Gene regulation patterns in triterpene biosynthetic pathway driven by overexpression of squalene synthase and methyl jasmonate elicitation in Bupleurum falcatum

Recent advancements in mogrosides: A review on biological activities, synthetic biology, and applications in the food industry

Mogrosides are low-calorie, biologically active sweeteners that face high production costs due to strict cultivation requirements and the low yield of monk fruit. The rapid advancement in synthetic biology holds the potential to overcome this challenge. This review presents mogrosides exhibiting antioxidant, anti-inflammatory, anti-cancer, anti-diabetic, and liver protective activities, with their efficacy in diabetes treatment surpassing that of Xiaoke pills (a Chinese diabetes medication). It also discusses the latest elucidated biosynthesis pathways of mogrosides, highlighting the challenges and research gaps in this field. The critical and most challenging step in this pathway is the transformation of mogrol into a variety of mogrosides by different UDP-glucosyltransferases (UGTs), primarily hindered by the poor substrate selectivity, product specificity, and low catalytic efficiency of current UGTs. Finally, the applications of mogrosides in the current food industry and the challenges they face are discussed.

Differential regulation of key triterpene synthase gene under abiotic stress in Withania somnifera L. Dunal and its co-relation to sterols and withanolides

Withania somnifera (Ashwagandha), is one of the most reputed Indian medicinal plants, having immense pharmacological activities due to the occurrence of withanolides. The withanolides are biosynthesized through triterpenoid biosynthetic pathway with the involvement of WsCAS leading to cyclization of 2, 3 oxidosqualene, which is a key metabolite to further diversify to a myriad of phytochemicals. In contrast to the available reports on the studies of WsCAS in withanolide biosynthesis, its involvement in phytosterol biosynthesis needs investigation. Present work deals with the understanding of role of WsCAS triterpenoid synthase gene in the regulation of biosynthesis of phytosterols & withanolides. Docking studies of WsCAS protein revealed Conserved amino acids, DCATE motif, and QW motif which are involved in efficient substrate binding, structure stabilization, and catalytic activity. Overexpression/silencing of WsCAS leading to increment/decline of phytosterols confers its stringent regulation in phytosterols biosynthesis. Differential regulation of WsCAS on the metabolic flux towards phytosterols and withanolide biosynthesis was observed under abiotic stress conditions. The preferential channelization of 2, 3 oxidosqualene towards withanolides and/or phytosterols occurred under heat/salt stress and cold/water stress, respectively. Stigmasterol and β-sitosterol showed major contribution in high/low temperature and salt stress, and campesterol in water stress management. Overexpression of WsCAS in Arabidopsis thaliana led to the increment in phytosterols in general. Thus, the WsCAS plays important regulatory role in the biosynthetic pathway of phytosterols and withanolides under abiotic stress conditions.

Enhancing Centelloside Production in Centella asiatica Hairy Root Lines through Metabolic Engineering of Triterpene Biosynthetic Pathway Early Genes

Centella asiatica is a medicinal plant with a rich tradition of use for its therapeutic properties. Among its bioactive compounds are centellosides, a group of triterpenoid secondary metabolites whose potent pharmacological activities have attracted significant attention. Metabolic engineering has emerged as a powerful biotechnological tool to enhance the production of target compounds. In this study, we explored the effects of overexpressing the squalene synthase (SQS) gene and transcription factor TSAR2 on various aspects of C. asiatica hairy root lines: the expression level of centelloside biosynthetic genes, morphological traits, as well as squalene, phytosterol, and centelloside content. Three distinct categories of transformed lines were obtained: LS, harboring At-SQS; LT, overexpressing TSAR2; and LST, simultaneously carrying both transgenes. These lines displayed noticeable alterations in morphological traits, including changes in branching rate and biomass production. Furthermore, we observed that the expression of T-DNA genes, particularly aux2 and rolC genes, significantly modulated the expression of pivotal genes involved in centelloside biosynthesis. Notably, the LS lines boasted an elevated centelloside content but concurrently displayed reduced phytosterol content, a finding that underscores the intriguing antagonistic relationship between phytosterol and triterpene pathways. Additionally, the inverse correlation between the centelloside content and morphological growth values observed in LS lines was countered by the action of TSAR2 in the LST and LT lines. This difference could be attributed to the simultaneous increase in the phytosterol content in the TSAR2-expressing lines, as these compounds are closely linked to root development. Overall, these discoveries offer valuable information for the biotechnological application of C. asiatica hairy roots and their potential to increase centelloside production.

Expression of PnSS Promotes Squalene and Oleanolic Acid (OA) Accumulation in Aralia elata via Methyl Jasmonate (MeJA) Induction

Aralia elata is an important herb due to the abundance of pentacyclic triterpenoid saponins whose important precursors are squalene and OA. Here, we found that MeJA treatment promoted both precursors accumulation, especially the latter, in transgenic A. elata, overexpressing a squalene synthase gene from Panax notoginseng(PnSS). In this study, Rhizobium-mediated transformation was used to express the PnSS gene. Gene expression analysis and high-performance liquid chromatography (HPLC) were used to identify the effect of MeJA on squalene and OA accumulation. The PnSS gene was isolated and expressed in A. elata. Transgenic lines showed a very high expression of the PnSS gene and farnesyl diphosphate synthase gene (AeFPS) and a slightly higher squalene content than the wild-type, but endogenous squalene synthase (AeSS), squalene epoxidase (AeSE), and β-amyrin synthase (Aeβ-AS) gene were decreased as well as OA content. Following one day of MeJA treatment, the expression levels of PeSS, AeSS, and AeSE genes increased significantly. On day 3, the maximum content of both products reached 17.34 and 0.70 mg·g^-1, which increased 1.39- and 4.90-fold than in the same lines without treatment. Transgenic lines expressing PnSS gene had a limited capability to promote squalene and OA accumulation. MeJA strongly activated their biosynthesis pathways, leading to enhance yield.

Comparative Transcriptomic Analysis of Genes in the 20-Hydroxyecdysone Biosynthesis in the Fern Microsorum scolopendria towards Challenges with Foliar Application of Chitosan

Microsorum scolopendria is an important medicinal plant that belongs to the Polypodiaceae family. In this study, we analyzed the effects of foliar spraying of chitosan on growth promotion and 20-hydroxyecdysone (20E) production in M. scolopendria. Treatment with chitosan at a concentration of 50 mg/L in both young and mature sterile fronds induced the highest increase in the amount of accumulated 20E. Using RNA sequencing, we identified 3552 differentially expressed genes (DEGs) in response to chitosan treatment. The identified DEGs were associated with 236 metabolic pathways. We identified several DEGs involved in the terpenoid and steroid biosynthetic pathways that might be associated with secondary metabolite 20E biosynthesis. Eight upregulated genes involved in cholesterol and phytosterol biosynthetic pathway, five upregulated genes related to the methylerythritol 4-phosphate (MEP) and mevalonate (MVA) pathways, and several DEGs that are members of cytochrome P450s and ABC transporters were identified. Quantitative real-time RT-PCR confirmed the results of RNA-sequencing. Taken together, we showed that chitosan treatment increased plant dry weight and 20E accumulation in M. scolopendria. RNA-sequencing and DEG analyses revealed key enzymes that might be related to the production of the secondary metabolite 20E in M. scolopendria.

Transcriptome Level Reveals the Triterpenoid Saponin Biosynthesis Pathway of Bupleurum falcatum L

Bupleurum falcatum L. is frequently used in traditional herbal medicine in Asia. Saikosaponins (SSs) are the main bioactive ingredients of B. falcatum, but the biosynthetic pathway of SSs is unclear, and the biosynthesis of species-specific phytometabolites is little known. Here we resolved the transcriptome profiles of B. falcatum to identify candidate genes that might be involved in the biosynthesis of SSs. By isoform sequencing (Iso-Seq) analyses of the whole plant, a total of 26.98 Gb of nucleotides were obtained and 124,188 unigenes were identified, and 81,594 unigenes were successfully annotated. A total of 1033 unigenes of 20 families related to the mevalonate (MVA) pathway and methylerythritol phosphate (MEP) pathway of the SS biosynthetic pathway were identified. The WGCNA (weighted gene co-expression network analysis) of these unigenes revealed that only the co-expression module of MEmagenta, which contained 343 unigenes, was highly correlated with the biosynthesis of SSs. Comparing differentially expressed gene analysis and the WGCNA indicated that 130 out of 343 genes of the MEmagenta module exhibited differential expression levels, and genes with the most "hubness" within this module were predicted. Manipulation of these genes might improve the biosynthesis of SSs.

The Influence of Exogenous Jasmonic Acid on the Biosynthesis of Steroids and Triterpenoids in Calendula officinalis Plants and Hairy Root Culture

The interplay between steroids and triterpenoids, compounds sharing the same biosynthetic pathway but exerting distinctive functions, is an important part of the defense strategy of plants, and includes metabolic modifications triggered by stress hormones such as jasmonic acid. Two experimental models, Calendula officinalis hairy root cultures and greenhouse cultivated plants (pot plants), were applied for the investigation of the effects of exogenously applied jasmonic acid on the biosynthesis and accumulation of steroids and triterpenoids, characterized by targeted GC-MS (gas chromatography-mass spectroscopy) metabolomic profiling. Jasmonic acid elicitation strongly increased triterpenoid saponin production in hairy root cultures (up to 86-fold) and their release to the medium (up to 533-fold), whereas the effect observed in pot plants was less remarkable (two-fold enhancement of saponin biosynthesis after a single foliar application). In both models, the increase of triterpenoid biosynthesis was coupled with hampering the biomass formation and modifying the sterol content, involving stigmasterol-to-sitosterol ratio, and the proportions between ester and glycoside conjugates. The study revealed that various organs in the same plant can react differently to jasmonic acid elicitation; hairy root cultures are a useful in vitro model to track metabolic changes, and enhanced glycosylation (of both triterpenoids and sterols) seems to be important strategy in plant defense response.

Metabolic Modifications in Terpenoid and Steroid Pathways Triggered by Methyl Jasmonate in Taxus × media Hairy Roots

The in vitro cultures of Taxus spp. were one of the first plant in vitro systems proved to exert the positive effect of elicitation with methyl jasmonate (MeJA) on the biosynthesis of specialized metabolites. The main aim of the present study is to examine the effect of MeJA treatment on the steroid and triterpenoid content of two genetically different hairy root lines of Taxus × media, KT and ATMA. The results revealed that the two lines differed in the total content of steroids and triterpenoids (in the ATMA root line, their amounts were lower than those in the KT line by 43% and 30%, respectively), but not in the composition of these compounds. The metabolic response to elicitation with MeJA was different: in the KT root line, the content of steroids decreased by 18%, whereas it increased by 38% in the ATMA line. Several metabolic features were common, including the characteristic changes in the ratio of sitosterol to stigmasterol content, caused by the very sharp boost in stigmasterol levels, the increase in the amount of glycoside forms of sterols, as well as in triterpenoid and total phenolic content. It is the first report on modifications of the terpenoid biosynthetic pathway in Taxus hairy root cultures triggered by MeJA, concerning steroids and triterpenoids.

Chromosome-Level Genome Assembly of Bupleurum chinense DC Provides Insights Into the Saikosaponin Biosynthesis

Bupleurum chinense DC is a plant widely used in Chinese traditional medicine. Saikosaponins are the major bioactive constituents of B. chinense DC. Saikosaponins biosynthesis in Bupleurum has been more intensively studied than any other metabolic processes or bioactive constituents. However, whole-genome sequencing and chromosome-level assembly for Bupleurum genus have not been reported yet. Here, we report a high-quality chromosome-level genome of B. chinense DC. through the integration of PacBio long-read sequencing, Illumina short-read sequencing, and Hi-C sequencing. The genome was phased into haplotype 0 (621.27 Mb with a contig N50 of 16.86 Mb and a scaffold N50 of 92.25 Mb) and haplotype 1 (600.48 Mb with a contig N50 of 23.90 Mb and a scaffold N50 of 102.68 Mb). A total of 45,909 and 35,805 protein-coding genes were predicted in haplotypes 0 and 1, respectively. The enrichment analyses suggested that the gene families that expanded during the evolution of B. chinense DC are involved in the biosynthesis of isoquinoline alkaloid, tyrosine, and anthocyanin. Furthermore, we analyzed the genes involved in saikosaponin biosynthesis and determined the candidate P450 and UGT genes in the third stage of saikosaponins biosynthetic, which provided new insight into the saikosaponins biosynthetic. The genomic data provide a valuable resource for future investigations of the molecular mechanisms, biological functions, and evolutionary adaptations of B. chinense DC.

Downregulation of Squalene Synthase Broadly Impacts Isoprenoid Biosynthesis in Guayule

Production of natural rubber by Parthenium argentaum (guayule) requires increased yield for economic sustainability. An RNAi gene silencing strategy was used to engineer isoprenoid biosynthesis by downregulation of squalene synthase (SQS), such that the pool of farnesyl diphosphate (FPP) substrate might instead be available to initiate natural rubber synthesis. Downregulation of SQS resulted in significantly reduced squalene and slightly increased rubber, but not in the same tissues nor to the same extent, partially due to an apparent negative feedback regulatory mechanism that downregulated mevalonate pathway isoprenoid production, presumably associated with excess geranyl pyrophosphate levels. A detailed metabolomics analysis of isoprenoid production in guayule revealed significant differences in metabolism in different tissues, including in active mevalonate and methylerythritol phosphate pathways in stem tissue, where rubber and squalene accumulate. New insights and strategies for engineering isoprenoid production in guayule were identified.

Molecular cloning and functional characterization of two squalene synthase genes in Atractylodes lancea

Two squalene synthase genes AlSQS1 and AlSQS2 were isolated from Atractylodes lancea and functionally characterized using in vitro enzymatic reactions. Atractylodes lancea is a traditional herb used for the treatment of rheumatic diseases, gastric disorders, and influenza. Its major active ingredients include sesquiterpenoids and triterpenes. Squalene synthase (SQS; EC 2.5.1.21) catalyzes the first enzymatic step in the central isoprenoid pathway towards sterol and triterpenoid biosynthesis. In this study, we aimed to investigate two SQSs from A. lancea using cloning and in vitro enzymatic characterization. Bioinformatics and phylogenetic analyses revealed that the AlSQSs exhibited high homology with other plant SQSs. Furthermore, AlSQS1 was observed to be localized in both the nucleus and cytoplasm, whereas AlSQS2 was localized in the cytoplasm and endoplasmic reticulum. To obtain soluble recombinant enzymes, AlSQS1 and AlSQS2 were successfully expressed as glutathione S-transferase (GST)-tagged fusion proteins in Escherichia coli Transetta (DE3). Approximately 68 kDa recombinant proteins were obtained using GST-tag affinity chromatography and Western blot analysis. Results of the in vitro enzymatic reactions established that both AlSQS1 and AlSQS2 were functional, which verifies their catalytic ability in converting two farnesyl pyrophosphates to squalene. The expression patterns of AlSQS and selected terpenoid genes were also investigated in two A. lancea chemotypes using available RNA sequencing data. AlSQS1 and AlSQS2, which showed relatively similar expression in the three tissues, were more highly expressed in the stems than in the leaves and rhizomes. Methyl jasmonate (MeJA) was used as an elicitor to analyze the expression profiles of AlSQSs. The results of qRT-PCR analysis revealed that the gene expression of AlSQS1 and AlSQS2 plummeted at lowest value at 12 h and reached its peak at 24 h. This study is the first report on the cloning, characterization, and expression of SQSs in A. lancea. Therefore, our findings contribute novel insights that may be useful for future studies regarding terpenoid biosynthesis in A. lancea.

RNA in situ hybridization and expression of related genes regulating the accumulation of triterpenoids in Cyclocarya paliurus

Cyclocarya paliurus (Batal.) Iljinskaja, a woody medicinal species in the Juglandaceae, grows extensively in subtropical areas of China. Triterpenoids in the leaves have health-promoting effects, including hypoglycemic and hypolipidemic activities. To understand triterpenoid biosynthesis, transport and accumulation in C. paliurus during the growing season, gene cloning, gene expression and RNA in situ hybridization of related genes were used, and accumulation was examined in various organs. The complete coding sequences (CDSs) of three genes, CpHMGR, CpDXR and CpSQS, were obtained from GenBank and RACE. RNA in situ hybridization signals of the three genes mainly occurred in the epidermis, palisade tissue, phloem and xylem of leaf, shoot and root, with the signals generally consistent with the accumulation of metabolites in tissues, except in the xylem. Both gene expression and triterpenoid accumulations showed seasonal variations in all organs. However, total triterpenoid content in the leaves was significantly higher than that in the shoots, with the maximum in shoots in August and in leaves in October. According to Pearson correlation analysis, triterpenoid accumulation in the leaves was significantly positively related with the relative expression of CpSQS. However, the relation between gene expression and accumulation was dependent on the role of the gene in the pathway as well as on the plant organ. The results suggested that most of the intermediates catalyzed by CpHMGR and CpDXR in young shoots and roots were used in growth and flowering in the spring, whereas subsequent triterpenoid biosynthesis in the downstream catalyzed by CpSQS mainly occurred in the leaves by using transferred and in situ intermediates as substrates. Thus, this study provides a reference to improve triterpenoid accumulation in future C. paliurus plantations.

Enhancement of Phytosterol and Triterpenoid Production in Plant Hairy Root Cultures-Simultaneous Stimulation or Competition?

Plant in vitro cultures, including hairy roots, can be applied for controlled production of valuable natural products, such as triterpenoids and sterols. These compounds originate from the common precursor squalene. Sterols and triterpenoids distinctly differ in their functions, and the 2,3-oxidosqualene cyclization step is often regarded as a branch point between primary and secondary (more aptly: general and specialized) metabolism. Considering the crucial role of phytosterols as membrane constituents, it has been postulated that unconstrained biosynthesis of triterpenoids can occur when sterol formation is already satisfied, and these compounds are no longer needed for cell growth and division. This hypothesis seems to follow directly the growth-defense trade-off plant dilemma. In this review, we present some examples illustrating the specific interplay between the two divergent pathways for sterol and triterpenoid biosynthesis appearing in root cultures. These studies were significant for revealing the steps of the biosynthetic pathway, understanding the role of particular enzymes, and discovering the possibility of gene regulation. Currently, hairy roots of many plant species can be considered not only as an efficient tool for production of phytochemicals, but also as suitable experimental models for investigations on regulatory mechanisms of plant metabolism.

Integrated Analysis of Transcriptome and Metabolome and Evaluation of Antioxidant Activities in Lavandulapubescens

Lavandula pubescens, belonging to the Labiatae family, is a newly discovered strongly aromatic species of lavender that is potentially beneficial for human health. Given the economic importance of lavender species, we sought in this study to characterize the terpenoid biosynthesis of L. pubescens by obtaining transcriptomic and metabolic datasets. Transcriptome analysis of L. pubescens grown aseptically in tissue culture medium yielded 124,233 unigenes with an average length of 470 bp and N50 value of 522 bp from 9,476,122,928 raw reads. In order to provide relevant biological information, the unigenes were annotated using the following public databases: National Center for Biotechnology Information (NCBI) nucleotide (NT) and non-redundant protein (NR), Brassica (BRAD), Arabidopsis Information Resource (TAIR), Clusters of Orthologous Groups (COG), and Gene Ontology (GO). NR annotation results revealed that L. pubescens is genetically closely related to Sesamum indicum. On the basis of the transcriptome data, a total of 14 cDNA clones encoding the terpene biosynthetic genes LpDXS, LpMCT, LpMCS, LpHDR, LpIDI, LpAACT, LpHMGS, LpHMGR, LpMVK, LpPMK, LpMVD, LpGPPS, LpSQS, and LpGGPPS were identified in L. pubescens. These were quantified in the roots, stems, and leaves of L. pubescens using quantitative real-time polymerase chain reaction (qRT-PCR), which revealed that the gene expression levels were higher in the leaves and stems than in the roots, which was found to be consistent with the levels of ursolic and oleanolic acids in the different organs using high-performance liquid chromatography (HPLC). A total of 48 hydrophilic metabolites were identified and quantified in the organs using gas chromatography time-of-flight mass spectrometry (GC-TOFMS). Furthermore, the antioxidant activity of an ethyl acetate extract of L. pubescens leaves was examined using different methods to determine the potential therapeutic properties. A reducing power assay revealed that the absorbance values increased in a concentration-dependent manner, whereas a 2,2-diphenyl-1-picrylhydrazyl radical scavenging assay indicated the strong activity (60.4 ± 0.9%) of the ethyl acetate extract at a concentration of 100 µg/mL, which also showed strong hydrogen peroxide (57.4 ± 2.7%), superoxide radical (62.1 ± 0.7%), and hydroxyl radical (58.6 ± 0.4%) scavenging activities.

Impact of potential stimulants on asiaticoside and madecassoside levels and expression of triterpenoid-related genes in axenic shoot cultures of Centella asiatica (L.) Urb

The triterpenoid saponins, asiaticoside and madecassoside from Centella asiatica (L.) Urb. are known to have a wide range of applications in pharmaceutical and cosmetic industries. The effect of addition of Potential Metabolite Stimulants (PMSs) - casein acid hydrolysate, meat peptone, salicylic acid, copper sulphate, and silver nitrate, on the concentrations of these saponins and transcript levels of associated genes encoding important biosynthetic enzymes, was assessed in axenic shoot cultures of C. asiatica. Among the stimulants, silver nitrate induced asiaticoside content approximately 6-fold increase in madecassoside levels, after three weeks post-treatment with a decrease in biomass compared to its control. Gene expression analysis of essential genes involved in triterpenoid synthesis such as β-amyrin synthase showed an upregulation of approximately 50-fold at the third week of silver nitrate treatment compared to control. These findings suggest that silver nitrate can act as a metabolite stimulant, to enhance the formation of triterpenoids in axenic shoot culture of C. asiatica, which could be utilized in studying the regulation of terpenoid biosynthesis and biotechnological application for the increased production of these bioactive molecules.

Recent Progress in Saikosaponin Biosynthesis in Bupleurum

BACKGROUND

Chaihu is a popular traditional Chinese medicine that has been used for centuries. It is traditionally used to treat cold fever and liver-related diseases. Saikosaponins (SSs) are one of the main active components of chaihu, in addition to essential oils, flavonoids, and polysaccharides. Considerable effort is needed to reveal the biosynthesis and regulation of SSs on the basis of current progress.

OBJECTIVE

The aim of this study is to provide a reference for further studies and arouse attention by summarizing the recent achievements of SS biosynthesis.

METHODS

All the data compiled and presented here were obtained from various online resources, such as PubMed Scopus and Baidu Scholar in Chinese, up to October 2019.

RESULTS

A few genes of the enzymes of SSs participating in the biosynthesis of SSs were isolated. Among these genes, only the P450 gene was verified to catalyze the SS skeleton β-amyrin synthase. Several UDP-glycosyltransferase genes were predicted to be involved in the biosynthesis of SSs. SSs could be largely biosynthesized in the phloem and then transported from the protoplasm, which is the biosynthetic site, to the vacuoles to avoid self-poisoning. As for the other secondary metabolites, the biosynthesis of SSs was strongly affected by environmental factors and the different species belonging to the genus of Bupleurum. Transcriptional regulation was studied at the molecular level.

CONCLUSION

Profound discoveries in SSs may elucidate the mechanism of diverse the monomer formation of SSs and provide a reference for maintaining the stability of SS content in Radix Bupleuri.

Influence of different elicitors on BIA production in Macleaya cordata

Sanguinarine (SAN) and chelerythrine (CHE) have been widely used as substitutes for antibiotics for decades. For a long time, SAN and CHE have been extracted from mainly Macleaya cordata, a plant species that is a traditional herb in China and belongs to the Papaveraceae family. However, with the sharp increase in demand for SAN and CHE, it is necessary to develop a new method to enhance the supply of raw materials. Here, we used methyl jasmonate (MJ), salicylic acid (SA) and wounding alone and in combination to stimulate aseptic seedlings of M. cordata at 0 h, 24 h, 72 h and 120 h and then compared the differences in metabolic profiles and gene expression. Ultimately, we found that the effect of using MJ alone was the best treatment, with the contents of SAN and CHE increasing by 10- and 14-fold, respectively. However, the increased SAN and CHE contents in response to combined wounding and MJ were less than those for induced by the treatment with MJ alone. Additionally, after MJ treatment, SAN and CHE biosynthetic pathway genes, such as those encoding the protopine 6-hydroxylase and dihydrobenzophenanthridine oxidase enzymes, were highly expressed, which is consistent with the accumulation of SAN and CHE. At the same time, we have also studied the changes in the content of synthetic intermediates of SAN and CHE after elicitor induction. This study is the first systematic research report about using elicitors to increase the SAN and CHE in Macleaya cordata.

Effects of moderate high temperature and UV-B on accumulation of withanolides and relative expression of the squalene synthase gene in Physalis peruviana

Physalis peruviana L. (Cape gooseberry) is a source for a variety of phytocompounds such as withanolides, withanone, withaferin A, and withanolide A. These withanolides are high-value drug candidates due to their various pharmacological properties. To meet the increasing demands for these compounds, plant cell technology offers a reliable alternative. Exogenous addition of elicitors is considered the most effective strategy for enhanced production of secondary metabolites. In this study, we investigated changes in withanolide accumulation and characterized the gene expression level changes of squalene synthase enzyme in P. peruviana shoot cultures exposed to mild nonlethal heat stress (45°C for 2 and 5 h) and UV-B radiation (313 nm for 15 min and 3 h). We demonstrated significant changes in withanolide content with 7.86- and 12.5-fold increases for 2- and 5-hmild high-temperature exposure times, respectively. Exposure to UV-B also changed the withanolide content by 7.22- and 7-fold increases for 15 min and 3 h exposure times, respectively. The relative expression level of squalene synthase gene showed consistent results with1.80- and 10.13-fold increases in withanolide for 2- and 5-h mild high-temperature exposure times, and 1.34- and 2.01-fold increases with 15 min and 3 h UV-B exposure times, respectively.

Differential Expression of Genes Involved in Saikosaponin Biosynthesis Between Bupleurum chinense DC. and Bupleurum scorzonerifolium Willd

Radix Bupleuri (roots of Bupleurum spp.) is an important medicinal herb. Triterpenoid saponins of saikosaponins generally constitute the main class of secondary metabolites of plants in the Bupleurum genus. However, the molecular regulatory mechanism underlying their biosynthesis remains elusive. In this study, we observed significantly different saikosaponin biosynthesis between Bupleurum chinense and Bupleurum scorzonerifolium at the seedling stage. The sequential and expression characterization of 232 genes in the triterpenoid saponin biosynthetic pathway, which includes the mevalonate (MVA) pathway and methylerythritol phosphate (MEP) pathway, between B. chinense and B. scorzonerifolium was also investigated. Sixty of these genes may be involved in saikosaponin biosynthesis. Manipulation of these genes, especially those of the β-AS, P450, and UGT families, may improve saikosaponin production.

In silico structural modeling and analysis of physicochemical properties of curcumin synthase (CURS1, CURS2, and CURS3) proteins of Curcuma longa

Background

Pharmaceutically important curcuminoid synthesis in C. longa is controlled by CURS1, CURS2, and CURS3 genes. The present study detected the physicochemical properties and structural characteristics including the secondary and 3D structure of CURS proteins. The primary, secondary, and tertiary structure of the CURS proteins were modeled and characterized using multiple bioinformatics tools such as ExPasy ProtParam tools, self-optimized prediction method with alignment (SOPMA), PSIPRED, and SWISS-MODEL. The predicted secondary structure of curcumin synthase provided an α-helix and random coil as the major components. The reliability of the modeled structure was confirmed using PROCHECK and QMEAN programs.

Results

The molecular weight of CURS1 is 21093.19 Da, theoretical pI as 4.93, and an aliphatic index of 99.19. Molecular weight of CURS2 and CURS3 proteins are 20266.13 Da and 20629.52 Da, theoretical pI as 5.28 and 4.96, and an aliphatic index of 89.30 and 86.37, respectively. In the predicted secondary structure of CURS proteins, alpha helices and random coils of CURS1, CUR2, and CURS3 were 42.72, 41.38, and 44.74% and 24.87, 31.03, and 17.89, respectively. The extended strands were 16.24, 19.40, and 17.89. QMEAN Z-score is − 0.83, − 0.89, and − 1.09 for CURS1, CURS2, and CURS3, respectively.

Conclusion

Prediction of the 3D model of a protein by in silico analysis is a highly challenging aspect to confirm the NMR or X-ray crystallographic data. This report can contribute to the understanding of the structure, physicochemical properties, structural motifs, and protein-protein interaction of CURS1, CUR2, and CURS3.

Identification of key genes involved in the biosynthesis of triterpenic acids in the mint family

Triterpenic acids (TAs), a large group of natural compounds with diverse biological activity, are produced by several plant taxa. Betulinic, oleanolic, and ursolic acids are the most medicinally important TAs and are mainly found in plants of the mint family. Metabolic engineering is strongly dependent on identifying the key genes in biosynthetic pathways toward the products of interest. In this study, gene expression tracking was performed by transcriptome mining, co-expression network analysis, and tissue-specific metabolite-expression analysis in order to identify possible key genes involved in TAs biosynthetic pathways. To this end, taxa-specific degenerate primers of six important genes were designed using an effective method based on the MEME algorithm in a phylogenetically related group of sequences and successfully applied in three members of the Lamiaceae (Rosmarinus officinalis, Salvia officinalis, and Thymus persicus). Based on the results of in-depth data analysis, genes encoding squalene epoxidase and oxido squalene cyclases are proposed as targets for boosting triterpene production. The results emphasize the importance of identifying key genes in triterpene biosynthesis, which may facilitate genetic manipulation or overexpression of target genes.

Molecular Cloning and Functional Identification of a Squalene Synthase Encoding Gene from Alfalfa (Medicago sativa L.)

The quality of alfalfa, a main forage legume worldwide, is of great importance for the dairy industry and is affected by the content of triterpene saponins. These natural terpenoid products of triterpene aglycones are catalyzed by squalene synthase (SQS), a highly conserved enzyme present in eukaryotes. However, there is scare information on alfalfa SQS. Here, an open reading frame (ORF) of SQS was cloned from alfalfa. Sequence analysis showed MsSQS had the same exon/intron composition and shared high homology with its orthologs. Bioinformatic analysis revealed the deduced MsSQS had two transmembrane domains. When transiently expressed, GFP-MsSQS fusion protein was localized on the plasma membrane of onion epidermal cells. Removal of the C-terminal transmembrane domain of MsSQS improved solubility in Escherichia coli. MsSQS was preferably expressed in roots, followed by leaves and stems. MeJA treatment induced MsSQS expression and increased the content of total saponins. Overexpression of MsSQS in alfalfa led to the accumulation of total saponins, suggesting a correlation between MsSQS expression level with saponins content. Therefore, MsSQS is a canonical squalene synthase and contributes to saponin synthesis in alfalfa. This study provides a key candidate gene for genetic manipulation of the synthesis of triterpene saponins, which impact both plant and animal health.

Positive Selection of Squalene Synthase in Cucurbitaceae Plants

Triterpenoid saponins are secondary metabolites synthesized through isoprenoid pathways in plants. Cucurbitaceae represent an important plant family in which many species contain cucurbitacins as secondary metabolites synthesized through isoprenoid and triterpenoid pathways. Squalene synthase (SQS) is required for the biosynthesis of isoprenoids, but the forces driving the evolution of SQS remain undetermined. In this study, 10 SQS cDNA sequences cloned from 10 species of Cucurbitaceae and 49 sequences of SQS downloaded from GenBank and UniProt databases were analyzed in a phylogenetic framework to identify the evolutionary forces for functional divergence. Through phylogenetic construction and positive selection analysis, we found that SQS sequences are under positive selection. The sites of positive selection map to functional and transmembrane domains. 180L, 189S, 194S, 196S, 265I, 289P, 389P, 390T, 407S, 408A, 410R, and 414N were identified as sites of positive selection that are important during terpenoid synthesis and map to transmembrane domains. 196S and 407S are phosphorylated and influence SQS catalysis and triterpenoid accumulation. These results reveal that positive selection is an important evolutionary force for SQS in plants. This provides new information into the molecular evolution of SQS within the Cucurbitaceae family.

Boosting the biosynthesis of betulinic acid and related triterpenoids in Yarrowia lipolytica via multimodular metabolic engineering

BACKGROUND

Betulinic acid is a pentacyclic lupane-type triterpenoid and a potential antiviral and antitumor drug, but the amount of betulinic acid in plants is low and cannot meet the demand for this compound. Yarrowia lipolytica, as an oleaginous yeast, is a promising microbial cell factory for the production of highly hydrophobic compounds due to the ability of this organism to accumulate large amounts of lipids that can store hydrophobic products and supply sufficient precursors for terpene synthesis. However, engineering for the heterologous production of betulinic acid and related triterpenoids has not developed as systematically as that for the production of other terpenoids, thus the production of betulinic acid in microbes remains unsatisfactory.

RESULTS

In this study, we applied a multimodular strategy to systematically improve the biosynthesis of betulinic acid and related triterpenoids in Y. lipolytica by engineering four functional modules, namely, the heterogenous CYP/CPR, MVA, acetyl-CoA generation, and redox cofactor supply modules. First, by screening 25 combinations of cytochrome P450 monooxygenases (CYPs) and NADPH-cytochrome P450 reductases (CPRs), each of which originated from 5 different sources, we selected two optimal betulinic acid-producing strains. Then, ERG1, ERG9, and HMG1 in the MVA module were overexpressed in the two strains, which dramatically increased betulinic acid production and resulted in a strain (YLJCC56) that exhibited the highest betulinic acid yield of 51.87 ± 2.77 mg/L. Then, we engineered the redox cofactor supply module by introducing NADPH- or NADH-generating enzymes and the acetyl-CoA generation module by directly overexpressing acetyl-CoA synthases or reinforcing the β-oxidation pathway, which further increased the total triterpenoid yield (the sum of the betulin, betulinic acid, betulinic aldehyde yields). Finally, we engineered these modules in combination, and the total triterpenoid yield reached 204.89 ± 11.56 mg/L (composed of 65.44% betulin, 23.71% betulinic acid and 10.85% betulinic aldehyde) in shake flask cultures.

CONCLUSIONS

Here, we systematically engineered Y. lipolytica and achieved, to the best of our knowledge, the highest betulinic acid and total triterpenoid yields reported in microbes. Our study provides a suitable reference for studies on heterologous exploitation of P450 enzymes and manipulation of triterpenoid production in Y. lipolytica.

Ecological Insights to Track Cytotoxic Compounds among Maytenus ilicifolia Living Individuals and Clones of an Ex Situ Collection

Biodiversity is key for maintenance of life and source of richness. Nevertheless, concepts such as phenotype expression are also pivotal to understand how chemical diversity varies in a living organism. Sesquiterpene pyridine alkaloids (SPAs) and quinonemethide triterpenes (QMTs) accumulate in root bark of Celastraceae plants. However, despite their known bioactive traits, there is still a lack of evidence regarding their ecological functions. Our present contribution combines analytical tools to study clones and individuals of Maytenus ilicifolia (Celastraceae) kept alive in an ex situ collection and determine whether or not these two major biosynthetic pathways could be switched on simultaneously. The relative concentration of the QMTs maytenin (1) and pristimerin (2), and the SPA aquifoliunin E1 (3) were tracked in raw extracts by HPLC-DAD and ¹H-NMR. Hierarchical Clustering Analysis (HCA) was used to group individuals according their ability to accumulate these metabolites. Semi-quantitative analysis showed an extensive occurrence of QMT in most individuals, whereas SPA was only detected in minor abundance in five samples. Contrary to QMTs, SPAs did not accumulate extensively, contradicting the hypothesis of two different biosynthetic pathways operating simultaneously. Moreover, the production of QMT varied significantly among samples of the same ex situ collection, suggesting that the terpene contents in root bark extracts were not dependent on abiotic effects. HCA results showed that QMT occurrence was high regardless of the plant age. This data disproves the hypothesis that QMT biosynthesis was age-dependent. Furthermore, clustering analysis did not group clones nor same-age samples together, which might reinforce the hypothesis over gene regulation of the biosynthesis pathways. Indeed, plants from the ex situ collection produced bioactive compounds in a singular manner, which postulates that rhizosphere environment could offer ecological triggers for phenotypical plasticity.

In silico analysis of squalene synthase in Fabaceae family using bioinformatics tools

Triterpenoid saponins are a diverse group of bioactive compounds, which are used for possessing of many biomedical and pharmaceutical products. Generally, squalene synthase (SQS) is defined as an emerging and essential branch point enzyme far from the major pathway of isoprenoids biosynthetic and a latent adjusting point, which manages carbon flux into triterpenes biosynthesis and sterols. The present study deals with the detailed characterization of SQS by bioinformatics approaches to evaluate physicochemical properties, structural characteristics including secondary and 3D structure prediction and functional analysis from eight plants related to Fabaceae family and Arabidopsis thaliana. Bioinformatics analysis revealed that SQS proteins have two transmembrane regions in the C-terminal. The predicted motifs were used to design universal degenerate primers for PCR analysis and other molecular applications. Phylogenetic analysis showed conserved regions at different stretches with maximum homology in amino acid residues within all SQSs. The secondary structure prediction results showed that the amino acid sequence of all squalene synthases had α helix and random coil as the main components. The reliability of the received model was confirmed using the ProSA and RAMPAGE programs. Determining of active site by CASTp proposes the possibility of using this protein as probable medication target. The findings of the present study may be useful for further assessments on characterization and cloning of squalene synthase.

Modification of isoprene synthesis to enable production of curcurbitadienol synthesis in Saccharomyces cerevisiae

Cucurbitane-type triterpenoids such as mogrosides and cucurbitacins that are present in the plants of Cucurbitaceae are widely used in Asian traditional medicine. Cucurbitadienol is the skeleton of cucurbitane-type triterpenoids. As an alternative production strategy, we developed baker's yeast Saccharomyces cerevisiae as a microbial host for the eventual transformation of cucurbitadienol. The synthetic pathway of cucurbitadienol was constructed in Saccharomyces cerevisiae by introducing the cucurbitadienol synthase gene from different plants, resulting in 7.80 mg cucurbitadienol from 1 L of fermentation broth. Improving supplies of isoprenoid precursors was then investigated for increasing cucurbitadienol production. Cucurbitadienol production increased to 21.47 mg/L through the overexpression of a global regulatory factor (UPC2) gene of triterpenoid synthase. In addition, knockout of the ERG7 gene increased cucurbitadienol production from 21.47 to 61.80 mg/L. Finally, fed-batch fermentation was performed, and 63.00 mg/L cucurbitadienol was produced. This work is an important step towards the total biosynthesis of valuable cucurbitane-type triterpenoids and demonstrates the potential for developing a sustainable and secure yeast biomanufacturing platform for triterpenoids.

A comprehensive review and perspectives on pharmacology and toxicology of saikosaponins

BACKGROUND

Radix Bupleuri (RB) has been widely used in Chinese Traditional Medicine for over 2000 years and is currently marketed in China as Chai-Hu-Shu-Gan tablets and Xiao-Yao-Wan tablets. Saikosaponins (SSs, especially SSa, SSc and SSd), as the major bioactive compounds in RB, represent anti-inflammatory, anti-tumor, anti-oxidant, anti-viral and hepatoprotective effects.

PURPOSE

To summarize recent findings regarding to the extraction, detection, biosynthesis, metabolism, pharmacological/toxicological effects of SSs.

METHODS

Online academic databases (including PubMed, Google Scholar, Web of Science and CNKI) were searched using search terms of "Saikosaponin", "Radix Bupleuri", "Bupleurum" and combinations to include published studies of SSs primarily from 2003 to 2018. Several critical previous studies beyond this period were also included.

RESULTS

354 papers were found and 165 papers were reviewed. SSs have drawn great attention for their anti-inflammation, anti-viral and anti-cancer effects and contradictory roles in the regulation of cell apoptosis, oxidative stress and liver fibrosis. Meanwhile, increased risks of overdose-induced acute or accumulation-related chronic hepatotoxicity of SSs and RB have also been reported. However, underlying mechanisms of SSs bioactivities, the metabolism of SSs and bioactivities of SSs metabolites are largely unknown.

CONCLUSION

This comprehensive review of SSs provides novel insights and perspectives on the limitations of current studies and the importance of metabolism study and the dose-pharmacological/toxic relationship of SSs for the future discovery of SSs-based therapeutic strategies and clinical safe practice.

A comprehensive review and perspectives on pharmacology and toxicology of saikosaponins

BACKGROUND

Radix Bupleuri (RB) has been widely used in Chinese Traditional Medicine for over 2000 years and is currently marketed in China as Chai-Hu-Shu-Gan tablets and Xiao-Yao-Wan tablets. Saikosaponins (SSs, especially SSa, SSc and SSd), as the major bioactive compounds in RB, represent anti-inflammatory, anti-tumor, anti-oxidant, anti-viral and hepatoprotective effects.

PURPOSE

To summarize recent findings regarding to the extraction, detection, biosynthesis, metabolism, pharmacological/toxicological effects of SSs.

METHODS

Online academic databases (including PubMed, Google Scholar, Web of Science and CNKI) were searched using search terms of "Saikosaponin", "Radix Bupleuri", "Bupleurum" and combinations to include published studies of SSs primarily from 2003 to 2018. Several critical previous studies beyond this period were also included.

RESULTS

354 papers were found and 165 papers were reviewed. SSs have drawn great attention for their anti-inflammation, anti-viral and anti-cancer effects and contradictory roles in the regulation of cell apoptosis, oxidative stress and liver fibrosis. Meanwhile, increased risks of overdose-induced acute or accumulation-related chronic hepatotoxicity of SSs and RB have also been reported. However, underlying mechanisms of SSs bioactivities, the metabolism of SSs and bioactivities of SSs metabolites are largely unknown.

CONCLUSION

This comprehensive review of SSs provides novel insights and perspectives on the limitations of current studies and the importance of metabolism study and the dose-pharmacological/toxic relationship of SSs for the future discovery of SSs-based therapeutic strategies and clinical safe practice.

A comprehensive review and perspectives on pharmacology and toxicology of saikosaponins

BACKGROUND

Radix Bupleuri (RB) has been widely used in Chinese Traditional Medicine for over 2000 years and is currently marketed in China as Chai-Hu-Shu-Gan tablets and Xiao-Yao-Wan tablets. Saikosaponins (SSs, especially SSa, SSc and SSd), as the major bioactive compounds in RB, represent anti-inflammatory, anti-tumor, anti-oxidant, anti-viral and hepatoprotective effects.

PURPOSE

To summarize recent findings regarding to the extraction, detection, biosynthesis, metabolism, pharmacological/toxicological effects of SSs.

METHODS

Online academic databases (including PubMed, Google Scholar, Web of Science and CNKI) were searched using search terms of "Saikosaponin", "Radix Bupleuri", "Bupleurum" and combinations to include published studies of SSs primarily from 2003 to 2018. Several critical previous studies beyond this period were also included.

RESULTS

354 papers were found and 165 papers were reviewed. SSs have drawn great attention for their anti-inflammation, anti-viral and anti-cancer effects and contradictory roles in the regulation of cell apoptosis, oxidative stress and liver fibrosis. Meanwhile, increased risks of overdose-induced acute or accumulation-related chronic hepatotoxicity of SSs and RB have also been reported. However, underlying mechanisms of SSs bioactivities, the metabolism of SSs and bioactivities of SSs metabolites are largely unknown.

CONCLUSION

This comprehensive review of SSs provides novel insights and perspectives on the limitations of current studies and the importance of metabolism study and the dose-pharmacological/toxic relationship of SSs for the future discovery of SSs-based therapeutic strategies and clinical safe practice.

A comprehensive review and perspectives on pharmacology and toxicology of saikosaponins

BACKGROUND

Radix Bupleuri (RB) has been widely used in Chinese Traditional Medicine for over 2000 years and is currently marketed in China as Chai-Hu-Shu-Gan tablets and Xiao-Yao-Wan tablets. Saikosaponins (SSs, especially SSa, SSc and SSd), as the major bioactive compounds in RB, represent anti-inflammatory, anti-tumor, anti-oxidant, anti-viral and hepatoprotective effects.

PURPOSE

To summarize recent findings regarding to the extraction, detection, biosynthesis, metabolism, pharmacological/toxicological effects of SSs.

METHODS

Online academic databases (including PubMed, Google Scholar, Web of Science and CNKI) were searched using search terms of "Saikosaponin", "Radix Bupleuri", "Bupleurum" and combinations to include published studies of SSs primarily from 2003 to 2018. Several critical previous studies beyond this period were also included.

RESULTS

354 papers were found and 165 papers were reviewed. SSs have drawn great attention for their anti-inflammation, anti-viral and anti-cancer effects and contradictory roles in the regulation of cell apoptosis, oxidative stress and liver fibrosis. Meanwhile, increased risks of overdose-induced acute or accumulation-related chronic hepatotoxicity of SSs and RB have also been reported. However, underlying mechanisms of SSs bioactivities, the metabolism of SSs and bioactivities of SSs metabolites are largely unknown.

CONCLUSION

This comprehensive review of SSs provides novel insights and perspectives on the limitations of current studies and the importance of metabolism study and the dose-pharmacological/toxic relationship of SSs for the future discovery of SSs-based therapeutic strategies and clinical safe practice.

Evolutionary analysis and structural characterization of Aquilaria sinensis sesquiterpene synthase in agarwood formation: A computational study

Agarwood originating from Aquilaria sinensis contains sesquiterpenoids that have tremendous commercial value in the pharmaceutical and fragrance industries. Aquilaria sinensis sesquiterpene synthase (AsSTS) is the key enzyme in the agarwood biosynthesis pathway, and its activity directly affects the chemical composition of agarwood; however, its role in species evolution remains unclear. In this study, we performed an evolutionary analysis based on 68 plant sesquiterpene synthase (STS) genes and further structural characterization of the gene encoding AsSTS to explore its molecular evolution. The phylogenetic tree indicated that these STS genes included three subfamilies. Additionally, 23 positively selected sites were detected, and no influence of recombination was found. Furthermore, the protein structure of AsSTS was characterized using primary sequence and structural analyses as having a functional active site lid domain, a substrate binding site, two post-translational modification sites and four conserved motifs. Finally, most virtual mutations of positively selected sites could be stabilized against thermal denaturation by a decrease in free energy, and three virtual mutations (D403R, G470Q and S538K) were shown to play important roles in the function and stability of AsSTS. The molecular evolutionary analysis of plant STSs provides essential clues for further experimental site-directed mutagenesis and molecular modification of AsSTS.

Cloning, Expression Analysis and Functional Characterization of Squalene Synthase (SQS) from Tripterygium wilfordii

Celastrol is an active triterpenoid compound derived from Tripterygium wilfordii which is well-known as a traditional Chinese medicinal plant. Squalene synthase has a vital role in condensing two molecules of farnesyl diphosphate to form squalene, a key precursor of triterpenoid biosynthesis. In the present study, T. wilfordii squalene synthase (TwSQS) was cloned followed by prokaryotic expression and functional verification. The open reading frame cDNA of TwSQS was 1242 bp encoding 413 amino acids. Bioinformatic and phylogenetic analysis showed that TwSQS had high homology with other plant SQSs. To obtain soluble protein, the truncated TwSQS without the last 28 amino acids of the carboxy terminus was inductively expressed in Escherichia coliTransetta (DE3). The purified protein was detected by SDS-PAGE and Western blot analysis. Squalene was detected in the product of in vitro reactions by gas chromatograph-mass spectrometry, which meant that TwSQS did have catalytic activity. Organ-specific and inducible expression levels of TwSQS were detected by quantitative real-time PCR. The results indicated that TwSQS was highly expressed in roots, followed by the stems and leaves, and was significantly up-regulated upon MeJA treatment. The identification of TwSQS is important for further studies of celastrol biosynthesis in T. wilfordii.

Two Cycloartenol Synthases for Phytosterol Biosynthesis in Polygala tenuifolia Willd

Oxidosqualene cyclases (OSCs) are enzymes that play a key role in control of the biosynthesis of phytosterols and triterpene saponins. In order to uncover OSC genes from Polygala tenuifolia seedlings induced by methyl jasmonate (MeJA), RNA-sequencing analysis was performed using the Illumina sequencing platform. A total of 148,488,632 high-quality reads from two samples (control and the MeJA treated) were generated. We screened genes related to phytosterol and triterpene saponin biosynthesis and analyzed the transcriptional changes of differentially expressed unigene (DEUG) values calculated by fragments per kilobase million (FPKM). In our datasets, two full-length cDNAs of putative OSC genes, PtCAS1, and PtCAS2, were found, in addition to the PtBS (β-amyrin synthase) gene reported in our previous studies and the two cycloartenol synthase genes of P. tenuifolia. All genes were isolated and characterized in yeast cells. The functional expression of the two PtCAS genes in yeast cells showed that the genes all produce a cycloartenol as the sole product. When qRT-PCR analysis from different tissues was performed, the expressions of PtCAS1 and PtCAS2 were highest in flowers and roots, respectively. After MeJA treatment, the transcripts of PtCAS1 and PtCAS2 genes increased by 1.5- and 2-fold, respectively. Given these results, we discuss the potential roles of the two PtCAS genes in relation to triterpenoid biosynthesis.

Cloning and characterization of squalene synthase and cycloartenol synthase from Siraitia grosvenorii

Mogrosides and steroid saponins are tetracyclic triterpenoids found in Siraitia grosvenorii. Squalene synthase (SQS) and cycloartenol synthase (CAS) are key enzymes in triterpenoid and steroid biosynthesis. In this study, full-length cDNAs of SgSQS and SgCAS were cloned by a rapid amplification of cDNA-ends with polymerase chain reaction (RACE-PCR) approach. The SgSQS cDNA has a 1254 bp open reading frame (ORF) encoding 417 amino acids, and the SgCAS cDNA contains a 2298 bp ORF encoding 765 amino acids. Bioinformatic analysis showed that the deduced SgSQS protein has two transmembrane regions in the C-terminal. Both SgSQS and SgCAS have significantly higher levels in fruits than in other tissues, suggesting that steroids and mogrosides are competitors for the same precursors in fruits. Combined in silico prediction and subcellular localization, experiments in tobacco indicated that SgSQS was probably in the cytoplasm or on the cytoskeleton, and SgCAS was likely located in the nucleus or cytosol. These results will provide a foundation for further study of SgSQS and SgCAS gene functions in S. grosvenorii, and may facilitate improvements in mogroside content in fruit by regulating gene expression.

Molecular characterization, expression, and regulation of Gynostemma pentaphyllum squalene epoxidase gene 1

Gynostemma pentaphyllum (Thunb.) Makino is a perennial medicinal herb widely distributed in China. This herb contains important medicinal components called gypenosides, which belong to dammarane-type triterpenoid saponins. Squalene epoxidase (SE, EC 1.14.99.7) catalyzes the epoxidation of squalene to form oxidosqualene and is a key regulatory enzyme in triterpenoid saponin biosynthesis. In this study, a SE gene designated as GpSE1 was isolated from G. pentaphyllum leaves. The deduced protein sequence of GpSE1 contained two conserved domains involved in the catalytic function of SE. GpSE1 was expressed as inclusion bodies in Escherichia coli cells, and the HIS-tagged recombinant protein was successfully purified and renatured in vitro. Immunofluorescence indicated that the polygonal reticular fluorescence signal of GpSE1 was significantly stronger in young leaves than in mature leaves and rhizomes. This finding is consistent with the tissue-specific expression pattern of GpSE1 and suggests that the young leaves of G. pentaphyllum mainly serve as the active site of gypenoside synthesis. Methyl jasmonate (MeJA) treatment upregulated GpSE1 expression in both the young and mature leaves of G. pentaphyllum, with greater upregulation in young leaves than in mature leaves. However, the expression of GpSE1 was not enhanced continually with the increase in MeJA concentration. Moreover, the GpSE1 expression was maximally regulated in response to 50 μM MeJA but not to 100 μM MeJA. This result indicates that MeJA exerts a concentration-dependent effect on GpSE1 expression.

Molecular cloning and functional analysis of squalene synthase (SS) in Panax notoginseng

Panax notoginseng (Burk.) F. H. Chen, which is a used traditional Chinese medicine known as Sanqi or Tianqi in China, is widely studied for its ability to accumulate the triterpene saponins. Squalene synthase (SS: EC 2.5.1.21) catalyzes the first enzymatic step from the central isoprenoid pathway toward sterol and triterpenoid biosynthesis. In this study, SS from P. notoginseng was cloned and investigated followed by its recombinant expression and preliminary enzyme activity. The nucleotide sequence of the ORF contains 1 248 nucleotides and encodes 415 amino acid residues with molecular weight of 47.16kDa and pI of 6.50. Bioinformatics analysis revealed that the deduced PnSS protein had a high similarity with other plant squalene synthases. To obtain soluble recombinant enzymes, 29 hydrophobic amino acids were deleted from the carboxy terminus and expressed as GST-Tag fusion protein in Escherichia coli BL21 (DE3). Approximately 66.46kDa recombinant protein was checked on SDS-PAGE and Western Blot analysis. Preliminary activity of the resultant bacterial crude extract was analyzed by gas chromatograph-mass spectrometer (GC-MS). The identification and function of PnSS is important for further studies of the triterpene saponins biosynthesis in P. notoginseng.

Bioactivity of Phytosterols and Their Production in Plant in Vitro Cultures

Phytosterols are a kind of plant metabolite belonging to the triterpene family. These compounds are essential biomolecules for human health, and so they must be taken from foods. β-Sitosterol, campesterol, and stigmasterol are the main phytosterols found in plants. Phytosterols have beneficial effects on human health since they are able to reduce plasma cholesterol levels and have antiinflammatory, antidiabetic, and anticancer activities. However, there are many difficulties in obtaining them, since the levels of these compounds produced from plant raw materials are low and their chemical synthesis is not economically profitable for commercial exploitation. A biotechnological alternative for their production is the use of plant cell and hairy root cultures. This review is focused on the biosynthesis of phytosterols and their function in both plants and humans as well as the different biotechnological strategies to increase phytosterol biosynthesis. Special attention is given to describing new methodologies based on the use of recombinant DNA technology to increase the levels of phytosterols.

Molecular cloning and promoter analysis of squalene synthase and squalene epoxidase genes from Betula platyphylla

Betula platyphylla is a rich repository of pharmacologically active secondary metabolites known as birch triterpenoids (TBP). Here, we cloned the squalene synthase (SS) and squalene epoxidase genetic (SE) sequences from B. platyphylla that encode the key enzymes that are involved in triterpenoid biosynthesis and analyzed the conserved domains and phylogenetics of their corresponding proteins. The full-length sequence of BpSS is 1588 bp with a poly-A tail, which contained an open reading frame (ORF) of 1241 bp that encoded a protein of 413 amino acids. Additionally, the BpSE full-length sequence of 2040 bp with a poly-A tail was also obtained, which contained an ORF of 1581 bp encoding a protein of 526 amino acids. Their organ-specific expression patterns in 4-week-old tissue culture seedlings of B. platyphylla were detected by real-time PCR and showed that they were all highly expressed in leaves, as compared to stem and root tissues. Additionaly, both BpSS and BpSE were enhanced following stimulation with ethephon and MeJA. The expression of BpSS was enhanced by ABA, whereas BpSE was not. The SA treatment did not affect the BpSS and BpSE transcripts notably. Using a genome walking approach, promoter sequences of 965 and 1193 bp, respectively, for BpSS and BpSE were isolated, and they revealed several key cis-regulatory elements known to be involved in the response to phytohormone and abiotic plant stress. We also found that the BpSS protein is localized in the cytoplasm. Opening reading frames of BpSS and BpSE were ligated into yeast expression plasmid pYES2 under control of GAL1 promoter and introduced into the yeast INVScl1 strain. The transformants were cultured for 12 h, the squalene content of galactose-induced BpSS expression yeast cells was 13.2 times of control (empty vector control yeast cells) by high-performance liquid chromatography (HPLC) test method. And, the squalene epoxidase activity of induced BpSE expression yeast cell was about 11.8 times of control. These indicated that we cloned birch BpSS and BpSE that were indeed involved in the synthesis of triteropenoids. This is the first report wherein SS and SE from B. platyphylla were cloned and may be of significant interest to understand the regulatory role of SS and SE in the triterpenoids biosynthesis of B. platyphylla. This is the first report wherein SS and SE from B. platyphylla were cloned and may be of significant interest to understand the regulatory role of SS and SE in the biosynthesis of birch triterpenoids.

Effect of salicylic acid on expression level of genes related with isoprenoid pathway in centella (Centella asiatica (L.) Urban) cells

In this study, we report the expression level of CaSQS, CabAS and CaCYS, the genes involved in phytosterol and triterpene metabolic pathway of centella (Centella asiatica (L.) Urban), in cells elicited with salicylic acid (50–200 µM). Reverse transcription-polymerase chain reaction (RT-PCR) and Northern blot analysis indicated CaSQS, CabAS, and CaCYS genes expressed in both the wild-type and cultured cells (with and without elicitation). In elicited cells, expressions of CaSQS, CabAS, and CaCYS genes showed strong dependence on salicylic acid concentration and elicitation day. The highest expression of CabAS gene was found in the cells elicited with 100 µM salicylic acid on day 10 of inoculation. Salicylic acid treatment (50–200 µM) decreased expression level of CaCYS and CaSQS genes in elicited cells compared with the control.

Volatile squalene from a nonseed plant Selaginella moellendorffii: Emission and biosynthesis

The triterpene squalene is a key metabolic intermediate for sterols, hopanoids and various other triterpenoids. The biosynthesis of squalene is catalyzed by squalene synthase (SQS), which converts two molecules of farnesyl diphosphate to squalene. In this study, a lycophyte Selaginella moellendorffii was found to emit squalene as a volatile compound under a number of conditions that mimic biotic stresses. Searching the genome sequence of S. moellendorffii led to the identification of a putative squalene synthase gene. It was designated as SmSQS. SmSQS is homologous to known squalene synthases from other plants and animals at both the amino acid level and structural level. Recombinant SmSQS expressed in Escherichia coli catalyzed the formation of squalene using farnesyl diphosphate as substrate. The expression of SmSQS was significantly induced by the same set of stress factors that induced the emission of volatile squalene from S. moellendorffii plants. Taken together, these results support that SmSQS is responsible for the biosynthesis of volatile squalene and volatile squalene may have a role in the defense of S. moellendorffii plants against biotic stresses.