Comparative Study of Withanolide Biosynthesis-Related miRNAs in Root and Leaf Tissues of Withania somnifera

Metabolic engineering for enhanced terpenoid production: Leveraging new horizons with an old technique

Terpenoids are a vast class of plant specialized metabolites (PSMs) manufactured by plants and are involved in their interactions with environment. In addition, they add health benefits to human nutrition and are widely used as pharmaceutically active compounds. However, native plants produce a limited amount of terpenes restricting metabolite yield of terpene-related metabolites. Exponential growth in the plant metabolome data and the requirement of alternative approaches for producing the desired amount of terpenoids, has redirected plant biotechnology research to plant metabolic engineering, which requires in-depth knowledge and precise expertise about dynamic plant metabolic pathways and cellular physiology. Metabolic engineering is an assuring tool for enhancing the concentration of terpenes by adopting specific strategies such as overexpression of the key genes associated with the biosynthesis of targeted metabolites, controlling the modulation of transcription factors, downregulation of competitive pathways (RNAi), co-expression of the biosynthetic pathway genes in heterologous system and other combinatorial approaches. Microorganisms, fast-growing host plants (such as Nicotiana benthamiana), and cell suspension/callus cultures have provided better means for producing valuable terpenoids. Manipulation in the biosynthetic pathways responsible for synthesis of terpenoids can provide opportunities to enhance the content of desired terpenoids and open up new avenues to enhance their production. This review deliberates the worth of metabolic engineering in medicinal plants to resolve issues associated with terpenoid production at a commercial scale. However, to bring the revolution through metabolic engineering, further implementation of genome editing, elucidation of metabolic pathways using omics approaches, system biology approaches, and synthetic biology tactics are essentially needed.

Predictive Role of Cluster Bean (Cyamopsis tetragonoloba) Derived miRNAs in Human and Cattle Health

MicroRNAs (miRNAs) are small non-coding conserved molecules with lengths varying between 18-25nt. Plants miRNAs are very stable, and probably they might have been transferred across kingdoms via food intake. Such miRNAs are also called exogenous miRNAs, which regulate the gene expression in host organisms. The miRNAs present in the cluster bean, a drought tolerant legume crop having high commercial value, might have also played a regulatory role for the genes involved in nutrients synthesis or disease pathways in animals including humans due to dietary intake of plant parts of cluster beans. However, the predictive role of miRNAs of cluster beans for gene-disease association across kingdoms such as cattle and humans are not yet fully explored. Thus, the aim of the present study is to (i) find out the cluster bean miRNAs (cb-miRs) functionally similar to miRNAs of cattle and humans and predict their target genes' involvement in the occurrence of complex diseases, and (ii) identify the role of cb-miRs that are functionally non-similar to the miRNAs of cattle and humans and predict their targeted genes' association with complex diseases in host systems. Here, we predicted a total of 33 and 15 functionally similar cb-miRs (fs-cb-miRs) to human and cattle miRNAs, respectively. Further, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed the participation of targeted genes of fs-cb-miRs in 24 and 12 different pathways in humans and cattle, respectively. Few targeted genes in humans like LCP2, GABRA6, and MYH14 were predicted to be associated with disease pathways of Yesinia infection (hsa05135), neuroactive ligand-receptor interaction (hsa04080), and pathogenic Escherichia coli infection (hsa05130), respectively. However, targeted genes of fs-cb-miRs in humans like KLHL20, TNS1, and PAPD4 are associated with Alzheimer's, malignant tumor of the breast, and hepatitis C virus infection disease, respectively. Similarly, in cattle, targeted genes like ATG2B and DHRS11 of fs-cb-miRs participate in the pathways of Huntington disease and steroid biosynthesis, respectively. Additionally, the targeted genes like SURF4 and EDME2 of fs-cb-miRs are associated with mastitis and bovine osteoporosis, respectively. We also found a few cb-miRs that do not have functional similarity with human and cattle miRNAs but are found to target the genes in the host organisms and as well being associated with human and cattle diseases. Interestingly, a few genes such as NRM, PTPRE and SUZ12 were observed to be associated with Rheumatoid Arthritis, Asthma and Endometrial Stromal Sarcoma diseases, respectively, in humans and genes like SCNN1B associated with renal disease in cattle.

Insights into microRNA-mediated interaction and regulation of metabolites in tomato

microRNAs direct regulation of various metabolic pathways in plants and animals. miRNAs may be useful in developing novel/elite genotypes, with enhanced metabolites and disease resistance. We examined miRNAs in tomato. In tomato, miRNAs in the carotenoid pathway have not been fully elucidated. We examined the potential role of miRNAs in biosynthesis of carotenoids, transcript profiling of miRNAs and their possible targets (genes and transcription factors) at different development stages of tomato using stem-loop PCR and RT-qPCR. We also identified miRNAs targeting key flavonoid genes, such as chalcone isomerase (CHI), and dihydroflavonol-4-reductase (DFR). Distinct expression profiles of miRNAs and their targets were found in fruits of three tomato accessions, suggesting carotenoid regulation by miRNAs at various stages of fruit development. This was also confirmed using HPLC of the carotenoids. The present study may help in understanding possible regulation of carotenoid biosynthesis. The identified miRNAs can be exploited to enhance biosynthesis of different carotenoids in plants.

A critical assessment of the whole plant-based phytotherapeutics from Withania somnifera (L.) Dunal with respect to safety and efficacy vis-a-vis leaf or root extract-based formulation

Withania somnifera (L.) Dunal, popularly known as Ashwagandha or Indian ginseng, is well acclaimed for its health-enhancing effects, including its potent immunomodulatory, anti-inflammatory, neuroprotective, and anti-tumorigenic properties. The prime biological effectors of these attributes are a diverse group of ergostane-based steroidal lactones termed withanolides. Withanones and withanosides are distributed differentially across the plant body, whereas withanolides and withanones are known to be more abundant in leaves, while withanosides are found exclusively in the roots of the plants. Standardized W. somnifera extract is Generally Recognized as Safe (GRAS)-affirmed, however, moderate to severe toxic manifestations may occur at high dosages. Withaferin A, which also happens to be the primary bioactive ingredient for the effectiveness of this plant. There have been contrasting reports regarding the distribution of withaferin A in W. somnifera. While most reports state that the roots of the plant have the highest concentrations of this phytochemical, several others have indicated that leaves can accumulate withaferin A in proportionately higher amounts. A comprehensive survey of the available reports suggests that the biological effects of Ashwagandha are grossly synergistic in nature, with many withanolides together mediating the desired physiological effect. In addition, an assorted formulation of withanolides can also neutralize the toxic effects (if any) associated with withaferin A. This mini-review presents a fresh take on the recent developments regarding the safety and toxicity of the plant, along with a critical assessment of the use of roots against leaves as well as whole plants to develop therapeutic formulations. Going by the currently available scientific evidence, it is safe to infer that the use of whole plant formulations instead of exclusively root or leaf recipes may present the best possible option for further exploration of therapeutic benefits from this novel medicinal plant.HighlightsTherapeutic potential of withanolides owes to the presence of α,β unsaturated ketone which binds to amines, alcohols, and esters and 5β, 6β epoxy group which react with side chain thiols of proteins.At concentrations above NOAEL (no observed adverse effect level), the same mechanisms contribute towards toxicity of the molecule.Although withanosides are found exclusively in roots, whole plants have higher contents of withanones and withanolides.Whole plant-based formulations have other metabolites which can nullify the toxicity associated with roots.Extracts made from whole plants, therefore can holistically impart all therapeutic benefits as well as mitigate toxicity.

Identification of Cumin (Cuminum cyminum) MicroRNAs through Deep Sequencing and Their Impact on Plant Secondary Metabolism

The pharmacological properties of plants lie in the content of secondary metabolites that are classified into different categories based on their biosynthesis, structures, and functions. MicroRNAs (miRNAs) are small non-coding RNA molecules that play crucial post-transcriptional regulatory roles in plants, including development and stress-response signaling; however, information about their involvement in secondary metabolism is still limited. Cumin is one of the most popular seeds from the plant Cuminum cyminum, with extensive applications in herbal medicine and cooking; nevertheless, no previous studies focus on the miRNA profile of cumin. In this study, the miRNA profile of C. cyminum and its association with the biosynthesis of secondary metabolites were determined using NGS technology. The sequencing data yielded 10,956,054 distinct reads with lengths ranging from 16 to 40 nt, of which 349 miRNAs were found to be conserved and 39 to be novel miRNAs. Moreover, this work identified 1959 potential target genes for C. cyminum miRNAs. It is interesting to note that several conserved and novel miRNAs have been found to specifically target important terpenoid backbone, flavonoid biosynthesis, and lipid/fatty acid pathways enzymes. We believe this investigation will aid in elucidating the implications of miRNAs in plant secondary metabolism.

MicroRNAs in Medicinal Plants

Medicinal plant microRNAs (miRNAs) are an endogenous class of small RNA central to the posttranscriptional regulation of gene expression. Biosynthetic research has shown that the mature miRNAs in medicinal plants can be produced from either the standard messenger RNA splicing mechanism or the pre-ribosomal RNA splicing process. The medicinal plant miRNA function is separated into two levels: (1) the cross-kingdom level, which is the regulation of disease-related genes in animal cells by oral intake, and (2) the intra-kingdom level, which is the participation of metabolism, development, and stress adaptation in homologous or heterologous plants. Increasing research continues to enrich the biosynthesis and function of medicinal plant miRNAs. In this review, peer-reviewed papers on medicinal plant miRNAs published on the Web of Science were discussed, covering a total of 78 species. The feasibility of the emerging role of medicinal plant miRNAs in regulating animal gene function was critically evaluated. Staged progress in intra-kingdom miRNA research has only been found in a few medicinal plants, which may be mainly inhibited by their long growth cycle, high demand for growth environment, immature genetic transformation, and difficult RNA extraction. The present review clarifies the research significance, opportunities, and challenges of medicinal plant miRNAs in drug development and agricultural production. The discussion of the latest results furthers the understanding of medicinal plant miRNAs and helps the rational design of the corresponding miRNA/target genes functional modules.

An insight into microRNA biogenesis and its regulatory role in plant secondary metabolism

The present review highlights the regulatory roles of microRNAs in plant secondary metabolism and focuses on different bioengineering strategies to modulate secondary metabolite content in plants. MicroRNAs (miRNAs) are the class of small endogenous, essential, non-coding RNAs that riboregulate the gene expression involved in various biological processes in most eukaryotes. MiRNAs has emerged as important regulators in plants that function by silencing target genes through cleavage or translational inhibition. These miRNAs plays an important role in a wide range of plant biological and metabolic processes, including plant development and various environmental response controls. Several important plant secondary metabolites like alkaloids, terpenoids, and phenolics are well studied for their function in plant defense against different types of pests and herbivores. Due to the presence of a wide range of biological and pharmaceutical properties of plant secondary metabolites, it is important to study the regulation of their biosynthetic pathways. The contribution of miRNAs in regulating plant secondary metabolism is not well explored. Recent advancements in molecular techniques have improved our knowledge in understanding the molecular function of genes, proteins, enzymes, and small RNAs involved in different steps of secondary metabolic pathways. In the present review, we have discussed the recent progress made on miRNA biogenesis, its regulation, and highlighted the current research developed in the field of identification, analysis, and characterizations of various miRNAs that regulate plant secondary metabolism. We have also discussed how different bioengineering strategies such as artificial miRNA (amiRNA), endogenous target mimicry, and CRISPR/Cas9 could be utilized to enhance the secondary metabolite production in plants.

Biosynthesis of Secondary Metabolites Based on the Regulation of MicroRNAs

MicroRNA (miRNA), a noncoding ribonucleic acid, is considered to be important for the progression of gene expression in plants and animals by rupture or translational repression of targeted mRNAs. Many types of miRNA regulate plant metabolism, growth, and response to biotic and abiotic factors. miRNA characterization helps to expose its function in regulating the process of post-transcriptional genetic regulation. There are a lot of factors associated with miRNA function, but the function of miRNA in the organic synthesis of by-products by natural products is not yet fully elucidated. The current review is aimed at observing and characterizing miRNAs and identifying those involved in the functioning of the biosynthesis of secondary metabolites in plants, with their use in controlled manipulation.

Identification of microRNAs from Medicinal Plant Murraya koenigii by High-Throughput Sequencing and Their Functional Implications in Secondary Metabolite Biosynthesis

MicroRNAs (miRNAs) are small noncoding RNA molecules that play crucial post-transcriptional regulatory roles in plants, including development and stress-response signaling. However, information about their involvement in secondary metabolism is still limited. Murraya koenigii is a popular medicinal plant, better known as curry leaves, that possesses pharmaceutically active secondary metabolites. The present study utilized high-throughput sequencing technology to investigate the miRNA profile of M. koenigii and their association with secondary metabolite biosynthesis. A total of 343,505 unique reads with lengths ranging from 16 to 40 nt were obtained from the sequencing data, among which 142 miRNAs were identified as conserved and 7 as novel miRNAs. Moreover, 6078 corresponding potential target genes of M. koenigii miRNAs were recognized in this study. Interestingly, several conserved and novel miRNAs of M. koenigii were found to target key enzymes of the terpenoid backbone and the flavonoid biosynthesis pathways. Furthermore, to validate the sequencing results, the relative expression of eight randomly selected miRNAs was determined by qPCR. To the best of our knowledge, this is the first report of the M. koenigii miRNA profile that may provide useful information for further elucidation of the involvement of miRNAs in secondary metabolism. These findings might be crucial in the future to generate artificial-miRNA-based, genetically engineered M. koenigii plants for the overproduction of medicinally highly valuable secondary metabolites.

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.

Noncoding RNAs in Medicinal Plants and their Regulatory Roles in Bioactive Compound Production

BACKGROUND

Noncoding RNAs (ncRNAs), such as microRNAs (miRNAs), small interfering RNAs (siRNAs) and long noncoding RNAs (lncRNAs), play significant regulatory roles in plant development and secondary metabolism and are involved in plant response to biotic and abiotic stresses. They have been intensively studied in model systems and crops for approximately two decades and massive amount of information have been obtained. However, for medicinal plants, ncRNAs, particularly their regulatory roles in bioactive compound biosynthesis, are just emerging as a hot research field.

OBJECTIVE

This review aims to summarize current knowledge on herbal ncRNAs and their regulatory roles in bioactive compound production.

RESULTS

So far, scientists have identified thousands of miRNA candidates from over 50 medicinal plant species and 11794 lncRNAs from Salvia miltiorrhiza, Panax ginseng, and Digitalis purpurea. Among them, more than 30 miRNAs and five lncRNAs have been predicted to regulate bioactive compound production.

CONCLUSION

The regulation may achieve through various regulatory modules and pathways, such as the miR397-LAC module, the miR12112-PPO module, the miR156-SPL module, the miR828-MYB module, the miR858-MYB module, and other siRNA and lncRNA regulatory pathways. Further functional analysis of herbal ncRNAs will provide useful information for quality and quantity improvement of medicinal plants.

The Critical Role of Small RNAs in Regulating Plant Innate Immunity

Plants, due to their sessile nature, have an innate immune system that helps them to defend against different pathogen infections. The defense response of plants is composed of a highly regulated and complex molecular network, involving the extensive reprogramming of gene expression during the presence of pathogenic molecular signatures. Plants attain proper defense against pathogens through the transcriptional regulation of genes encoding defense regulatory proteins and hormone signaling pathways. Small RNAs are emerging as versatile regulators of plant development and act in different tiers of plant immunity, including pathogen-triggered immunity (PTI) and effector-triggered immunity (ETI). The versatile regulatory functions of small RNAs in plant growth and development and response to biotic and abiotic stresses have been widely studied in recent years. However, available information regarding the contribution of small RNAs in plant immunity against pathogens is more limited. This review article will focus on the role of small RNAs in innate immunity in plants.

Blocking miR530 Improves Rice Resistance, Yield, and Maturity

MicroRNAs fine-tune plant growth and resistance against multiple biotic and abiotic stresses. The trade-off between biomass and resistance can penalize crop yield. In this study, we have shown that rice miR530 regulates blast disease resistance, yield, and growth period. While the overexpression of miR530 results in compromised blast disease resistance, reduced grain yield, and late maturity, blocking miR530 using a target mimic (MIM530) leads to enhanced resistance, increased grain yield, and early maturity. Further study revealed that the accumulation of miR530 was decreased in both leaves and panicles along with the increase of age. Such expression patterns were accordant with the enhanced resistance from seedlings to adult plants, and the grain development from panicle formation to fully-filled seeds. Divergence analysis of miR530 precursor with upstream 1,000-bp promoter sequence in 11 rice species revealed that miR530 was diverse in Oryza sativa japonica and O. sativa indica group, which was consistent with the different accumulation of miR530 in japonica accessions and indica accessions. Altogether, our results indicate that miR530 coordinates rice resistance, yield, and maturity, thus providing a potential regulatory module for breeding programs aiming to improve yield and disease resistance.

In Silico Identification of miRNA and Targets from Chrysopogon zizanioides (L.) Roberty with Functional Validation from Leaf and Root Tissues

microRNAs are small non-coding RNA molecule that plays an important role in metabolism. Chrysopogon zizanioides (L.) Roberty is an important aromatic plant used in perfumery industries, soil, water conservation, and agricultural practices. In this study, the transcriptomic sequence of vetiver leaf and root was subjected to miRNA identification by the computational methods. miRNA identification was carried out using a homology-based method by C-mii software with several other online tools. A total of 80 miRNA were identified from both leaf and root sequences. Target identification was done by identified miRNA sets. A total of 25 and 31 miRNA families were identified in both leaf and root, respectively, with ten common families involve in different ontological function. miR169 and miR5021 regulate most of the target in leaf and root. In vetiver, many primary and secondary metabolism elements are regulated by miRNA as photo-system, transcription factor, terpenoid metabolism, etc. Here is the first in silico study revealing the specific miRNAs and their target genes for corresponding root and leaf tissues respectively in C. zizanioides.

De novo transcriptome analysis unravels tissue-specific expression of candidate genes involved in major secondary metabolite biosynthetic pathways of Plumbago zeylanica: implication for pharmacological potential

KEY MESSAGE

The present study provides comparative transcriptome analysis, besides identifying functional secondary metabolite genes of Plumbago zeylanica with pharmacological potential for future functional genomics, and metabolomic engineering of secondary metabolites from this plant towards diversified biomedical applications.

ABSTRACT

Plumbago zeylanica is a widely used medicinal plant of the traditional Indian system of medicine with wide pharmacological potential to treat several disorders. The present study aimed to carry out comparative transcriptome analysis in leaf and root tissue of P. zeylanica using Illumina paired end sequencing to identify tissue-specific functional genes involved in the biosynthesis of secondary metabolites, contributing to its therapeutic efficacy. De novo sequencing assembly resulted in the identification of 62,321 "Unigenes" transcripts with an average size of 1325 bp. Functional annotation using BLAST2GO resulted in the identification of 50,301 annotated transcripts (80.71%) and GO assigned to 18,814 transcripts. KEGG pathway annotation of the "Unigenes" revealed that 2465 transcripts could be assigned to 242 KEGG pathway maps wherein the number of transcripts involved in secondary metabolism was distinct in root and leaf transcriptome. Among the secondary metabolite biosynthesis pathways, the cluster of "Unigenes" encoding enzymes of 'Phenylpropanoid biosynthesis pathway' represents the largest group (84 transcripts) followed by 'Terpenoid Backbone biosynthesis' (48 transcripts). The transcript levels of the candidate unigenes encoding key enzymes of phenylpropanoid (PAL, TAL) and flavanoid biosynthesis (CHS, ANS, FLS) pathways were up-regulated in root, while the expression levels of candidate "Unigenes" transcript for monoterpenoid (DXS, ISPF), diterpenoid biosynthesis (SPS, SDS) and indole alkaloid pathways (STR) were significantly higher in leaf of P. zeylanica. Interestingly, validation of differential gene expression profile by qRT-PCR also confirmed that candidate "Unigenes" enzymes of phenylpropanoid and flavonoid biosynthesis were highly expressed in the root, while the key regulatory enzymes of terpenoid and indole alkaloid compounds were up-regulated in the leaf, suggesting that (differences in) the levels of these functional genes could be attributed to the (differential) pharmacological activity (between root and leaf) in tissues of P. zeylanica.

Role of ashwagandha methanolic extract in the regulation of thyroid profile in hypothyroidism modeled rats

This study aimed to evaluate the anti-hypothyroidism potential of ashwagandha methanolic extract (AME). This target was performed through induction of animal model of hypothyroidism by propylthiouracil. After 1 month from treatments, blood samples were collected for biochemical determinations, and liver and kidney were removed for the determination of oxidative stress markers and thyroid gland was removed for histopathological examination. The total phenolic compounds in the extract and the in vitro radical scavenging activity of extract were also determined. The results revealed that the induction of hypothyroidism by propylthiouracil induced a significant increase in serum TSH level but it induced significant decreases in the levels of total T3, free T3, free T4, and total T4 hormones compared with the control values. Also, serum glucose, Il-6, and body weight gain increased significantly while Il-10 and blood hemoglobin levels showed significant decrease. Induction of hypothyroidism increased also the levels of hepatic and renal MDA and NO and decreased significantly the values of GSH, GPx and Na⁺/ K⁺-ATPase. Both AME and the anti-hypothyroidism drug significantly ameliorated the changes occurred in the levels of the above parameters and improved histological picture of thyroid gland but with different degrees; where ashwagandha methanolic extract showed the strongest effect. We can conclude that ashwagandha methanolic extract treatment improves thyroid function by ameliorating thyroid hormones and by preventing oxidative stress.

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).

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.