been manipulated through the genetic transformation of somatic embryos of juvenile or adult origin, providing a proof of the potential role that this technology could have in olive improvement. However, the optimization of these protocols for explants of adult origin is a prerequisite to obtain useful materials for the olive industry. In this review, initially, factors affecting plant regeneration via somatic embryogenesis are discussed. Subsequently, the different transformation approaches explored in olive are reviewed. Finally, transgenic experiments with genes of interest undertaken to manipulate selected traits are discussed.

Hairy Root Culture an Alternative for Bioactive Compound Production from Medicinal Plants

Medicinal plants produce a diverse group of phytocompounds like anthraquinones, alkaloids, anthocyanins, flavonoids, saponins, and terpenes which are used in pharmaceutical, perfume, cosmetics, dye and flavor industries. Commercial source of these metabolites is field-grown plants, which are generally influenced by seasonal changes. Biotechnology possesses a significant role in production of high-value secondary metabolites. By incorporating biotechnological methods, it is feasible to manage biosynthetic pathways of the plant to enhance phytocompound production that is of pharmaceutical interest. Plant cell suspension, shoot, adventitious root and hairy root culture are considered as alternative methods for important bioactive compound production. These methods are controllable, sustainable and overcome several inconveniences for large scale secondary metabolites production. At present research on hairy root culture for valuable bioactive compound production has gained a lot of attention. Agrobacterium rhizogenes is an agent which causes hairy root disease in a plant and this leads to the neoplastic growth of root which is characterized by higher growth rate and genetic stability. Various studies explore the hairy root culture for production of a wide range of bioactive compounds. Scale-up of hairy root culture using bioreactors has provided an opportunity to enhance bioactive compound production at the commercial level. The present review discusses the role of hairy root culture in the production of valuable bioactive compounds, the effect of culture parameters on bioactive compound production and bioreactor applications.

Establishment of Agrobacterium rhizogenes-mediated hairy root transformation of Crocus sativus L

Efficient transformation system for genetic improvement is essential in Crocus sativus, as it lacks sexual reproduction. This is the first report wherein an efficient protocol is developed for the transformation of Crocus sativus L. by Agrobacterium rhizogenes strain ARqua1 with a transformation efficiency of 78.51%. The ARqua1 strain harboring both Ri plasmid and binary vector plasmid pSITE-4NB, and marker genes for red fluorescent protein (RFP) and a β-glucuronidase (GUS) reporter gene were used for selection. Transformation was confirmed by RFP signal, GUS reporter assay and polymerase chain reaction (PCR) analysis of the test samples after 21 days post inoculation. These results confirm the establishment of protocol for hairy root transformation in C. sativus that can be further used for gene transfer or gene editing in Crocus for its genetic improvement.

Gene Assembly in Agrobacterium via Nucleic Acid Transfer Using Recombinase Technology (GAANTRY)

Plant biotechnology provides a means for the rapid genetic improvement of crops including the enhancement of complex traits like yield and nutritional quality through the introduction and coordinated expression of multiple genes. GAANTRY (gene assembly in Agrobacterium by nucleic acid transfer using recombinase technology) is a flexible and effective system for stably stacking multiple genes within an Agrobacterium virulence plasmid transfer DNA (T-DNA) region. The system provides a simple and efficient method for assembling and stably maintaining large stacked constructs within the GAANTRY ArPORT1 Agrobacterium rhizogenes strain. The assembly process utilizes unidirectional site-specific recombinases in vivo and an alternating bacterial selection scheme to sequentially assemble multiple genes into a single transformation construct. A detailed description of the procedures used for bacterial transformation, selection, counter selection, and genomic PCR validation with the GAANTRY system are presented. The methods described facilitate the efficient assembly and validation of large GAANTRY T-DNA constructs. This powerful, yet simple to use, technology will be a convenient tool for transgene stacking and plant genetic engineering of rice and other crop plants.

Harnessing the Potential of Roots of Traditional Power Plant: Ocimum

Genus Ocimum of Labiatae is well known in all traditional medicinal systems like Ayurveda, Unani, Siddha, and Homeopathy. The pharmaceutical activities of different species of Ocimum attributed to all plant parts. Roots are the most significant vital organ of the plant, as they absorb water and nutrients from soil and transport to aerial parts of the plants. Roots of Ocimum were found helpful with free-radical scavenging activity to improve physical and mental strength as well as to treat diabetes, malaria, and liver problems. Antibacterial activity of Ocimum roots and its main component, rosmarinic acid, is very beneficial to protect against several human pathogens, including bacteria and viruses. Being so important in every way, roots of Ocimum need healthy rhizosphere. Bacteria, fungi, nematodes, types of soil, fungicide, pesticides, salt, radioactive elements, as well as heavy metal contaminations, affect roots and overall growth of Ocimum in positive or negative ways. Each component of rhizosphere (natural, treatment or contamination) affects the roots, which highlights current ecological scenario to discover biosafe and more productive approaches. For such prestigious organ of Ocimum, development of in vitro root cultures and hairy root cultures assists to reduce the efforts and timing of the traditional cultivation process along with elimination of negative factors in rhizosphere. Different strains of Agrobacterium rhizogenes, various media compositions, as well as discrete treatments, like elicitors, on nonidentical species or cultivars of Ocimum boost the root induction, biomass, and accumulation of phytoceuticals differently. Hairy roots and in vitro roots of Ocimum accumulate higher quantity of therapeutic metabolites. These metabolites include several phenolics (like rosmarinic acid, 3-hydroxybenzoic acid, m-coumaric acid, p-coumaric acid, caffeic acid, ferulic acid, vanillic acid, chicoric acid, and lithospermic acid), triterpenes (such as betulinic acid, 3-epimaslinic acid, alphitolic acid, euscaphic acids, oleanolic acid, and ursolic acid) as well as flavonoids (flavones, flavonols, and dihydroflavonols). This review highlights pharmaceutical applications of Ocimum roots, a great deal of rhizosphere components and in vitro culturing techniques to enhance biomass as well as chief phytoceuticals.

Effect of different Agrobacterium rhizogenes strains for in-vitro hairy root induction, total phenolic, flavonoids contents, antibacterial and antioxidant activity of (Cucumis anguria L.)

The present study aimed to investigate the effect of different Agrobacterium rhizogenes on the induction of hairy root of Cucumis anguria and determine its total phenolic, flavonoids contents, antibacterial and antioxidant activity. In this investigation A. rhizogenes strains such as, 15834, 13333, A4, R1200, R1000, LBA9402, R1301 and R1601 are all investigated, were developing hairy root conception in cotyledon and leaf tissue explants. Polymerase chain response (PCR) and the converse transcription-PCR are transgenic clones of hairy roots has been utilized rolA and rolB particular primers. In the middle of the different attention of better regulators the extreme transformation frequency was achieved in (IBA + NAA) cotyledon explant. Transgenic hairy roots increase in MS liquid medium added to with IBA + NAA (2.46 + 1.07) displayed the maximum accumulation of biomass 0.68 g/l dry weight (DW) and 6.52 ± 0.49 g/l fresh weight (FW) were obtained at the 21 days of cotyledon explant. The flavonoid and total phenolic contents were estimated using aluminium chloride method and Folin-Ciocalteu method. The amount of phenolic compounds in Cucumis anguria L non transformed root (124.46 ± 6.13 mg GA/g) was lower than that in the methanol extracts of Cucumis anguria L. hairy roots (160.38 ± 5.0 mg GA/g), being was Cucumis anguria L non transformed root lower (42.93 ± 1.58 mg rutin/g) than that in the concentration of total flavonoids in Cucumis anguria L. hairy root (16.26 ± 1.84 mg rutin/g). Additionally, transgenic hairy roots professionally produced various phenolic and flavonoid composites. The total antimicrobial activity, phenolics, flavonoids content and antioxidant were more in the hairy roots related to non-transformed roots. In our discovery, the A. rhizogenes R1000 is promising candidate for hairy root initiation of C. anguria from cotyledone explants were realized large number of hairy roots compared with leaf explants. The antioxidant potential of methanol extracts of flavonoid and phenolic compounds from the hairy roots have great potential to treat various diseases.

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.

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.

Insight in the transcriptome data of hairy root disease-causing bacterium-Agrobacterium rhizogenes

Agrobacterium rhizogenes induce the production of the hairy root through the transformation of plant genomes. In this article, we executed the transcriptome of A. rhizogenes through RNA-sequencing. RNA-sequencing of A. rhizogenes generated a total of 2.6 Gb raw data with a 75 bp paired-end sequence. The raw data has been submitted to the SRA database of NCBI with accession number SRR5641651. Reads were generated 2946 unigenes and all unigenes were annotated in the database. The length of transcripts ranged from 90 to 6369 bp, with a median transcript length of 968. The transcripts were annotated through the number of databases to obtain information about SSRs, SNPs, Gene Ontology, Transcription factors, and pathways analysis .

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.

Steviol glycosides profile in Stevia rebaudiana Bertoni hairy roots cultured under oxidative stress-inducing conditions

The ability to synthesize particular steviol glycosides (SvGls) was studied in Stevia rebaudiana Bertoni hairy roots (HR) grown in the light or in the dark under the influence of different osmotic active compounds. Manipulation of culture conditions led to changes in the morphology and growth rate of HR, as well as to an increase in oxidative stress manifested as an enhancement in endogenous hydrogen peroxide concentration in the cultured samples. The highest level of H₂O₂ was noted in HR cultured under light or in the medium with the highest osmotic potential. This correlated with the highest increase in the expression level of ent-kaurenoic acid hydroxylase, responsible for the redirection of metabolic route to SvGls biosynthesis pathway. An analysis of transcriptional activity of some UDPglucosyltransferase (UGT85c2, UGT74g1, UGT76g1) revealed that all of them were upregulated due to the manipulation of culture conditions. However, the level of their upregulation depended on the type of stress factor used in our experiment. Analysis of SvGls content revealed that HR grown under all applied conditions were able to synthesize and accumulate several SvGls but their concentration differed between the samples across the different conditions. The level of rebaudioside A concentration exceeded the content of stevioside in HR in all tested conditions. Concomitantly, the presence of some minor SvGls, such as steviolbioside and rebaudioside F, was confirmed only in HR cultured in the lowest osmotic potential of the medium while rebaudioside D was also detected in the samples cultured in the media supplemented with NaCl or PEG.Key Points● Several steviol glycosides are synthesized in hairy roots of S. rebaudiana.● Light or osmotic factors cause enhancement in oxidative stress level in hairy roots.● It correlates with a significant increase in the level of KAH expression.● UGTs expression and steviol glycosides content depends on culture conditions.

One-step generation of composite soybean plants with transgenic roots by Agrobacterium rhizogenes-mediated transformation

BACKGROUND

Agrobacterium rhizogenes-mediated (ARM) transformation is a highly efficient technique for generating composite plants composed of transgenic roots and wild-type shoot, providing a powerful tool for studying root biology. The ARM transformation has been established in many plant species, including soybean. However, traditional transformation of soybean, transformation efficiency is low. Additionally, the hairy roots were induced in a medium, and then the generated composite plants were transplanted into another medium for growth. This two-step operation is not only time-consuming, but aggravates contamination risk in the study of plant-microbe interactions.

RESULTS

Here, we report a one-step ARM transformation method with higher transformation efficiency for generating composite soybean plants. Both the induction of hairy roots and continuous growth of the composite plants were conducted in a single growth medium. The primary root of a 7-day-old seedling was decapitated with a slanted cut, the residual hypocotyl (maintained 0.7-1 cm apical portion) was inoculated with A. rhizogenes harboring the gene construct of interest. Subsequently, the infected seedling was planted into a pot with wet sterile vermiculite. Almost 100% of the infected seedlings could produce transgenic positive roots 16 days post-inoculation in 7 tested genotypes. Importantly, the transgenic hairy roots in each composite plant are about three times more than those of the traditional ARM transformation, indicating that the one-step method is simpler in operation and higher efficiency in transformation. The reliability of the one-step method was verified by CRISPR/Cas9 system to knockout the soybean Rfg1, which restricts nodulation in Williams 82 (Nod-) by Sinorhizobium fredii USDA193. Furthermore, we applied this method to analyze the function of Arabidopsis YAO promoter in soybean. The activity of YAO promoter was detected in whole roots and stronger in the root tips. We also extended the protocol to tomato.

CONCLUSIONS

We established a one-step ARM transformation method, which is more convenient in operation and higher efficiency (almost 100%) in transformation for generating composite soybean plants. This method has been validated in promoter functional analysis and rhizobia-legume interactions. We anticipate a broad application of this method to analyze root-related events in tomato and other plant species besides soybean.

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.

Agrobacterium rhizogenes-mediated transformation enhances the antioxidant potential of Artemisia tilesii Ledeb

Plants belonging to the genus Artemisia L. have been used for medicinal purposes since ancient times. These aromatic plants produce and accumulate a wide range of potent secondary metabolites, many of which have shown antioxidant, antiparasitic, antimicrobial, anti-inflammatory, and even anticancer activities. Enhanced biosynthesis of these compounds is a prerequisite for comprehensive studies of their therapeutic properties and cost-efficient use. Transformation of plants with Agrobacterium rhizogenes native root locus (rol) genes is a promising approach to increase the biosynthesis of plant secondary metabolites. The aim of the present study was to evaluate the effects of A. rhizogenes-mediated transformation on the flavonoid contents in hairy roots of medicinal herb A. tilesii Ledeb. Transgenic A. tilesii hairy root lines were analyzed for stable integration of the rolB and rolC transgenes into the plant genome, total flavonoid contents, antioxidant activities of extracts, and the spatiotemporal expression of two flavonoid biosynthetic genes, phenylalanine ammonialyase (PAL) and chalcone synthase (CHS). The flavonoid contents of A. tilesii directly correlated with the antiradical activity and reducing power of their respective lines, with the greatest antioxidant activity found in the plants with the highest level of total flavonoids. Furthermore, all hairy root lines demonstrated altered expression of plant native PAL and CHS genes. Most importantly, A. rhizogenes-mediated transformation enhanced the biosynthesis of natural antioxidants in A. tilesii, producing almost twice the amount of flavonoids than controls. These findings provide an opportunity for the identification of the bioactive molecules in A. tilesii extracts and their potential health benefits.

Novel method for improving ardicrenin content in hairy roots of Ardisia crenata Sims plants

To develop an alternative medicine related with taxol/camptothecin, a hairy roots induction system for measuring triterpenoid saponin ardicrenin was established. In the current study, mature and healthy seeds of Ardisia crenata plants were selected for obtaining aseptic seedlings. Two Agrobacterium rhizogenes strains ATCC 15834 and A4 were used to infect aseptic euphylla for inducing hairy roots of A. crenata plants. For the best combination of seeds germination, a Murashige-Skoog medium containing 1.0 mg L^-1 6-benzylaminopurine and 1.0 mg L^-1 naphthalene acetic acid was made, which reached a rate of 92.4 %. Results showed that ATCC 15834 and A4 both induced hairy roots of A. crenata for improving ardicrenin production. The PCR analysis demonstrated that ATCC 15834 and A4 Ri plasmid T-DNA had been successfully transferred and integrated into the genome of leaf cell nuclei, however the Vir region was not. Further, ardicrenin content in hairy roots ACHR 15834 8.2 %) induced by ATCC 15834 was quantified by the RP-HPLC, which was also 1.8-, 2.7-, 9.4- and 2.6-fold greater than those of ACHR 4 induced by A4 (4.5 %), ACR C formed by tissue culture (3.1 %), euphylla (0.8 %) and NR C formed nature (3.2 %), respectively. Taken together, hairy root lines of A. crenata obtained were able to express naturally more ardicrenin than natural plants.

Hairy Root Cultures-A Versatile Tool With Multiple Applications

Hairy roots derived from the infection of a plant by Rhizobium rhizogenes (previously referred to as Agrobacterium rhizogenes) bacteria, can be obtained from a wide variety of plants and allow the production of highly diverse molecules. Hairy roots are able to produce and secrete complex active glycoproteins from a large spectrum of organisms. They are also adequate to express plant natural biosynthesis pathways required to produce specialized metabolites and can benefit from the new genetic tools available to facilitate an optimized production of tailor-made molecules. This adaptability has positioned hairy root platforms as major biotechnological tools. Researchers and industries have contributed to their advancement, which represents new alternatives from classical systems to produce complex molecules. Now these expression systems are ready to be used by different industries like pharmaceutical, cosmetics, and food sectors due to the development of fully controlled large-scale bioreactors. This review aims to describe the evolution of hairy root generation and culture methods and to highlight the possibilities offered by hairy roots in terms of feasibility and perspectives.

Establishment of in vitro culture system for Codonopsis pilosula transgenic hairy roots

The aim of the study was to establish a reliable system of transgenic hairy roots in Codonopsis pilosula through Agrobacterium-mediated genetic transformation. For this, we optimized several steps in the process of A. rhizogenes strain C58C1 mediated hairy root induction, including the most appropriate medium, explant type, time for infection and co-cultivation. We achieved an induction rate of up to 100% when the roots of C. pilosula seedlings were used as explants, infected with A. rhizogenes C58C1 harboring pCAMBIA1305 for 5 min, followed by induction on 1/2MS supplemented with 0.2 mg/L naphthylacetic acid and 200 mg/L cefotaxime sodium. The co-transformed hairy roots were confirmed by PCR amplification of hygromycin phosphotransferase II gene and histochemical GUS assay, and the efficiency of transformation was 70% and 68.3%, respectively, when no hygromycin selection pressure was exerted. To increase biomass production, we excised and self-propagated the transformed hairy roots, which produce saponins. Our successful establishment of an in vitro culture system of transgenic hairy root for this species lays the foundation not only for assessing gene expression and function but also for obtaining high levels of secondary metabolites through genetic engineering technology.

Antioxidative enzymes activities and accumulation of steroids in hairy roots of Trigonella

Steroidal sapogenins and phytosterols are a group of secondary metabolites which are very considerable in the pharmaceutical industry. Fenugreek (Trigonella foenum-graecum L.) is the good source of these compounds. In recent decades, there is a great interest to production of these compounds by cultivation of transformed roots. In present study, hairy roots induction in two Trigonella species (T. foenum-graeceum, T. monantha) with three strains of Agrobacterium rhizogenes (15,834, A4 and wt) was investigated. Transgenic status of roots was confirmed by PCR using rolB specific primers. Virulence of these strains was examined on explants of leaf, leaf cotyledone and hypocotyle in both species. The best strain was wt for hairy root induction in hypocotyle and leaf explants of T. foenum-graeceum and T. monantha. Significant quantitative differences were showed between shoot, root and hairy roots in both species. Protein content in root and hairy root of both species was significantly lower in comparison with shoot. Superoxide dismutase (SOD) and peroxidase (POX) activities in hairy roots of both species were higher as compared to other organs. The hairy roots of both species showed an ability to synthesize steroidal sapogenins. These results presented that hairy roots could be a suitable procedure for producing sapogenins compounds that have medicinal value in Trigonella.

Effect of far-red light exposure on photosynthesis and photoprotection in tomato plants transgenic for the Agrobacterium rhizogenes rolB gene

Previous work showed in tomato plants harbouring the Agrobacterium rhizogenes rolB gene overexpression of genes involved in chloroplast function and stress response, significant increase in non-photochemical quenching and chlorophyll a and b content, and reduced chlorophyll a/b ratio. The latter condition being typical of plant shade where far-red is dominant, suggested a role for rolB in improving photosynthesis in such condition. To gain a better insight into these results, the photosynthetic performance of transgenic and control plants was compared by means of variable fluorescence kinetics with a WATER-PAM chlorophyll fluorometer, after 6 days-exposure to white light and to a far-red-enriched light source. Photosynthetic parameters analysed were quantum yield of photosystem II photochemistry Y(II); q_L, corresponding to the fraction of open PSII reaction centers in a "lake" model of photosystem II; non-photochemical quenching and Y(NO), describing, respectively, regulated and non-regulated pathways for dissipation of excess energy. Chlorophyll a and b content was also analysed by HPLC. Finally, real-time PCR was performed to quantify the expression level of some of the chloroplast-related genes already shown to be overexpressed in transgenic plants. Quantum yield of photosystem II photochemistry decreased with increasing light intensity, showing no significant differences in both plant genotypes and light regimen. q_L, on the other hand, was significantly higher at low PAR intensities, in particular in FR-treated transgenic plants. Fate of remaining light energy, channelled into regulated or non-regulated dissipation pathways, was different in transgenic and control plants, indicating a higher capability for protection from photodamage in rolB plants, particularly after exposure to far-red-enriched light. Chlorophyll a/b ratio was also decreased in transgenic plants under far-red-enriched light with respect to white light. Finally, qPCR showed that the expression of genes encoding small heat shock protein, chlorophyll a/b binding protein and carbonic anhydrase was significantly induced by far-red-enriched condition. Taken together, these data suggest the involvement of rolB in photosynthesis modulation under far-red-rich light in tomato.

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.

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.

Antibody-Mediated Resistance to Rhizomania Disease in Sugar Beet Hairy Roots

Agrobacterium rhizogenes-mediated transformation of sugar beet hairy roots expressing single-chain variable fragment (scFv) was exploited to evaluate the efficacy of four antibody-based constructs for interfering with the Beet necrotic yellow vein virus infection. The scFv specific to a major coat protein of virus, p21, was targeted to various cellular compartments including the cytosol (pIC and pICC constructs), apoplast (pIA), and mitochondrion (pIM). After mechanical virus inoculation, most of the hairy root clones expressing scFv in the cytosol displayed low virus titers while the majority of transgenic hairy root clones accumulated antibody in outer membrane of mitochondria or apoplast were infected. This hairy root system provided an efficient and rapid approach to initially investigating root disease resistance like rhizomania prior to transform whole recalcitrant plants such as sugar beet.

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.

A critical review on use of Agrobacterium rhizogenes and their associated binary vectors for plant transformation

Agrobacterium rhizogenes, along with A. tumefaciens, has been used to affect genetic transformation in plants for many years. Detailed studies conducted in the past have uncovered the basic mechanism of foreign gene transfer and the implication of Ri/Ti plasmids in this process. A number of reviews exist describing the usage of binary vectors with A. tumefaciens, but no comprehensive account of the numerous binary vectors employed with A. rhizogenes and their successful applications has been published till date. In this review, we recollect a brief history of development of Ri-plasmid/Ri-T-DNA based binary vectors systems and their successful implementation with A. rhizogenes for different applications. The modification of native Ri plasmid to introduce foreign genes followed by development of binary vector using Ri plasmid and how it facilitated rapid and feasible genetic manipulation, earlier impossible with native Ri plasmid, have been discussed. An important milestone was the development of inducible plant expressing promoter systems which made expression of toxic genes in plant systems possible. The successful application of binary vectors in conjunction with A. rhizogenes in gene silencing and genome editing studies which are relatively newer developments, demonstrating the amenability and adaptability of hairy roots systems to make possible studying previously intractable research areas have been summarized in the present review.

Agrobacterium rhizogenes-induced soybean hairy roots versus Soybean mosaic virus (ARISHR-SMV) is an efficient pathosystem for studying soybean-virus interactions

BACKGROUND

Soybean mosaic virus (SMV), a Potyvirus, is the most prevalent viral pathogen of soybean that causes severe yield and seed quality reductions in world soybean production. So far, multiple resistance loci for different SMV strains have been fine-mapped while the candidate genes' functions need to be verified. However, identification of the resistance or susceptibility genes via stable genetic transformation is time-consuming and labor-intensive, which hinders further exploration of these genes' functions in soybean. Thus we tried to explore a rapid and efficient method for verification of SMV-related target gene function in soybean.

RESULTS

An Agrobacterium rhizogenes (A. rhizogenes) induced soybean hairy roots versus Soybean mosaic virus (ARISHR-SMV) pathosystem was established. The procedure is characterized with that (1) the soybean hairy roots that can be infected by SMV are induced by A. rhizogenes K599 using soybean cotyledons as explants, (2) the gene to be examined for its function, which may be the endogenous SMV-resistance or -susceptible gene or exogenous SMV-related gene, is transformed into soybean calluses mediated by A. rhizogenes, (3) the transformed calluses on explants further inoculated with the purified tester-SMV virions using pricking method under aseptic conditions, and (4) the measurement of the SMV content in positive hairy roots for evaluating the SMV-related target gene function. The procedure takes about 30 days for one cycle. Utilizing the established procedure, the soybean hairy roots induced by A. rhizogenes was efficiently infected by multiple different SMV strains, the SMV infectivity in soybean hairy roots can be retained at least twice successive transfer cultures and Tomato bushy stunt virus (TBSV) P19 promoting and SMV CP suppressing SMV infection in soybean hairy roots was demonstrated, respectively. This procedure can also be used for identification of resistance to SMV strains for soybean germplasms.

CONCLUSION

The ARISHR-SMV is an efficient pathosystem that allows a quick and convenient identification of SMV-related target gene function in soybean.