Biosynthetic pathway of terpenoid indole alkaloids in Catharanthus roseus

Microbial allies: exploring fungal endophytes for biosynthesis of terpenoid indole alkaloids

Terpenoid indole alkaloids (TIAs) are natural compounds found in medicinal plants that exhibit various therapeutic activities, such as antimicrobial, anti-inflammatory, antioxidant, anti-diabetic, anti-helminthic, and anti-tumor properties. However, the production of these alkaloids in plants is limited, and there is a high demand for them due to the increasing incidence of cancer cases. To address this research gap, researchers have focused on optimizing culture media, eliciting metabolic pathways, overexpressing genes, and searching for potential sources of TIAs in organisms other than plants. The insufficient number of essential genes and enzymes in the biosynthesis pathway is the reason behind the limited production of TIAs. As the field of natural product discovery from biological species continues to grow, endophytes are being investigated more and more as potential sources of bioactive metabolites with a variety of chemical structures. Endophytes are microorganisms (fungi, bacteria, archaea, and actinomycetes), that exert a significant influence on the metabolic pathways of both the host plants and the endophytic cells. Bio-prospection of fungal endophytes has shown the discovery of novel, high-value bioactive compounds of commercial significance. The discovery of therapeutically significant secondary metabolites has been made easier by endophytic entities' abundant but understudied diversity. It has been observed that fungal endophytes have better intermediate processing ability due to cellular compartmentation. This paper focuses on fungal endophytes and their metabolic ability to produce complex TIAs, recent advancements in this area, and addressing the limitations and future perspectives related to TIA production.

Integrated metabolome and transcriptome analysis identifies candidate genes involved in triterpenoid saponin biosynthesis in leaves of Centella asiatica (L.) Urban

Centella asiatica (L.) Urban is a well-known medicinal plant which has multiple pharmacological properties. Notably, the leaves of C. asiatica contain large amounts of triterpenoid saponins. However, there have only been a few studies systematically elucidating the metabolic dynamics and transcriptional differences regarding triterpenoid saponin biosynthesis during the leaf development stages of C. asiatica. Here, we performed a comprehensive analysis of the metabolome and transcriptome to reveal the dynamic patterns of triterpenoid saponin accumulation and identified the key candidate genes associated with their biosynthesis in C. asiatica leaves. In this study, we found that the key precursors in the synthesis of terpenoids, including DMAPP, IPP and β-amyrin, as well as 22 triterpenes and eight triterpenoid saponins were considered as differentially accumulated metabolites. The concentrations of DMAPP, IPP and β-amyrin showed significant increases during the entire stage of leaf development. The levels of 12 triterpenes decreased only during the later stages of leaf development, but five triterpenoid saponins rapidly accumulated at the early stages, and later decreased to a constant level. Furthermore, 48 genes involved in the MVA, MEP and 2, 3-oxidosqualene biosynthetic pathways were selected following gene annotation. Then, 17 CYP450s and 26 UGTs, which are respectively responsible for backbone modifications, were used for phylogenetic-tree construction and time-specific expression analysis. From these data, by integrating metabolomics and transcriptomics analyses, we identified CaHDR1 and CaIDI2 as the candidate genes associated with DMAPP and IPP synthesis, respectively, and CaβAS1 as the one regulating β-amyrin synthesis. Two genes from the CYP716 family were confirmed as CaCYP716A83 and CaCYP716C11. We also selected two UGT73 families as candidate genes, associated with glycosylation of the terpenoid backbone at C-3 in C. asiatica. These findings will pave the way for further research on the molecular mechanisms associated with triterpenoid saponin biosynthesis in C. asiatica.

Catalytic Site Constraints in the P450s Mediating Loganic Acid (7DLH) and Secologanic Acid Synthesis (SLAS) in Camptotheca

Terpene indole alkaloids (TIAs) are plant-derived natural products synthesized in low levels in medicinal plants such as Catharanthus roseus and Camptotheca acuminata. TIA pathways species utilize several CYP72A subfamily members to form loganic acid from 7-deoxyloganic acid (a simple hydroxylation) as well as secologanin and secologanic acid from loganin and loganic acid (a C-C bond scission). Divergences in the specificities of these P450s have allowed Camptotheca secologanic acid synthases (SLASs) to become bifunctional enzymes capable of performing both reactions. In contrast, Catharanthus 7-deoxyloganic acid hydroxylase (7DLH) and secologanin synthase (SLS) have remained monofunctional enzymes capable either of monooxygenation or C-C bond scission. Our in vitro reconstitutions have now demonstrated that Camptotheca also contains a monofunctional 7DLH capable only of hydroxylating 7-deoxyloganic acid. Mutageneses aimed at evaluating residues important for the tight specificity of Camptotheca 7DLH (CYP72A729) and the broad specificity of SLAS (CYP72A564) have identified several residues where reciprocal switches substantially affect their activities: Lys128His in 7DLH increases hydroxylation of 7-deoxyloganic acid, and His132Lys in SLAS decreases this hydroxylation and C-C bond scissions of loganic acid and loganin; Gly321Ser in 7DLH does not affect hydroxylation of 7-deoxyloganic acid, whereas Ser324Gly in SLAS significantly increases C-C bond scission of loganic acid; Asp332Glu in the acid-alcohol pair of 7DLH increases hydroxylation of 7-deoxyloganic acid, whereas Glu335Asp in SLAS completely eliminates both of its activities. These mutations that enhance or eliminate these respective activities have significant potential to aid engineering efforts aimed at increasing TIA production in cell cultures, microbial systems, and/or other plants.

Comparative transcriptome analysis of different tissues of Solanum khasianum reveals candidate genes involved in steroidal glycoalkaloid biosynthesis

Fruits and leaves of Solanum khasianum C. B. Clarke have long been used as a common Chinese herbal medicine. Steroidal glycoalkaloids (SGAs), the main active ingredient in S. khasianum, exhibit various pharmacological effects. However, genes involved in the SGA biosynthetic pathway in S. khasianum have not yet been identified. Genes encoding potential key SGA biosynthesis enzymes were identified through comprehensive RNA sequencing analysis (RNA-seq) of S. khasianum leaves, stems, and fruits. A total of 123,704 unigenes were obtained, of which 109,775 (88.74%) were annotated in seven public databases. Among these, 54 unigenes potentially involved in SGA biosynthesis were identified. Additionally, 23,636 differentially expressed genes were identified by comparing gene expression levels among the fruits, stems, and leaves of S. khasianum. The structural characteristics and phylogenetic relationship of cycloartenol synthase involved in SGA biosynthesis were further analyzed. Solasodine constituent was detected by high-performance liquid chromatography. This is the first study to report the comparative transcriptome analysis of different tissues of S. khasianum that identifies valuable genes potentially involved in SGA biosynthesis in this species.

Single-cell RNA sequencing provides a high-resolution roadmap for understanding the multicellular compartmentation of specialized metabolism

Monoterpenoid indole alkaloids (MIAs) are among the most diverse specialized metabolites in plants and are of great pharmaceutical importance. We leveraged single-cell transcriptomics to explore the spatial organization of MIA metabolism in Catharanthus roseus leaves, and the transcripts of 20 MIA genes were first localized, updating the model of MIA biosynthesis. The MIA pathway was partitioned into three cell types, consistent with the results from RNA in situ hybridization experiments. Several candidate transporters were predicted to be essential players shuttling MIA intermediates between inter- and intracellular compartments, supplying potential targets to increase the overall yields of desirable MIAs in native plants or heterologous hosts through metabolic engineering and synthetic biology. This work provides not only a universal roadmap for elucidating the spatiotemporal distribution of biological processes at single-cell resolution, but also abundant cellular and genetic resources for further investigation of the higher-order organization of MIA biosynthesis, transport and storage.

Saudi Arabian Plants: A Powerful Weapon against a Plethora of Diseases

The kingdom of Saudi Arabia (SA) ranks fifth in Asia in terms of area. It features broad biodiversity, including interesting flora, and was the historical origin of Islam. It is endowed with a large variety of plants, including many herbs, shrubs, and trees. Many of these plants have a long history of use in traditional medicine. The aim of this review is to evaluate the present knowledge on the plants growing in SA regarding their pharmacological and biological activities and the identification of their bioactive compounds to determine which plants could be of interest for further studies. A systematic summary of the plants' history, distribution, various pharmacological activities, bioactive compounds, and clinical trials are presented in this paper to facilitate future exploration of their therapeutic potential. The literature was obtained from several scientific search engines, including Sci-Finder, PubMed, Web of Science, Google Scholar, Scopus, MDPI, Wiley publications, and Springer Link. Plant names and their synonyms were validated by 'The Plant List' on 1 October 2021. SA is home to approximately 2247 plant species, including native and introduced plants that belong to 142 families and 837 genera. It shares the flora of three continents, with many unique features due to its extreme climate and geographical and geological conditions. As plants remain the leading supplier of new therapeutic agents to treat various ailments, Saudi Arabian plants may play a significant role in the fight against cancer, inflammation, and antibiotic-resistant bacteria. To date, 102 active compounds have been identified in plants from different sites in SA. Plants from the western and southwestern regions have been evaluated for various biological activities, including antioxidant, anti-cancer, antimicrobial, antimalarial, anti-inflammatory, anti-glycation, and cytotoxic activities. The aerial parts of the plants, especially the leaves, have yielded most of the bioactive compounds. Most bioactivity tests involve in vitro assessments for the inhibition of the growth of tumour cell lines, and several compounds with in vitro antitumour activity have been reported. More in-depth studies to evaluate the mode of action of the compounds are necessary to pave the way for clinical trials. Ecological and taxonomical studies are needed to evaluate the flora of SA, and a plan for the conservation of wild plants should be implemented, including the management of the protection of endemic plants.

Ethyl Methane Sulfonate and Sodium Azide-Mediated Chemical and X-ray-Mediated Physical Mutagenesis Positively Regulate Peroxidase 1 Gene Activity and Biosynthesis of Antineoplastic Vinblastine in Catharanthus roseus

Catharanthus roseus synthesizes bioactive therapeutic metabolites, known as monoterpenoid indole alkaloids (MIAs), including antineoplastic vinblastine and vincristine, which have high global demand, and antihypertensive ajmalicine, a serpentine. However, the in planta biosynthesis and accumulation of these phytopharmaceuticals are very low, attributed to their high cytotoxicity in the plant. Considering the low in planta concentration and over-harvesting of plant resources, biotechnological interventions have been undertaken to enhance the production of MIAs in plant systems. The present study was carried out to mutation through chemical and physical mutagenesis with sodium azide, ethyl methane sulfonate and X-rays, respectively, on C. roseus to determine their possible effects on the transcriptional modulation of MIA biosynthetic pathways in planta. The chemical mutagenesis resulted in delayed seed pod development in mutated C. roseus plants, with distinct leaf morphology and flower color. However, X-ray mutagenesis resulted in pollen-less sterile flowers. An HPLC analysis confirmed the higher catharanthine, vindoline and vinblastine content in sodium azide and X-ray mutants, and was further supported by higher PRX1 transcript levels estimated through real-time PCR analysis. The transcription factors WRKY1 and ORCA2 were found negatively regulated along with major MIA pathway genes in chemical mutants and their M₁ generation, but showed positive regulation in X-ray M₀ mutants. The induced mutagenesis of C. roseus provides a prospective strategy to modulate plant transcriptomes and enhance the biosynthesis of pharmaceutically important antineoplastic vinblastine in the plant.

De Novo transcriptome assembly and differential expression analysis of catharanthus roseus in response to salicylic acid

The anti-cancer vinblastine and vincristine alkaloids can only be naturally found in periwinkle (Catharanthus roseus). Both of these alkaloids' accumulations are known to be influenced by salicylic acid (SA). The transcriptome data to reveal the induction effect (s) of SA, however, seem restricted at this time. In this study, the de novo approach of transcriptome assembly was performed on the RNA-Sequencing (RNA-Seq) data in C. roseus. The outcome demonstrated that SA treatment boosted the expression of all the genes in the Terpenoid Indole Alkaloids (TIAs) pathway that produces the vinblastine and vincristine alkaloids. These outcomes supported the time-course measurements of vincristine alkaloid, the end product of the TIAs pathway, and demonstrated that SA spray had a positive impact on transcription and alkaloid synthesis. Additionally, the abundance of transcription factor families including bHLH, C3H, C2H2, MYB, MYB-related, AP2/ ERF, NAC, bZIP, and WRKY suggests a role for a variety of transcription families in response to the SA stimuli. Di-nucleotide and tri-nucleotide SSRs were the most prevalent SSR markers in microsatellite analyses, making up 39% and 34% of all SSR markers, respectively, out of the 77,192 total SSRs discovered.

Effect of the plant probiotic bacteria on terpenoid indole alkaloid biosynthesis pathway gene expression profiling, vinblastine and vincristine content in the root of Catharanthus roseus

BACKGROUND

Catharanthus roseus is the sole resource of vinblastine and vincristine, two TIAs of great interest for their powerful anticancer activities. Increasing the concentration of these alkaloids in various organs of the plant is one of the important goals in C. roseus breeding programs. Plant probiotic bacteria (PBB) act as biotic elicitors and can induce the synthesis of secondary products in plants. The purpose of this research is to study the effects of PBB on expression of the TIA biosynthetic pathway genes and the content of alkaloids in C. roseus.

METHODS AND RESULTS

The individual and combined effects of P. fluorescens strains 169 and A. brasilense strains Ab-101 was studied for expression of the TIA biosynthetic pathway genes (G10H, DAT, T16H and CrPRX) using qRT-PCR and the content of vinblastine and vincristine using HPLC method in roots of C. roseus. P. fluorescens. This drastically increased the content of vinblastine and vincristine alkaloids, compared to the control in the roots, to 174 and 589 (µg/g), respectively. Molecular analysis showed bacterium significantly increased the expression of more genes in the TIA biosynthetic pathway compared to the control. P. fluorescens increased the expression of the final gene of the biosynthetic pathway (CrPRX) 47.9 times compared to the control. Our findings indicate the correlation between transcriptional and metabolic outcomes. The same was true for A. brasilense.

CONCLUSIONS

It can be concluded that seed treatments and seedling root treatments composed of naturally occurring probiotic bacteria are likely to be widely applicable for inducing enhanced alkaloid contents in medicinal plants.

Agrobacterium-Mediated in Planta Transformation in Periwinkle

Madagascar periwinkle (Catharanthus roseus, family Apocynaceae) is a reservoir of more than 130 monoterpene indole alkaloids (MIAs) including the famous anti-neoplastic dimeric MIAs vinblastine and vincristine, and anti-hypertensive monomeric MIAs ajmalicine and serpentine. Understanding the biosynthetic steps and regulatory factors leading to the formation of MIAs is crucial for rational engineering to achieve targeted enhancement of different MIAs. Due to its highly recalcitrant nature, C. roseus is considered genetically non-tractable for transformation at the whole-plant level. Though few reports have demonstrated tissue culture-mediated regeneration and transformation of C. roseus at whole-plant level recently, the efficiency and reproducibility of these protocols have been a major challenge. To overcome this, we have developed a tissue-culture-independent Agrobacterium-mediated in planta transformation method in C. roseus. Using this method, we were able to efficiently generate stable transgenic plants without relying on the cumbersome methods of tissue-culture regeneration and transformation. Moreover, the transformed plants obtained through this in planta method exhibited stability in subsequent generations. Our method is useful not only for the elucidation of biosynthetic and regulatory steps involved in MIA formation through transgenic plant approach but also for metabolic engineering at the whole-plant level in C. roseus.

Natural Composition and Biosynthetic Pathways of Alkaloids in Medicinal Dendrobium Species

Dendrobium is the second biggest genus in the Orchidaceae family, some of which have both ornamental and therapeutic values. Alkaloids are a group of active chemicals found in Dendrobium plants. Dendrobine has emerged specific pharmacological and therapeutic properties. Although Dendrobium alkaloids have been isolated and identified since the 1930s, the composition of alkaloids and their biosynthesis pathways, including metabolic intermediates, alkaloid transporters, concrete genes involved in downstream pathways, and associated gene clusters, have remained unresolved scientific issues. This paper comprehensively reviews currently identified and tentative alkaloids from the aspect of biogenic pathways or metabolic genes uncovered based on the genome annotations. The biosynthesis pathways of each class of alkaloids are highlighted. Moreover, advances of the high-throughput sequencing technologies in the discovery of Dendrobium alkaloid pathways have been addressed. Applications of synthetic biology in large-scale production of alkaloids are also described. This would serve as the basis for further investigation into Dendrobium alkaloids.

Biosynthesis and Modulation of Terpenoid Indole Alkaloids in Catharanthus roseus: A Review of Targeting Genes and Secondary Metabolites

The medicinal plant C. roseus synthesizes biologically active alkaloids via the terpenoid indole alkaloid (TIAs) biosynthetic pathway. Most of these alkaloids have high therapeutic value, such as vinblastine and vincristine. Plant signaling components, plant hormones, precursors, growth hormones, prenylated proteins, and transcriptomic factors regulate the complex networks of TIA biosynthesis. For many years, researchers have been evaluating the scientific value of the TIA biosynthetic pathway and its potential in commercial applications for market opportunities. Metabolic engineering has revealed the major blocks in metabolic pathways regulated at the molecular level, unknown structures, metabolites, genes, enzyme expression, and regulatory genes. Conceptually, this information is necessary to create transgenic plants and microorganisms for the commercial production of high-value dimer alkaloids, such as vinca alkaloids, vinblastine, and vincristine In this review, we present current knowledge of the regulatory mechanisms of these components in the C. roseus TIA pathway, from genes to metabolites.

Enhancement of vincristine under in vitro culture of Catharanthus roseus supplemented with Alternaria sesami endophytic fungal extract as a biotic elicitor

Vincristine, one of the major vinca alkaloid of Catharanthus roseus (L.) G. Don. (Apocynaceae), was enhanced under in vitro callus culture of C. roseus using fungal extract of an endophyte Alternaria sesami isolated from the surface-sterilized root cuttings of C. roseus. Vindoline, a precursor molecule for vincristine production, was detected for the first time in the fungal endophyte A. sesami which was used as a biotic elicitor in this study to enhance vincristine content in the C. roseus callus. It was identified using high-performance liquid chromatography and mass spectroscopy techniques by matching retention time and mass data with reference molecule. Supplementing the heat sterilized A. sesami endophytic fungal culture extract into the callus culture medium of C. roseus resulted in the enhancement of vincristine content in C. roseus callus by 21.717% after 105-day culture.

Novel Homologs of Isopentenyl Phosphate Kinase Reveal Class-Wide Substrate Flexibility

The widespread utility of isoprenoids has recently sparked interest in efficient synthesis of isoprene-diphosphate precursors. Current efforts have focused on evaluating two-step "isoprenol pathways," which phosphorylate prenyl alcohols using promiscuous kinases/phosphatases. The convergence on isopentenyl phosphate kinases (IPKs) in these schemes has prompted further speculation about the class's utility in synthesizing non-natural isoprenoids. However, the substrate promiscuity of IPKs in general has been largely unexplored. Towards this goal, we report the biochemical characterization of five novel IPKs from Archaea and the assessment of their substrate specificity using 58 alkyl-monophosphates. This study reveals the IPK-catalyzed synthesis of 38 alkyl-diphosphate analogs and discloses broad substrate specificity of IPKs. Further, to demonstrate the biocatalytic utility of IPK-generated alkyl-diphosphates, we also highlight the synthesis of alkyl-l-tryptophan derivatives using coupled IPK-prenyltransferase reactions. These results reveal IPK-catalyzed reactions are compatible with downstream isoprenoid enzymes and further support their development as biocatalytic tools for the synthesis of non-natural isoprenoids.

Strictosidine synthase, an indispensable enzyme involved in the biosynthesis of terpenoid indole and β-carboline alkaloids

Terpenoid indole (TIAs) and β-carboline alkaloids (BCAs), such as suppressant reserpine, vasodilatory yohimbine, and antimalarial quinine, are natural compounds derived from strictosidine. These compounds can exert powerful pharmacological effects but be obtained from limited source in nature. the whole biosynthetic pathway of TIAs and BCAs, The Pictet-Spengler reaction catalyzed by strictosidine synthase (STR; EC: 4.3.3.2) is the rate-limiting step. Therefore, it is necessary to investigate their biosynthesis pathways, especially the role of STR, and related findings will support the biosynthetic generation of natural and unnatural compounds. This review summarizes the latest studies concerning the function of STR in TIA and BCA biosynthesis, and illustrates the compounds derived from strictosidine. The substrate specificity of STR based on its structure is also summarized. Proteins that contain six-bladed four-stranded β-propeller folds in many organisms, other than plants, are listed. The presence of these folds may lead to similar functions among organisms. The expression of STR gene can greatly influence the production of many compounds. STR is mainly applied to product various valuable drugs in plant cell suspension culture and biosynthesis in other carriers.

Putative genes in alkaloid biosynthesis identified in Dendrobium officinale by correlating the contents of major bioactive metabolites with genes expression between Protocorm-like bodies and leaves

BACKGROUND

Dendrobium officinale, an endangered Chinese herb, possesses extensive therapeutic effects and contains bioactive ingredients such as major polysaccharides, alkaloids, and minimal flavonoids. We first obtained the protocorm-like bodies (PLBs) of this plant through tissue culture in order to determine the distribution of the main secondary metabolites in each organelle and the PLBs. We then analyzed the correlation between gene expression level from comparative transcriptome sequencing and metabolite content in different organs to identify putative genes encoding enzymes involved in the biosynthesis of polysaccharides, alkaloids, and flavonoids.

RESULTS

We used seeds as explants for protocorm induction and PLB propagation of D. officinale. The optimal medium formula for PLB propagation was 1/2 MS + α-NAA 0.5 mg·L- 1 + 6-BA 1.0 mg·L- 1 + 2, 4-D 1.5-2.0 mg·L- 1 + potato juice 100 g·L- 1. Stems, PLBs and leaves of D. officinale had the highest content of polysaccharides, alkaloids and flavonoids, respectively. Naringenin was only produced in stem; however, PLBs with high alkaloid content can replace other organs producing alkaloids. The hot water extraction method outperformed the ultrasound-assisted extraction method for extracting polysaccharides from D. officinale. A comparative transcriptome analysis of PLBs and leaves of D. officinale revealed differential expression of genes encoding enzymes involved in polysaccharide, alkaloid and flavonoid biosynthetic pathways. Putative genes encoding enzymes involved in these biosynthetic pathways were identified. Notably, we identified genes encoding the alkaloid biosynthesis enzymes strictosidine β-D-Glucosidase, geissoschizine synthase and vinorine synthase in D. officinale.

CONCLUSIONS

The identification of candidate genes encoding enzymes involved in metabolite biosynthesis will help to explore and protect this endangered species and facilitate further analysis of the molecular mechanism of secondary metabolite biosynthesis in D. officinale.

Chemistry, Pharmacology and Therapeutic Potential of Swertiamarin - A Promising Natural Lead for New Drug Discovery and Development

Swertiamarin, a seco-iridoid glycoside, is mainly found in Enicostemma littorale Blume (E. littorale) and exhibits therapeutic activities for various diseases. The present study aimed to provide a review of swertiamarin in terms of its phytochemistry, physicochemical properties, biosynthesis, pharmacology and therapeutic potential. Relevant literature was collected from several scientific databases, including PubMed, ScienceDirect, Scopus and Google Scholar, between 1990 and the present. This review included the distribution of swertiamarin in medicinal plants and its isolation, characterization, physicochemical properties and possible biosynthetic pathways. A comprehensive summary of the pharmacological activities, therapeutic potential and metabolic pathways of swertiamarin was also included after careful screening and tabulation. Based on the reported evidence, swertiamarin meets all five of Lipinski’s rules for drug-like properties. Thereafter, the physicochemical properties of swertiamarin were detailed and analyzed. A simple and rapid method for isolating swertiamarin from E. littorale has been described. The present review proposed that swertiamarin may be biosynthesized by the mevalonate or nonmevalonate pathways, followed by the seco-iridoid pathway. It has also been found that swertiamarin is a potent compound with diverse pharmacological activities, including hepatoprotective, analgesic, anti-inflammatory, antiarthritis, antidiabetic, antioxidant, neuroprotective and gastroprotective activities. The anticancer activity of swertiamarin against different cancer cell lines has been recently reported. The underlying mechanisms of all these pharmacological effects are diverse and seem to involve the regulation of different molecular targets, including growth factors, inflammatory cytokines, protein kinases, apoptosis-related proteins, receptors and enzymes. Swertiamarin also modulates the activity of several transcription factors, and their signaling pathways in various pathological conditions are also discussed. Moreover, we have highlighted the toxicity profile, pharmacokinetics and possible structural modifications of swertiamarin. The pharmacological activities and therapeutic potential of swertiamarin have been extensively investigated. However, more advanced studies are required including clinical trials and studies on the bioavailability, permeability and administration of safe doses to offer swertiamarin as a novel candidate for future drug development.

Characterization of MYB35 regulated methyl jasmonate and wound responsive Geraniol 10-hydroxylase-1 gene from Bacopa monnieri

BmG10H-1 transcript from B. monnieri was functionally active. BmG10H-1 promoter drives GUS activity in response to MeJA and wounding. BmMYB35 regulates BmG10H-1 transcript by binding to its promoter. Geraniol 10-hydroxylase (G10H) is one of the important regulatory cytochrome P450 monooxygenase, which is involved in the biosynthesis of monoterpene alkaloids. However, G10H is not characterized at the enzymatic or at the regulatory aspect in B. monnieri. In the present study, we have identified two transcripts of BmG10H (BmG10H-1and BmG10H-2) and characterized the methyl jasmonate (MeJA) and wound responsive BmG10H-1 transcript from B. monnieri. BmG10H-1 showed induced expression after 3 h of MeJA and wounding treatment in the shoot. Yeast purified recombinant BmG10H-1 protein is enzymatically active, having V_max of 0.16 µMsec^-1 μg^-1 protein and catalyzes the hydroxylation of geraniol to 10-hydroxy geraniol. The BmG10H-1 promoter was isolated by using the genome walking method. BmG10H-1 promoter can drive GUS expression in transgenic Arabidopsis thaliana. GUS activity of MeJA and wound-treated Arabidopsis seedlings were found to be increased as compared to the control untreated seedlings, whereas no GUS activity was found in deleted MeJA responsive and W-box cis-elements. This shows that the BmG10H-1 promoter contains functional MeJA (TGACG) and wound responsive (TGACCT) cis-elements. Further, shoot specific and MeJA responsive recombinant BmMYB35 protein was purified, which binds with the MYB recognition cis-element (TGGTTA) present in the BmG10H-1 promoter and transcriptionally activates the reporter gene in yeast. In conclusion, the characterization of MeJA and wound responsive BmG10H-1 provides novel information about its transcriptional regulation by binding with MYB transcription factor in B. monnieri.

A vital role of chitosan nanoparticles in improvisation the drought stress tolerance in Catharanthus roseus (L.) through biochemical and gene expression modulation

Drought is a main abiotic stress that restricts plant growth and development. The increased global demand of anti-cancer alkaloids extracted from periwinkle (Catharanthus roseus) is mainly related to plant growth and development, which are severely affected by drought. Chitosan nanoparticles (CSNPs) have been used to boost plant growth and defense mechanism, however their impact to alleviate drought stress of C. roseus has not been investigated yet. In this study, control and stressed plants (100 and 50% of field capacity [FC], respectively) were subjected to CSNPs application at 1%. Drought stress considerably reduced plant growth, relative water content (RWC), stomatal conductance and total chlorophyll; however, CSNPs mitigated these effects. They enhanced proline accumulation and the activity of catalase (CAT) and ascorbate peroxidase (APX) with possible mitigation of drought-induced oxidative stress. Therefore, they reduced H₂O₂ and malondialdehyde (MDA) accumulation, and eventually preserved membrane integrity. Drought stress increased alkaloid accumulation, and further increase was observed with the application of CSNPs. High alkaloid content was associated with induced gene expression of strictosidine synthase (STR), deacetylvindoline-4-O-acetyltransferase (DAT), peroxidase 1 (PRX1) and geissoschizine synthase (GS) up to 5.6 folds under drought stress, but more accumulation was noticed with the application of CSNPs. Overall, this study is the first on using CSNPs to mitigate drought stress of C. roseus by inducing the antioxidant potential and gene expression of alkaloid biosynthesis.

P450 variations bifurcate the early terpene indole alkaloid pathway in Catharanthus roseus and Camptotheca acuminata

Divergent terpene indole alkaloid (TIA) pathways in Catharanthus roseus and Camptotheca acuminata generate vinblastine and vincristine, and camptothecin, respectively. In contrast to Catharanthus which feeds secologanin (from methylated loganin) into its species-specific late pathway, Camptotheca feeds secologanic acid (from unmethylated loganic acid) into its late pathway. Having identified putative Camptotheca secologanic acid synthases (SLASs) and cytochrome P450 reductases (CPRs) in transcriptome databases, we have demonstrated that two P450s, CYP72A564 and CYP72A565, are capable of utilizing both loganic acid and loganin to generate secologanic acid and secologanin. We have extended the previous report of these activities by CYP72A565 and CYP72A610 (Yang et al., 2019) by demonstrating that both Arabidopsis CPRs (ATR1, ATR2) couple with these CYP72A proteins in yeast microsomal assays and that purified Camptotheca CPR1 couples with them in in vitro reconstitution assays. Kinetic analyses of purified full-length Camptotheca SLASs have indicated that both process loganic acid with nearly identical catalytic rates and efficiencies as measured by their k_cat and k_cat/K_M. In contrast, CYP72A564 processes loganin with two-fold greater efficiency than CYP72A565 correlating with the former's 3-fold greater affinity for loganin. The closely-related CYP72A730 does not bind or process either compound. Molecular modeling of these three proteins and comparisons with Catharanthus secologanin synthase (SLS) have identified key differences that likely determine their SLAS versus SLS selectivities. Our ability to reconstitute these SLAS/SLS activities provides valuable tools for further examinations of the residues involved in substrate recognition and determinations of their unusual mechanism of C-C bond scission.

Chemical Diversity and Bioactivities of Monoterpene Indole Alkaloids (MIAs) from Six Apocynaceae Genera

By the end of the twentieth century, the interest in natural compounds as probable sources of drugs has declined and was replaced by other strategies such as molecular target-based drug discovery. However, in the recent times, natural compounds regained their position as extremely important source drug leads. Indole-containing compounds are under clinical use which includes vinblastine and vincristine (anticancer), atevirdine (anti-HIV), yohimbine (erectile dysfunction), reserpine (antihypertension), ajmalicine (vascular disorders), ajmaline (anti-arrhythmic), vincamine (vasodilator), etc. Monoterpene Indole Alkaloids (MIAs) deserve the curiosity and attention of researchers due to their chemical diversity and biological activities. These compounds were considered as an impending source of drug-lead. In this review 444 compounds, were identified from six genera belonging to the family Apocynaceae, will be discussed. These genera (Alstonia, Rauvolfia, Kopsia, Ervatamia, and Tabernaemontana, and Rhazya) consist of 400 members and represent 20% of Apocynaceae species. Only 30 (7.5%) species were investigated, whereas the rest are promising to be investigated. Eleven bioactivities, including antibacterial, antifungal, anti-inflammatory and immunosuppressant activities, were reported. Whereas cytotoxic effect represents 47% of the reported activities. Convincingly, the genera selected in this review are a wealthy source for future anticancer drug lead.

Biotechnological approaches to the production of plant-derived promising anticancer agents: An update and overview

The plant kingdom is a rich source of bioactive compounds, many of which have been used since pre-history for their therapeutic properties to treat a range of illnesses. These metabolites have recently attracted attention to their antineoplastic activities to treat various cancers relying on different mechanisms. Some of these molecules are glycosides, which have proven useful as anti-cancer agents, namely podophyllotoxin (PPT) anaryltetralin lignan or alkaloids. There are three primary forms of alkaloids, such as indole alkaloids (vincristine and vinblastine from Catharanthus roseus), quinoline alkaloid (camptothecin from Camptotheca acuminata), and diterpenoid alkaloid (taxol and it's analogous from Taxus and Corylus species). This review considers various plant biotechnology approaches used to enhance the production of these anticancer molecules in different species. In this regard, many in vitro culture techniques such as stimulation of suspension culture and hairy roots are being used to investigate the effects of plant growth regulators and elicitors on various explants.

Comparative Analysis and Expression Patterns of the PLP_deC Genes in Dendrobium officinale

Studies have shown that the type II pyridoxal phosphate-dependent decarboxylase (PLP_deC) genes produce secondary metabolites and flavor volatiles in plants, and TDC (tryptophan decarboxylase), a member of the PLP_deC family, plays an important role in the biosynthesis of terpenoid indole alkaloids (TIAs). In this study, we identified eight PLP_deC genes in Dendrobium officinale (D. officinale) and six in Phalaenopsis equestris (P. equestris), and their structures, physicochemical properties, response elements, evolutionary relationships, and expression patterns were preliminarily predicted and analyzed. The results showed that PLP_deC genes play important roles in D. officinale and respond to different exogenous hormone treatments; additionally, the results support the selection of appropriate candidates for further functional characterization of PLP_deC genes in D. officinale.

The Recruitment Model of Metabolic Evolution: Jasmonate-Responsive Transcription Factors and a Conceptual Model for the Evolution of Metabolic Pathways

Plants produce a vast array of structurally diverse specialized metabolites with various biological activities, including medicinal alkaloids and terpenoids, from relatively simple precursors through a series of enzymatic steps. Massive metabolic flow through these pathways usually depends on the transcriptional coordination of a large set of metabolic, transport, and regulatory genes known as a regulon. The coexpression of genes involved in certain metabolic pathways in a wide range of developmental and environmental contexts has been investigated through transcriptomic analysis, which has been successfully exploited to mine the genes involved in various metabolic processes. Transcription factors are DNA-binding proteins that recognize relatively short sequences known as cis-regulatory elements residing in the promoter regions of target genes. Transcription factors have positive or negative effects on gene transcription mediated by RNA polymerase II. Evolutionarily conserved transcription factors of the APETALA2/ETHYLENE RESPONSE FACTOR (AP2/ERF) and basic helix-loop-helix (bHLH) families have been identified as jasmonate (JA)-responsive transcriptional regulators of unrelated specialized pathways in distinct plant lineages. Here, I review the current knowledge and propose a conceptual model for the evolution of metabolic pathways, termed "recruitment model of metabolic evolution." According to this model, structural genes are repeatedly recruited into regulons under the control of conserved transcription factors through the generation of cognate cis-regulatory elements in the promoters of these genes. This leads to the adjustment of catalytic activities that improve metabolic flow through newly established passages.

Transcriptomics comparison reveals the diversity of ethylene and methyl-jasmonate in roles of TIA metabolism in Catharanthus roseus

Background

The medicinal plant, Catharanthus roseus (C. roseus), accumulates a wide range of terpenoid indole alkaloids (TIAs). Ethylene (ET) and methyl-jasmonate (MeJA) were previously reported as effective elicitors for the production of various valuable secondary metabolites of C. roseus, while a few ET or MeJA induced transcriptomic research is yet reported on this species. In this study, the de-novo transcriptome assembly of C. roseus is performed by using the next-generation sequencing technology.

Results

The result shows that phenolic biosynthesis genes respond specifically to ET in leaves, monoterpenoid biosynthesis genes respond specifically to MeJA in roots. By screening the database, 23 ATP-binding cassette (ABC) transporter partial sequences are identified in C. roseus. On this basis, more than 80 key genes that encode key enzymes (namely TIA pathway, transcriptional factor (TF) and candidate ABC transporter) of alkaloid synthesis in TIA biosynthetic pathways are chosen to explore the integrative responses to ET and MeJA at the transcriptional level. Our data indicated that TIA accumulation is strictly regulated by the TF ethylene responsive factor (ERF) and bHLH iridoid synthesis 1 (BIS1). The heatmap, combined with principal component analysis (PCA) of C. roseus, shows that ERF co-expression with ABC2 and ABC8 specific expression in roots affect the root-specific accumulation of vinblastine in C. roseus. On the contrast, BIS1 activities follow a similar pattern of ABC3 and CrTPT2 specific expression in leaves, which affects the leaf-specific accumulation of vindoline in C. roseus.

Conclusions

Results presented above illustrate that ethylene has a stronger effect than MeJA on TIA induction at both transcriptional and metabolite level. Furthermore, meta-analysis reveals that ERF and BIS1 form a positive feedback loop connecting two ABC transporters respectively and are actively involved in TIAs responding to ET and MeJA in C. roseus.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4879-3) contains supplementary material, which is available to authorized users.

Metabolic Profiling of Dendrobium officinale in Response to Precursors and Methyl Jasmonate

Alkaloids are the main active ingredients in the medicinal plant Dendrobium officinale. Based on the published genomic and transcriptomic data, a proposed terpenoid indole alkaloid (TIA) biosynthesis pathway may be present in D. officinale. In this study, protocorm-like bodies (PLBs) with a high-yielding production of alkaloids were obtained by the optimization of tryptophan, secologanin and methyl jasmonate (MeJA) treatment. The results showed that the total alkaloid content was 2.05 times greater than that of the control group when the PLBs were fed with 9 µM tryptophan, 6 µM secologanin and 100 µM MeJA after 36 days. HPLC analysis showed that strictosidine synthase (STR) activity also increased in the treated plants. A total of 78 metabolites were identified using gas chromatography-mass spectrometry (GC-MS) in combination with liquid chromatography-mass spectrometry (LC-MS) methods; 29 differential metabolites were identified according to the multivariate statistical analysis. Among them, carapanaubine, a kind of TIA, exhibited dramatically increased levels. In addition, a possible underlying process of the metabolic flux from related metabolism to the TIA biosynthetic pathway was enhanced. These results provide a comprehensive view of the metabolic changes related to alkaloid biosynthesis, especially TIA biosynthesis, in response to tryptophan, secologanin and MeJA treatment.

De novo transcriptome analyses reveals putative pathway genes involved in biosynthesis and regulation of camptothecin in Nothapodytes nimmoniana (Graham) Mabb

Comprehensive transcriptome analysis of leaf and root tissues of Nothapodytes nimmoniana unravels several putative pathway genes, transcription factors and CYPs related to camptothecin (CPT) biosynthesis. Additionally, post-transcriptional suppression by artificial microRNA (aMIR) of NnCYP76B6 (geraniol 10-hydroxylase) suggests its role in CPT biosynthesis. Tissue-specific LC-MS/MS analysis revealed the presence of secologanin as the central intermediate of MIA pathway in N. nimmoniana. Nothapodytes nimmoniana is a rich source of potent anticancer drug camptothecin (CPT) whose biosynthetic pathway is unresolved due to the lack of genomic and transcriptomic information. Present investigation entails deep transcriptome analysis of N. nimmoniana which led to identification of putative pathway genes and regulatory components involved in CPT biosynthesis. Using Illumina HiSeq 2500 sequencing platform a total of 31,172,889 (6.23 Gb) and 31,218,626 (6.24 Gb) raw reads were generated from leaf and root wood, respectively. These were assembled de novo into 138,183 unique contigs. Additionally, 16 cytochrome P450 transcripts related to secondary metabolism were also identified. Further, transcriptome data pool presented 1683 putative transcription factors of which transcripts corresponding to WRKY TFs were the most abundant (14.14%). A total of 2741 transcripts were differentially expressed out of which 478 contigs showed downregulation in root wood and 2263 contigs were up-regulated. Further, comparative analyses of 17 genes involved in CPT biosynthetic pathway were validated by qRT-PCR. On basis of intermediates, two distinct seco-iridoid pathways are involved in the biosynthesis of monoterpene indole alkaloids either through multiple isomers of strictosidinic acid or strictosidine. Tissue-specific LC-MS/MS analysis revealed the presence of secologanin as the central intermediate of MIA pathway in N. nimmoniana. Geraniol-10 hydroxylase (NnCYP76B6) an important enzyme in CPT biosynthesis which specifically shunts geraniol into the secologanin pathway was also cloned from the trancriptome resource. In planta transient expression of NnCYP76B6 showed a significant enhancement in mRNA transcript levels coincident with enhanced CPT accumulation. Further, artificial microRNA (aMIR) mediated downregulation of NnCYP76B6 resulted in reduction of mRNA transcript levels as well as CPT content in comparison to control. These empirical results suggest a plausible regulatory role for NnCYP76B6 in CPT biosynthesis and also establish a valuable repository for deciphering various structural, rate limiting and regulatory genes of CPT biosynthetic pathway.

Modulation of benzylisoquinoline alkaloid biosynthesis by heterologous expression of CjWRKY1 in Eschscholzia californica cells

Transcription factors control many processes in plants and have high potentials to manipulate specialized metabolic pathways. Transcriptional regulation of the biosynthesis of monoterpenoid indole alkaloids (MIAs), nicotine alkaloids, and benzylisoquinoline alkaloids (BIAs) has been characterized using Catharanthus roseus, Nicotiana and Coptis plants. However, metabolic engineering in which specific transcription factors are used in alkaloid biosynthesis is limited. In this study, we characterized the effects of ectopic expression of CjWRKY1, which is a transcriptional activator with many targets in BIA biosynthesis in Coptis japonica (Ranunculaceae) and Eschscholzia californica (California poppy, Papaveraceae). Heterologous expression of CjWRKY1 in cultured California poppy cells induced increases in transcripts of several genes encoding BIA biosynthetic enzymes. Metabolite analyses indicated that the overexpression of the CjWRKY1 gene also induced increases in the accumulation of BIAs such as sanguinarine, chelerythrine, chelirubine, protopine, allocryptopine, and 10-hydroxychelerythrine in the culture medium. Previous characterization of EcbHLH1 and current results indicated that both transcription factors, WRKY1 and bHLH1, are substantially involved in the regulation of BIA biosynthesis. We discuss the function of CjWRKY1 in E. californica cells and its potential for metabolic engineering in BIA biosynthesis.

De novo Sequencing and Transcriptome Analysis Reveal Key Genes Regulating Steroid Metabolism in Leaves, Roots, Adventitious Roots and Calli of Periploca sepium Bunge

Periploca sepium Bunge is a traditional medicinal plant, whose root bark is important for Chinese herbal medicine. Its major bioactive compounds are C21 steroids and periplocin, a kind of cardiac glycoside, which are derived from the steroid synthesis pathway. However, research on P. sepium genome or transcriptomes and their related genes has been lacking for a long time. In this study we estimated this species nuclear genome size at 170 Mb (using flow cytometry). Then, RNA sequencing of four different tissue samples of P. sepium (leaves, roots, adventitious roots, and calli) was done using the sequencing platform Illumina/Solexa Hiseq 2,500. After de novo assembly and quantitative assessment, 90,375 all-transcripts and 71,629 all-unigenes were finally generated. Annotation efforts that used a number of public databases resulted in detailed annotation information for the transcripts. In addition, differentially expressed genes (DEGs) were identified by using digital gene profiling based on the reads per kilobase of transcript per million reads mapped (RPKM) values. Compared with the leaf samples (L), up-regulated genes and down-regulated genes were eventually obtained. To deepen our understanding of these DEGs, we performed two enrichment analyses: gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG). Here, the analysis focused upon the expression characteristics of those genes involved in the terpene metabolic pathway and the steroid biosynthesis pathway, to better elucidate the molecular mechanism of bioactive steroid synthesis in P. sepium. The bioinformatics analysis enabled us to find many genes that are involved in bioactive steroid biosynthesis. These genes encoded acetyl-CoA acetyltransferase (ACAT), HMG-CoA synthase (HMGS), HMG-CoA reductase (HMGR), mevalonate kinase (MK), phosphomevalonate kinase (PMK), mevalonate diphosphate decarboxylase (MDD), isopentenylpyrophosphate isomerase (IPPI), farnesyl pyrophosphate synthase (FPS), squalene synthase (SS), squalene epoxidase (SE), cycloartenol synthase (CAS), sterol C-24 methyltransferase (SMT1), sterol-4alpha-methyl oxidase 1 (SMO1), sterol 14alpha-demethylase (CYP51/14-SDM), delta(14)-sterol reductase (FK/14SR), C-8,7 sterol isomerase (HYD1), sterol-4alpha-methyl oxidase 2 (SMO2), delta(7)-sterol-C5(6)-desaturase (STE1/SC5DL), 7-dehydrocholesterol reductase (DWF5/DHCR7), delta (24)-sterol reductase (DWF1/DHCR24), sterol 22-desaturase (CYP710A), progesterone 5beta-reductase (5β-POR), 3-beta-hydroxysteroid dehydrogenase (3β-HSD). This research will be helpful to further understand the mechanism of bioactive steroid biosynthesis in P. sepium, namely C21 steroid and periplocin biosynthesis.

Engineering overexpression of ORCA3 and strictosidine glucosidase in Catharanthus roseus hairy roots increases alkaloid production

Catharanthus roseus produces many pharmaceutically important terpenoid indole alkaloids (TIAs) such as vinblastine, vincristine, ajmalicine, and serpentine. Past metabolic engineering efforts have pointed to the tight regulation of the TIA pathway and to multiple rate-limiting reactions. Transcriptional regulator ORCA3 (octadecanoid responsive Catharanthus AP2-domain protein), activated by jasmonic acid, plays a central role in regulating the TIA pathway. In this study, overexpressing ORCA3 under the control of a glucocorticoid-inducible promoter in C. roseus hairy roots resulted in no change in the total amount of TIAs measured. RT-qPCR results showed that ORCA3 overexpression triggered the upregulation of transcripts of most of the known TIA pathway genes. One notable exception was the decrease in strictosidine glucosidase (SGD) transcripts. These results corresponded to previously published results. In this study, ORCA3 and SGD were both engineered in hairy roots under the control of a glucocorticoid-inducible promoter. Co-overexpression of ORCA3 and SGD resulted in a significant (p < 0.05) increase in serpentine by 44 %, ajmalicine by 32 %, catharanthine by 38 %, tabersonine by 40 %, lochnericine by 60 % and hörhammericine by 56 % . The total alkaloid pool was increased significantly by 47 %. Thus, combining overexpression of a positive regulator and a pathway gene which is not controlled by this regulator provided a way to enhance alkaloid production.

Tyrosine phosphorylation and protein degradation control the transcriptional activity of WRKY involved in benzylisoquinoline alkaloid biosynthesis

Benzylisoquinoline alkaloids (BIQ) are among the most structurally diverse and pharmaceutically valuable secondary metabolites. A plant-specific WRKY-type transcription factor, CjWRKY1, was isolated from Coptis japonica and identified as a transcriptional activator of BIQ biosynthesis. However, the expression of CjWRKY1 gene alone was not sufficient for the activation of genes encoding biosynthetic enzymes. Here, we report the importance of post-translational regulation of CjWRKY1 in BIQ biosynthesis. First, we detected the differential accumulation of CjWRKY1 protein in two cell lines with similar CjWRKY1 gene expression but different levels of accumulated alkaloids. Further investigation of the WRKY protein identified the phosphorylation of the WRKYGQK core domain at Y115. The CjWRKY^Y115E phosphorylation-mimic mutant showed loss of nuclear localization, DNA-binding activity, and transactivation activity compared to wild-type CjWRKY1. Rapid degradation of the CjWRKY1 protein was also confirmed following treatment with inhibitors of the 26S proteasome and protease inhibitors. The existence of two independent degradation pathways as well as protein phosphorylation suggests the fine-tuning of CjWRKY1 activities is involved in the regulation of biosynthesis of BIQs.

Characterization of the Promoter Region of Biosynthetic Enzyme Genes Involved in Berberine Biosynthesis in Coptis japonica

The presence of alkaloids is rather specific to certain plant species. However, berberine, an isoquinoline alkaloid, is relatively broadly distributed in the plant kingdom. Thus, berberine biosynthesis has been intensively investigated, especially using Coptis japonica cell cultures. Almost all biosynthetic enzyme genes have already been characterized at the molecular level. Particularly, two transcription factors (TFs), a plant-specific WRKY-type TF, CjWRKY1, and a basic helix-loop-helix TF, CjbHLH1, were shown to comprehensively regulate berberine biosynthesis in C. japonica cells. In this study, we characterized the promoter region of some biosynthetic enzyme genes and associated cis-acting elements involved in the transcriptional regulation via two TFs. The promoter regions of three berberine biosynthetic enzyme genes (CYP80B2, 4'OMT and CYP719A1) were isolated, and their promoter activities were dissected by a transient assay involving the sequentially truncated promoter::luciferase (LUC) reporter constructs. Furthermore, transactivation activities of CjWRKY1 were determined using the truncated promoter::LUC reporter constructs or constructs with mutated cis-elements. These results suggest the involvement of a putative W-box in the regulation of biosynthetic enzyme genes. Direct binding of CjWRKY1 to the W-box DNA sequence was also confirmed by an electrophoresis mobility shift assay and by a chromatin immunoprecipitation assay. In addition, CjbHLH1 also activated transcription from truncated 4'OMT and CYP719A1 promoters independently of CjWRKY1, suggesting the involvement of a putative E-box. Unexpected transcriptional activation of biosynthetic enzyme genes via a non-W-box sequence and by CjWRKY1 as well as the possible involvement of a GCC-box in berberine biosynthesis in C. japonica are discussed.