Cloning and characterization of 2-C-methyl-D-erythritol-4-phosphate pathway genes for isoprenoid biosynthesis from Indian ginseng, Withania somnifera

Natural Products from Physalis alkekengi L. var. franchetii (Mast.) Makino: A Review on Their Structural Analysis, Quality Control, Pharmacology, and Pharmacokinetics

The calyxes and fruits of Physalis alkekengi L. var. franchetii (Mast.) Makino (P. alkekengi), a medicinal and edible plant, are frequently used as heat-clearing and detoxifying agents in thousands of Chinese medicine prescriptions. For thousands of years in China, they have been widely used in clinical practice to treat throat disease, hepatitis, and bacillary dysentery. This systematic review summarizes their structural analysis, quality control, pharmacology, and pharmacokinetics. Furthermore, the possible development trends and perspectives for future research studies on this medicinal plant are discussed. Relevant information on the calyxes and fruits of P. alkekengi was collected from electronic databases, Chinese herbal classics, and Chinese Pharmacopoeia. Moreover, information was collected from ancient documents in China. The components isolated and identified in P. alkekengi include steroids, flavonoids, phenylpropanoids, alkaloids, nucleosides, terpenoids, megastigmane, aliphatic derivatives, organic acids, coumarins, and sucrose esters. Steroids, particularly physalins and flavonoids, are the major characteristic and bioactive ingredients in P. alkekengi. According to the literature, physalins are synthesized by the mevalonate and 2-C-methyl-d-erythritol-4-phosphate pathways, and flavonoids are synthesized by the phenylpropanoid pathway. Since the chemical components and pharmacological effects of P. alkekengi are complex and varied, there are different standards for the evaluation of its quality and efficacy. In most cases, the analysis was performed using high-performance liquid chromatography coupled with ultraviolet detection. A pharmacological study showed that the crude extracts and isolated compounds from P. alkekengi had extensive in vitro and in vivo biological activities (e.g., anti-inflammatory, anti-tumor, immunosuppressive, antibacterial, anti-leishmanial, anti-asthmatic, anti-diabetic, anti-oxidative, anti-malarial, anti-Alzheimer's disease, and vasodilatory). Moreover, the relevant anti-inflammatory and anti-tumor mechanisms were elucidated. The reported activities indicate the great pharmacological potential of P. alkekengi. Similarly, studies on the pharmacokinetics of specific compounds will also contribute to the progress of clinical research in this setting.

Natural withanolides, an update

Covering: March 2010 to December 2020. Previous review: Nat. Prod. Rep., 2011, 28, 705This review summarizes the latest progress and perspectives on the structural classification, biological activities and mechanisms, metabolism and pharmacokinetic investigations, biosynthesis, chemical synthesis and structural modifications, as well as future research directions of the promising natural withanolides. The literature from March 2010 to December 2020 is reviewed, and 287 references are cited.

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

ETHNOPHARMACOLOGICAL RELEVANCE

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

AIM OF THE STUDY

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSION

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

In silico characterization and differential expression analysis of 1-deoxy-d-xylulose-5-phosphate reductoisomerase (DXR) of Centella asiatica

The 1-deoxy-d-xylulose-5-phosphate reductoisomerase (DXR; EC1.1.1.267), an NADPH-dependent reductase, plays a pivotal role in the methylerythritol 4-phosphate pathway (MEP), in the conversion of 1-deoxy-d-xylulose-5-phosphate (DXP) into MEP. Photochemical profiles, as well as pharmaceutical activities of Centella asiatica (L.), one of the most valuable medicinal plants, divulge the presence of secondary metabolites called Centellosides. Despite well-studied pharmaceutical activities, not much is known about the genes responsible for the synthesis of these compounds. In the present study, the full-length DXR gene sequence (JQ965955) of Centella submitted in NCBI was characterized using various bioinformatics tools and tissue specific differential expression studies were also carried out. The full-length CDNA of CaDXR contains an open reading frame (ORF) of 1425 bp which encodes a peptide of 474 amino acids. The molecular weight of this protein was found to be 51.5 kDa with isoelectric point of 6.33. The protein contains three conserved domain, namely NADPH (GSTGSIGT and LAAGSNV), substrate binding (LPADSEHSAI and NKGLEVIEAHY) and Cys-Ser-(Ala/Met/Val/Thr) cleavage-site domains. Phylogenetic studies of CaDXR sequence show close homology with DXR sequence of Angelica sinensis and Daucus carota subsp sativus as they all belong to Apiaceae family. In silico analysis predicted that CaDXR protein contains 21 α-helix and 11 β-sheets and further DXR protein model was validated by Ramachandran plot analysis. The results of molecular dynamics (MD) simulations unveil dynamic stability of the proposed model and docking studies suggest that the NDP cofactor tightly binds in the active site of the protein with a strong network of hydrogen and hydrophobic interactions. The expression studies by semi-RT followed by qRT-PCR suggests that CaDXR is differentially expressed in different tissues (with maximal expression in the node and lowest in the roots). Thus, characterization and structure-function analysis of DXR gene in Centella facilitate us to understand not only the functions of DXR gene but also regulatory mechanisms involved in the MEP pathway in C. asiatica plant at the molecular level.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02723-w.

RNAi of Sterol Methyl Transferase1 Reveals its Direct Role in Diverting Intermediates Towards Withanolide/Phytosterol Biosynthesis in Withania somnifera

The medicinal properties of Ashwagandha (Withania somnifera) are accredited to a group of compounds called withanolides. 24-Methylene cholesterol is the intermediate for sterol biosynthesis and a proposed precursor of withanolide biogenesis. However, conversion of 24-methylene cholesterol to withaferin A and other withanolides has not yet been biochemically dissected. Hence, in an effort to fill this gap, an important gene, encoding S-adenosyl l-methionine-dependent sterol-C24-methyltransferase type 1 (SMT1), involved in the first committed step of sterol biosynthesis, from W. somnifera was targeted in the present study. Though SMT1 has been characterized in model plants such as Nicotiana tabacum and Arabidopsis thaliana, its functional role in phytosterol and withanolide biosynthesis was demonstrated for the first time in W. somnifera. Since SMT1 acts at many steps preceding the withanolide precursor, the impact of this gene in channeling of metabolites for withanolide biosynthesis and its regulatory nature was illustrated by suppressing the gene in W. somnifera via the RNA interference (RNAi) approach. Interestingly, down-regulation of SMT1 in W. somnifera led to reduced levels of campesterol, sitosterol and stigmasterol, with an increase of cholesterol content in the transgenic RNAi lines. In contrast, SMT1 overexpression in transgenic N. tabacum enhanced the level of all phytosterols except cholesterol, which was not affected. The results established that SMT1 plays a crucial role in W. somnifera withanolide biosynthesis predominantly through the campesterol and stigmasterol routes.

Innate endophytic fungus, Aspergillus terreus as biotic elicitor of withanolide A in root cell suspension cultures of Withania somnifera

In the present study, root cell suspension cultures of W. somnifera were elicited with mycelial extract (1% w/v) and culture filtrate (5% v/v) of their native endophytic fungus Aspergillus terreus 2aWF in shake flask. Culture filtrate of A. terreus 2aWF significantly elicits withanolide A at 6H (12.20 ± 0.52 µg/g FCB). However, with A. terreus 2aWF mycelial extract, withanolide A content was higher at 24H (10.29 µg/g FCB). Withanolide A content was maximum with salicylic acid (0.1 mM) treatment at 24H (8.3 ± 0.20 µg/g FCB). Further, expression analysis of withanolide pathway genes, hydrogen peroxide production, and lipid peroxidation was carried out after 48H of elicitation with 2aWF mycelial extract and culture filtrate. The expression levels of withanolides biosynthetic pathway genes, viz. HMGR, DXR, FPPS, SQS, SQE, CAS, SMT1, STE1 and CYP710A1 were quantified by real time PCR at 48H of elicitation. In all the treatments, the expression levels of key genes were significantly upregulated as compared to untreated suspension cells. Hydrogen peroxide was noticeably enhanced in SA, mycelia extract and culture filtrate, at 20% (115 ± 4.40 nM/g FCB), 42% (137.5 ± 3.62 nM/g FCB), and 27% (122.8 ± 1.25 nM/g FCB) respectively; however, lipid peroxidation was 0.288 ± 0.014, 0.305 ± 0.041 and 0.253 ± 0.007 (µM/gm FCB) respectively, higher than the control (0.201 ± 0.007 µM/gm FCB).

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.

Comprehensive assessment of the genes involved in withanolide biosynthesis from Withania somnifera: chemotype-specific and elicitor-responsive expression

Withania somnifera (L.) Dunal (Family, Solanaceae), is among the most valuable medicinal plants used in Ayurveda owing to its rich reservoir of pharmaceutically active secondary metabolites known as withanolides. Withanolides are C₂₈-steroidal lactones having a triterpenoidal metabolic origin synthesised via mevalonate (MVA) pathway and methyl-D-erythritol-4-phosphate (MEP) pathway involving metabolic intermediacy of 24-methylene (C₃₀-terpenoid) cholesterol. Phytochemical studies suggest differences in the content and/or nature of withanolides in different tissues of different chemotypes. Though development of genomic resources has provided information about putative genes encoding enzymes for biosynthesis of intermediate steps of terpenoid backbone, not much is known about their regulation and response to elicitation. In this study, we generated detailed molecular information about genes catalysing key regulatory steps of withanolide biosynthetic pathway. The full-length sequences of genes encoding enzymes for intermediate steps of terpenoid backbone biosynthesis and their paralogs have been characterized for their functional and structural properties as well as phylogeny using bioinformatics approach. The expression analysis suggests that these genes are differentially expressed in different tissues (with maximal expression in young leaf), chemotypes and in response to salicylic acid (SA) and methyl jasmonate (MJ) treatments. Sub-cellular localization studies suggest that both paralogs of sterol ∆-7 reductase (WsDWF5-1 and WsDWF5-2) are localized in the endoplasmic reticulum (ER) thus supporting their indispensible role in withanolide biosynthesis. Comprehensive information developed, in this study, will lead to elucidation of chemotype- as well as tissue-specific withanolide biosynthesis and development of new tools for functional genomics in this important medicinal plant.

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

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

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.

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

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

Comparative transcriptome analysis of different chemotypes elucidates withanolide biosynthesis pathway from medicinal plant Withania somnifera

Withania somnifera is one of the most valuable medicinal plants synthesizing secondary metabolites known as withanolides. Despite pharmaceutical importance, limited information is available about the biosynthesis of withanolides. Chemo-profiling of leaf and root tissues of Withania suggest differences in the content and/or nature of withanolides in different chemotypes. To identify genes involved in chemotype and/or tissue-specific withanolide biosynthesis, we established transcriptomes of leaf and root tissues of distinct chemotypes. Genes encoding enzymes for intermediate steps of terpenoid backbone biosynthesis with their alternatively spliced forms and paralogous have been identified. Analysis suggests differential expression of large number genes among leaf and root tissues of different chemotypes. Study also identified differentially expressing transcripts encoding cytochrome P450s, glycosyltransferases, methyltransferases and transcription factors which might be involved in chemodiversity in Withania. Virus induced gene silencing of the sterol ∆7-reductase (WsDWF5) involved in the synthesis of 24-methylene cholesterol, withanolide backbone, suggests role of this enzyme in biosynthesis of withanolides. Information generated, in this study, provides a rich resource for functional analysis of withanolide-specific genes to elucidate chemotype- as well as tissue-specific withanolide biosynthesis. This genomic resource will also help in development of new tools for functional genomics and breeding in Withania.

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

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

Molecular Cloning and Characterization of DXS and DXR Genes in the Terpenoid Biosynthetic Pathway of Tripterygium wilfordii

1-Deoxy-d-xylulose-5-phosphate synthase (DXS) and 1-deoxy-d-xylulose-5-phosphate reductoisomerase (DXR) genes are the key enzyme genes of terpenoid biosynthesis but still unknown in Tripterygium wilfordii Hook. f. Here, three full-length cDNA encoding DXS1, DXS2 and DXR were cloned from suspension cells of T. wilfordii with ORF sizes of 2154 bp (TwDXS1, GenBank accession no.KM879187), 2148 bp (TwDXS2, GenBank accession no.KM879186), 1410 bp (TwDXR, GenBank accession no.KM879185). And, the TwDXS1, TwDXS2 and TwDXR were characterized by color complementation in lycopene accumulating strains of Escherichia coli, which indicated that they encoded functional proteins and promoted lycopene pathway flux. TwDXS1 and TwDXS2 are constitutively expressed in the roots, stems and leaves and the expression level showed an order of roots > stems > leaves. After the suspension cells were induced by methyl jasmonate, the mRNA expression level of TwDXS1, TwDXS2, and TwDXR increased, and triptophenolide was rapidly accumulated to 149.52 µg·g⁻¹, a 5.88-fold increase compared with the control. So the TwDXS1, TwDXS2, and TwDXR could be important genes involved in terpenoid biosynthesis in Tripterygium wilfordii Hook. f.

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.

Comparative interactions of withanolides and sterols with two members of sterol glycosyltransferases from Withania somnifera

Background

Sterol glycosyltransferases (SGTs) are ubiquitous but one of the most diverse group of enzymes of glycosyltransferases family. Members of this family modulate physical and chemical properties of secondary plant products important for various physiological processes. The role of SGTs has been demonstrated in the biosynthesis of pharmaceutically important molecules of medicinal plants like Withania somnifera.

Results

Analysis suggested conserved behaviour and high similarity in active sites of WsSGTs with other plant GTs. Substrate specificity of WsSGTs were analysed through docking performance of WsSGTs with different substrates (sterols and withanolides). Best docking results of WsSGTL1 in the form of stable enzyme-substrate complex having lowest binding energies were obtained with brassicasterol, transandrosteron and WsSGTL4 with solasodine, stigmasterol and 24-methylene cholesterol.

Conclusion

This study reveals topological characters and conserved nature of two SGTs from W. somnifera (WsSGTs) i.e. WsSGTL1 and WsSGTL4. However, besides being ubiquitous in nature and with broad substrate specificity, difference between WsSGTL1 and WsSGTL4 is briefly described by difference in stability (binding energy) of enzyme-substrate complexes through comparative docking.

Electronic supplementary material

The online version of this article (doi:10.1186/s12859-015-0563-7) contains supplementary material, which is available to authorized users.

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.

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.

Comparative transcripts profiling of fruit mesocarp and endocarp relevant to secondary metabolism by suppression subtractive hybridization in Azadirachta indica (neem)

Azadirachta indica (neem) is a medicinally important plant that is valued for its bioactive secondary metabolites. Higher levels of the bioactive phytochemicals are accumulated in fruits than in other tissues. In the present study, a total of 387 and 512 ESTs, respectively, from endocarp and mesocarp of neem fruits were isolated and analyzed. Out of them 318 ESTs (82.17%) clones from endocarp and 418 ESTs (81.64%) from mesocarp encoded putative proteins that could be classified into three major gene ontology categories: biological process, molecular function and cellular component. From the analyses of contigs, 73 unigenes from the forward subtracted library and 35 unigenes from the reverse subtracted library were obtained. The ESTs from mesocarp encoded cytochrome P450 enzymes, which indicated hydroxylation to be a major metabolic event and that biogeneration of hydroxylated neem fruit phytochemicals was differentially regulated with developmental stage-specificity of synthesis. Through this study, we present the first report of any gene expression data in neem tissues. Neem hydroxy-methyl glutaryl-coenzyme A reductase (NHMGR) gene was used as expressing control vis-a-vis subtracted tissues. NHMGR was present in fruit, endocarp and mesocarp tissues, but absent in subtractive libraries, revealing that it was successfully eliminated during subtraction. Eight genes of interest from subtracted libraries were profiled for their expression in fruit, mesocarp and endocarp. Expression profiles validated the quality of the libraries and functional diversity of the tissues. The subtractive cDNA library and EST database described in this study represent a valuable transcript sequence resource for future research aimed at improving the economically important medicinal plant.

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.

De novo assembly, functional annotation and comparative analysis of Withania somnifera leaf and root transcriptomes to identify putative genes involved in the withanolides biosynthesis

Withania somnifera is one of the most valuable medicinal plants used in Ayurvedic and other indigenous medicine systems due to bioactive molecules known as withanolides. As genomic information regarding this plant is very limited, little information is available about biosynthesis of withanolides. To facilitate the basic understanding about the withanolide biosynthesis pathways, we performed transcriptome sequencing for Withania leaf (101L) and root (101R) which specifically synthesize withaferin A and withanolide A, respectively. Pyrosequencing yielded 8,34,068 and 7,21,755 reads which got assembled into 89,548 and 1,14,814 unique sequences from 101L and 101R, respectively. A total of 47,885 (101L) and 54,123 (101R) could be annotated using TAIR10, NR, tomato and potato databases. Gene Ontology and KEGG analyses provided a detailed view of all the enzymes involved in withanolide backbone synthesis. Our analysis identified members of cytochrome P450, glycosyltransferase and methyltransferase gene families with unique presence or differential expression in leaf and root and might be involved in synthesis of tissue-specific withanolides. We also detected simple sequence repeats (SSRs) in transcriptome data for use in future genetic studies. Comprehensive sequence resource developed for Withania, in this study, will help to elucidate biosynthetic pathway for tissue-specific synthesis of secondary plant products in non-model plant organisms as well as will be helpful in developing strategies for enhanced biosynthesis of withanolides through biotechnological approaches.

Qualitative and quantitative variations in withanolides and expression of some pathway genes during different stages of morphogenesis in Withania somnifera Dunal

Withania somnifera Dunal is an important and extensively studied medicinal plant; however, there is no report available that relates withanolide content and its profile in relation to the expression of pathway genes during different morphogenic stages. In this study, withanolide A, withaferin A, and withanone, the major withanolides of W. somnifera, were measured in different in vitro stages during organogenesis, viz., shoot to root (direct rhizogenesis)/root to shoot (indirect via callus phase) transition vis-à-vis expression levels of key pathway genes involved in withanolide biosynthetic pathways. The morphogenic transitions were found to be tightly linked to the pattern of accumulation of withanolides. The high expression levels of most of the pathway genes in in vitro shoots in comparison to in vitro root and callus tissues exhibited a direct co-relation with the maximum withanolide content (>2.7 mg/gDW). The biogenesis of withaferin A, a major constituent of the leaves, was however found to be tightly linked to shoots/green tissue. In addition, we were also able to establish an efficient regeneration system from roots for their further utilization in biotechnological applications.

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.