Dietary inclusion of Withania somnifera and Asparagus racemosus induces growth, activities of digestive enzymes, and transcriptional modulation of MyoD, MyoG, Myf5, and MRF4 genes in fish, Channa punctatus

The present study explores growth potential of two medicinal herbs, Withania somnifera (Ashwagandha or 'A') and Asparagus racemosus (Shatavari or 'S') after their dietary inclusion in fish, Channa punctatus (13.5 ± 2 g; 11.5 ± 1 cm). Three hundred well-acclimatized fish were distributed into 10 groups- C (Control), S1 (1% S), S2 (2% S), S3 (3% S), A1 (1% A), A2 (2% A), A3 (3% A), AS1 (1% A and S), AS2 (2% A and S), and AS3 (3% A and S), each having 10 specimens. Fish were fed with these diets for 60 days. The study was performed in triplicate. Growth indices- weight gain (WG), specific growth rate percentage (SGR%), feed intake (FI), and condition factor (CF), after 30 and 60 days, were found significantly (p < 0.05) up-regulated in all the groups, except S1, when compared to the C. A significant (p < 0.05) increase in final body weight (FBW) was noticed in all the groups, except S1, after 60 days. Relative to the control group, activities of lipase and amylase in the gut tissue were elevated in all groups, at both sampling times, with the exception of lipase in S1 at 60 days, and amylase in S1 at day 30 and day 60 and S2 at day 60. The mRNA expression of myogenic regulatory factors (MRFs) was also found to be significantly (p < 0.05) up-regulated with the highest fold changes recorded in AS3 for myoD (3.93 ± 0.91); myoG (6.71 ± 0.30); myf5 (4.40 ± 0.33); MRF4 (4.94 ± 0.21) in comparison to the C.

Enhanced production of withaferin A from the hairy root culture of Withania somnifera via synergistic effect of Methyl jasmonate and β-cyclodextrin

Due to low amounts of withanolides produced in some plants and high demand for various applications, their biotechnological production is widely researched. The effects of two explant types (i.e., leaf and stem from the in vitro seedlings of three genotypes of Withania somnifera) and four Rhizobium strains (i.e., LBA 9402, A4, ATCC 15834, and C58C1) to improve hairy root formation efficiency was studied. Furthermore, the combined effects of β-cyclodextrin (β-CD) and methyl jasmonate (MeJA) on withaferin A production after 48 h exposure time was examined. Four hairy roots having the maximum percentage of induced roots and mean number of induced roots to analyze their growth kinetics and identified G3/ATCC/LEAF culture having the maximum specific growth rate (μ = 0.036 day-1) and growth index (GI = 9.18), and the shortest doubling time (Td = 18.82 day) were selected. After 48 h exposure of G3/ATCC/LEAF culture to different elicitation conditions, maximum amounts of withaferin A were produced in samples co-treated with 0.5 mM β-CD + 100 μM MeJA (9.57 mg/g DW) and 5.0 mM β-CD + 100 μM MeJA (17.45 mg/g DW). These outcomes represented a 6.8-fold and 12.5-fold increase, respectively, compared to the control. Similarly, combined β-CD/MeJA elicitation increased gene expression levels of HMGR, SQS, SMT-1, and SDS/CYP710A involved in withanolides biosynthetic pathway, of which just SMT-1 had significant correlation with withaferin A production. These results demonstrated the superiority of G1-leaf explant and ATCC 15834 for hairy root induction, and revealed synergistic effect of MeJA and β-CD on withaferin A production.

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.

The growth performance, antioxidant and immune responses, and disease resistance of Litopenaeus vannamei fed on diets supplemented with Indian ginseng (Withania somnifera)

In the current study, white-leg shrimp (Litopenaeus vannamei) were fed on diets containing varying doses of Withania somnifera aqueous extract (WSAE) at a rate of 0 (control), 0.5, 1.0, and 2.0 g/kg feed for 56 days. After the feeding trial, shrimps in all groups were challenged with the exposure to Vibrio harveyi for ten days during which animals' mortality was observed. It is noted that the dietary WSAE linearly and quadratically stimulated shrimp's growth indices particularly at the treatment of 2.0 g/kg feed. Compared to the control group, the WSAE-fed L. vannamei had significantly higher villi length, villi width, and absorption area particularly in the treatment of 2.0 g/kg feed. Furthermore, L. vannamei fed on WSAE-enriched diets consumed more feed and exhibited higher total proteolytic activity, lipase, and α-amylase activities as compared with the control group. The dietary WSAE at escalating levels linearly and quadratically enhanced the antioxidant activity (serum superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), total antioxidant capacity, and reduced glutathione) and the immune response (total hemocyte counts, total protein, lysozyme, and phagocytic activity). Similarly, the mRNA expression levels of cMn-SOD, CAT, and GPx genes were linearly and quadratically upregulated in the hepatopancreas of L. vannamei fed on WSAE-enriched diets (especially in the 2.0 g/kg feed treatment), while their lowest levels were significantly observed in the control group. On the other hand, malondialdehyde levels were significantly decreased in WSAE-supplemented shrimp groups, and its highest levels were observed in animals fed on the control diet. After the bacterial exposure, the survival rates of L. vannamei fed on 1.0 and 2.0 g WSAE/kg feed (61.3% and 66.7%, respectively) were higher than those in the control animals. Taken together, the results obtained herein indicate that inclusion of WSAE in diets of L. vannamei effectively enhanced the growth, antioxidant biomarkers, immune response, and resistance to the V. harveyi infection, particularly at the treatment of 2.0 g/kg feed.

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.

Overexpression of WssgtL3.1 gene from Withania somnifera confers salt stress tolerance in Arabidopsis

Overexpression of Withania somnifera SGT gene (WssgtL3.1) in transgenic Arabidopsis improves various agronomic and physiological traits and alters conjugated sterol levels to mitigate the effect of salt stress. Sterols are essential constituents of cell membranes that are involved in several biological functions, including response to various biotic and abiotic stresses by altering membrane permeability and signaling pathways. Sterol glycosyltransferases (SGTs) are enzymes that are involved in sterol modification by converting sterols into sterol-conjugates to play essential roles in adaptive responses. However, their roles under abiotic stresses are lesser-known. Among abiotic stresses, salinity imposes serious threat to crop yield worldwide, hence the present study intends to investigate the role of WssgtL3.1-overexpressed Arabidopsis plants under salt stress indicating the crosstalk between SGT gene and salinity to develop improved crop varieties with better stress tolerance ability. The findings revealed that overexpression of WssgtL3.1 gene in A. thaliana improved the resistance against salt stress in the overexpressing lines. Transgenic lines showed significantly higher germination rate, increased plant growth with less chlorophyll damage compared to wild-type (WT) control plants. Moreover, better tolerance also correlated with enhanced osmolytes (proline and soluble sugar), better membrane integrity, decreased H₂O₂ production and lesser MDA accumulation and Na⁺/K⁺ ratio with more negative osmotic potential in overexpressed lines. Additionally, in sterol profiling, significant enhancement in stigmasterol was also observed in transgenic lines than WT plants. Furthermore, in expression profiling, salt responsive genes LEA 4-5, sucrose synthase, and transporter of monosaccharide (ERD) significantly upregulated in overexpressing lines as compared to WT. Thus our data strongly support the defensive role of Withania somnifera SGT gene (WssgtL3.1) against salt stress and contribute to improved salinity tolerance in plants through sterol modulation.

Impact of green synthesized WcAgNPs on in-vitro plant regeneration and withanolides production by inducing key biosynthetic genes in Withania coagulans

Withania coagulans (L.) Dunal bio-synthesized silver nanoparticles (WcAgNPs) worked as an abiotic elicitor or auto-catalyst that enhanced root regeneration and withanolides production in in-vitro regenerated W. coagulans. Rapid development in the production / consumption of silver nanoparticles (AgNPs) raised serious concern over its effects on the growth of natural plant community. The knowledge related to impact of AgNPs on plant growth and biocompatibility is increasing day by day, but comprehensive mechanism and gaps regarding their impacts on plant health have yet to be addressed. In the present study, we investigated the impact of Withania coagulans biosynthesized AgNPs (WcAgNPs) on in-vitro plant growth and withanolides production. Obtained results showed that the low concentrations of WcAgNPs significantly induced the plant growth by regulating oxidative stress via anti-oxidative defense system. Physiological, morphology and anatomical features also reflected healthy plant growth under low WcAgNPs exposure. While higher concentrations of WcAgNPs have a negative impact on W. coagulans plant growth due to induced lipid peroxidation, ROS accumulation, and root cell death. At lower concentrations, WcAgNPs have shown a positive effect on in-planta withanolides biosynthesis stimulating withanolide A and withaferin A up to 11.15-22.8-fold, respectively. Furthermore, the expression of withanolides biosynthetic genes were also quantified upon WcAgNPs exposure and terpenes biosynthetic genes showed over-expression. Thus, the present study concludes that the lower concentrations of WcAgNPs positively induced plant growth via improved root organogenesis and also have potential to act as an elicitor for withanolides production.

Defining the role of a caffeic acid 3-O-methyltransferase from Azadirachta indica fruits in the biosynthesis of ferulic acid through heterologous over-expression in Ocimum species and Withania somnifera

The recombinant caffeic acid 3-O-methyltransferase gene has been cloned and characterized from Neem. The gene is involved in ferulic acid biosynthesis, a key intermediate component of lignin biosynthesis. Azadirachta indica (Neem) is a highly reputed traditional medicinal plant and is phytochemically well-known for its limonoids. Besides limonoids, phenolics are also distinctively present, which add more medicinal attributes to Neem. Caffeic acid is one of such phenolic compound and it can be converted enzymatically into another bioactive phytomolecule, ferulic acid. This conversion requires transfer of a methyl group from a donor to caffeic acid under the catalytic action of an appropriate methyltransferase. In this study, caffeic acid 3-O-methyltransferase gene from Neem (NCOMT) fruits has been isolated and heterologously expressed in E. coli. The recombinant NCOMT enzyme was purified, which exhibited efficient catalytic conversion of caffeic acid into ferulic acid, a highly potential pharmaceutical compound. The purified recombinant enzyme was physico-kinetically characterized for its catalysis. The analysis of tissue-wide expression of NCOMT gene revealed interesting pattern of transcript abundance reflecting its role in the development of fruit tissues. Further, NCOMT was heterologously overexpressed in Withania somnifera and Ocimum species, to analyze its role in ferulic acid biosynthesis in planta. Thus, the study provides insight for the endogenous role of NCOMT in ferulic acid biosynthesis en route to lignin, an important structural component. To the best of our knowledge, NCOMT pertains to be the first enzyme of the secondary metabolism that has been purified and kinetically characterized from Neem. This study may also have important prospects of applications as the observation on heterologous expression of NCOMT showed its involvement in the maintenance of the in vivo pool of ferulic acid in the plants. Thus, the study involving NCOMT opens up new dimensions of metabolic engineering approaches for the biosynthesis of potential therapeutically important phytomolecules in heterologous systems.

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.

Production of pharmaceutical active recombinant globular adiponectin as a secretory protein in Withania Somnifera hairy root culture

Among various in vitro plant culture systems, hairy root systems seem to be one of the most appealing methods of recombinant protein production due to their advantages in combining both whole-plant cultivation and suspension cell culture platform. This is a report on production and secretion of a recombinant pharmaceutically active protein from hairy roots cultures of Withania somnifera to improve the economic potential of this plant for the production pharmaceutical compounds. In this study, we selected and synthesized a codon-optimized globular adiponectin (gAd) gene with a calreticulin signal peptide and cloned the sequence into a plant expression binary vector containing a nptII gene as a selectable marker gene. The transgenic hairy roots were produced by Agrobacterium rhizogenes-mediated transformation protocol developed by our group. Among ten established nptII positive hairy roots lines, six colons significantly accumulated gAd protein in the biomass and extracellular medium. The presence of gAd was confirmed by western blot analysis of root extracts. The maximum level of hairy root biomass, growth rate (GR), intra- and extracellular gAd expressions were obtained after 25-26 days of culture on MS medium. The maximum level of intra- and extracellular gAd proteins were found to be 15.19 μg/gFW and 215.7 μg/L, respectively, which resulted in a significant decrease in the amount of intra- and extracellular withanolide A and withaferin A production. The addition of PVP, KNO3 and NaCl significantly increased the level of extracellular gAd by approximately 13 folds. This improvement could significantly increase the amount of intra- and extracellular withanolide A and withaferin A production, too. The recombinant gAd produced from W. somnifera is functional as proved by induction the phosphorylation of ACC in C2C12 muscle cells, as its functional amount was 5.1-fold more than gAd produced from E. coli and 45 % lower than CHO cells.

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.

Authentication of the market samples of Ashwagandha by DNA barcoding reveals that powders are significantly more adulterated than roots

ETHNOPHARMACOLOGICAL RELEVANCE

Ashwagandha, also known as Indian Ginseng, is a highly traded medicinal plant, which is used in Ayurveda, Siddha and Unani systems of medicine to improve cognitive function, decrease inflammation, and to counter the ill-effects of aging. Withanolide A and Withaferin A from Ashwagandha were shown to improve immunity and have anti-cancer property, respectively.

AIM OF THE STUDY

Here, we aimed to create reference DNA barcodes for W. somnifera and to authenticate root and powder samples of Ashwagandha collected from markets.

MATERIALS AND METHODS

Three plant specimen of W. somnifera were collected, and reference DNA barcodes were generated using rbcL, matK, trnH-psbA, and ITS2 DNA barcode markers. Market samples in the form of root (n = 33) and powder (n = 70) were collected and authenticated using ITS2 and trnH-psbA DNA barcodes.

RESULTS

Genomic DNA was successfully isolated from all plant specimens and market samples. DNA barcoding showed that 77% of samples were authentic. About 22% of non-authentic samples were powder samples and only 1% were root samples. Among the non-authentic samples, 18% were completely substituted with single species (Mucuna pruriens (L.) DC., Trigonella foenum-graceum L., or Senna auriculata (L.) Roxb.) and 82% were mixed samples containing more than one species. About 63% of the mixed samples contained Ashwagandha as the major ingredient. Furthermore, we identified that six taxonomically divergent plant species from four families were present as adulterants in the mixed samples.

CONCLUSION

DNA barcoding revealed that botanical adulteration in the market samples of Ashwagandha is significant. Powder samples are more prone to adulteration than root samples. The adulterated samples contained plant material that is not related to Ashwagandha, which warrants strict quantity control and market surveillance to derive the true medicinal benefits of this medicinal plant.

Elucidation of genotype-environment interactions and genetic stability parameters for yield, quality and agromorphological traits in ashwagandha (Withania somnifera (L.) Dunal)

The present study was undertaken to delineate genotype-environment interactions and stability status of 16 genotypes of ashwagandha (Withania somnifera (L.) Dunal) in context to the 12 characters, namely plant height, number of primary branches, number of secondary branches, days to flowering, days to maturity, number of berries, number of seeds/berry, root length, root diameter, root branches, dry root yield and total alkaloid content (%). Experiment was carried out in a randomized complete block design with three replicationsover three different locations (S. K. Nagar, Jagudan and Bhiloda) in north Gujarat for three years (2016-17, 2017-18 and 2018-19). Pooled analysis of variance revealed that the mean squares due to genotypes and genotype 9 environment interaction along with linear and nonlinear components were highly significant (P<0.01) for most of the traits under study. Stability parameters for component traits through Eberhart and Russell model showed that genotypes that can be used directly in breeding programme are SKA-4 for early flowering, SKA-21 for early maturity and SKA-1, SKA-4, SKA-6 and SKA-17 for shorter plant height. Further, SKA-21 could be used for improving number of primary branches per plant, SKA-11 and SKA-17 for number of secondary branches per plant, SKA-19 for number of berries per plant, SKA-6, SKA-21, SKA-27 and AWS-1 for root branches and SKA-17 for root length as these genotypes were found to be moststable across the environments for mentioned traits. The result revealed that some reliable predictions about genotype 9 environment interaction and its unpredictable components were involved significantly in determining the stability of genotypes. Hence, the present investigation can be exploited for the identification of more productive genotypes in specific environments, leading to significant increase in root productivity of ashwagandha.

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.

Virus-Induced Gene Silencing for Functional Genomics in Withania somnifera, an Important Indian Medicinal Plant

Virus-induced gene silencing (VIGS) has emerged as a fast and efficient reverse and forward genetics tool to study gene function in model plants as well as in agriculturally important plants. In addition, VIGS approach has been successfully used to provide insights into the role of several genes and regulators involved in plant secondary metabolism. Ashwagandha (Withania somnifera) is an important Indian medicinal plant that accumulates pharmacologically important triterpenoid steroidal lactones, which are collectively termed as withanolides. W. somnifera being a highly recalcitrant plant for genetic transformation, Tobacco rattle virus (TRV)-mediated VIGS was established by our group to facilitate understanding of withanolides' pathway. Here, we describe a detailed procedure to carry out VIGS for gene function studies in W. somnifera.

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.

Third DWF1 paralog in Solanaceae, sterol Δ24-isomerase, branches withanolide biosynthesis from the general phytosterol pathway

A large part of chemodiversity of plant triterpenes is due to the modification of their side chains. Reduction or isomerization of double bonds in the side chains is often an important step for the diversification of triterpenes, although the enzymes involved are not fully understood. Withanolides are a large group of structurally diverse C28 steroidal lactones derived from 24-methylenecholesterol. These compounds are found in the Indian medicinal plant Withania somnifera, also known as ashwagandha, and other members of the Solanaceae. The pathway for withanolide biosynthesis is unknown, preventing sustainable production via white biotechnology and downstream pharmaceutical usages. In the present study, based on genome and transcriptome data we have identified a key enzyme in the biosynthesis of withanolides: a DWF1 paralog encoding a sterol Δ24-isomerase (24ISO). 24ISO originated from DWF1 after two subsequent duplication events in Solanoideae plants. Withanolides and 24ISO appear only in the medicinal plants in the Solanoideae, not in crop plants such as potato and tomato, indicating negative selection during domestication. 24ISO is a unique isomerase enzyme evolved from a reductase and as such has maintained the FAD-binding oxidoreductase structure and requirement for NADPH. Using phylogenetic, metabolomic, and gene expression analysis in combination with heterologous expression and virus-induced gene silencing, we showed that 24ISO catalyzes the conversion of 24-methylenecholesterol to 24-methyldesmosterol. We propose that this catalytic step is the committing step in withanolide biosynthesis, opening up elucidation of the whole pathway and future larger-scale sustainable production of withanolides and related compounds with pharmacological properties.

Modulations in primary and secondary metabolic pathways and adjustment in physiological behaviour of Withania somnifera under drought stress

In general medicinal plants grown under water limiting conditions show much higher concentrations of secondary metabolites in comparison to control plants. In the present study, Withania somnifera plants were subjected to water stress and data related to drought tolerance phenomenon was collected and a putative mechanistic concept considering growth responses, physiological behaviour, and metabolite content and gene expression aspects is presented. Drought induced metabolic and physiological responses as well as drastic decrease in CO₂ uptake due to stomatal limitations. As a result, the consumption of reduction equivalents (NADPH²⁺) for CO₂ assimilation via the calvin cycle declines significantly resulting in the generation of a large oxidative stress and an oversupply of antioxidant enzymes. Drought also results in the shifting of metabolic processes towards biosynthetic activities that consume reduction equivalents. Thus, biosynthesis of reduced compounds (isoprenoids, phenols and alkaloids) is enhanced. The dynamics of various metabolites have been discussed in the light of gene expression analysis of control and drought treated leaves. Gene encoding enzymes of pathways leading to glucose, fructose and fructan production, conversion of triose phosphates to hexoses and hexose phosphorylation were up-regulated in the drought stressed leaves. The down-regulated Calvin cycle genes were co-ordinately regulated with the down-regulation of chloroplast triosephosphate/phosphate translocator, cytoplasmic fructose-1,6-bisphosphate aldolase and fructose bisphosphatase. Expression of gene encoding Squalene Synthase (SQS) was highly upregulated under drought stress which is responsible for the diversion of carbon flux towards withanolides biosynthesis from isoprenoid pathway.

HMG-CoA reductase from Camphor Tulsi (Ocimum kilimandscharicum) regulated MVA dependent biosynthesis of diverse terpenoids in homologous and heterologous plant systems

Ocimum kilimandscharicum is unique in possessing terpenoids whereas other Ocimum species are renowned for phenylpropanoids as major constituents of essential oil. The key enzyme of MVA/terpenoid metabolic pathway viz 3-hydroxy-3-methylglutaryl Co-A reductase (OkHMGR) of 1.7-Kb ORF encoding ~60-kDa protein was cloned from O. kilimandscharicum and its kinetic characteristics revealed the availability of HMG-CoA as a control point of MVA-pathway. Transcript profiling of the OkHMGR elucidated tissue-specific functions of the gene in flower and leaf tissues in accumulation of terpenoidal essential oil. OkHMGR was differentially regulated in response to exposure to methyl-jasmonate, salicylic-acid, and stress conditions such-as salt and temperature stress, demonstrating its key role in managing signaling and stress-responses. To elucidate its functional role, OkHMGR was transiently over-expressed in homologous and heterologous plants such as O. sanctum, O. basilicum, O. gratissimum, Withania somnifera and Artemisia annua. The over-expression and inhibition dual strategy revealed that the additional OkHMGR in-planta could afford endogenous flow of isoprenoid units towards synthesis of terpenoids. The present study provides in-depth insight of OkHMGR in regulation of biosynthesis of non-plastidal isoprenoids. This is first report on any gene of MVA/isoprenoid pathway from under-explored Camphor Tulsi belonging to genus Ocimum. Studies also suggested that OkHMGR could be a potential tool for attempting metabolic engineering for enhancing medicinally important terpenoidal metabolites in plants.

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.

Comparative study of withanolide production and the related transcriptional responses of biosynthetic genes in fungi elicited cell suspension culture of Withania somnifera in shake flask and bioreactor

Ashwagandha (Withania somnifera) is one of the most reputed medicinal plants in the traditional medicinal system. In this study, cell suspension culture of W. somnifera was elicited with cell homogenates of fungi (A. alternata, F. solani, V. dahliae and P. indica) in shake flask and the major withanolides like withanolide A, withaferin A and withanone were analysed. Simultaneously expression levels of key pathway genes from withanolides biosynthetic pathways were also checked via quantitative PCR in shake flask as well as in bioreactor. The results show that highest gene expression of 10.8, 5.8, 4.9, and 3.3 folds were observed with HMGR among all the expressed genes in cell suspension cultures with cell homogenates of 3% P. indica, 5% V. dahliae, 3% A. alternata and 3% F. solani, respectively, in comparison to the control in shake flask. Optimized concentration of cell homogenate of P. indica (3% v/v) was added to the growing culture in 5.0-l bioreactor under optimized up-scaling conditions and harvested after 22 days. The genes of MVA, MEP and withanolides biosynthetic pathways like HMGR, SS, SE, CAS, FPPS, DXR and DXS were up-regulated by 12.5, 4.9, 2.18, 4.65, 2.34, 1.89 and 1.4 folds, respectively in bioreactor. The enhancement of biomass (1.13 fold) and withanolides [withanolide A (1.7), withaferin A (1.5), and withanone (1.5) folds] in bioreactor in comparison to shake flask was also found to be in line with the up-regulation of genes of withanolide biosynthetic pathways.

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 coagulans tryptophan decarboxylase gene cloning, heterologous expression, and catalytic characteristics of the recombinant enzyme

Tryptophan decarboxylase (EC 4.1.1.28) catalyzes pyridoxal 5'-phosphate (PLP)-dependent decarboxylation of tryptophan to produce tryptamine for recruitment in a myriad of biosynthetic pathways of metabolites possessing indolyl moiety. A recent report of certain indolyl metabolites in Withania species calls for a possible predominant functional role of tryptophan decarboxylase (TDC) in the genome of Withania species to facilitate production of the indolyl progenitor molecule, tryptamine. Therefore, with this metabolic prospection, we have identified and cloned a full-length cDNA sequence of TDC from aerial tissues of Withania coagulans. The functional WcTDC gene comprises of 1506 bp open reading frame (ORF) encoding a 502 amino acid protein with calculated molecular mass and pI value of 56.38 kDa and 8.35, respectively. The gene was expressed in Escherichia coli, and the recombinant enzyme was affinity-purified to homogeneity to discern its kinetics of catalysis. The enzyme (WcTDC) exhibited much higher K_m value for tryptophan than for pyridoxal 5'-phosphate and was dedicated to catalyze decarboxylation of only tryptophan or, to a limited extent, of its analogue (like 5-hydroxy tryptophan). The observed optimal catalytic functionality of the enzyme on the slightly basic side of the pH scale and at slightly higher temperatures reflected adaptability of the plant to hot and arid regions, the predominant natural habitat of the herb. This pertains to be the first report on cloning and characterization of heterologously expressed recombinant enzyme from W. coagulans and forms a starting point to further understanding of withanamide biosynthesis.

Nitrogen treatment enhances sterols and withaferin A through transcriptional activation of jasmonate pathway, WRKY transcription factors, and biosynthesis genes in Withania somnifera (L.) Dunal

The medicinal plant Withania somnifera is researched extensively to increase the quantity of withanolides and specifically withaferin A, which finds implications in many pharmacological activities. Due to insufficient knowledge on biosynthesis and unacceptability of transgenic approach, it is preferred to follow alternative physiological methods to increase the yield of withanolides. Prior use of elicitors like salicylic acid, methyl jasmonate, fungal extracts, and even mechanical wounding have shown to increase the withanolide biosynthesis with limited success; however, the commercial viability and logistics of application are debatable. In this investigation, we tested the simple nitrogeneous fertilizers pertaining to the enhancement of withaferin A biosynthesis. Application of ammonium sulfate improved the sterol contents required for the withanolide biosynthesis and correlated to higher expression of pathway genes like FPPS, SMT1, SMT2, SMO1, SMO2, and ODM. Increased expression of a gene homologous to allene oxide cyclase, crucial in jasmonic acid biosynthetic pathway, suggested the involvement of jasmonate signaling. High levels of WRKY gene transcripts indicated transcriptional regulation of the pathway genes. Increase in transcript level could be correlated with a corresponding increase in the protein levels for WsSMT1 and WsWRKY1. The withaferin A increase was also demonstrated in the potted plants growing in the glasshouse and in the open field. These results implicated simple physiological management of nitrogen fertilizer signal to improve the yield of secondary metabolite through probable involvement of jasmonate signal and WRKY transcription factor for the first time, in W. somnifera besides improving the foliage.

WSA206, a paralog of duplicated MPF2-like MADS-box family is recruited in fertility function in Withania

Best known for their implication in calyx inflation, MPF2-like genes pertinent to the STMADS11 clade of the MADS-box family exert their functions in leaf development, flowering time, inflorescence architecture and floral reversion to just name but a few. However, our knowledge about their involvement in fertility function remained obscure. Therefore the major thrust of this study was to probe the recruitment of WSA206 (MPF2-like) protein in fertility function. The WSA206 functions were revealed by knocking down and overexpressing this protein in Withania somnifera. The WSA206 promoter functions were defined by stable integration in Arabidopsis using GUS tag. The interactions of WSA206 were investigated by screening Arabidopsis Oligo-dT yeast library and YFP-split analysis. WSA206 knockdown plants revealed fewer flowers, abortion in seed set, reduction in pollen number and deformed non-viable pollen in comparison with wild type counterparts. Overexpression of WSA206 in Withania generated more berries/seeds and healthier viable pollen grains. Remarkably, along with fertility control, the impairment in calyx inflation in knockdown Withania plants and extraordinary growth of sepals in overexpression lines is observed. Thus, fertility and calyx inflation are tightly coupled traits under the control of WSA206. Coding sequence revealed SNP mutations from arginine to lysine as well as a leucine-rich motif duplication at the C-terminus, a characteristic feature of pollen specific and fertility function proteins. The protein-protein interaction spectrum of WSA206 comprises 40% of those MADS and non-MADS-box proteins implicated in floral/anther expression and embryogenesis. Predominant WSA206 promoter:GUS expression accrued in the anthers/pollen may be attributed to of the presence of GAAATTGTTA pollen specific proximal motifs along with several other anther specific homotypic cis-clusters. MPF2-like protein WSA206 through interactions with MADS-box and non-MADS-domain proteins confers male fertility in Withania regulated by anther/pollen specific promoter motif GAAATTGTTA.

Ectopic overexpression of WsSGTL1, a sterol glucosyltransferase gene in Withania somnifera, promotes growth, enhances glycowithanolide and provides tolerance to abiotic and biotic stresses

Overexpression of sterol glycosyltransferase (SGTL1) gene of Withania somnifera showing its involvement in glycosylation of withanolide that leads to enhanced growth and tolerance to biotic and abiotic stresses. Withania somnifera is widely used in Ayurvedic medicines for over 3000 years due to its therapeutic properties. It contains a variety of glycosylated steroids called withanosides that possess neuroregenerative, adaptogenic, anticonvulsant, immunomodulatory and antioxidant activities. The WsSGTL1 gene specific for 3β-hydroxy position has a catalytic specificity to glycosylate withanolide and sterols. Glycosylation not only stabilizes the products but also alters their physiological activities and governs intracellular distribution. To understand the functional significance and potential of WsSGTL1 gene, transgenics of W. somnifera were generated using Agrobacterium tumefaciens-mediated transformation. Stable integration and overexpression of WsSGTL1 gene were confirmed by Southern blot analysis followed by quantitative real-time PCR. The WsGTL1 transgenic plants displayed number of alterations at phenotypic and metabolic level in comparison to wild-type plants which include: (1) early and enhanced growth with leaf expansion and increase in number of stomata; (2) increased production of glycowithanolide (majorly withanoside V) and campesterol, stigmasterol and sitosterol in glycosylated forms with reduced accumulation of withanolides (withaferin A, withanolide A and withanone); (3) tolerance towards biotic stress (100 % mortality of Spodoptera litura), improved survival capacity under abiotic stress (cold stress) and; (4) enhanced recovery capacity after cold stress, as indicated by better photosynthesis performance, chlorophyll, anthocyanin content and better quenching regulation of PSI and PSII. Our data demonstrate overexpression of WsSGTL1 gene which is responsible for increase in glycosylated withanolide and sterols, and confers better growth and tolerance to both biotic and abiotic stresses.

Ectopic overexpression of WsSGTL1, a sterol glucosyltransferase gene in Withania somnifera, promotes growth, enhances glycowithanolide and provides tolerance to abiotic and biotic stresses

Overexpression of sterol glycosyltransferase (SGTL1) gene of Withania somnifera showing its involvement in glycosylation of withanolide that leads to enhanced growth and tolerance to biotic and abiotic stresses. Withania somnifera is widely used in Ayurvedic medicines for over 3000 years due to its therapeutic properties. It contains a variety of glycosylated steroids called withanosides that possess neuroregenerative, adaptogenic, anticonvulsant, immunomodulatory and antioxidant activities. The WsSGTL1 gene specific for 3β-hydroxy position has a catalytic specificity to glycosylate withanolide and sterols. Glycosylation not only stabilizes the products but also alters their physiological activities and governs intracellular distribution. To understand the functional significance and potential of WsSGTL1 gene, transgenics of W. somnifera were generated using Agrobacterium tumefaciens-mediated transformation. Stable integration and overexpression of WsSGTL1 gene were confirmed by Southern blot analysis followed by quantitative real-time PCR. The WsGTL1 transgenic plants displayed number of alterations at phenotypic and metabolic level in comparison to wild-type plants which include: (1) early and enhanced growth with leaf expansion and increase in number of stomata; (2) increased production of glycowithanolide (majorly withanoside V) and campesterol, stigmasterol and sitosterol in glycosylated forms with reduced accumulation of withanolides (withaferin A, withanolide A and withanone); (3) tolerance towards biotic stress (100 % mortality of Spodoptera litura), improved survival capacity under abiotic stress (cold stress) and; (4) enhanced recovery capacity after cold stress, as indicated by better photosynthesis performance, chlorophyll, anthocyanin content and better quenching regulation of PSI and PSII. Our data demonstrate overexpression of WsSGTL1 gene which is responsible for increase in glycosylated withanolide and sterols, and confers better growth and tolerance to both biotic and abiotic stresses.

Virus-induced gene silencing of Withania somnifera squalene synthase negatively regulates sterol and defence-related genes resulting in reduced withanolides and biotic stress tolerance

Withania somnifera (L.) Dunal is an important Indian medicinal plant that produces withanolides, which are triterpenoid steroidal lactones having diverse biological activities. To enable fast and efficient functional characterization of genes in this slow-growing and difficult-to-transform plant, a virus-induced gene silencing (VIGS) was established by silencing phytoene desaturase (PDS) and squalene synthase (SQS). VIGS of the gene encoding SQS, which provides precursors for triterpenoids, resulted in significant reduction of squalene and withanolides, demonstrating its application in studying withanolides biosynthesis in W. somnifera leaves. A comprehensive analysis of gene expression and sterol pathway intermediates in WsSQS-vigs plants revealed transcriptional modulation with positive feedback regulation of mevalonate pathway genes, and negative feed-forward regulation of downstream sterol pathway genes including DWF1 (delta-24-sterol reductase) and CYP710A1 (C-22-sterol desaturase), resulting in significant reduction of sitosterol, campesterol and stigmasterol. However, there was little effect of SQS silencing on cholesterol, indicating the contribution of sitosterol, campesterol and stigmasterol, but not of cholesterol, towards withanolides formation. Branch-point oxidosqualene synthases in WsSQS-vigs plants exhibited differential regulation with reduced CAS (cycloartenol synthase) and cycloartenol, and induced BAS (β-amyrin synthase) and β-amyrin. Moreover, SQS silencing also led to the down-regulation of brassinosteroid-6-oxidase-2 (BR6OX2), pathogenesis-related (PR) and nonexpressor of PR (NPR) genes, resulting in reduced tolerance to bacterial and fungal infection as well as to insect feeding. Taken together, SQS silencing negatively regulated sterol and defence-related genes leading to reduced phytosterols, withanolides and biotic stress tolerance, thus implicating the application of VIGS for functional analysis of genes related to withanolides formation in W. somnifera leaves.

Physiological performance, secondary metabolite and expression profiling of genes associated with drought tolerance in Withania somnifera

Physiological, biochemical, and gene expression responses under drought stress were studied in Withania somnifera. Photosynthesis rate, stomatal conductance, transpiration rate, relative water content, chlorophyll content, and quantum yield of photosystems I and II (PSI and PSII) decreased in response to drought stress. Comparative expression of genes involved in osmoregulation, detoxification, signal transduction, metabolism, and transcription factor was analyzed through quantitative RT-PCR. The genes encoding 1-pyrroline-5-carboxylate synthetase (P5CS), glutathione S-transferase (GST), superoxide dismutase (SOD), serine threonine-protein kinase (STK), serine threonine protein phosphatase (PSP), aldehyde dehydrogenase (AD), leucoanthocyanidin dioxygenase/anthocyanin synthase (LD/AS), HSP, MYB, and WRKY have shown upregulation in response to drought stress condition in leaf tissues. Enhanced detoxification and osmoregulation along with increased withanolides production were also observed under drought stress. The results of this study will be helpful in developing stress-tolerant and high secondary metabolite yielding genotypes.

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

Cytochrome P450s (CYPs) catalyse a wide variety of oxygenation/hydroxylation reactions that facilitate diverse metabolic functions in plants. Specific CYP families are essential for the biosynthesis of species-specialized metabolites. Therefore, we investigated the role of different CYPs related to secondary metabolism in Withania somnifera, a medicinally important plant of the Indian subcontinent. In this study, complete complementary DNAs (cDNAs) of four different CYP genes were isolated and christened as WSCYP93Id, WSCYP93Sm, WSCYP734B and WSCYP734R. These cDNAs encoded polypeptides comprising of 498, 496, 522 and 550 amino acid residues with their deduced molecular mass of 56.7, 56.9, 59.4 and 62.2 kDa, respectively. Phylogenetic study and molecular modelling analysis of the four cloned WSCYPs revealed their categorization into two CYP families (CYP83B1 and CYP734A1) belonging to CYP71 and CYP72 clans, respectively. BLASTp searches showed similarity of 75 and 56 %, respectively, between the two CYP members of CYP83B1 and CYP734A1 with major variances exhibited in their N-terminal regions. The two pairs of homologues exhibited differential expression profiles in the leaf tissues of selected chemotypes of W. somnifera as well as in response to treatments such as methyl jasmonate, wounding, light and auxin. Light and auxin regulated two pairs of WSCYP homologues in a developing seedling in an interesting differential manner. Their lesser resemblance and homology with other CYP sequences suggested these genes to be more specialized and distinct ones. The results on chemotype-specific expression patterns of the four genes strongly suggested their key/specialized involvement of the CYPs in the biosynthesis of chemotype-specific metabolites, though their further biochemical characterization would reveal the specificity in more detail. It is revealed that WSCYP93Id and WSCYP93Sm may be broadly involved in the oxygenation reactions in the plant and, thereby, control various pathways involving such metabolic reactions in the plant. As a representative experimental validation of this notion, WSCYP93Id was heterologouly expressed in Escherichia coli and catalytic capabilities of the recombinant WSCYP93Id protein were evaluated using withanolides as substrates. Optimized assays with some major withanolides (withanone, withaferin A and withanolide A) involving spectrophotometric as well as high-pressure liquid chromatography (HPLC)-based evaluation (product detection) of the reactions showed conversion of withaferin A to a hydroxylated product. The genes belonging to other CYP group are possibly involved in some specialised synthesis such as that of brassinosteroids.

Expression of important pathway genes involved in withanolides biosynthesis in hairy root culture of Withania somnifera upon treatment with Gracilaria edulis and Sargassum wightii

The investigation of seaweeds, Gracilaria edulis and Sargassum wightii extracts was carried out for the estimation of growth characteristics and major withanolides production in hairy root culture of Withania somnifera. The extract of G. edulis (50%) in MS liquid basal medium enabled maximum production of dry biomass (5.46 g DW) and withanolides contents (withanolide A 5.23 mg/g DW; withaferin A 2.24 mg/g DW and withanone 4.83 mg/g DW) in hairy roots after 40 days of culture with 48 h contact time. The obtained withanolides contents were significantly higher (2.32-fold-2.66-fold) in hairy root culture when compared to the control. RT PCR analysis of important pathway genes such as SE, SS, HMGR and FPPS exhibited substantial higher expression upon the seaweed extracts treatment in hairy root culture. This experiment would paw a platform for withanolides production in hairy root culture with the influence of sea weed extracts for pharmaceutical companies in the future.

WsMAGO2, a duplicated MAGO NASHI protein with fertility attributes interacts with MPF2-like MADS-box proteins

WsMAGO2 a duplicated protein in Withania through interactions with MPF2-like proteins affects male fertility by producing fewer flowers and aborted non-viable pollens/seeds regulated by anther-specific GAATTTGTGA motif. The MAGO NASHIs are highly conserved genes that encode proteins known to be involved in RNA physiology and many other developmental processes including germ cell differentiation in animals. However, their structural and functional implications in plants as fertility function proteins remained fragmented. MAGO (shorter name of MAGO NASHI) proteins form heterodimers with MPF2-like MADS-box proteins which are recruited in calyx identity and male fertility in Solanaceous plants. Four MAGO genes namely WsMAGO1 and WsMAGO2 and TaMAGO1 and TaMAGO2 were isolated from Withania somnifera and Tubocapsicum anomalum, respectively. These genes have duplicated probably due to whole genome duplication event. Dysfunction of WsMAGO2 through double-stranded RNAi in Withania revealed suppression of RNA transcripts, non-viable pollens, fewer flowers and aborted non-viable seeds in the developing berry suggesting a role of this protein in many traits particularly male fertility. WsMAGO2 flaunted stronger yeast 2-hybrid interactions with MPF2-like proteins WSA206, WSB206 and TAB201 than other MAGO counterparts. The native transcripts of WsMAGO2 culminated in stamens and seed-bearing berries though other MAGO orthologs also exhibited expression albeit at lower level. Coding sequences of the two orthologs are highly conserved, but they differ substantially in their upstream promoter regions. Remarkably, WsMAGO2 promoter is enriched with many anther-specific cis-motifs common in fertility function genes promoters. Among them, disruption of GAATTTGTGA abolished YFP/GUS gene expression in anthers alluding towards its involvement in regulating expression of MAGO in anther. Our findings support a possible recruitment of WsMAGO2 in fertility trait in Withania. These genes have practical application in hybrid production through cytoplasmic male sterility maintenance for enhancement in crops yield.

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.

Evaluation and selection of candidate reference genes for normalization of quantitative RT-PCR in Withania somnifera (L.) Dunal

Quantitative real-time PCR (qRT-PCR) is now globally used for accurate analysis of transcripts levels in plants. For reliable quantification of transcripts, identification of the best reference genes is a prerequisite in qRT-PCR analysis. Recently, Withania somnifera has attracted lot of attention due to its immense therapeutic potential. At present, biotechnological intervention for the improvement of this plant is being seriously pursued. In this background, it is important to have comprehensive studies on finding suitable reference genes for this high valued medicinal plant. In the present study, 11 candidate genes were evaluated for their expression stability under biotic (fungal disease), abiotic (wounding, salt, drought, heat and cold) stresses, in different plant tissues and in response to various plant growth regulators (methyl jasmonate, salicylic acid, abscisic acid). The data as analyzed by various software packages (geNorm, NormFinder, Bestkeeper and ΔCt method) suggested that cyclophilin (CYP) is a most stable gene under wounding, heat, methyl jasmonate, different tissues and all stress conditions. T-SAND was found to be a best reference gene for salt and salicylic acid (SA) treated samples, while 26S ribosomal RNA (26S), ubiquitin (UBQ) and beta-tubulin (TUB) were the most stably expressed genes under drought, biotic and cold treatment respectively. For abscisic acid (ABA) treated samples 18S-rRNA was found to stably expressed gene. Finally, the relative expression level of the three genes involved in the withanolide biosynthetic pathway was detected to validate the selection of reliable reference genes. The present work will significantly contribute to gene analysis studies in W. somnifera and facilitate in improving the quality of gene expression data in this plant as well as and other related plant species.

Effect of iron stress on Withania somnifera L.: antioxidant enzyme response and nutrient elemental uptake of in vitro grown plants

In the present study the response of antioxidant enzyme activities and the level of expression of their corresponding genes on bioaccumulation of iron (Fe) were investigated. In vitro germinated Withania somnifera L. were grown in Murashige and Skoog's liquid medium with increasing concentrations (0, 25, 50, 100 and 200 µM) of FeSO4 for 7 and 14 days. Root and leaf tissues analyzed for catalase (CAT, EC 1.11.1.6), superoxide dismutase (SOD, EC 1.15.1.1) and guaiacol peroxidase (GPX, EC 1.11.1.7), have shown an increase in content with respect to exposure time. Isoforms of CAT, SOD and GPX were separated using non-denaturing polyacrylamide gel electrophoresis and observed that the isoenzymes were greatly affected by higher concentrations of Fe. Reverse transcriptase polymerase chain reaction analysis performed by taking three pairs of genes of CAT (RsCat, Catalase1, Cat1) and SOD (SodCp, TaSOD1.2, MnSOD) to find out the differential expression of antioxidant genes under Fe excess. RsCat from CAT and MnSOD from SOD have exhibited high levels of gene expression under Fe stress, which was consistent with the changes of the activity assayed in solution after 7 days of treatment. Analysis by proton induced X-ray emission exhibited an increasing uptake of Fe in plants by suppressing and expressing of other nutrient elements. The results of the present study suggest that higher concentration of Fe causes disturbance in nutrient balance and induces oxidative stress in plant.

RNAi-mediated gene silencing of WsSGTL1 in W.somnifera affects growth and glycosylation pattern

Sterol glycosyltransferases (SGTs) belong to family 1 of glycosyltransferases (GTs) and are enzymes responsible for synthesis of sterol-glucosides (SGs) in many organisms. WsSGTL1 is a SGT of Withania somnifera that has been found associated with plasma membranes. However its biological function in W.somnifera is largely unknown. In the present study, we have demonstrated through RNAi silencing of WsSGTL1 gene that it performs glycosylation of withanolides and sterols resulting in glycowithanolides and glycosylated sterols respectively, and affects the growth and development of transgenic W.somnifera. For this, RNAi construct (pFGC1008-WsSGTL1) was made and genetic transformation was done by Agrobacterium tumefaciens. HPLC analysis depicts the reduction of withanoside V (the glycowithanolide of W.somnifera) and a large increase of withanolides (majorly withaferin A) content. Also, a significant decrease in level of glycosylated sterols has been observed. Hence, the obtained data provides an insight into the biological function of WsSGTL1 gene in W.somnifera.

Sterol partitioning by HMGR and DXR for routing intermediates toward withanolide biosynthesis

Withanolides biosynthesis in the plant Withania somnifera (L.) Dunal is hypothesized to be diverged from sterol pathway at the level of 24-methylene cholesterol. The conversion and translocation of intermediates for sterols and withanolides are yet to be characterized in this plant. To understand the influence of mevalonate (MVA) and 2-C-methyl-d-erythritol-4-phosphate (MEP) pathways on sterols and withanolides biosynthesis in planta, we overexpressed the WsHMGR2 and WsDXR2 in tobacco, analyzed the effect of transient suppression through RNAi, inhibited MVA and MEP pathways and fed the leaf tissue with different sterols. Overexpression of WsHMGR2 increased cycloartenol, sitosterol, stigmasterol and campesterol compared to WsDXR2 transgene lines. Increase in cholesterol was, however, marginally higher in WsDXR2 transgenic lines. This was further validated through transient suppression analysis, and pathway inhibition where cholesterol reduction was found higher due to WsDXR2 suppression and all other sterols were affected predominantly by WsHMGR2 suppression in leaf. The transcript abundance and enzyme analysis data also correlate with sterol accumulation. Cholesterol feeding did not increase the withanolide content compared to cycloartenol, sitosterol, stigmasterol and campesterol. Hence, a preferential translocation of carbon from MVA and MEP pathways was found differentiating the sterols types. Overall results suggested that MVA pathway was predominant in contributing intermediates for withanolides synthesis mainly through the campesterol/stigmasterol route in planta.

Molecular characterization of two A-type P450s, WsCYP98A and WsCYP76A from Withania somnifera (L.) Dunal: expression analysis and withanolide accumulation in response to exogenous elicitations

BACKGROUND

Pharmacological investigations position withanolides as important bioactive molecules demanding their enhanced production. Therefore, one of the pivotal aims has been to gain knowledge about complete biosynthesis of withanolides in terms of enzymatic and regulatory genes of the pathway. However, the pathway remains elusive at the molecular level. P450s monooxygenases play a crucial role in secondary metabolism and predominantly help in functionalizing molecule core structures including withanolides.

RESULTS

In an endeavor towards identification and characterization of different P450s, we here describe molecular cloning, characterization and expression analysis of two A-type P450s, WsCYP98A and WsCYP76A from Withania somnifera. Full length cDNAs of WsCYP98A and WsCYP76A have open reading frames of 1536 and 1545 bp encoding 511 (58.0 kDa) and 515 (58.7 kDa) amino acid residues, respectively. Entire coding sequences of WsCYP98A and WsCYP76A cDNAs were expressed in Escherichia coli BL21 (DE3) using pGEX4T-2 expression vector. Quantitative real-time PCR analysis indicated that both genes express widely in leaves, stalks, roots, flowers and berries with higher expression levels of WsCYP98A in stalks while WsCYP76A transcript levels were more obvious in roots. Further, transcript profiling after methyl jasmonate, salicylic acid, and gibberellic acid elicitations displayed differential transcriptional regulation of WsCYP98A and WsCYP76A. Copious transcript levels of both P450s correlated positively with the higher production of withanolides.

CONCLUSIONS

Two A-types P450 WsCYP98A and WsCYP76A were isolated, sequenced and heterologously expressed in E. coli. Both P450s are spatially regulated at transcript level showing differential tissue specificity. Exogenous elicitors acted as both positive and negative regulators of mRNA transcripts. Methyl jasmonate and salicylic acid resulted in copious expression of WsCYP98A and WsCYP76A. Enhanced mRNA levels also corroborated well with the increased accumulation of withanolides in response to elicitations. The empirical findings suggest that elicitors possibly incite defence or stress responses of the plant by triggering higher accumulation of withanolides.

WsSGTL1 gene from Withania somnifera, modulates glycosylation profile, antioxidant system and confers biotic and salt stress tolerance in transgenic tobacco

Glycosylation of sterols, catalysed by sterol glycosyltransferases (SGTs), improves the sterol solubility, chemical stability and compartmentalization, and helps plants to adapt to environmental changes. The SGTs in medicinal plants are of particular interest for their role in the biosynthesis of pharmacologically active substances. WsSGTL1, a SGT isolated from Withania somnifera, was expressed and functionally characterized in transgenic tobacco plants. Transgenic WsSGTL1-Nt lines showed an adaptive mechanism through demonstrating late germination, stunted growth, yellowish-green leaves and enhanced antioxidant system. The reduced chlorophyll content and chlorophyll fluorescence with decreased photosynthetic parameters were observed in WsSGTL1-Nt plants. These changes could be due to the enhanced glycosylation by WsSGTL1, as no modulation in chlorophyll biogenesis-related genes was observed in transgenic lines as compared to wildtype (WT) plants. Enhanced accumulation of main sterols like, campesterol, stigmasterol and sitosterol in glycosylated form was observed in WsSGTL1-Nt plants. Apart from these, other secondary metabolites related to plant's antioxidant system along with activities of antioxidant enzymes (SOD, CAT; two to fourfold) were enhanced in WsSGTL1-Nt as compared to WT. WsSGTL1-Nt plants showed significant resistance towards Spodoptera litura (biotic stress) with up to 27 % reduced larval weight as well as salt stress (abiotic stress) with improved survival capacity of leaf discs. The present study demonstrates that higher glycosylation of sterols and enhanced antioxidant system caused by expression of WsSGTL1 gene confers specific functions in plants to adapt under different environmental challenges.

Characterization of Withania somnifera leaf transcriptome and expression analysis of pathogenesis-related genes during salicylic acid signaling

Withania somnifera (L.) Dunal is a valued medicinal plant with pharmaceutical applications. The present study was undertaken to analyze the salicylic acid induced leaf transcriptome of W. somnifera. A total of 45.6 million reads were generated and the de novo assembly yielded 73,523 transcript contig with average transcript contig length of 1620 bp. A total of 71,062 transcripts were annotated and 53,424 of them were assigned GO terms. Mapping of transcript contigs to biological pathways revealed presence of 182 pathways. Seventeen genes representing 12 pathogenesis-related (PR) families were mined from the transcriptome data and their pattern of expression post 17 and 36 hours of salicylic acid treatment was documented. The analysis revealed significant up-regulation of all families of PR genes by 36 hours post treatment except WsPR10. The relative fold expression of transcripts ranged from 1 fold to 6,532 fold. The two families of peroxidases including the lignin-forming anionic peroxidase (WsL-PRX) and suberization-associated anionic peroxidase (WsS-PRX) recorded maximum expression of 377 fold and 6532 fold respectively, while the expression of WsPR10 was down-regulated by 14 fold. Additionally, the most stable reference gene for normalization of qRT-PCR data was also identified. The effect of SA on the accumulation of major secondary metabolites of W. somnifera including withanoside V, withaferin A and withanolide A was also analyzed and an increase in content of all the three metabolites were detected. This is the first report on expression patterns of PR genes during salicylic acid signaling in W. somnifera.

Functional evolution of cis-regulatory modules of STMADS11 superclade MADS-box genes

Evolution of phenotypic morphologies is closely associated with modular organization of cis-regulatory elements underlying expression divergence. The MADS-box gene family is the subject of extensive studies that try to unscramble the structural complexity of flowering plants. This study is envisaged to explore the potential of CRMs in highly constrained non-coding elements of STMADS11superclade MADS-box genes in expression divergence. Phylogenetic reconstruction differentiated the STMADS11 genes into SVP-like, ZMM19-like, MPF1-like and MPF2-like clades. Differential gene expression in vegetative and floral organs was evident within the clades as well as at inter-clade level. The genomic DNA search for clusters of short motifs and sequence conservation of the -2 kb promoter region of particularly, MPF2-like clade permitted to establish three well defined CRMs where transcription factors bind, being CRM1 the activator, CRM2 the repressor, and CRM3 the enhancer element. Similar clusters were also mapped in the large 1st introns in the coding region. Within these CRMs many transcription factor-binding sites, particularly the hotspots for MADS-domain TF binding elements--CArG-boxes, directing sepal specific expression in Arabidopsis--were accrued in the CRM1 of MPF2-like promoters. Site-directed mutagenesis and motif swapping through reporter assays allude towards their implication as functionally active elements. In terms of directional evolution of MPF2-like promoters, CRMs are significantly more conserved than flanking regions, hence, bearing the signatures for purifying selection. Thus, CRMs are the pervasive feature of STMADS11 genes and mutations and/or appearance of new transcription factor binding sites and position of the CRMs are responsible for the divergence in expression patterns in this clade. These results have implications in understanding functional evolution of cis-regulatory modules in plants.

Tropine forming tropinone reductase gene from Withania somnifera (Ashwagandha): biochemical characteristics of the recombinant enzyme and novel physiological overtones of tissue-wide gene expression patterns

Withania somnifera is one of the most reputed medicinal plants of Indian systems of medicine synthesizing diverse types of secondary metabolites such as withanolides, alkaloids, withanamides etc. Present study comprises cloning and E. coli over-expression of a tropinone reductase gene (WsTR-I) from W. somnifera, and elucidation of biochemical characteristics and physiological role of tropinone reductase enzyme in tropane alkaloid biosynthesis in aerial tissues of the plant. The recombinant enzyme was demonstrated to catalyze NADPH-dependent tropinone to tropine conversion step in tropane metabolism, through TLC, GC and GC-MS-MS analyses of the reaction product. The functionally active homodimeric ∼60 kDa enzyme catalyzed the reaction in reversible manner at optimum pH 6.7. Catalytic kinetics of the enzyme favoured its forward reaction (tropine formation). Comparative 3-D models of landscape of the enzyme active site contours and tropinone binding site were also developed. Tissue-wide and ontogenic stage-wise assessment of WsTR-I transcript levels revealed constitutive expression of the gene with relatively lower abundance in berries and young leaves. The tissue profiles of WsTR-I expression matched those of tropine levels. The data suggest that, in W. somnifera, aerial tissues as well possess tropane alkaloid biosynthetic competence. In vivo feeding of U-[¹⁴C]-sucrose to orphan shoot (twigs) and [¹⁴C]-chasing revealed substantial radiolabel incorporation in tropinone and tropine, confirming the de novo synthesizing ability of the aerial tissues. This inherent independent ability heralds a conceptual novelty in the backdrop of classical view that these tissues acquire the alkaloids through transportation from roots rather than synthesis. The TR-I gene expression was found to be up-regulated on exposure to signal molecules (methyl jasmonate and salicylic acid) and on mechanical injury. The enzyme's catalytic and structural properties as well as gene expression profiles are discussed with respect to their physiological overtones.

Overexpression of WsSGTL1 gene of Withania somnifera enhances salt tolerance, heat tolerance and cold acclimation ability in transgenic Arabidopsis plants

Background

Sterol glycosyltrnasferases (SGT) are enzymes that glycosylate sterols which play important role in plant adaptation to stress and are medicinally important in plants like Withania somnifera. The present study aims to find the role of WsSGTL1 which is a sterol glycosyltransferase from W. somnifera, in plant’s adaptation to abiotic stress.

Methodology

The WsSGTL1 gene was transformed in Arabidopsis thaliana through Agrobacterium mediated transformation, using the binary vector pBI121, by floral dip method. The phenotypic and physiological parameters like germination, root length, shoot weight, relative electrolyte conductivity, MDA content, SOD levels, relative electrolyte leakage and chlorophyll measurements were compared between transgenic and wild type Arabidopsis plants under different abiotic stresses - salt, heat and cold. Biochemical analysis was done by HPLC-TLC and radiolabelled enzyme assay. The promoter of the WsSGTL1 gene was cloned by using Genome Walker kit (Clontech, USA) and the 3D structures were predicted by using Discovery Studio Ver. 2.5.

Results

The WsSGTL1 transgenic plants were confirmed to be single copy by Southern and homozygous by segregation analysis. As compared to WT, the transgenic plants showed better germination, salt tolerance, heat and cold tolerance. The level of the transgene WsSGTL1 was elevated in heat, cold and salt stress along with other marker genes such as HSP70, HSP90, RD29, SOS3 and LEA4-5. Biochemical analysis showed the formation of sterol glycosides and increase in enzyme activity. When the promoter of WsSGTL1 gene was cloned from W. somnifera and sequenced, it contained stress responsive elements. Bioinformatics analysis of the 3D structure of the WsSGTL1 protein showed functional similarity with sterol glycosyltransferase AtSGT of A. thaliana.

Conclusions

Transformation of WsSGTL1 gene in A. thaliana conferred abiotic stress tolerance. The promoter of the gene in W.somnifera was found to have stress responsive elements. The 3D structure showed functional similarity with sterol glycosyltransferases.

Cloning and functional characterization of 3-hydroxy-3-methylglutaryl coenzyme A reductase gene from Withania somnifera: an important medicinal plant

Withania somnifera (L.) Dunal is one of the most valuable medicinal plants synthesizing a large number of pharmacologically active secondary metabolites known as withanolides, the C28-steroidal lactones derived from triterpenoids. Though the plant has been well characterized in terms of phytochemical profiles as well as pharmaceutical activities, not much is known about the biosynthetic pathway and genes responsible for biosynthesis of these compounds. In this study, we have characterized the gene encoding 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR; EC 1.1.1.34) catalyzing the key regulatory step of the isoprenoid biosynthesis. The 1,728-bp full-length cDNA of Withania HMGR (WsHMGR) encodes a polypeptide of 575 amino acids. The amino acid sequence homology and phylogenetic analysis suggest that WsHMGR has typical structural features of other known plant HMGRs. The relative expression analysis suggests that WsHMGR expression varies in different tissues as well as chemotypes and is significantly elevated in response to exposure to salicylic acid, methyl jasmonate, and mechanical injury. The functional color assay in Escherichia coli showed that WsHMGR could accelerate the biosynthesis of carotenoids, establishing that WsHMGR encoded a functional protein and may play a catalytic role by its positive influence in isoprenoid biosynthesis.

Efficient genetic transformation of Withania coagulans (Stocks) Dunal mediated by Agrobacterium tumefaciens from leaf explants of in vitro multiple shoot culture

An efficient and reproducible Agrobacterium-mediated genetic transformation of Withania coagulans was achieved using leaf explants of in vitro multiple shoot culture. The Agrobacterium strain LBA4404 harboring the binary vector pIG121Hm containing β-glucuronidase gene (gusA) under the control of CaMV35S promoter was used in the development of transformation protocol. The optimal conditions for the Agrobacterium-mediated transformation of W. coagulans were found to be the co-cultivation of leaf explants for 20 min to agrobacterial inoculum (O.D. 0.4) followed by 3 days of co-cultivation on medium supplemented with 100 μM acetosyringone. Shoot bud induction as well as differentiation occurred on Murashige and Skoog medium supplemented with 10.0 μM 6-benzylaminopurine, 8.0 μM indole 3-acetic acid, and 50.0 mgl(-1) kanamycin after three consecutive cycles of selection. Elongated shoots were rooted using a two-step procedure involving root induction in a medium containing 2.5 μM indole 3-butyric acid for 1 week and then transferred to hormone free one-half MS basal for 2 weeks. We were successful in achieving 100 % frequency of transient GUS expression with 5 % stable transformation efficiency using optimized conditions. PCR analysis of T0 transgenic plants showed the presence of gusA and nptII genes confirming the transgenic event. Histochemical GUS expression was observed in the putative transgenic W. coagulans plants. Thin layer chromatography showed the presence of similar type of withanolides in the transgenic and non-transgenic regenerated plants. A. tumefaciens mediated transformation system via leaf explants developed in this study will be useful for pathway manipulation using metabolic engineering for bioactive withanolides in W. coagulans, an important medicinal plant.

NADPH-cytochrome P450 reductase: molecular cloning and functional characterization of two paralogs from Withania somnifera (L.) dunal

Withania somnifera (L.) Dunal, a highly reputed medicinal plant, synthesizes a large array of steroidal lactone triterpenoids called withanolides. Although its chemical profile and pharmacological activities have been studied extensively during the last two decades, limited attempts have been made to decipher the biosynthetic route and identification of key regulatory genes involved in withanolide biosynthesis. Cytochrome P450 reductase is the most imperative redox partner of multiple P450s involved in primary and secondary metabolite biosynthesis. We describe here the cloning and characterization of two paralogs of cytochrome P450 reductase from W. somnifera. The full length paralogs of WsCPR1 and WsCPR2 have open reading frames of 2058 and 2142 bp encoding 685 and 713 amino acid residues, respectively. Phylogenetic analysis demonstrated that grouping of dual CPRs was in accordance with class I and class II of eudicotyledon CPRs. The corresponding coding sequences were expressed in Escherichia coli as glutathione-S-transferase fusion proteins, purified and characterized. Recombinant proteins of both the paralogs were purified with their intact membrane anchor regions and it is hitherto unreported for other CPRs which have been purified from microsomal fraction. Southern blot analysis suggested that two divergent isoforms of CPR exist independently in Withania genome. Quantitative real-time PCR analysis indicated that both genes were widely expressed in leaves, stalks, roots, flowers and berries with higher expression level of WsCPR2 in comparison to WsCPR1. Similar to CPRs of other plant species, WsCPR1 was un-inducible while WsCPR2 transcript level increased in a time-dependent manner after elicitor treatments. High performance liquid chromatography of withanolides extracted from elicitor-treated samples showed a significant increase in two of the key withanolides, withanolide A and withaferin A, possibly indicating the role of WsCPR2 in withanolide biosynthesis. Present investigation so far is the only report of characterization of CPR paralogs from W. somnifera.

Overexpression of WsSGTL1 gene of Withania somnifera enhances salt tolerance, heat tolerance and cold acclimation ability in transgenic Arabidopsis plants

BACKGROUND

Sterol glycosyltrnasferases (SGT) are enzymes that glycosylate sterols which play important role in plant adaptation to stress and are medicinally important in plants like Withania somnifera. The present study aims to find the role of WsSGTL1 which is a sterol glycosyltransferase from W. somnifera, in plant's adaptation to abiotic stress.

METHODOLOGY

The WsSGTL1 gene was transformed in Arabidopsis thaliana through Agrobacterium mediated transformation, using the binary vector pBI121, by floral dip method. The phenotypic and physiological parameters like germination, root length, shoot weight, relative electrolyte conductivity, MDA content, SOD levels, relative electrolyte leakage and chlorophyll measurements were compared between transgenic and wild type Arabidopsis plants under different abiotic stresses--salt, heat and cold. Biochemical analysis was done by HPLC-TLC and radiolabelled enzyme assay. The promoter of the WsSGTL1 gene was cloned by using Genome Walker kit (Clontech, USA) and the 3D structures were predicted by using Discovery Studio Ver. 2.5.

RESULTS

The WsSGTL1 transgenic plants were confirmed to be single copy by Southern and homozygous by segregation analysis. As compared to WT, the transgenic plants showed better germination, salt tolerance, heat and cold tolerance. The level of the transgene WsSGTL1 was elevated in heat, cold and salt stress along with other marker genes such as HSP70, HSP90, RD29, SOS3 and LEA4-5. Biochemical analysis showed the formation of sterol glycosides and increase in enzyme activity. When the promoter of WsSGTL1 gene was cloned from W. somnifera and sequenced, it contained stress responsive elements. Bioinformatics analysis of the 3D structure of the WsSGTL1 protein showed functional similarity with sterol glycosyltransferase AtSGT of A. thaliana.

CONCLUSIONS

Transformation of WsSGTL1 gene in A. thaliana conferred abiotic stress tolerance. The promoter of the gene in W.somnifera was found to have stress responsive elements. The 3D structure showed functional similarity with sterol glycosyltransferases.

Reciprocal loss of CArG-boxes and auxin response elements drives expression divergence of MPF2-Like MADS-box genes controlling calyx inflation

Expression divergence is thought to be a hallmark of functional diversification between homologs post duplication. Modification in regulatory elements has been invoked to explain expression divergence after duplication for several MADS-box genes, however, verification of reciprocal loss of cis-regulatory elements is lacking in plants. Here, we report that the evolution of MPF2-like genes has entailed degenerative mutations in a core promoter CArG-box and an auxin response factor (ARF) binding element in the large 1(st) intron in the coding region. Previously, MPF2-like genes were duplicated into MPF2-like-A and -B through genome duplication in Withania and Tubocapsicum (Withaninae). The calyx of Withania grows exorbitantly after pollination unlike Tubocapsicum, where it degenerates. Besides inflated calyx syndrome formation, MPF2-like transcription factors are implicated in functions both during the vegetative and reproductive development as well as in phase transition. MPF2-like-A of Withania (WSA206) is strongly expressed in sepals, while MPF2-like-B (WSB206) is not. Interestingly, their combined expression patterns seem to replicate the pattern of their closely related hypothetical progenitors from Vassobia and Physalis. Using phylogenetic shadowing, site-directed mutagenesis and motif swapping, we could show that the loss of a conserved CArG-box in MPF2-like-B of Withania is responsible for impeding its expression in sepals. Conversely, loss of an ARE in MPF2-like-A relaxed the constraint on expression in sepals. Thus, the ARE is an active suppressor of MPF2-like gene expression in sepals, which in contrast is activated via the CArG-box. The observed expression divergence in MPF2-like genes due to reciprocal loss of cis-regulatory elements has added to genetic and phenotypic variations in the Withaninae and enhanced the potential of natural selection for the adaptive evolution of ICS. Moreover, these results provide insight into the interplay of floral developmental and hormonal pathways during ICS development and add to the understanding of the importance of polyploidy in plants.