Withanolide production by root cultures of Withania somnifera transformed with Agrobacterium rhizogenes

Optimization of Elicitation Conditions to Enhance the Production of Potent Metabolite Withanolide from Withania somnifera (L.)

This study aimed at optimizing conditions for increased withanolide production in Withania somnifera. The elicitors used for the foliar spray on the aerial parts of the plant were salicylic acid, jasmonic acid, and chitosan for the enhancement of withanolides in Withania somnifera under different environmental regimes. Three different elicitors, i.e., chitosan, jasmonic acid and salicylic acid, were applied on the plants through foliar route every 15th day for 6 months, and later plants were used for sample preparation. Further, the elicitors were used in different concentration, i.e., jasmonic acid (50, 200 and 400 ppm), chitosan (10, 50 and 100 ppm) and salicylic acid (0.5, 1 and 2 ppm). The elicitors were sprayed on the foliar parts of the plant between 10:00-11:00 a.m. on application days. For elicitor spray, a calibrated sprayer was used. The withanolide A/withaferin A was quantified through HPLC. It was found that in an open environment, maximum withaferin A content, i.e., 0.570 mg/g (DW), was recorded with jasmonic acid (50 ppm) treatment in comparison to control (0.067 mg/g DW). Thus, there was an 8.5-fold increase in the withaferin A content. Maximum withanolide A content of 0.352 mg/g (DW) was recorded when chitosan (50 ppm) was sprayed, while in the control, withanolide A content was recorded to be 0.031 mg/g (DW); thus, chitosan application increased the production of withanolide A by 11.3-fold. Under controlled conditions, maximum withaferin A content of 1.659 mg/g (DW) was recorded when plants were sprayed with chitosan (100 ppm), which was 8.1 times greater than the control content of 0.203 mg/g (DW). Maximum withanolide A content of 0.460 mg/g (DW) was recorded when chitosan (100 ppm) was applied, whereas in the control, withanolide A content was found to be 0.061 mg/g (DW). Thus, foliar spraying of elicitors in very low concentrations can serve as a low-cost, eco-friendly, labor-intensive and elegant alternative approach that can be practiced by farmers for the enhancement, consistent production and improved yield of withanolide A/withaferin A. This can be a suitable way to enhance plant productivity, thus increasing the availability of withanolide A and withaferin A for the health and pharma industry.

Metabolomic and biotechnological approaches to determine therapeutic potential of Withania somnifera (L.) Dunal: A review

BACKGROUND

Withania somnifera, a high value medicinal plant is a major source of pharmaceutically important active compounds withanolides. Withania somnifera has been used in ayurveda as health restorative and anabolic agent besides having anti-arthritic, antidepressant, anti-microbial, anti-inflammatory, anti-diabetic, anti-stress, neuroprotective and cardio-protective activities.

HYPOTHESIS/PURPOSE

The mining of the compound(s) of interest offers opportunity to identify desired attributes in the therapeutic area of interest. Metabolomic has become an important tool in the field of pharmacological and functional genomics of medicinal plants. The analysis supports the information regarding differential outline of the gene expression for increasing important withanolides viz. withanolide A and withaferin A in W. somnifera.

STUDY DESIGN

The bioinformatics and biotechnological approaches viz. tissue culture, genetic transformation, genomic, transcriptomic, proteomic, gene mining and metabolomic studies have opened new windows about engineering of withanolide production.

METHODS

Target and network analysis for maximum therapeutic potential of Withania somnifera have been determined by employing Genemania software for finding interactions among various human genes that are being affected by active constituents.

RESULTS

Some of the major bioactive compounds of Withania somnifera have been discussed on protein-protein, protein-DNA and genetic interactions with respect to gene and protein expression data, protein domains, metabolic profiling, root organ culture, genetic transformation and phenotypic screening profiles CONCLUSION: The implementation of latest bioinformatic tools in combination with biotechnological techniques for breeding platforms are important in conservation of medicinal plant species in danger. The current review is based on molecular and in vitro methodologies employed in W. somnifera for accepting their importance in the improvement of this valuable medicinal species.

Addressing Challenges to Enhance the Bioactives of Withania somnifera through Organ, Tissue, and Cell Culture Based Approaches

Withania somnifera is a highly valued medicinal plant in traditional home medicine and is known for a wide range of bioactivities. Its commercial cultivation is adversely affected by poor seed viability and germination. Infestation by various pests and pathogens, survival under unfavourable environmental conditions, narrow genetic base, and meager information regarding biosynthesis of secondary metabolites are some of the other existing challenges in the crop. Biotechnological interventions through organ, tissue, and cell culture provide promising options for addressing some of these issues. In vitro propagation facilitates conservation and sustainable utilization of the existing germplasms and broadening the genetic base. It would also provide means for efficient and rapid mass propagation of elite chemotypes and generating uniform plant material round the year for experimentation and industrial applications. The potential of in vitro cell/organ cultures for the production of therapeutically valuable compounds and their large-scale production in bioreactors has received significant attention in recent years. In vitro culture system further provides distinct advantage for studying various cellular and molecular processes leading to secondary metabolite accumulation and their regulation. Engineering plants through genetic transformation and development of hairy root culture system are powerful strategies for modulation of secondary metabolites. The present review highlights the developments and sketches current scenario in this field.

Withania somnifera: Advances and Implementation of Molecular and Tissue Culture Techniques to Enhance Its Application

Withania somnifera, commonly known as Ashwagandha an important medicinal plant largely used in Ayurvedic and indigenous medicine for over 3,000 years. Being a medicinal plant, dried powder, crude extract as well as purified metabolies of the plant has shown promising therapeutic properties. Withanolides are the principal metabolites, responsible for the medicinal properties of the plant. Availability and amount of particular withanolides differ with tissue type and chemotype and its importance leads to identification characterization of several genes/ enzymes related to withanolide biosynthetic pathway. The modulation in withanolides can be achieved by controlling the environmental conditions like, different tissue culture techniques, altered media compositions, use of elicitors, etc. Among all the in vitro techniques, hairy root culture proved its importance at industrial scale, which also gets benefits due to more accumulation (amount and number) of withanolides in roots tissues of W. somnifera. Use of media compostion and elicitors further enhances the amount of withanolides in hairy roots. Another important modern day technique used for accumulation of desired secondary metabolites is modulating the gene expression by altering environmental conditions (use of different media composition, elicitors, etc.) or through genetic enginnering. Knowing the significance of the gene and the key enzymatic step of the pathway, modulation in withanolide contents can be achieved upto required amount in therapeutic industry. To accomplish maximum productivity through genetic enginnering different means of Withania transformation methods have been developed to obtain maximum transformation efficiency. These standardized transformation procedues have been used to overexpress/silence desired gene in W. somnifera to understand the outcome and succeed with enhanced metabolic production for the ultimate benefit of human race.

A Decade of Molecular Understanding of Withanolide Biosynthesis and In vitro Studies in Withania somnifera (L.) Dunal: Prospects and Perspectives for Pathway Engineering

Withania somnifera, a multipurpose medicinal plant is a rich reservoir of pharmaceutically active triterpenoids that are steroidal lactones known as withanolides. Though the plant has been well-characterized in terms of phytochemical profiles as well as pharmaceutical activities, limited attempts have been made to decipher the biosynthetic route and identification of key regulatory genes involved in withanolide biosynthesis. This scenario limits biotechnological interventions for enhanced production of bioactive compounds. Nevertheless, recent emergent trends vis-à-vis, the exploration of genomic, transcriptomic, proteomic, metabolomics, and in vitro studies have opened new vistas regarding pathway engineering of withanolide production. During recent years, various strategic pathway genes have been characterized with significant amount of regulatory studies which allude toward development of molecular circuitries for production of key intermediates or end products in heterologous hosts. Another pivotal aspect covering redirection of metabolic flux for channelizing the precursor pool toward enhanced withanolide production has also been attained by deciphering decisive branch point(s) as robust targets for pathway modulation. With these perspectives, the current review provides a detailed overview of various studies undertaken by the authors and collated literature related to molecular and in vitro approaches employed in W. somnifera for understanding various molecular network interactions in entirety.

Metabolic shift from withasteroid formation to phenylpropanoid accumulation in cryptogein-cotransformed hairy roots of Withania somnifera (L.) Dunal

Cotransformed hairy roots containing a gene that encodes a fungal elicitor protein, β-cryptogein, were established in Withania somnifera, a medicinal plant widely used in Indian systems of medicine. To find out whether β-cryptogein protein endogenously elicits the pathway of withasteroid biosynthesis, withaferin A and withanolide A contents along with transcript accumulation of farnesyl pyrophosphate (FPP) synthase, 3-hydroxy-3-methyl-glutaryl-CoA reductase (HMGR), and sterol glycosyltransferase (SGT) were analyzed in both cryptogein-cotransformed and normal hairy roots of W. somnifera. It was observed that the withaferin A and withanolide A contents were drastically higher in normal hairy roots than cryptogein-cotransformed ones. Similar trends were also observed on the levels of transcript accumulation. Subsequently, the enzyme activity of phenylalanine ammonia lyase (PAL), one of the key enzymes of phenylpropanoid pathway, was measured in both cryptogein-cotransformed and normal hairy roots of W. somnifera along with the levels of PAL transcript accumulation. Upliftment of PAL activity was observed in cryptogein-cotransformed hairy roots as compared to the normal ones, and the PAL expression also reflected a similar trend, i.e., enhanced expression in the cryptogein-cotransformed lines. Upliftment of wall-bound ferulic acid accumulation was also observed in the cryptogein-cotransformed lines, as compared to normal hairy root lines. Thus, the outcome of the above studies suggests a metabolic shift from withanolide accumulation to phenylpropanoid biosynthesis in cryptogein-cotransformed hairy roots of W. somnifera.

Sonication, Vacuum Infiltration and Thiol Compounds Enhance the Agrobacterium-Mediated Transformation Frequency of Withania somnifera (L.) Dunal

In the present study, we have established a stable transformation protocol via Agrobacterium tumafacines for the pharmaceutically important Withania somnifera. Six day-old nodal explants were used for 3 day co-cultivation with Agrobacterium tumefaciens strain LBA4404 harbouring the vector pCAMIBA2301. Among the different injury treatments, sonication, vacuum infiltration and their combination treatments tested, a vacuum infiltration for 10 min followed by sonication for 10 sec with A. tumefaciens led to a higher transient GUS expression (84% explants expressing GUS at regenerating sites). In order to improve gene integration, thiol compounds were added to co-cultivation medium. A combined treatment of L-Cys at 100 mg/l, STS at 125 mg/l, DTT at 75 mg/l resulted in a higher GUS expression (90%) in the nodal explants. After 3 days of co-cultivation, the explants were subjected to three selection cycles with increasing concentrations of kanamycin [100 to 115 mg/l]. The integration and expression of gusA gene in T0 and T1 transgenic plants were confirmed by polymerase chain reaction (PCR), and Southern blott analysis. These transformed plants (T0 and T1) were fertile and morphologically normal. From the present investigation, we have achieved a higher transformation efficiency of (10%). Withanolides (withanolide A, withanolide B, withanone and withaferin A) contents of transformed plants (T0 and T1) were marginally higher than control plants.

Influence of plant growth regulators on callus mediated regeneration and secondary metabolites synthesis in Withania somnifera (L.) Dunal

Withania somnifera (L.) Dunal, is an important medicinal plant being the source of extremely important compounds like withanolides and withaferin. Influence of different plant growth regulators (PGRs) were evaluated for induction of callus, callus mediated regeneration and production of secondary metabolites in them. Explants for callusing were collected from plants grown in vitro and maximum callusing (98 %) was obtained on MS medium supplemented with a combination of 2,4-dichlorophenoxy acetic acid (2,4-D) (0.5 mg l(-1)) and kinetin (KN) (0.2 mg l(-1)). Among different types of calli, best shoot regeneration was observed on green, compact calli produced on MS medium with a combination of 6-benzylamino purine (BAP) and indole butyric acid (IBA). MS medium supplemented with BAP (2 mg l(-1)) showed highest frequency (98 %) of shoot bud regeneration. The micro-shoots were efficiently rooted on MS media supplemented with 0.5 mg l(-1) IBA. Rooted plants were transferred to soil-vermi-compost (1:3; w/w) medium in greenhouse for acclimatization. Presence of withanolide A and withaferin A in calli was validated through high performance thin layer chromatography (HPTLC). It was interesting to observe that the PGRs showed significant influence on the secondary metabolites production in callus and 2,4-D having the least effect. Histological studies revealed the origin of shoot tip in the callus during regeneration.

Establishment of cell suspension cultures of Withania somnifera for the production of withanolide A

Cell suspension cultures of Withania somnifera were established in shake flasks and the effect of different growth regulators (auxins, combination of auxin and cytokinin), inoculum density (2.5-20 g L(-1)), different media (MS, B5, NN and N6), the strength of the MS medium (0.25-2.0 x), carbon source (sucrose, glucose, fructose, maltose), concentration of the sucrose (1-8% (w/v)) and the initial pH (4.0-6.5) of the medium were determined for the production of withanolide A. The optimized conditions for biomass accumulation and withanolide A production were found to be 10 g L(-1) of the inoculum on fresh weight basis, the full strength MS medium, 3% (w/v) sucrose, four weeks culture period and the initial medium pH of 5.8. The results of present study are useful for scale-up process.

Agrobacterium tumefaciens-mediated transformation of Withania somnifera (L.) Dunal: an important medicinal plant

This report describes Agrobacterium tumefaciens-mediated transformation of Withania somnifera--an important Indian medicinal plant. A. tumefaciens strain LBA4404, containing the binary vector pIG121Hm was used for transformation, along with the gusA reporter gene with intron under the transcriptional control of the Cauliflower Mosaic Virus (CaMV) 35S promoter. The leaf segments from two-and-a-half-month-old green house-grown seedlings were more efficient in transformation, as compared to those from the in vitro-grown shoots. Second expanded leaf from the shoot tip gave the highest transient transformation efficiency. Selection of transgenic shoots was done in the presence of 50 mg l(-1) kanamycin. Polymerase chain reaction analysis of T(0) transgenic plants showed the presence of gusA and nptII genes. The expression of these transgenes in T(1) progeny was confirmed by RT-PCR. The integration of gusA gene was confirmed by Southern blot analysis. The transformation efficiency was found to be 1.67%.

Dual elicitation for improved production of withaferin A by cell suspension cultures of Withania somnifera

High yielding transformed callus culture of W. somnifera was established by infecting hypocotyls with Agrobacterium tumefaciens MTCC-2250. Maximum withaferin A content of 0.0875 mg/g dry cell weight and transformation efficiency of 80% were obtained. Confirmation of transformation was done on the basis of the presence of the ags gene by using polymerase chain reaction. Various abiotic elicitors (arachidonic acid, methyl jasmonate, calcium chloride, and copper sulfate) and biotic elicitors (cell extracts and culture filtrates of Alternia alternata, Fusarium solani, and Verticilium dahaliae) were tested at different concentrations to enhance withaferin A production in suspension culture of transformed cells. Maximum enhancements of 5.4 times and 9.7 times, respectively, were obtained when copper sulfate (100 microM) and the cell extract of V. dahaliae (5% v/v) were added separately to suspension cultures. The dual elicitation strategy by the combined addition of these two elicitors resulted in 13.8-fold enhancement of withaferin A content in comparison to control cultures (2.65 mg/L). The present study indicates the potential of this biotechnology-based methodology for the large-scale production of withaferin A.

Toxic Chemical Compounds of the Solanaceae

The Solanaceae is comprised of some 2500 species of cosmopolitan plants, especially native to the American continent. They have great value as food, like the well-known potato, tomato and eggplants, and medicines, like species of Atropa, Withania and Physalis, but many plants of this family are toxic, and sometimes lethal to mammals, in particular to man. Some of them also produce hallucinations and perceptual changes. The toxic species of this family are characterized by the occurrence of a variety of chemical compounds, some of which are responsible for the toxicity and lethality observed after ingestion, while others are suspected to be toxic. In this review, the following toxic compounds belonging to different members of the Solanaceae family are described: Tropane alkaloids ( Atropa, Datura, Hyoscyamus, Mandragora); pyrrolidine and pyrrolic alkaloids ( Nierembergia, Physalis, Solanum); protoalkaloids ( Nierembergia); glycoalkaloids ( Lycopersicon, Solanum); nicotine ( Nicotiana); cardenolides ( Cestrum, Nierembergia); capsaicinoids ( Capsicum); kaurene-type tetracyclic diterpenes ( Cestrum); steroidal glycosides ( Cestrum, Solanum); 1,25-dihydroxyvitamin D3 and vitamin D3 ( Cestrum, Solanum, Nierembergia); and withasteroids, withanolides ( Withania), and physalins ( Physalis). Other bioactive chemical constituents of members of this family are sugar esters and lectins. Phenylpropanoids are not included in this paper.

Withanolide A biogeneration in in vitro shoot cultures of ashwagandha (Withania somnifera DUNAL), a main medicinal plant in Ayurveda

Multiple shoot cultures of two experimental lines of Withania somnifera plants (RS-Selection-1 and RS-Selection-2) were established using nodal segments as explants. The hormonal combinations of benzyl adenine and kinetin not only influenced their morphogenetic response but also differentially modulated the level of biogeneration of withanolide A in the in vitro shoots of the two lines. Interestingly, withanolide-A, that was hardly detectable in the aerial parts of field-grown Withania somnifera (explant source), accumulated considerably in the in vitro shoot cultures of the plant. The productivity of withanolide A in the cultures varied considerably (ca. 10-fold, 0.014 to 0.14 mg per gram fresh weight) with the change in the hormone composition of the culture media as well as genotype used as source of the explant. The shoot culture of RS-Selection-1 raised at 1.00 ppm of BAP and 0.50 ppm of kinetin displayed the highest concentration of withanolide A in the green shoots of 0.238 g per 100 g dry weight tissue. This was a more analytical concentration keeping in view the isolation yields so far reported from the dried roots of the field-grown plant (ca. 0.015 g per 100 g dry weight), even if isolation losses are considered during purification. The enhanced de novo biogenesis of withanolide A in shoot cultures was corroborated with radiolabel incorporation studies using [2-(14)C] acetate as a precursor. Production of withaferin A was also found in the in vitro shoot cultures. As this compound is a predominant withanolide of native shoots as well and has been already reported to be accumulated in in vitro shoot cultures, its biogeneration observed in these shoot cultures is not discussed in detail.

Changes in morphological phenotypes and withanolide composition of Ri-transformed roots of Withania somnifera

Developmental variability was introduced into Withania somnifera using genetic transformation by Agrobacterium rhizogenes, with the aim of changing withasteroid production. Inoculation of W. somnifera with A. rhizogenes strains LBA 9402 and A4 produced typical transformed root lines, transformed callus lines, and rooty callus lines with simultaneous root dedifferentiation and redifferentiation. These morphologically distinct transformed lines varied in T-DNA content, growth rates, and withasteroid accumulation. All of the lines with the typical transformed root morphology contained the T(L) T-DNA, and 90% of them carried the T(R) T-DNA, irrespective of the strain used for infection. Accumulation of withaferin A was maximum (0.44% dry weight) in the transformed root line WSKHRL-1. This is the first detection of withaferin A in the roots of W. somnifera. All of the rooty callus lines induced by strain A4 contained both the T(L) and the T(R)-DNAs. In contrast, 50% of the rooty-callus lines obtained with strain LBA 9402 contained only the T(R) T-DNA. All the rooty callus lines accumulated both withaferin A and withanolide D. The callusing lines induced by LBA 9402 lacked the T(L) T-DNA genes, while all the callusing lines induced by strain A4 contained the T(L) DNA. Four of these callus lines produced both withaferin A (0.15-0.21% dry weight) and withanolide D (0.08-0.11% dry weight), and they grew faster than the transformed root lines. This is the first report of the presence of withasteroids in undifferentiated callus cultures of W. somnifera.