Elicitation Based Enhancement of Secondary Metabolites in Rauwolfia serpentina and Solanum khasianum Hairy Root Cultures

Enhancement of production of glycoalkaloids by elicitors along with characterization of gene expression of pathways in Solanum xanthocarpum

Solanum xanthocarpum fruits are used in the treatment of cough, fever, and heart disorders. It possesses antipyretic, hypotensive, antiasthmatic, aphrodisiac and antianaphylactic properties. In the present study, 24 elicitors (both biotic and abiotic) were used to enhance the production of glycoalkaloids in cell cultures of S. xanthocarpum. Four concentrations of elicitors were added into the MS culture medium. The maximum accumulation (5.56-fold higher than control) of demissidine was induced by sodium nitroprusside at 50 mM concentration whereas the highest growth of cell biomass (4.51-fold higher than control) stimulated by systemin at 30 mM concentration. A total of 17 genes of biosynthetic pathways of glycoalkaloids were characterized from the cells of S. xanthocarpum. The greater accumulation of demissidine was confirmed with the expression analysis of 11 key biosynthetic pathway enzymes e.g., acetoacetic-CoA thiolase, 3- hydroxy 3-methyl glutaryl synthase, β-hydroxy β-methylglutaryl CoA reductase, mevalonate kinase, farnesyl diphosphate synthase, squalene synthase, squalene epoxidase, squalene-2,3- epoxide cyclase, cycloartenol synthase, UDP-glucose: solanidine glucosyltransferase and UDP-rhamnose: solanidine rhamno-galactosyl transferase. The maximum expression levels of UDP-rhamnose: solanidine rhamno-galactosyl transferase gene was recorded in this study.

Identification and Functional Characterization of the SaMYB113 Gene in Solanum aculeatissimum

The MYB transcription factors (TFs) have substantial functions in anthocyanin synthesis as well as being widely associated with plant responses to various adversities. In the present investigation, we found an unreported MYB TF from Solanum aculeatissimum (a wild relative of eggplant) and named it SaMYB113 in reference to its homologous gene. Bioinformatics analysis demonstrated that the open reading frame of SaMYB113 was 825 bp in length, encoding 275 amino acids, with a typical R2R3-MYB gene structure, and predicted subcellular localization in the nucleus. Analysis of the tissue-specific expression pattern through qRT-PCR showed that the SaMYB113 was expressed at a high level in young stems as well as leaves of S. aculeatissimum. Transgenic Arabidopsis and tobacco plants overexpressing SaMYB113 pertinent to the control of the 35S promoter exhibited a distinct purple color trait, suggesting a significant change in their anthocyanin content. Furthermore, we obtained three tobacco transgenic lines with significant differences in anthocyanin accumulation and analyzed the differences in anthocyanin content by LC-MS/MS. The findings demonstrated that overexpression of SaMYB113 caused tobacco to have considerably raised levels of several anthocyanin components, with the most significant increases in delphinidin-like anthocyanins and cyanidin-like anthocyanins. The qRT-PCR findings revealed significant differences in the expression levels of structural genes for anthocyanin synthesis among various transgenic lines. In summary, this study demonstrated that the SaMYB113 gene has a substantial impact on anthocyanin synthesis, and overexpression of the SaMYB113 gene leads to significant modifications to the expression levels of a variety of anthocyanin-synthesizing genes, which leads to complex changes in anthocyanin content and affects plant phenotypes. This present research offers the molecular foundation for the research of the mechanism of anthocyanin formation within plants, as well as providing some reference for the improvement of traits in solanum crops.

Hairy root culture: a potent method for improved secondary metabolite production of Solanaceous plants

Secondary metabolites synthesized by the Solanaceous plants are of major therapeutic and pharmaceutical importance, many of which are commonly obtained from the roots of these plants. 'Hairy roots', mirroring the same phytochemical pattern of the corresponding root of the parent plant with higher growth rate and productivity, are therefore extensively studied as an effective alternative for the in vitro production of these metabolites. Hairy roots are the transformed roots, generated from the infection site of the wounded plants with Agrobacterium rhizogenes. With their fast growth, being free from pathogen and herbicide contamination, genetic stability, and autotrophic nature for plant hormones, hairy roots are considered as useful bioproduction systems for specialized metabolites. Lately, several elicitation methods have been employed to enhance the accumulation of these compounds in the hairy root cultures for both small and large-scale production. Nevertheless, in the latter case, the cultivation of hairy roots in bioreactors should still be optimized. Hairy roots can also be utilized for metabolic engineering of the regulatory genes in the metabolic pathways leading to enhanced production of metabolites. The present study summarizes the updated and modern biotechnological aspects for enhanced production of secondary metabolites in the hairy root cultures of the plants of Solanaceae and their respective importance.

Stability estimation through multivariate approach among solasodine-rich lines of Solanum khasianum (C.B. Clarke): an important industrial plant

Solanum khasianum is a medicinally important plant that is a source of steroidal alkaloids 'solasodine.' It has various industrial applications, including oral contraceptives and other pharmaceutical uses. The present study was based on 186 germplasm of S. khasianum, which were analyzed for the stability of economically important traits like solasodine content and fruit yield. The collected germplasm was planted during Kharif 2018, 2019, and 2020 in RCBD with three replications at the experimental farm of CSIR-NEIST, Jorhat, Assam, India. A multivariate approach for stability analysis was applied to identify stable germplasm of S. khasianum for economically important traits. The germplasm was analyzed for additive main effects and multiplicative interaction (AMMI), GGE biplot, multi-trait stability index, and Shukla's variance which were evaluated for three environments. The AMMI ANOVA revealed significant GE interaction for all the studied traits. The stable and high-yielding germplasm was identified from the AMMI biplot, GGE biplot, Shukla's variance value, and MTSI plot analysis. Lines no. 90, 85, 70, 107, and 62 were identified as highly stable fruit yielders while, lines no. 1, 146, and 68 were identified as stable high solasodine lines. However, considering both traits, i.e., high fruit yield and solasodine content, MTSI analysis was performed which showed that lines 1, 85, 70,155, 71, 114, 65, 86, 62, 116, 32, and 182 could be used in a breeding program. Thus, this identified germplasm can be considered for further varietal development and could be used in a breeding program. The findings of the present study would be beneficial for the S. khasianum breeding program.

Differential Response of Phenol Metabolism Associated with Antioxidative Network in Elicited Grapevine Suspension Cultured Cells under Saline Conditions

Highly productive trans-resveratrol (t-R) grapevine suspension cultured cells (SCC) and two effective elicitors, methyl jasmonate (MJ) and randomly methylated β-cyclodextrins (CDs), were used to analyze the extent to which salt treatments alter the production of bioactive phenolic compounds. The expression/activity profile of the enzymes involved in phenol metabolism and antioxidant networks were also studied. A marked extracellular accumulation of phenolic compounds, especially t-R, was found in SCC elicited with CDs and/or MJ under saline conditions. However, the treatments with MJ alone and all those combined with salt favored the intracellular accumulation of catechin and ferulic acid. The salt-induced accumulation of phenolics was correlated with the higher total antioxidant capacity values found in cells, suggesting that cellular redox homeostasis under saline conditions was largely maintained by increasing phenolic compound production. These higher levels of phenolics found in elicited cells under saline conditions fit well with the highest activity of phenylalanine ammonia-lyase. Moreover, antioxidant enzyme activities were boosted in treatments with MJ and/or in those combined with salt and decreased in those treated with CDs. These results suggest a differential response of the antioxidative network to the presence of elicitors under saline conditions.

Ajmalicine and its Analogues Against AChE and BuChE for the Management of Alzheimer's Disease: An In-silico Study

BACKGROUND

Alzheimer's disease (AD) is the most well-known reason for disability in persons aged greater than 65 years worldwide. AD influences the part of the brain that controls cognitive and non-cognitive functions.

OBJECTIVE

The study focuses on the screening of natural compounds for the inhibition of AChE and BuChE using a computational methodology.

METHODS

We performed a docking-based virtual screening utilizing the 3D structure of AChE and BuChE to search for potential inhibitors for AD. In this work, a screened inhibitor Ajmalicine similarity search was carried out against a natural products database (Super Natural II). Lipinski rule of five was carried out and docking studies were performed between ligands and enzyme using 'Autodock4.2'.

RESULTS

Two phytochemical compounds SN00288228 and SN00226692 were predicted for the inhibition of AChE and BuChE, respectively. The docking results revealed Ajmalicine, a prominent natural alkaloid, showing promising inhibitory potential against AChE and BuChE with the binding energy of -9.02 and -8.89 kcal/mole, respectively. However, SN00288228- AChE, and SN00226692-BuChE were found to have binding energy -9.88 and -9.54 kcal/mole, respectively. These selected phytochemical compounds showed better interactions in comparison to Ajmalicine with the target molecule.

CONCLUSION

The current study verifies that SN00288228 and SN00226692 are more capable inhibitors of human AChE and BuChE as compared to Ajmalicine with reference to ΔG values.

Metabolic Regulation Analysis of Ajmalicine Biosynthesis Pathway in Catharanthus roseus (L.) G. Don Suspension Culture Using Nanosensor

Ajmalicine is one of the most popular antihypertensive drugs obtained from the root barks of Cathranthus roseus (L.) G. Don and Rauvolfia serpentine (L.) Benth. ex Kurz. It has also potential antimicrobial, cytotoxic, central depressant and antioxidant activities. As the demand for the alkaloid is significantly high, metabolic engineering approaches are being tried to increase its production in both homologous and heterologous systems. The metabolic engineering approach requires knowledge of the metabolic regulation of the alkaloid. For understanding the metabolic regulation, fluxomic analysis is important as it helps in understanding the flux of the alkaloid through the complicated metabolic pathway. The present study was conducted to analyse the flux analysis of the ajmalicine biosynthesis, using a genetically encoded Fluorescent Resonance Energy Transfer FRET-based nanosensor for ajmalicine (FLIP-Ajn). Here, we have silenced six important genes of terpenoid indole alkaloid (TIA), namely G10H, 10HGO, TDC, SLS, STR and SDG, through RNA-mediated gene silencing in different batches of C. roseus suspension cells, generating six silenced cell lines. Monitoring of the ajmalicine level was carried out using FLIP-Ajn in these silenced cell lines, with high spatial and temporal resolution. The study offers the rapid, high throughput real-time measurement of ajmalicine flux in response to the silenced TIA genes, thereby identifying the regulatory gene controlling the alkaloid flux in C. roseus suspension cells. We have reported that the STR gene encoding strictosidine synthase of the TIA pathway could be the regulatory gene of the ajmalicine biosynthesis.

Hairy Root Cultures-A Versatile Tool With Multiple Applications

Hairy roots derived from the infection of a plant by Rhizobium rhizogenes (previously referred to as Agrobacterium rhizogenes) bacteria, can be obtained from a wide variety of plants and allow the production of highly diverse molecules. Hairy roots are able to produce and secrete complex active glycoproteins from a large spectrum of organisms. They are also adequate to express plant natural biosynthesis pathways required to produce specialized metabolites and can benefit from the new genetic tools available to facilitate an optimized production of tailor-made molecules. This adaptability has positioned hairy root platforms as major biotechnological tools. Researchers and industries have contributed to their advancement, which represents new alternatives from classical systems to produce complex molecules. Now these expression systems are ready to be used by different industries like pharmaceutical, cosmetics, and food sectors due to the development of fully controlled large-scale bioreactors. This review aims to describe the evolution of hairy root generation and culture methods and to highlight the possibilities offered by hairy roots in terms of feasibility and perspectives.

Growth and alkaloid production along with expression profiles of biosynthetic pathway genes in two contrasting morphotypes of prickly and prickleless Solanum viarum Dunal

Growth and production kinetics of three important glycoalkaloids viz. α-solanine, solanidine, and solasodine in two contrasting prickly and prickleless plants of Solanum viarum Dunal were evaluated under in vitro conditions. The prickleless plants showed improved accumulation of total glycoalkaloid content [7.11 and 6.85 mg g^-1 dry weight (DW)] and growth (GI = 11.08 and 19.26) after 45 and 50 days of culture cycle, respectively. For higher biomass (91.18 g l^-1) as well as glycoalkaloid (52.56 mg l^-1) recovery, the prickleless plants served as highly profitable platform. All the three studied glycoalkaloids were identified and quantified by mass spectrometry and HPLC. All the three studied glycoalkaloids accumulated in age-dependent manner. The presence of two constituents, i.e., solasodine and solanidine mainly contributed for higher accumulation of total glycoalkaloid content in the prickleless plants. However, the synthesis of α-solanine was highly age specific and could be detected after 4 to 5 weeks of culture cycle in both prickle containing as well as prickleless plants of S. viarum. The higher accumulation of glycoalkaloids in prickleless plants was also supported with the expression analysis of six key pathway enzymes viz. mevalonate kinase (MVK), 3-hydroxy-3-methyl-glutaryl coenzyme A reductase (HMGR), farnesyl diphosphate synthase (FPS), UDP-galactose/solanidine galactosyltransferase (SGT1), UDP-glucose/solanidine glucosyltransferase (SGT2), and cytochrome P450 monooxygenase (CYP). The results indicated that the plants harvested after 45 and 50 days of culture cycle accumulated maximum bioactive in-demand glycoalkaloids in the prickly and prickleless plants of S. viarum Dunal, respectively.

Elicitation: A biotechnological tool for enhanced production of secondary metabolites in hairy root cultures

Elicitation is a possible aid to overcome various difficulties associated with the large-scale production of most commercially important bioactive secondary metabolites from wild and cultivated plants, undifferentiated or differentiated cultures. Secondary metabolite accumulation in vitro or their efflux in culture medium has been elicited in the undifferentiated or differentiated tissue cultures of several plant species by the application of a low concentration of biotic and abiotic elicitors in the last three decades. Hairy root cultures are preferred for the application of elicitation due to their genetic and biosynthetic stability, high growth rate in growth regulator-free media, and production consistence in response to elicitor treatment. Elicitors act as signal, recognized by elicitor-specific receptors on the plant cell membrane and stimulate defense responses during elicitation resulting in increased synthesis and accumulation of secondary metabolites. Optimization of various parameters, such as elicitor type, concentration, duration of exposure, and treatment schedule is essential for the effectiveness of the elicitation strategies. Combined application of different elicitors, integration of precursor feeding, or replenishment of medium or in situ product recovery from the roots/liquid medium with the elicitor treatment have showed improved accumulation of secondary metabolites due to their synergistic effect. This is a comprehensive review about the progress in the elicitation approach to hairy root cultures from 2010 to 2019 and the information provided is valuable and will be of interest for scientists working in this area of plant biotechnology.

Enhancement of Medicinally Important Bioactive Compounds in Hairy Root Cultures of Glycyrrhiza, Rauwolfia, and Solanum Through In Vitro Stress Application

Enhancement of secondary metabolites through elicitation in hairy root culture is a very effective method which is broadly used to simulate the stress responses in plants. Elicitors are compounds that induce plants to produce secondary metabolites at elevated levels and reduce the processing time required to achieve high product concentrations. Hairy root cultures are considered as an excellent alternative for the supply of pharmaceutically important secondary metabolites/bioactives, due to their inherent genetic and biochemical stability. Plant-based secondary metabolites are well accepted in India as well as other countries to cure even the serious medical problems. In this chapter, three medicinally important plants are discussed in which stress-based elicitation of secondary metabolites has been achieved in hairy root cultures. These three plants contain important secondary metabolites in their different parts. Glycyrrhizin found in Glycyrrhiza glabra plant is used as antiulcer, immunomodulatory, antiallergic, and anti-inflammatory. Glycyrrhizin is also effective against HIV and severe acute respiratory syndrome (SARS)-like viruses. In Solanum plant, steroidal glycoalkaloids contain pharmaceutically important secondary metabolites. Solasodine, a major alkaloid of Solanum plant, is used as a contraceptive in different parts of the world. Ajmaline and ajmalicine are important root-specific indole alkaloids of Rauwolfia serpentina. Ajmalicine is useful in circulatory disorders, while ajmaline is principally known for its antiarrhythmic and antihypertensive activities. The main objective of this chapter is to provide knowledge in these plants regarding elicitation-based enhancement of valuable secondary metabolites in the form of research studies conducted till date (as per author’s knowledge).