Light and auxin responsive cytochrome P450s from Withania somnifera Dunal: cloning, expression and molecular modelling of two pairs of homologue genes with differential regulation

Differential regulation of key triterpene synthase gene under abiotic stress in Withania somnifera L. Dunal and its co-relation to sterols and withanolides

Withania somnifera (Ashwagandha), is one of the most reputed Indian medicinal plants, having immense pharmacological activities due to the occurrence of withanolides. The withanolides are biosynthesized through triterpenoid biosynthetic pathway with the involvement of WsCAS leading to cyclization of 2, 3 oxidosqualene, which is a key metabolite to further diversify to a myriad of phytochemicals. In contrast to the available reports on the studies of WsCAS in withanolide biosynthesis, its involvement in phytosterol biosynthesis needs investigation. Present work deals with the understanding of role of WsCAS triterpenoid synthase gene in the regulation of biosynthesis of phytosterols & withanolides. Docking studies of WsCAS protein revealed Conserved amino acids, DCATE motif, and QW motif which are involved in efficient substrate binding, structure stabilization, and catalytic activity. Overexpression/silencing of WsCAS leading to increment/decline of phytosterols confers its stringent regulation in phytosterols biosynthesis. Differential regulation of WsCAS on the metabolic flux towards phytosterols and withanolide biosynthesis was observed under abiotic stress conditions. The preferential channelization of 2, 3 oxidosqualene towards withanolides and/or phytosterols occurred under heat/salt stress and cold/water stress, respectively. Stigmasterol and β-sitosterol showed major contribution in high/low temperature and salt stress, and campesterol in water stress management. Overexpression of WsCAS in Arabidopsis thaliana led to the increment in phytosterols in general. Thus, the WsCAS plays important regulatory role in the biosynthetic pathway of phytosterols and withanolides under abiotic stress conditions.

Recent Advancements in Extraction Techniques of Ashwagandha (Withania somnifera) with Insights on Phytochemicals, Structural Significance, Pharmacology, and Current Trends in Food Applications

Ashwagandha, also known as Withania somnifera (WS), is an ayurvedic botanical plant with numerous applications in dietary supplements and traditional medicines worldwide. Due to the restorative qualities of its roots, WS has potent therapeutic value in traditional Indian (Ayurvedic, Unani, Siddha) and modern medicine recognized as the "Indian ginseng". The presence of phytochemical bioactive compounds such as withanolides, withanosides, alkaloids, flavonoids, and phenolic compounds has an important role in the therapeutic and nutritional properties of WS. Thus, the choice of WS plant part and extraction solvents, with conventional and modern techniques, plays a role in establishing WS as a potential nutraceutical product. WS has recently made its way into food supplements and products, such as baked goods, juices, beverages, sweets, and dairy items. The review aims to cover the key perspectives about WS in terms of plant description, phytochemistry, structural significance, and earlier reported extraction methodologies along with the analytical and pharmacological landscape in the area. It also attempts to iterate the key limitations and further insights into extraction techniques and bioactive standardization with the regulatory framework. It presents a key to the future development of prospective applications in foods such as food supplements or functional foods.

Cloning and homologous characterization of geranylgeranyl pyrophosphate synthase (GGPPS) from Withania somnifera revealed alterations in metabolic flux towards gibberellic acid biosynthesis

Overexpression of a novel geranylgeranyl pyrophosphate synthase gene (WsGGPPS) in planta resulted in increased levels of gibberellic acid and decrease in withanolide content. Withania somnifera (L.) Dunal, the herb from family Solanaceae is one of the most treasured medicinal plant used in traditional medicinal systems owing to its unique stockpile of pharmaceutically active secondary metabolites. Phytochemical and pharmacological studies in this plant were well established, but the genes affecting the regulation of biosynthesis of major metabolites were not well elucidated. In this study cloning and functional characterization of a key enzyme in terpenoid biosynthetic pathway viz. geranylgeranyl pyrophosphate synthase (EC 2.5.1.29) gene from Withania somnifera was performed. The full length WsGGPPS gene contained 1,104 base pairs that encode a polypeptide of 365 amino acids. The quantitative expression analysis suggested that WsGGPPS transcripts were expressed maximally in flower tissues followed by berry tissues. The expression levels of WsGGPPS were found to be regulated by methyl jasmonate (MeJA) and salicylic acid (SA). Amino acid sequence alignment and phylogenetic studies suggested that WsGGPPS had close similarities with GGPPS of Solanum tuberosum and Solanum pennellii. The structural analysis provided basic information about three dimensional features and physicochemical parameters of WsGGPPS protein. Overexpression of WsGGPPS in planta for its functional characterization suggested that the WsGGPPS was involved in gibberellic acid biosynthesis.

Molecular characterization of three CYP450 genes reveals their role in withanolides formation and defense in Withania somnifera, the Indian Ginseng

The medicinal properties of Ashwagandha (Withania somnifera) are attributed to triterpenoid steroidal lactones, withanolides, which are proposed to be derived from phytosterol pathway, through the action of cytochrome P450 (CYP450) enzymes. Here, we report the characterization of three transcriptome-mined CYP450 genes (WsCYP749B1, WsCYP76 and WsCYP71B10), which exhibited induced expression in response to methyl jasmonate treatment indicating their role in secondary metabolism. All three WsCYP450s had the highest expression in leaf compared to other tissues. In planta characterization of WsCYP450s through virus induced gene silencing (VIGS) and transient overexpression approaches and subsequent metabolite analysis indicated differential modulation in the accumulation of certain withanolides in W. somnifera leaves. While WsCYP749B1-vigs significantly enhanced withaferin A (~ 450%) and reduced withanolide A (~ 50%), its overexpression drastically led to enhanced withanolide A (> 250%) and withanolide B (> 200%) levels and reduced 12-deoxywithastramonolide (~ 60%). Whereas WsCYP76-vigs led to reduced withanolide A (~ 60%) and its overexpression increased withanolide A (~ 150%) and reduced 12-deoxywithastramonolide (~ 60%). Silencing and overexpression of WsCYP71B10 resulted in significant reduction of withanolide B (~ 50%) and withanolide A (~ 60%), respectively. Further, while VIGS of WsCYP450s negatively affected the expression of pathogenesis-related (PR) genes and compromised tolerance to bacteria P. syringae DC3000, their overexpression in W. somnifera and transgenic tobacco led to improved tolerance to the bacteria. Overall, these results showed that the identified WsCYP450s have a role in one or several steps of withanolides biosynthetic pathway and are involved in conferring tolerance to biotic stress.

Ashwagandha: Advances in plant biotechnological approaches for propagation and production of bioactive compounds

ETHNOPHARMACOLOGICAL RELEVANCE

Withania somnifera is one of the most extensively delved Ayurvedic medicine. Apart from rejuvenation and increasing longevity, it has several other properties such as immunomodulation, anti-cancer, anti-stress and neuroprotection. Because of its prevailing use and increasing demand, it becomes prudent to scientifically evaluate and document both its propagation and production of desired phytoconstituents.

AIM OF THE STUDY

This review aims to highlight the research progress achieved on various biotechnological and tissue culture aspects of Withania somnifera and to cover up-to-date information regarding in-vitro propagation and production of withanolides.

MATERIALS AND METHODS

Significant published studies were identified for the years 2000-2018 using Elsevier-Science Direct, Pubmed and Google scholar and several research studies in our laboratory. Following keywords such as "plant extracts", "in vitro cultures", "callus and suspension culture", "micropropagation", "hairy root cultures" were used. Further, "Withania somnifera", "secondary metabolites specially withanolides", "molecular techniques" and "in vitro conservation" were used to cross-reference the keywords.

RESULTS

Ashwagandha comprises a broad spectrum of phytochemicals with a wide range of pharmacological properties. W. somnifera seeds have reduced viability and germination rates; thus, its regular cultivation method fails to achieve commercial demands mainly for the production of desired phytoconstituents. Cultivation of plant cells/tissues under in vitro conditions and development of various biotechnological strategies will help to build an attractive alternative to provide adequate quality and quantity raw materials. Recently, a large number of in vitro protocols has developed for W. somnifera not only for its propagation but for the production of secondary metabolites as well. Present work highlights a variety of biotechnological strategies both for prompt propagation and production of different bioactive secondary metabolites.

CONCLUSION

The present review focuses on the development and opportunities in various biotechnological approaches to accomplish the global demand of W. somnifera and its secondary metabolites. This review underlines the advances in plant biotechnological approaches for the propagation of W. somnifera and production of its bioactive compounds.

Characterization and overexpression of sterol Δ22-desaturase, a key enzyme modulates the biosyntheses of stigmasterol and withanolides in Withania somnifera (L.) Dunal

Withanolides constitute an extensive and vital class of metabolites displaying wide array of structural and therapeutic properties with unique side-chain modifications. These show diversified scaffolds and are promising pharmaceutical molecules with well documented anti-inflammatory and anti-cancer properties. Sterols are dynamic class of compounds and essential molecules having structural and functional significance. These contribute to the synthesis of withanolides by providing structural precursors. In this context, we have characterized sterol Δ22-desaturase from Withania somnifera and also functionally validating it by confirming its desaturase nature in conjunction with quantitative real-time expression profiling and metabolite evaluation. Further, transgenic hairy roots of W. somnifera displayed a higher accumulation of stigmasterol and withanolides. The increase in chemical constituents was concomitant with an increased gene copy number predicted via Southern blotting. Additionally, transgenic lines of tobacco over-expressing WsCYP710A11 displayed a substantial increase in its expression, corroborating well with enhanced stigmasterol content. Characterization of CYP710A11 from W. somnifera and its homologous transgenic expression has demonstrated its role in the regulation of withanolides biosynthesis. It also exhibited a differential transcriptional profile in response to exogenous elicitations. These empirical findings suggest the crucial role of CYP710A11 in stigmasterol biosynthesis. This in turn has implications for the overproduction of withanolides via pathway channelling.

Unravelling the molecular mechanisms of abscisic acid-mediated drought-stress alleviation in pomegranate (Punica granatum L.)

Pomegranate (Punica granatum L.), a fruit tree of great economic and nutritional importance, is sensitive to drought stress, which largely affects its transplantation survival rate, fruit yield and quality. Abscisic acid (ABA) treatment can reduce the drought-induced adverse impacts on plants. However, our knowledge on the molecular mechanisms behind ABA-mediated drought tolerance in pomegranates is still limited. In this study, we treated the pomegranates under drought stress with exogenous ABA of different concentrations (30, 60 and 90 μM) and found that, compared to those without treatment, ABA can improve pomegranate's growth condition and related physiological responding processes. We also performed comparative transcriptome analysis between the ABA-treated and untreated pomegranates to reveal the ABA-induced mechanisms in response to drought-stress. Our results showed that exogenous ABA application substantially enhanced pomegranate drought resistance by strengthening some metabolic pathways, such as brassinosteroid synthesis, peroxisome biogenesis, photosynthesis and hemicelluloses synthesis. Furthermore, the over-dose treatment of exogenous ABA was found to trigger ABA degradation process and a feedback loop in pomegranate to balances the ABA accumulation that exceeds the optimal ABA requirement, at the cost of suppressed growth process and stress resistance. Our findings provide new insights into the molecular regulation mechanisms underlying the ABA-mediated drought-stress resistance in pomegranates.

WRKY1-mediated regulation of tryptophan decarboxylase in tryptamine generation for withanamide production in Withania somnifera (Ashwagandha)

WsWRKY1-mediated transcriptional modulation of Withania somnifera tryptophan decarboxylase gene (WsTDC) helps to regulate fruit-specific tryptamine generation for production of withanamides. Withania somnifera is a highly valued medicinal plant. Recent demonstration of novel indolyl metabolites called withanamides in its fruits (berries) prompted us to investigate its tryptophan decarboxylase (TDC), as tryptophan is invariably a precursor for indole moiety. TDC catalyzes conversion of tryptophan into tryptamine, and the catalytic reaction constitutes a committed metabolic step for synthesis of an array of indolyl metabolites. The TDC gene (WsTDC) was cloned from berries of the plant and expressed in E. coli. The recombinant enzyme was purified and characterized for its catalytic attributes. Catalytic and structural aspects of the enzyme indicated its regulatory/rate-limiting significance in generation of the indolyl metabolites. Novel tissue-wise and developmentally differential abundance of WsTDC transcripts reflected its preeminent role in withanamide biogenesis in the fruits. Transgenic lines overexpressing WsTDC gene showed accumulation of tryptamine at significantly higher levels, while lines silenced for WsTDC exhibited considerably depleted levels of tryptamine. Cloning and sequence analysis of promoter of WsTDC revealed the presence of W-box in it. Follow-up studies on isolation of WsWRKY1 transcription factor and its overexpression in W. somnifera revealed that WsTDC expression was substantially induced by WsWRKY1 resulting in overproduction of tryptamine. The study invokes a key role of TDC in regulating the indolyl secondary metabolites through enabling elevated flux/supply of tryptamine at multiple levels from gene expression to catalytic attributes overall coordinated by WsWRKY1. This is the first biochemical, molecular, structural, physiological and regulatory description of a fruit-functional TDC.

In silico mining and functional analysis of AP2/ERF gene in Withania somnifera

Withania somnifera owing to its strong and remarkable stress tolerance property is a reliable candidate for the determination of genes involved in mechanism of adaption/tolerance of various stress conditions. 187 AP2/ERF gene related transcripts (GRTs) were identified during comprehensive search in W. somnifera transcriptome repertoire. Major hits in homology search were observed from the model plant Arabidopsis and members of Solanaceae family. Cloning, expression analysis of the gene and genetic transient transformation with the gene (WsAP2) were performed to predict its functional role in planta. Enhanced expression of some of the pathway genes for terpenoid biosynthesis was observed in transformed tissues in comparison to the control tissues. It is speculated that WsAP2 gene crucially regulates the expression of GGPPS gene in addition to the regulation of other important genes of terpenoid pathway via induction of expression of other genes such as HMGR, CAS, DXS and DXR. To the best of our knowledge, this is the first report representing detailed study of AP2/ERF gene family in W. somnifera. It is also suggested from the study that gene might have role in eliciting responses to combat stress and attribute the strong stress tolerant property associated with the plant.

Berry transcriptome: insights into a novel resource to understand development dependent secondary metabolism in Withania somnifera (Ashwagandha)

Withania somnifera (Ashwagandha) is considered as Rasayana in Indian systems of medicine. This study reports a novel transcriptome of W. somnifera berries, with high depth, quality and coverage. Assembled and annotated transcripts for nearly all genes related with the withanolide biosynthetic pathway were obtained. Tissue-wide gene expression analysis reflected almost similar definitions for the terpenoid pathway in leaf, root and berry tissues with relatively higher abundance of transcripts linked to steroid, phenylpropanoid metabolism as well as flavonoid metabolism in berries. The metabolome map generated from the data embodied transcripts from 143 metabolic pathways connected together and mediated collectively by about 1792 unique enzyme functions specific to berry, leaf and root tissues, respectively. Transcripts specific to cytochrome p450 (CYP450), methyltransferases and glycosyltransferases were distinctively located in a tissue specific manner and exhibited a complex network. Significant distribution of transcription factor genes such as MYB, early light inducible protein (ELI), minichromosome maintenance1, agamous, deficiens and serum response factor (MADS) and WRKY etc. was observed, as the major transcriptional regulators of secondary metabolism. Validation of the assembly was ascertained by cloning WsELI, which has a light dependent regulatory role in development. Quantitative expression of WsELI was observed to be considerably modulated upon exposure to abiotic stress and elicitors. Co-relation of over-expression of WsELI, may provide new aspects for the functional role of ELI proteins in plants linked to secondary metabolism. The study offers the first comprehensive and comparative evaluation of W. somnifera transcriptome data between the three tissues and across other members of Solanaceae (Nicotiana, Solanum and Capsicum) with respect to major pathways and their metabolome regulation.

ROS management is mediated by ascorbate-glutathione-α-tocopherol triad in co-ordination with secondary metabolic pathway under cadmium stress in Withania somnifera

Being static, plants are frequently exposed to various essential and non-essential heavy metals from the surroundings. This exposure results in considerable ROS generation leading to oxidative stress, the primary response of the plants under heavy metal stress. Withania somnifera is a reputed Indian medicinal plant in Ayurveda, having various pharmacological activities due to the presence of withanolides. The present study deals with the understanding endurance of oxidative stress caused by heavy metal exposure and its management through antioxidant partners in synchronization with secondary metabolites in W. somnifera. The quantitative assessment of enzymatic/non-enzymatic antioxidants revealed significant participation of ascorbate-glutathione-α-tocopherol triad in ROS management. Higher activities of glutathione reductase (GR), monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR) resulted in glutathione and ascorbate accumulation. In addition, superoxide dismutase (SOD), glutathione peroxidase (GPX) and peroxidase (POD) were contributed considerably in ROS homeostasis maintenance. In-situ localization and assays related to ROS generation/scavenging revealed key management of ROS status under Cd stress. Higher antioxidative and reducing power activity attributed to the tolerance capability to the plant. Increased expression of withanolide biosynthetic pathway genes such as WsHMGR, WsDXS, WsDXR and WsCAS correlated with enhanced withanolides. The present study indicated the crucial role of the ascorbate-glutathione-α-tocopherol triad in co-ordination with withanolide biosynthesis in affording the oxidative stress, possibly through a cross-talk between the antioxidant machinery and secondary metabolite biosynthesis. The knowledge may be useful in providing the guidelines for developing abiotic stress resistance in plants using conventional and molecular approaches.

Virus-Induced Silencing of Key Genes Leads to Differential Impact on Withanolide Biosynthesis in the Medicinal Plant, Withania somnifera

Withanolides are a collection of naturally occurring, pharmacologically active, secondary metabolites synthesized in the medicinally important plant, Withania somnifera. These bioactive molecules are C28-steroidal lactone triterpenoids and their synthesis is proposed to take place via the mevalonate (MVA) and 2-C-methyl-d-erythritol-4-phosphate (MEP) pathways through the sterol pathway using 24-methylene cholesterol as substrate flux. Although the phytochemical profiles as well as pharmaceutical activities of Withania extracts have been well studied, limited genomic information and difficult genetic transformation have been a major bottleneck towards understanding the participation of specific genes in withanolide biosynthesis. In this study, we used the Tobacco rattle virus (TRV)-mediated virus-induced gene silencing (VIGS) approach to study the participation of key genes from MVA, MEP and triterpenoid biosynthesis for their involvement in withanolide biosynthesis. TRV-infected W. somnifera plants displayed unique phenotypic characteristics and differential accumulation of total Chl as well as carotenoid content for each silenced gene suggesting a reduction in overall isoprenoid synthesis. Comprehensive expression analysis of putative genes of withanolide biosynthesis revealed transcriptional modulations conferring the presence of complex regulatory mechanisms leading to withanolide biosynthesis. In addition, silencing of genes exhibited modulated total and specific withanolide accumulation at different levels as compared with control plants. Comparative analysis also suggests a major role for the MVA pathway as compared with the MEP pathway in providing substrate flux for withanolide biosynthesis. These results demonstrate that transcriptional regulation of selected Withania genes of the triterpenoid biosynthetic pathway critically affects withanolide biosynthesis, providing new horizons to explore this process further, in planta.

Transcription factor repertoire in Ashwagandha (Withania somnifera) through analytics of transcriptomic resources: Insights into regulation of development and withanolide metabolism

Transcription factors (TFs) are important regulators of cellular and metabolic functions including secondary metabolism. Deep and intensive RNA-seq analysis of Withania somnifera using transcriptomic databases provided 3532 annotated transcripts of transcription factors in leaf and root tissues, belonging to 90 different families with major abundance for WD-repeat (174 and 165 transcripts) and WRKY (93 and 80 transcripts) in root and leaf tissues respectively, followed by that of MYB, BHLH and AP2-ERF. Their detailed comparative analysis with Arabidopsis thaliana, Capsicum annum, Nicotiana tabacum and Solanum lycopersicum counterparts together gave interesting patterns. However, no homologs for WsWDR representatives, LWD1 and WUSCHEL, were observed in other Solanaceae species. The data extracted from the sequence read archives (SRA) in public domain databases were subjected to re-annotation, re-mining, re-analysis and validation for dominant occurrence of WRKY and WD-repeat (WDR) gene families. Expression of recombinant LWD1 and WUSCHEL proteins in homologous system led to enhancements in withanolide content indicating their regulatory role in planta in the biosynthesis. Contrasting expression profiles of WsLWD1 and WsWUSCHEL provided tissue-specific insights for their participation in the regulation of developmental processes. The in-depth analysis provided first full-spectrum and comparative characteristics of TF-transcripts across plant species, in the perspective of integrated tissue-specific regulation of metabolic processes including specialized metabolism.

A WRKY transcription factor from Withania somnifera regulates triterpenoid withanolide accumulation and biotic stress tolerance through modulation of phytosterol and defense pathways

Withania somnifera produces pharmacologically important triterpenoid withanolides that are derived via phytosterol pathway; however, their biosynthesis and regulation remain to be elucidated. A jasmonate- and salicin-inducible WRKY transcription factor from W. somnifera (WsWRKY1) exhibiting correlation with withaferin A accumulation was functionally characterized employing virus-induced gene silencing and overexpression studies combined with transcript and metabolite analyses, and chromatin immunoprecipitation assay. WsWRKY1 silencing resulted in stunted plant growth, reduced transcripts of phytosterol pathway genes with corresponding reduction in phytosterols and withanolides in W. somnifera. Its overexpression elevated the biosynthesis of triterpenoids in W. somnifera (phytosterols and withanolides), as well as tobacco and tomato (phytosterols). Moreover, WsWRKY1 binds to W-box sequences in promoters of W. somnifera genes encoding squalene synthase and squalene epoxidase, indicating its direct regulation of triterpenoid pathway. Furthermore, while WsWRKY1 silencing in W. somnifera compromised the tolerance to bacterial growth, fungal infection, and insect feeding, its overexpression in tobacco led to improved biotic stress tolerance. Together these findings demonstrate that WsWRKY1 has a positive regulatory role on phytosterol and withanolides biosynthesis, and defense against biotic stress, highlighting its importance as a metabolic engineering tool for simultaneous improvement of triterpenoid biosynthesis and plant defense.

Over-expression of DXS gene enhances terpenoidal secondary metabolite accumulation in rose-scented geranium and Withania somnifera: active involvement of plastid isoprenogenic pathway in their biosynthesis

Rose-scented geranium (Pelargonium spp.) is one of the most important aromatic plants and is well known for its diverse perfumery uses. Its economic importance is due to presence of fragrance rich essential oil in its foliage. The essential oil is a mixture of various volatile phytochemicals which are mainly terpenes (isoprenoids) in nature. In this study, on the geranium foliage genes related to isoprenoid biosynthesis (DXS, DXR and HMGR) were isolated, cloned and confirmed by sequencing. Further, the first gene of 2-C-methyl-d-erythritol-4-phosphate (MEP) pathway, 1-deoxy-d-xylulose-5-phosphate synthase (GrDXS), was made full length by using rapid amplification of cDNA ends strategy. GrDXS contained a 2157 bp open reading frame that encoded a polypeptide of 792 amino acids having calculated molecular weight 77.5 kDa. This study is first report on heterologous expression and kinetic characterization of any gene from this economically important plant. Expression analysis of these genes was performed in different tissues as well as at different developmental stages of leaves. In response to external elicitors, such as methyl jasmonate, salicylic acid, light and wounding, all the three genes showed differential expression profiles. Further GrDXS was over expressed in the homologous (rose-scented geranium) as well as in heterologous (Withania somnifera) plant systems through genetic transformation approach. The over-expression of GrDXS led to enhanced secondary metabolites production (i.e. essential oil in rose-scented geranium and withanolides in W. somnifera). To the best of our knowledge, this is the first report showing the expression profile of the three genes related to isoprenoid biosynthesis pathways operated in rose-scented geranium as well as functional characterization study of any gene from rose-scented geranium through a genetic transformation system.

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.

Plant cytochrome P450s: nomenclature and involvement in natural product biosynthesis

Cytochrome P450s constitute the largest family of enzymatic proteins in plants acting on various endogenous and xenobiotic molecules. They are monooxygenases that insert one oxygen atom into inert hydrophobic molecules to make them more reactive and hydro-soluble. Besides for physiological functions, the extremely versatile cytochrome P450 biocatalysts are highly demanded in the fields of biotechnology, medicine, and phytoremediation. The nature of reactions catalyzed by P450s is irreversible, which makes these enzymes attractions in the evolution of plant metabolic pathways. P450s are prime targets in metabolic engineering approaches for improving plant defense against insects and pathogens and for production of secondary metabolites such as the anti-neoplastic drugs taxol or indole alkaloids. The emerging examples of P450 involvement in natural product synthesis in traditional medicinal plant species are becoming increasingly interesting, as they provide new alternatives to modern medicines. In view of the divergent roles of P450s, we review their classification and nomenclature, functions and evolution, role in biosynthesis of secondary metabolites, and use as tools in pharmacology.

RNAi and Homologous Over-Expression Based Functional Approaches Reveal Triterpenoid Synthase Gene-Cycloartenol Synthase Is Involved in Downstream Withanolide Biosynthesis in Withania somnifera

Withania somnifera Dunal, is one of the most commonly used medicinal plant in Ayurvedic and indigenous medicine traditionally owing to its therapeutic potential, because of major chemical constituents, withanolides. Withanolide biosynthesis requires the activities of several enzymes in vivo. Cycloartenol synthase (CAS) is an important enzyme in the withanolide biosynthetic pathway, catalyzing cyclization of 2, 3 oxidosqualene into cycloartenol. In the present study, we have cloned full-length WsCAS from Withania somnifera by homology-based PCR method. For gene function investigation, we constructed three RNAi gene-silencing constructs in backbone of RNAi vector pGSA and a full-length over-expression construct. These constructs were transformed in Agrobacterium strain GV3101 for plant transformation in W. somnifera. Molecular and metabolite analysis was performed in putative Withania transformants. The PCR and Southern blot results showed the genomic integration of these RNAi and overexpression construct(s) in Withania genome. The qRT-PCR analysis showed that the expression of WsCAS gene was considerably downregulated in stable transgenic silenced Withania lines compared with the non-transformed control and HPLC analysis showed that withanolide content was greatly reduced in silenced lines. Transgenic plants over expressing CAS gene displayed enhanced level of CAS transcript and withanolide content compared to non-transformed controls. This work is the first full proof report of functional validation of any metabolic pathway gene in W. somnifera at whole plant level as per our knowledge and it will be further useful to understand the regulatory role of different genes involved in the biosynthesis of withanolides.

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.