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 ß-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.

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

KEY MESSAGE: 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.

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.

Effect of cadmium stress on inductive enzymatic and nonenzymatic responses of ROS and sugar metabolism in multiple shoot cultures of Ashwagandha (Withania somnifera Dunal).

Withania somnifera is one of the most important medicinal plant and is credited with various pharmacological activities. In this study, in vitro multiple shoot cultures were exposed to different concentrations (5-300 µM) of cadmium (Cd) as cadmium sulphate to explore its ability to accumulate the heavy metal ion and its impact on the metabolic status and adaptive responses. The results showed that supplemental exposure to Cd interfered with N, P, and K uptake creating N, P, and K deficiency at higher doses of Cd that also caused stunting of growth, chlorosis, and necrosis. The study showed that in vitro shoots could markedly accumulate Cd in a concentration-dependent manner. Enzymatic activities and isozymic pattern of catalase, ascorbate peroxidase, guaiacol peroxidase, peroxidase, glutathione-S-transferase, glutathione peroxidase, monodehydroascorbate reductase, and dehydroascorbate reductase were altered substantially under Cd exposure. Sugar metabolism was also markedly modulated under Cd stress. Various other parameters including contents of photosynthetic pigments, phenolics, tocopherol, flavonoids, reduced glutathione, nonprotein thiol, ascorbate, and proline displayed major inductive responses reflecting their protective role. The results showed that interplay of enzymatic as well as nonenzymatic responses constituted a system endeavor of tolerance of Cd accumulation and an efficient scavenging strategy of its stress implications.

Withanolides from Withania somnifera Dunal: development of cellular technology and their production.

Withania somnifera Dunal is one of the most commonly used plants in Ayurvedic and indigenous system of medicine in India for over thousands of years. In view of its varied therapeutic potential, the plant has also been the subject of considerable scientific attention. The major chemical constituents of the Withania genus, the withanolides, are a group of naturally occurring C28-steroidal lactones built on an intact or rearranged ergostane framework, in which C22 and C26 are oxidized to form a six-member lactone ring. In recent years, numerous pharmacological investigations have been carried out utilizing W. somnifera extracts and several patents have been filed on pharmacological and medicinal importance of withanolides and extracts of W. somnifera, individually or in combination. Considering the immense importance of withanolides for medicinal purposes, the establishment of strategies to improve withanolides yield are highly desirable. Under natural conditions, W. somnifera possesses restricted levels of withanolides then, alternatives for obtaining withanolides in better yields are imperative. In vitro approaches followed by metabolic engineering could be attractive tools to achieve this goal. Therefore, we present here an overview of the development of various protocols for in vitro tissue regeneration from W. somnifera and in vitro secondary metabolite production as well. The review also gives an account of selected patents on various important activities of phytochemicals and extracts of W. somnifera.

Effect of gibberellic acid and calliterpenone on plant growth attributes, trichomes, essential oil biosynthesis and pathway gene expression in differential manner in Mentha arvensis L.

Extensive research is going on throughout the world to find out new molecules from natural sources to be used as plant growth promoter. Mentha arvensis L. is the main source of menthol rich essential oil used commercially in various food, pharmaceutical and other preparations. Experiments were conducted on field grown plants for understanding the effect of calliterpenone (CA), a stereo-isomer of abbeokutone, in comparison to gibberellic acid (GA3) on growth attributes, trichomes, essential oil biosynthesis and expression of some oil biosynthetic pathway genes. The exogenous application of CA (1 µM, 10 µM and 100 µM) was found to be better in improving plant biomass and stolon yield, leaf area, branching and leaf stem ratio than with counterpart GA3 at the same concentrations. CA treated plants showed higher glandular trichome number, density and diameter and also correlated with enhanced oil biogenetic capacity as revealed by feeding labeled (14)C-sucrose for 72 h to excised shoots. Semi-quantitative PCR analysis of key pathway genes revealed differential up regulation under CA treatments. Transcript level of menthol dehydrogenase/menthone reductase was found highly up regulated in CA treated plants with increased content of menthone and menthol in oil. These findings demonstrate that CA positively regulated the yields by enhanced branching and higher density of trichomes resulting into higher accumulation of essential oil. The results suggest CA as a novel plant derived diterpenoid with growth promoting action and opens up new possibilities for improving the crop yields and essential oil biosynthesis in qualitative and quantitative manner.

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.

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 ß-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.