Vinca drug components accumulate exclusively in leaf exudates of Madagascar periwinkle

The evolution and history of Vinca alkaloids: From the Big Bang to the treatment of pediatric acute leukemia

An attractive flower from the island of Madagascar has in part saved the lives of thousands of children with acute lymphoblastic leukemia (ALL). Random mutations and alterations to the genome led to the evolution of genes encoding enzymes, which would provide the periwinkle flower an arsenal of secondary metabolites to survive within the Madagascar ecosystem. Of the over 200 alkaloid compounds synthesized by the periwinkle, vincristine and vinblastine are the two most well-known being used for chemotherapy treatments, including for children with ALL. The complexities of the multi-step biosynthesis of vincristine and vinblastine, which has taken years to decode, highlight the importance of protecting the vast biodiversity on earth as other natural products that can save lives await to be discovered. This review addresses the discovery of vincristine and vinblastine, as well as the history of their existence, in nature.

Characterization of a CrPME indicates its possible role in determining vindoline accumulation in Catharanthus roseus leaves

The leaf-specific Catharanthus roseus alkaloid, vindoline, is the major bottleneck precursor in the production of scarce and costly anticancer bisindoles (vincristine and vinblastine). The final steps of its biosynthesis and storage occur in the laticifers. Earlier, we have shown that vindoline content is directly related to laticifer number. Pectin remodeling enzymes, like pectin methylesterase (PME), are known to be involved in laticifer development. A search in the croFGD yielded a leaf-abundant CrPME isoform that co-expressed with a few vindoline biosynthetic genes. Full-length cloning, tissue-specific expression profiling, and in silico analysis of CrPME were carried out. It was found to possess all the specific characteristics of a typical plant PME. Transient silencing (through VIGS) and overexpression of CrPME in C. roseus indicated a direct relationship between its expression and vindoline content. Comparative analysis of transcript abundance and enzyme activity in three familial C. roseus genotypes differing significantly in their vindoline content and laticifer count (CIM-Sushil > Dhawal > Nirmal) also corroborated the positive relationship of CrPME expression with vindoline content. This study highlights the possible role of CrPME, a cell wall remodeling enzyme, in modulating laticifer-associated secondary metabolism.

The leaf idioblastome of the medicinal plant Catharanthus roseus is associated with stress resistance and alkaloid metabolism

Catharanthus roseus leaves produce a range of monoterpenoid indole alkaloids (MIAs) that include low levels of the anticancer drugs vinblastine and vincristine. The MIA pathway displays a complex architecture spanning different subcellular and cell type localizations, and is under complex regulation. As a result, the development of strategies to increase the levels of the anticancer MIAs has remained elusive. The pathway involves mesophyll specialized idioblasts where the late unsolved biosynthetic steps are thought to occur. Here, protoplasts of C. roseus leaf idioblasts were isolated by fluorescence-activated cell sorting, and their differential alkaloid and transcriptomic profiles were characterized. This involved the assembly of an improved C. roseus transcriptome from short- and long-read data, IDIO+. It was observed that C. roseus mesophyll idioblasts possess a distinctive transcriptomic profile associated with protection against biotic and abiotic stresses, and indicative that this cell type is a carbon sink, in contrast to surrounding mesophyll cells. Moreover, it is shown that idioblasts are a hotspot of alkaloid accumulation, suggesting that their transcriptome may hold the key to the in-depth understanding of the MIA pathway and the success of strategies leading to higher levels of the anticancer drugs.

Development of an efficient Agrobacterium-mediated transformation method and its application in tryptophan pathway modification in Catharanthus roseus

The biosynthetic pathway of Catharanthus roseus vinca alkaloids has a long research history, including not only identification of metabolic intermediates but also the mechanisms of inter-cellular transport and accumulation of biosynthesized components. Vinca alkaloids pathway begins with strictosidine, which is biosynthesized by condensing tryptamine from the tryptophan pathway and secologanin from the isoprenoid pathway. Therefore, increasing the supply of precursor tryptophan may enhance vinca alkaloid content or their metabolic intermediates. Many reports on the genetic modification of C. roseus use cultured cells or hairy roots, but few reports cover the production of transgenic plants. In this study, we first investigated a method for stably producing transgenic plants of C. roseus, then, using this technique, we modified the tryptophan metabolism system to produce transgenic plants with increased tryptophan content. Transformed plants were obtained by infecting cotyledons two weeks after sowing with Agrobacterium strain A13 containing a plant expression vector, then selecting with 1/2 B5 medium supplemented with 50 mg l-1 kanamycin and 20 mg l-1 meropenem. Sixty-eight regenerated plants were obtained from 4,200 cotyledons infected with Agrobacterium, after which genomic PCR analysis using NPTII-specific primers confirmed gene presence in 24 plants with a transformation rate of 0.6%. Furthermore, we performed transformation into C. roseus using an expression vector to join trpE8 and aroG4 genes, which are feedback-resistant mutant genes derived from Escherichia coli. The resulting transformed plants showed exactly the same morphology as the wild-type, albeit with a marked increase in tryptophan and alkaloids content, especially catharanthine in leaves.

Evaluation of Reference Genes for Normalizing RT-qPCR and Analysis of the Expression Patterns of WRKY1 Transcription Factor and Rhynchophylline Biosynthesis-Related Genes in Uncaria rhynchophylla

Uncaria rhynchophylla (Miq.) Miq. ex Havil, a traditional medicinal herb, is enriched with several pharmacologically active terpenoid indole alkaloids (TIAs). At present, no method has been reported that can comprehensively select and evaluate the appropriate reference genes for gene expression analysis, especially the transcription factors and key enzyme genes involved in the biosynthesis pathway of TIAs in U. rhynchophylla. Reverse transcription quantitative PCR (RT-qPCR) is currently the most common method for detecting gene expression levels due to its high sensitivity, specificity, reproducibility, and ease of use. However, this methodology is dependent on selecting an optimal reference gene to accurately normalize the RT-qPCR results. Ten candidate reference genes, which are homologues of genes used in other plant species and are common reference genes, were used to evaluate the expression stability under three stress-related experimental treatments (methyl jasmonate, ethylene, and low temperature) using multiple stability analysis methodologies. The results showed that, among the candidate reference genes, S-adenosylmethionine decarboxylase (SAM) exhibited a higher expression stability under the experimental conditions tested. Using SAM as a reference gene, the expression profiles of 14 genes for key TIA enzymes and a WRKY1 transcription factor were examined under three experimental stress treatments that affect the accumulation of TIAs in U. rhynchophylla. The expression pattern of WRKY1 was similar to that of tryptophan decarboxylase (TDC) under ETH treatment. This research is the first to report the stability of reference genes in U. rhynchophylla and provides an important foundation for future gene expression analyses in U. rhynchophylla. The RT-qPCR results indicate that the expression of WRKY1 is similar to that of TDC under ETH treatment. It may coordinate the expression of TDC, providing a possible method to enhance alkaloid production in the future through synthetic biology.

Medicinal plants enter the single-cell multi-omics era

Elucidating biosynthetic pathways of plant specialized metabolites is a tricky but essential task for the biotechnological production of plant drugs. In a new report, Li et al. used a single-cell multi-omics approach to provide an integrative view of the architecture and regulation of anticancer alkaloid routes in Madagascar periwinkle.

Temperature-induced lipocalin-mediated membrane integrity: Possible implications for vindoline accumulation in Catharanthus roseus leaves

Plant lipocalins perform diverse functions. Recently, allene oxide cyclase, a lipocalin family member, has been shown to co-express with vindoline pathway genes in Catharanthus roseus under various biotic/abiotic stresses. This brought focus to another family member, a temperature-induced lipocalin (CrTIL), which was selected for full-length cloning, tissue-specific expression profiling, in silico characterization, and upstream genomic region analysis for cis-regulatory elements. Stress-mediated variations in CrTIL expression were reflected as disturbances in cell membrane integrity, assayed through measurement of electrolyte leakage and lipid peroxidation product, MDA, which implicated the role of CrTIL in maintaining cell membrane integrity. For ascertaining the function of CrTIL in maintaining membrane stability and elucidating the relationship between CrTIL expression and vindoline content, if any, a direct approach was adopted, whereby CrTIL was transiently silenced and overexpressed in C. roseus. CrTIL silencing and overexpression confirmed its role in the maintenance of membrane integrity and indicated an inverse relationship of its expression with vindoline content. GFP fusion-based subcellular localization indicated membrane localization of CrTIL, which was in agreement with its role in maintaining membrane integrity. Altogether, the role of CrTIL in maintaining membrane structure has possible implications for the intracellular sequestration, storage, and viability of vindoline.

Bacterial endophytes of sugar maple leaves vary more idiosyncratically than epiphytes across a large geographic area

Bacteria from the leaf surface and the leaf tissue have been attributed with several beneficial properties for their plant host. Though physically connected, the microbial ecology of these compartments has mostly been studied separately such that we lack an integrated understanding of the processes shaping their assembly. We sampled leaf epiphytes and endophytes from the same individuals of sugar maple across the northern portion of its range to evaluate if their community composition was driven by similar processes within and across populations differing in plant traits and overall abiotic environment. Leaf compartment explained most of the variation in community diversity and composition across samples. Leaf epiphytic communities were driven more by host and site characteristics than endophytic communities, whose community composition was more idiosyncratic across samples. Our results suggest a greater importance of priority effects and opportunistic colonization in driving community assembly of leaf endophytes. Understanding the comparative assembly of bacterial communities at the surface and inside plant leaves may be particularly useful for leveraging their respective potential for improving the health of plants in natural and anthropized ecosystems.

Spatial localization of monoterpenoid indole alkaloids in Rauvolfia tetraphylla by high resolution mass spectrometry imaging

Monoterpenoid indole alkaloids (MIAs) are a large group of biosynthetic compounds, which have pharmacological properties. One of these MIAs, reserpine, was discovered in the 1950s and has shown properties as an anti-hypertension and anti-microbial agent. Reserpine was found to be produced in various plant species within the genus of Rauvolfia. However, even though its presence is well known, it is still unknown in which tissues Rauvolfia produce reserpine and where the individual steps in the biosynthetic pathway take place. In this study, we explore how matrix assisted laser desorption ionization (MALDI) and desorption electrospray ionization (DESI) mass spectrometry imaging (MSI) can be used in the investigation of a proposed biosynthetic pathway by localizing reserpine and the theoretical intermediates of it. The results show that ions corresponding to intermediates of reserpine were localized in several of the major parts of Rauvolfia tetraphylla when analyzed by MALDI- and DESI-MSI. In stem tissue, reserpine and many of the intermediates were found compartmentalized in the xylem. For most samples, reserpine itself was mainly found in the outer layers of the sample, suggesting it may function as a defense compound. To further confirm the place of the different metabolites in the reserpine biosynthetic pathway, roots and leaves of R. tetraphylla were fed a stable-isotope labelled version of the precursor tryptamine. Subsequently, several of the proposed intermediates were detected in the normal version as well as in the isotope labelled versions, confirming that they were synthesized in planta from tryptamine. In this experiment, a potential novel dimeric MIA was discovered in leaf tissue of R. tetraphylla. The study constitutes to date the most comprehensive spatial mapping of metabolites in the R. tetraphylla plant. In addition, the article also contains new illustrations of the anatomy of R. tetraphylla.

Regulation of the regulators: Transcription factors controlling biosynthesis of plant secondary metabolites during biotic stresses and their regulation by miRNAs

Biotic stresses threaten to destabilize global food security and cause major losses to crop yield worldwide. In response to pest and pathogen attacks, plants trigger many adaptive cellular, morphological, physiological, and metabolic changes. One of the crucial stress-induced adaptive responses is the synthesis and accumulation of plant secondary metabolites (PSMs). PSMs mitigate the adverse effects of stress by maintaining the normal physiological and metabolic functioning of the plants, thereby providing stress tolerance. This differential production of PSMs is tightly orchestrated by master regulatory elements, Transcription factors (TFs) express differentially or undergo transcriptional and translational modifications during stress conditions and influence the production of PSMs. Amongst others, microRNAs, a class of small, non-coding RNA molecules that regulate gene expression post-transcriptionally, also play a vital role in controlling the expression of many such TFs. The present review summarizes the role of stress-inducible TFs in synthesizing and accumulating secondary metabolites and also highlights how miRNAs fine-tune the differential expression of various stress-responsive transcription factors during biotic stress.

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.

Molecular and biochemical characterization of Catharanthus roseus perivine-Nβ-methyltransferase

The biosynthesis of monoterpenoid indole alkaloids in Catharanthus roseus has been most extensively studied, leading to the detailed characterization of the pathway for the formation of their well-known anticancer alkaloids. The present study describes the identification, molecular cloning, and functional expression of C. roseus perivine-N_β-methyltransferase (PeNMT) that converts perivine to N_β-methylperivine (vobasine). PeNMT is member of a recently discovered γ-tocopherol-like N-methyltransferase (γ-TLMT) gene family that displays high substrate specificity and that appears to have evolved in the Vinceae tribe of Apocynaceae family where most N-methylated MIAs have been identified in the phytochemical literature.

Plant-based engineering for production of high-valued natural products

Covering: up to March 2022Plants are a unique source of complex specialized metabolites, many of which play significant roles in human society. In many cases, however, the availability of these metabolites from naturally occurring sources fails to meet current demands. Thus, there is much interest in expanding the production capacity of target plant molecules. Traditionally, plant breeding, chemical synthesis, and microbial fermentation are considered the primary routes towards large scale production of natural products. Here, we explore the advances, challenges, and future of plant engineering as a complementary path. Although plants are an integral part of our food and agricultural systems and sustain an extensive array of chemical constituents, their complex genetics and physiology have prevented the optimal exploitation of plants as a production chassis. We highlight emerging engineering tools and scientific advances developed in recent years that have improved the prospects of using plants as a sustainable and scalable production platform. We also discuss technological limitations and overall economic outlook of plant-based production of natural products.

A Catharanthus roseus Fe(II)/α-ketoglutarate-dependent dioxygenase catalyzes a redox-neutral reaction responsible for vindolinine biosynthesis

The Madagascar's periwinkle is the model plant for studies of plant specialized metabolism and monoterpenoid indole alkaloids (MIAs), and an important source for the anticancer medicine vinblastine. The elucidation of entire 28-step biosynthesis of vinblastine allowed further investigations for the formation of other remarkably complex bioactive MIAs. In this study, we describe the discovery and characterization of vindolinine synthase, a Fe(II)/α-ketoglutarate-dependent (Fe/2OG) dioxygenase, that diverts assembly of tabersonine to vinblastine toward the formation of three alternatively cyclized MIAs: 19S-vindolinine, 19R-vindolinine, and venalstonine. Vindolinine synthase catalyzes a highly unusual, redox-neutral reaction to form a radical from dehydrosecodine, which is further cyclized by hydrolase 2 to form the three MIA isomers. We further show the biosynthesis of vindolinine epimers from tabersonine using hydrolase 2 catalyzed reverse cycloaddition. While the occurrence of vindolinines is rare in nature, the more widely found venalstonine derivatives are likely formed from similar redox-neutral reactions by homologous Fe/2OG dioxygenases.

More than a Catharanthus plant: A multicellular and pluri-organelle alkaloid-producing factory

Plants represent a huge reservoir of natural products. A broad series of these compounds now find application for human health. In this respect, the monoterpene indole alkaloids (MIAs), particularly from Madagascar periwinkle, are a prominent example of plant specialized metabolites with an important therapeutic potential. However, the supply of MIA drugs has always been a challenge since the low-yield accumulation in planta. This mainly results from the complex architecture of the MIA biosynthetic pathway that involves several organs, tissue types and subcellular organelles. Here, we describe the most recent advances towards the elucidation of this pathway route as well as its spatial organization in planta. Besides allowing a better understanding of the MIA biosynthetic flux in the whole plant, such knowledge will also probably pave the way for the development of metabolic engineering strategies to sustain the MIA supply.

Stress responsiveness of vindoline accumulation in Catharanthus roseus leaves is mediated through co-expression of allene oxide cyclase with pathway genes

Vindoline is an important alkaloid produced in Catharanthus roseus leaves. It is the more important monomer of the scarce and costly anticancer bisindole alkaloids, vincristine, and vinblastine, as unlike catharanthine (the other monomer), its biosynthesis is restricted to the leaves. Here, biotic (bacterial endophyte, phytoplasma, virus) and abiotic (temperature, salinity, SA, MeJa) factors were studied for their effect on vindoline accumulation in C. roseus. Variations in vindoline pathway-related gene expression were reflected in changes in vindoline content. Since allene oxide cyclase (CrAOC) is involved in jasmonate biosynthesis and MeJa modulates many vindoline pathway genes, the correlation between CrAOC expression and vindoline content was studied. It was taken up for full-length cloning, tissue-specific expression profiling, in silico analyses, and upstream genomic region analysis for cis-regulatory elements. Co-expression analysis of CrAOC with vindoline metabolism-related genes under the influence of aforementioned abiotic/biotic factors indicated its stronger direct correlation with the tabersonine-to-vindoline genes (t16h, omt, t3o, t3r, nmt, d4h, dat) as compared to the pre-tabersonine genes (tdc, str, sgd). Its expression was inversely related to that of downstream-acting peroxidase (prx) (except under temperature stress). Direct/positive relationship of CrAOC expression with vindoline content established it as a key gene modulating vindoline accumulation in C. roseus.

Understanding the possible influence of Pumilio RNA binding proteins on terpenoid indole alkaloid biosynthesis in Catharanthus roseus

Catharanthus roseus is a clinically significant medicinal plant; the sole source of chemotherapy agents, vincristine and vinblastine (specialized metabolites, terpenoid indole alkaloids/TIAs). Owing to large clinical demand and low bioavailability, several studies have focused on biosynthesis and regulation of TIA biosynthesis in C. roseus. However, transcription factor mediated regulation has been a major research focus, and the impact of post-transcriptional regulation remains under-explored. RNA binding proteins (RBPs) are an emerging class of post-transcriptional regulators having a profound influence on transcript stability. Pumilio (Pum) RBPs are evolutionarily conserved post-transcriptional regulators, involved in RNA degradation across eukaryotes. However, their potential influence on TIA biosynthesis has not been studied till date in any medicinal plants including C. roseus. Thus, the present study aimed at identification and computational characterization of Pum in C. roseus, followed by expression and functional analyses. The genome-wide identification and characterization revealed twelve CrPum isoforms. The effect of CrPum2, 3, and 5 knockdown on TIA biosynthesis (specifically vindoline and catharanthine) was analyzed via high performance liquid chromatography. CrPum5 knockdown was associated with increased TIA levels and upregulation of key TIA pathway genes. Thus, the present study is the first to report the potential influence of Pum on TIA biosynthesis in C. roseus. Further studies to elucidate the mechanism of Pum activity could provide new insights into the molecular regulation of TIA biosynthesis. A holistic understanding of regulatory mechanisms could benefit the metabolic engineering programs aimed at higher productivity of plant specialized metabolites.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-022-01193-5.

Generating an EMS Mutant Population and Rapid Mutant Screening by Thin-Layer Chromatography Enables the Studies of Monoterpenoid Indole Alkaloids Biosynthesis in Catharanthus Roseus

Decades of research on the medicinal plant Catharanthus roseus have led to the complete elucidation of the 29-step pathway for the biosynthesis of the anticancer drug vinblastine from geraniol and tryptophan precursors. Several approaches have been used to identify the enzymes involved in this iconic and remarkably complex pathway. This chapter describes the use of the classic ethyl methanesulfonate (EMS) mutagenesis to create a selfed M2 mutant population, which can be rapidly screened to select mutants with altered monoterpenoid indole alkaloid (MIA) biosynthesis with a simple, high-throughput thin-layer chromatography (TLC)-based screening strategy. This TLC-based MIA screening has led to the discovery and characterization of three enzymes responsible for vinblastine biosynthesis.

Terpenoid indole alkaloid biosynthesis in Catharanthus roseus: effects and prospects of environmental factors in metabolic engineering

Plants synthesize a vast array of specialized metabolites that primarily contribute to their defense and survival under adverse conditions. Many of the specialized metabolites have therapeutic values as drugs. Biosynthesis of specialized metabolites is affected by environmental factors including light, temperature, drought, salinity, and nutrients, as well as pathogens and insects. These environmental factors trigger a myriad of changes in gene expression at the transcriptional and posttranscriptional levels. The dynamic changes in gene expression are mediated by several regulatory proteins that perceive and transduce the signals, leading to up- or down-regulation of the metabolic pathways. Exploring the environmental effects and related signal cascades is a strategy in metabolic engineering to produce valuable specialized metabolites. However, mechanistic studies on environmental factors affecting specialized metabolism are limited. The medicinal plant Catharanthus roseus (Madagascar periwinkle) is an important source of bioactive terpenoid indole alkaloids (TIAs), including the anticancer therapeutics vinblastine and vincristine. The emerging picture shows that various environmental factors significantly alter TIA accumulation by affecting the expression of regulatory and enzyme-encoding genes in the pathway. Compared to our understanding of the TIA pathway in response to the phytohormone jasmonate, the impacts of environmental factors on TIA biosynthesis are insufficiently studied and discussed. This review thus focuses on these aspects and discusses possible strategies for metabolic engineering of TIA biosynthesis. PURPOSE OF WORK: Catharanthus roseus is a rich source of bioactive terpenoid indole alkaloids (TIAs). The objective of this work is to present a comprehensive account of the influence of various biotic and abiotic factors on TIA biosynthesis and to discuss possible strategies to enhance TIA production through metabolic engineering.

Subfunctionalization of Paralog Transcription Factors Contributes to Regulation of Alkaloid Pathway Branch Choice in Catharanthus roseus

Catharanthus roseus produces a diverse range of specialized metabolites of the monoterpenoid indole alkaloid (MIA) class in a heavily branched pathway. Recent great progress in identification of MIA biosynthesis genes revealed that the different pathway branch genes are expressed in a highly cell type- and organ-specific and stress-dependent manner. This implies a complex control by specific transcription factors (TFs), only partly revealed today. We generated and mined a comprehensive compendium of publicly available C. roseus transcriptome data for MIA pathway branch-specific TFs. Functional analysis was performed through extensive comparative gene expression analysis and profiling of over 40 MIA metabolites in the C. roseus flower petal expression system. We identified additional members of the known BIS and ORCA regulators. Further detailed study of the ORCA TFs suggests subfunctionalization of ORCA paralogs in terms of target gene-specific regulation and synergistic activity with the central jasmonate response regulator MYC2. Moreover, we identified specific amino acid residues within the ORCA DNA-binding domains that contribute to the differential regulation of some MIA pathway branches. Our results advance our understanding of TF paralog specificity for which, despite the common occurrence of closely related paralogs in many species, comparative studies are scarce.

The Phytochemical Analysis of Vinca L. Species Leaf Extracts Is Correlated with the Antioxidant, Antibacterial, and Antitumor Effects

The phytochemical analysis of Vinca minor, V. herbacea, V. major, and V. major var. variegata leaf extracts showed species-dependent antioxidant, antibacterial, and cytotoxic effects correlated with the identified phytoconstituents. Vincamine was present in V. minor, V. major, and V. major var. variegata, while V. minor had the richest alkaloid content, followed by V. herbacea. V. major var. variegata was richest in flavonoids and the highest total phenolic content was found in V. herbacea which also had elevated levels of rutin. Consequently, V. herbacea had the highest antioxidant activity followed by V. major var. variegata. Whereas, the lowest one was of V. major. The V. minor extract showed the most efficient inhibitory effect against both Staphylococcusaureus and E. coli. On the other hand, V. herbacea had a good anti-bacterial potential only against S. aureus, which was most affected at morphological levels, as indicated by scanning electron microscopy. The Vinca extracts acted in a dose-depended manner against HaCaT keratinocytes and A375 melanoma cells and moreover, with effects on the ultrastructure, nitric oxide concentration, and lactate dehydrogenase release. Therefore, the Vinca species could be exploited further for the development of alternative treatments in bacterial infections or as anticancer adjuvants.

The Morphological and Anatomical Traits of the Leaf in Representative Vinca Species Observed on Indoor- and Outdoor-Grown Plants

Morphological and anatomical traits of the Vinca leaf were examined using microscopy techniques. Outdoor Vinca minor and V. herbacea plants and greenhouse cultivated V. major and V. major var. variegata plants had interspecific variations. All Vinca species leaves are hypostomatic. However, except for V. minor leaf, few stomata were also present on the upper epidermis. V. minor leaf had the highest stomatal index and V. major had the lowest, while the distribution of trichomes on the upper epidermis was species-specific. Differentiated palisade and spongy parenchyma tissues were present in all Vinca species' leaves. However, V. minor and V. herbacea leaves had a more organized anatomical aspect, compared to V. major and V. major var. variegata leaves. Additionally, as a novelty, the cellular to intercellular space ratio of the Vinca leaf's mesophyll was revealed herein with the help of computational analysis. Lipid droplets of different sizes and aspects were localized in the spongy parenchyma cells. Ultrastructural characteristics of the cuticle and its epicuticular waxes were described for the first time. Moreover, thick layers of cutin seemed to be characteristic of the outdoor plants only. This could be an adaptation to the unpredictable environmental conditions, but nevertheless, it might influence the chemical composition of plants.

Visualizing vinca alkaloids in the petal of Catharanthus roseus using functionalized titanium oxide nanowire substrate for surface-assisted laser desorption/ionization imaging mass spectrometry

Imaging mass spectrometry (IMS) is a powerful technique that enables analysis of various molecular species at a high spatial resolution with low detection limits. In contrast to the matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) approach, surface-assisted laser desorption/ionization (SALDI) can be more effective in the detection of small molecules due to the absence of interfering background signals in low m/z ranges. We developed a functionalized TiO₂ nanowire as a solid substrate for IMS of low-molecular-weight species in plant tissues. We prepared TiO₂ nanowires using an inexpensive modified hydrothermal process and subsequently functionalized them chemically with various silane analogs to overcome the problem of superhydrophilicity of the substrate. Chemical modification changed the selectivity of imprinting of samples deposited on the substrate surface and thus improved the detection limits. The substrate was applied to image distribution of the metabolites in very fragile specimens such as the petal of Catharanthus roseus. We observed that the metabolites are distributed heterogeneously in the petal, which is consistent with previous results reported for the C. roseus plant leaf and stem. The intermediates corresponding to the biosynthesis pathway of some vinca alkaloids were clearly shown in the petal. We also performed profiling of petals from five different cultivars of C. roseus plant. We verified the semi-quantitative capabilities of the imprinting/imaging approach by comparing results using the LC-MS analysis of the plant extracts. This suggested that the functionalized TiO₂ nanowire substrate-based SALDI is a powerful technique complementary to MALDI-MS.

Identifying Genes Involved in alkaloid Biosynthesis in Vinca minor Through Transcriptomics and Gene Co-Expression Analysis

The lesser periwinkle Vinca minor accumulates numerous monoterpene indole alkaloids (MIAs) including the vasodilator vincamine. While the biosynthetic pathway of MIAs has been largely elucidated in other Apocynaceae such as Catharanthus roseus, the counterpart in V. minor remains mostly unknown, especially for reactions leading to MIAs specific to this plant. As a consequence, we generated a comprehensive V. minor transcriptome elaborated from eight distinct samples including roots, old and young leaves exposed to low or high light exposure conditions. This optimized resource exhibits an improved completeness compared to already published ones. Through homology-based searches using C. roseus genes as bait, we predicted candidate genes for all common steps of the MIA pathway as illustrated by the cloning of a tabersonine/vincadifformine 16-O-methyltransferase (Vm16OMT) isoform. The functional validation of this enzyme revealed its capacity of methylating 16-hydroxylated derivatives of tabersonine, vincadifformine and lochnericine with a Km 0.94 ± 0.06 µM for 16-hydroxytabersonine. Furthermore, by combining expression of fusions with yellow fluorescent proteins and interaction assays, we established that Vm16OMT is located in the cytosol and forms homodimers. Finally, a gene co-expression network was performed to identify candidate genes of the missing V. minor biosynthetic steps to guide MIA pathway elucidation.

Investigating distributions and changes of alkaloids in living Catharanthus roseus under low-phosphorus stress using wooden-tip electrospray ionisation mass spectrometry

INTRODUCTION

Vinca alkaloids are important sources for producing anticancer drugs from Catharanthus roseus. The phosphorus of soil is one of crucial factors for planting C. roseus.

OBJECTIVES

We aim to develop an in vivo sampling technique coupled with direct mass spectrometry with wooden tip for investigating distributions and changes of alkaloids in flowers, leaves, stems, veins and roots of living C. roseus under low-phosphorus stress.

MATERIALS AND METHODS

Living C. roseus were prepared under low-phosphorus stress (n = 10) and control conditions (n = 10). Wooden-tip electrospray ionisation mass spectrometry and conventional liquid chromatography-mass spectrometry were applied to analyse living C. roseus and extracts of C. roseus, respectively.

RESULTS

Distributions and changes of serpentine, vindoline, catharanthine, and anhydrovinblastine in living C. roseus under low-phosphorus stress and control conditions were successfully obtained.

CONCLUSION

Compared to control soil conditions, low-phosphorus soil was found to induce C. roseus to generate more serpentine but less catharanthine and vindoline in leaves, veins, stems and roots, and to generate more anhydrovinblastine in flowers, leaves, stems and roots. Overall, our results showed a simple, rapid, and effective method for in vivo sampling and direct analysis of living plants.

The expression of Terpenoid Indole Alkaloid (TIAs) pathway genes in Catharanthus roseus in response to salicylic acid treatment

Vinblastine and vincristine are two important anti-cancer drugs that are synthesized by the Terpenoid Indole Alkaloids (TIAs) pathway in periwinkle (Catharanthus roseus). The major challenge in the pharmaceutical industry is the low production rate of these Alkaloids. TIA pathway is affected by elicitors, such as salicylic acid (SA). This study aimed to investigate the expression pattern of some key genes in TIAs pathway under SA treatment. Foliar application of SA (0.01 and 0.1 mM) was used and leaves samples were taken at 0, 12, 18, 24 and 48 h after the treatment. qRT-PCR was used to investigate the expression pattern of Chorismate mutase (Cm), tryptophan decarboxylase (Tdc), Geraniol-10-hydroxylase (G10h), Secologanin synthase (Sls), Strictosidine synthase (Str), Desacetoxyvindoline-4-hydroxylase (D4h) and Deacetylvindoline-4-O-acetyltransferase (Dat) genes, following the SA treatment. The results of this experiment showed that transcript levels of Tdc, G10h, Sls, Str, D4h and Dat genes were significantly up-regulated in both SA concentration treatments. Furthermore, the highest transcript levels of Dat was observed after 48 h of the SA treatments. qRT-PCR results suggests that SA induces transcription of major genes involved in Alkaloids biosynthesis in Catharanthus roseus. It can be concluded that up-regulation of Tdc, G10h, Sls, Str, D4h and Dat genes can result in a higher production rate of Vinblastine and vincristine Alkaloids.

Transcriptional Factors Regulate Plant Stress Responses through Mediating Secondary Metabolism

Plants are adapted to sense numerous stress stimuli and mount efficient defense responses by directing intricate signaling pathways. They respond to undesirable circumstances to produce stress-inducible phytochemicals that play indispensable roles in plant immunity. Extensive studies have been made to elucidate the underpinnings of defensive molecular mechanisms in various plant species. Transcriptional factors (TFs) are involved in plant defense regulations through acting as mediators by perceiving stress signals and directing downstream defense gene expression. The cross interactions of TFs and stress signaling crosstalk are decisive in determining accumulation of defense metabolites. Here, we collected the major TFs that are efficient in stress responses through regulating secondary metabolism for the direct cessation of stress factors. We focused on six major TF families including AP2/ERF, WRKY, bHLH, bZIP, MYB, and NAC. This review is the compilation of studies where researches were conducted to explore the roles of TFs in stress responses and the contribution of secondary metabolites in combating stress influences. Modulation of these TFs at transcriptional and post-transcriptional levels can facilitate molecular breeding and genetic improvement of crop plants regarding stress sensitivity and response through production of defensive compounds.

A GDSL Esterase/Lipase Catalyzes the Esterification of Lutein in Bread Wheat

Xanthophylls are a class of carotenoids that are important micronutrients for humans. They are often found esterified with fatty acids in fruits, vegetables, and certain grains, including bread wheat (Triticum aestivum). Esterification promotes the sequestration and accumulation of carotenoids, thereby enhancing stability, particularly in tissues such as in harvested wheat grain. Here, we report on a plant xanthophyll acyltransferase (XAT) that is both necessary and sufficient for xanthophyll esterification in bread wheat grain. XAT contains a canonical Gly-Asp-Ser-Leu (GDSL) motif and is encoded by a member of the GDSL esterase/lipase gene family. Genetic evidence from allelic variants of wheat and transgenic rice (Oryza sativa) calli demonstrated that XAT catalyzes the formation of xanthophyll esters. XAT has broad substrate specificity and can esterify lutein, β-cryptoxanthin, and zeaxanthin using multiple acyl donors, yet it has a preference for triacylglycerides, indicating that the enzyme acts via transesterification. A conserved amino acid, Ser-37, is required for activity. Despite xanthophylls being synthesized in plastids, XAT accumulated in the apoplast. Based on analysis of substrate preferences and xanthophyll ester formation in vitro and in vivo using xanthophyll-accumulating rice callus, we propose that disintegration of the cellular structure during wheat grain desiccation facilitates access to lutein-promoting transesterification.plantcell;31/12/3092/FX1F1fx1.

The genuine localization of indole alkaloids in Vinca minor and Catharanthus roseus

Based on the occurrence of indole alkaloids in so-called "chloroform leaf surface extracts", it was previously deduced that these alkaloids are present in the cuticle at the leaf surface of Catharanthus roseus and Vinca minor. As no symplastic markers were found in these extracts this deduction seemed to be sound. However, since chloroform is known to destroy biomembranes very rapidly, these data have to be judged with scepticism. We reanalyzed the alleged apoplastic localization of indole alkaloids by employing slightly acidic aqueous surface extracts and comparing the corresponding alkaloid patterns with those of aqueous total leaf extracts. Whereas in the "chloroform leaf surface extracts" all alkaloids are present in the same manner as in the total leaf extracts, no alkaloids occur in the aqueous leaf surface extracts. These results clearly show that chloroform had rapidly destroyed cell integrity, and the related extracts also contain the alkaloids genuinely accumulated within the protoplasm. The related decompartmentation was verified by the massively enhanced concentration of amino acids in aqueous surface extracts of chloroform treated leaves. Furthermore, the chloroform-induced cell disintegration was vividly visualized by confocal laser scanning microscopical analyses, which clearly displayed a strong decrease in the chlorophyll fluorescence in chloroform treated leaves. These findings unequivocally display that the indole alkaloids are not located in the apoplastic space, but exclusively are present symplastically within the cells of V. minor and C. roseus leaves. Accordingly, we have to presume that also other leaf surface extracts employing organic solvents have to be re-investigated.

The complexity of intercellular localisation of alkaloids revealed by single-cell metabolomics

Catharanthus roseus is a medicinal plant well known for producing bioactive compounds such as vinblastine and vincristine, which are classified as terpenoid indole alkaloids (TIAs). Although the leaves of this plant are the main source of these antitumour drugs, much remains unknown on how TIAs are biosynthesised from a central precursor, strictosidine, to various TIAs in planta. Here, we have succeeded in showing, for the first time in leaf tissue of C. roseus, cell-specific TIAs localisation and accumulation with 10 μm spatial resolution Imaging mass spectrometry (Imaging MS) and live single-cell mass spectrometry (single-cell MS). These metabolomic studies revealed that most TIA precursors (iridoids) are localised in the epidermal cells, but major TIAs including serpentine and vindoline are localised instead in idioblast cells. Interestingly, the central TIA intermediate strictosidine also accumulates in both epidermal and idioblast cells of C. roseus. Moreover, we also found that vindoline accumulation increases in laticifer cells as the leaf expands. These discoveries highlight the complexity of intercellular localisation in plant specialised metabolism.

What Makes Species Productive of Anti-Cancer Drugs? Clues from Drugs’ Species Origin, Druglikeness, Target and Pathway

Background:

Despite the substantial contribution of natural products to the FDA drug approval list, the discovery of anti-cancer drugs from the huge amount of species on the planet remains looking for a needle in a haystack. Objective: Drug-productive clusters in the phylogenetic tree are thus proposed to narrow the searching scope by focusing on much smaller amount of species within each cluster, which enable prioritized and rational bioprospecting for novel drug-like scaffolds. However, the way anti-cancer nature-derived drugs distribute in phylogenetic tree has not been reported, and it is oversimplified to just focus anti-cancer drug discovery on the drug-productive clusters, since the number of species in each cluster remains too large to be managed.

Objective:

Drug-productive clusters in the phylogenetic tree are thus proposed to narrow the searching scope by focusing on much smaller amount of species within each cluster, which enable prioritized and rational bioprospecting for novel drug-like scaffolds. However, the way anti-cancer nature-derived drugs distribute in phylogenetic tree has not been reported, and it is oversimplified to just focus anti-cancer drug discovery on the drug-productive clusters, since the number of species in each cluster remains too large to be managed.

Methods:

In this study, 260 anti-cancer drugs approved in the past 70 years were comprehensively analyzed by hierarchical clustering of phylogenetic distribution.

Results:

207 out of these 260 drugs were derived from or inspired by the natural products isolated from 58 species. Phylogenetic distribution of those drugs further revealed that nature-derived anti-cancer drugs originated mostly from drug-productive families that tend to be clustered rather than scattered on the phylogenetic tree. Moreover, based on their productivity, drug-producing species were categorized into productive (CPS), newly emerging (CNS) and lessproductive (CLS). Statistical significances in druglikeness between drugs from CPS and CLS were observed, and drugs from CNS were found to share similar drug-like properties to those from CPS.

Conclusion:

This finding indicated a great raise in drug approval standard, which suggested us to focus bioprospecting on the species yielding multiple drugs and keeping productive for long period of time.

Inter-organ transport of secologanin allows assembly of monoterpenoid indole alkaloids in a Catharanthus roseus mutant

The medicinal value of the monoterpenoid indole alkaloids (MIAs) such as 3',4'-anhydrovinblastine, as well as their chemical complexity have stimulated extensive efforts to understand the biochemical and molecular pathways involved in their biosynthesis in plants such as Catharanthus roseus, Rawvolfia serpentina and others. Ethyl methane sulphonate (EMS) mutagenesis has been used successfully together with simple MIA thin layer chromatography screening to identify C. roseus mutants with altered MIA profiles. This study describes the isolation of very low iridoid and MIA containing C. roseus mutant (M2-1582) that accumulates MIAs when the plant is provided with secologanin by feeding mutant roots or by grafting the mutant scion onto wild type roots. The observed low iridoid and MIA content was correlated with lowered expression of BIS1/BIS2 transcription factors and several genes involved in secologanin biosynthesis that are expressed in internal phloem parenchyma cells of leaves. When exogenous secologanin was applied to the roots of the mutant plant, secologanin levels rose more than 13-fold, while two major MIAs catharanthine and vindoline rose more than 8- and 4- fold, respectively. Grafting the mutant on WT stocks led to 27-, 11- and 27-fold increases in secologanin, catharanthine and vindoline, respectively in leaves of the scion one week after graft initiation. Other minor MIAs (serpentine, anhydrovinblastine, vindolidine, deacetylvindoline, tabersonine and 16-methoxytabersonine) that were not detected in the mutant, became detectable in leaves of the scion. These results provide strong evidence for a secologanin transport mechanism that mobilizes this iridoid between different plant organs in C. roseus and that secologanin transport to the mutant across the graft union permits the formation of MIAs in leaves of the mutant.

Completion of the canonical pathway for assembly of anticancer drugs vincristine/vinblastine in Catharanthus roseus

The important anticancer drugs, vinblastine, vincristine and analogs, are composed of the monoterpenoid indole alkaloids (MIAs), catharanthine and vindoline, found uniquely in the medicinal plant, Catharanthus roseus. While 26 genes involved in the assembly of these two MIAs are known, two key reactions have eluded characterization to complete the documentation of the vinblastine pathway in this plant species. The assembly of these dimeric MIAs requires O-acetylstemmadenine oxidase (ASO) and a dual function geissoschizine synthase (GS) that reduces cathenamine to form geissoschizine, and that also reduces the ASO product to form a common intermediate for subsequent conversion by four separate hydrolases to catharanthine, tabersonine or vincadifformine, respectively. The in planta role of ASO is supported by identifying a single amino acid-substituted ASO mutant with very low enzyme activity and by virus-induced gene silencing of ASO to produce plants that accumulate O-acetylstemmadenine rather than catharanthine and vindoline found in wild-type (WT) plants. The in planta role of GS is supported by showing that a low GS-expressing mutant accumulating lower levels of catharanthine and vindoline also displays significantly lower tabersonine-forming activity in coupled enzyme assays than in the WT background. Gene expression analyses demonstrate that both ASO and GS are highly enriched in the leaf epidermis where the pathways for catharanthine and tabersonine biosynthesis are expressed. The full elucidation of this canonical pathway enables synthetic biology approaches for manufacturing a broad range of MIAs, including these dimers used in cancer treatment.

Electrostatic field-induced tip-electrospray ionization mass spectrometry for direct analysis of raw food materials

Rapid characterization of metabolites and risk compounds such as chemical residues and natural toxins in raw food materials such as vegetables, meats, and edible living plants and animals plays an important part in ensuing food quality and safety. To rapidly characterize the analytes in raw food materials, it is essential to develop in situ method for directly analyzing raw food materials. In this work, raw food materials including biological tissues and living samples were placed between an electrode and mass spectrometric (MS) inlet under a strong electrostatic field; analytes were rapidly induced to generate electrospray ionization (ESI) from the sample tip by adding a drop of solvent onto the sample. Therefore, the electrostatic field-induced tip-ESI-MS allows raw samples to avoid contacting high voltage, and thus this method has the advantage for in vivo analysis of food living plants and animals. Metabolite profiling, residues of pesticides and veterinary drugs, and natural toxins from raw food materials have been successfully detected. The analytical performances, including the linear ranges, sensitivity, and reproducibility, were investigated for direct sample analysis. The ionization mechanism of electrostatic field-induced tip-ESI was also discussed in this work.

Expression analysis of Cell wall invertase under abiotic stress conditions influencing specialized metabolism in Catharanthus roseus

Catharanthus roseus is a commercial source for anti-cancer terpenoid indole alkaloids (TIAs: vincristine and vinblastine). Inherent levels of these TIAs are very low, hence research studies need to focus on enhancing their levels in planta. Since primary metabolism provides precursors for specialized-metabolism, elevating the former can achieve higher amounts of the latter. Cell Wall Invertase (CWIN), a key enzyme in sucrose-metabolism catalyses the breakdown of sucrose into glucose and fructose, which serve as carbon-skeleton for specialized-metabolites. Understanding CWIN regulation could unravel metabolic-engineering approaches towards enhancing the levels of TIAs in planta. Our study is the first to characterize CWIN at gene-expression level in the medicinal plant, C. roseus. The CWINs and their inter-relationship with sucrose and TIA metabolism was studied at gene and metabolite levels. It was found that sucrose-supplementation to C. roseus leaves significantly elevated the monomeric TIAs (vindoline, catharanthine) and their corresponding genes. This was further confirmed in cross-species, wherein Nicotiana benthamiana leaves transiently-overexpressing CrCWIN2 showed significant upregulation of specialized-metabolism genes: NbPAL2, Nb4CL, NbCHS, NbF3H, NbANS, NbHCT and NbG10H. The specialized metabolites- cinnamic acid, coumarin, and fisetin were significantly upregulated. Thus, the present study provides a valuable insight into metabolic-engineering approaches towards augmenting the levels of therapeutic TIAs.

Two Tabersonine 6,7-Epoxidases Initiate Lochnericine-Derived Alkaloid Biosynthesis in Catharanthus roseus

Lochnericine is a major monoterpene indole alkaloid (MIA) in the roots of Madagascar periwinkle (Catharanthus roseus). Lochnericine is derived from the stereoselective C6,C7-epoxidation of tabersonine and can be metabolized further to generate other complex MIAs. While the enzymes responsible for its downstream modifications have been characterized, those involved in lochnericine biosynthesis remain unknown. By combining gene correlation studies, functional assays, and transient gene inactivation, we identified two highly conserved P450s that efficiently catalyze the epoxidation of tabersonine: tabersonine 6,7-epoxidase isoforms 1 and 2 (TEX1 and TEX2). Both proteins are quite divergent from the previously characterized tabersonine 2,3-epoxidase and are more closely related to tabersonine 16-hydroxylase, involved in vindoline biosynthesis in leaves. Biochemical characterization of TEX1/2 revealed their strict substrate specificity for tabersonine and their inability to epoxidize 19-hydroxytabersonine, indicating that they catalyze the first step in the pathway leading to hörhammericine production. TEX1 and TEX2 displayed complementary expression profiles, with TEX1 expressed mainly in roots and TEX2 in aerial organs. Our results suggest that TEX1 and TEX2 originated from a gene duplication event and later acquired divergent, organ-specific regulatory elements for lochnericine biosynthesis throughout the plant, as supported by the presence of lochnericine in flowers. Finally, through the sequential expression of TEX1 and up to four other MIA biosynthetic genes in yeast, we reconstituted the 19-acetylhörhammericine biosynthetic pathway and produced tailor-made MIAs by mixing enzymatic modules that are naturally spatially separated in the plant. These results lay the groundwork for the metabolic engineering of tabersonine/lochnericine derivatives of pharmaceutical interest.

An engineered combinatorial module of transcription factors boosts production of monoterpenoid indole alkaloids in Catharanthus roseus

To fend off microbial pathogens and herbivores, plants have evolved a wide range of defense strategies such as physical barriers, or the production of anti-digestive proteins or bioactive specialized metabolites. Accumulation of the latter compounds is often regulated by transcriptional activation of the biosynthesis pathway genes by the phytohormone jasmonate-isoleucine. Here, we used our recently developed flower petal transformation method in the medicinal plant Catharanthus roseus to shed light on the complex regulatory mechanisms steering the jasmonate-modulated biosynthesis of monoterpenoid indole alkaloids (MIAs), to which the anti-cancer compounds vinblastine and vincristine belong. By combinatorial overexpression of the transcriptional activators BIS1, ORCA3 and MYC2a, we provide an unprecedented insight into the modular transcriptional control of MIA biosynthesis. Furthermore, we show that the expression of an engineered de-repressed MYC2a triggers a tremendous reprogramming of the MIA pathway, finally leading to massively increased accumulation of at least 23 MIAs. The current study unveils an innovative approach for future metabolic engineering efforts for the production of valuable bioactive plant compounds in non-model plants.

Loganic Acid Methyltransferase: Insights into the Specificity of Methylation on an Iridoid Glycoside

Loganin is an iridoid glycoside of interest as both an intermediate in the biosynthesis of indole alkaloids in plants and as a bioactive compound itself. Loganic acid methyltransferase catalyzes the methylation of a monoterpenoid glycoside precursor to produce loganin and demonstrates stereospecificity for the (6S,7R) substrate. We have biochemically characterized this biocatalyst and elucidated the basis for its strict substrate specificity. These studies could help facilitate the design of new classes of monoterpenoid indole alkaloids of pharmaceutical interest.

Solution of the multistep pathway for assembly of corynanthean, strychnos, iboga, and aspidosperma monoterpenoid indole alkaloids from 19E-geissoschizine

The multistep assembly of catharanthine and tabersonine from strictosidine remains poorly characterized for understanding the biochemistry of anticancer monoterpenoid indole alkaloid (MIA) biosynthesis in the medicinal plant, Catharanthus roseus. The seven-step pathway from 19E-geissoschizine to four major MIA skeletons enables the assembly of catharanthine and tabersonine that complete the pathway for biosynthesis of the anticancer drugs, anhydrovinblastine and vincristine as well as for production of other biologically active MIAs.

Monoterpenoid indole alkaloids (MIAs) possess a diversity of alkaloid skeletons whose biosynthesis is poorly understood. A bioinformatic search of candidate genes, combined with their virus-induced gene silencing, targeted MIA profiling and in vitro/in vivo pathway reconstitution identified and functionally characterized six genes as well as a seventh enzyme reaction required for the conversion of 19E-geissoschizine to tabersonine and catharanthine. The involvement of pathway intermediates in the formation of four MIA skeletons is described, and the role of stemmadenine-O-acetylation in providing necessary reactive substrates for the formation of iboga and aspidosperma MIAs is described. The results enable the assembly of complex dimeric MIAs used in cancer chemotherapy and open the way to production of many other biologically active MIAs that are not easily available from nature.

Geissoschizine synthase controls flux in the formation of monoterpenoid indole alkaloids in a Catharanthus roseus mutant

A Catharanthus roseus mutant accumulates high levels of ajmalicine at the expense of catharanthine and vindoline. The altered chemistry depends on increased expression and biochemical activities of strictosidine β-glucosidase and ajmalicine synthase activities and reduced expression and biochemical activity of geissoschizine synthase. The Madagascar periwinkle [Catharanthus roseus (L.) G. Don] is a commercially important horticultural flower species and is a valuable source for several monoterpenoid indole alkaloids (MIAs), such as the powerful antihypertensive drug ajmalicine and the antineoplastic agents, vinblastine and vincristine. While biosynthesis of the common MIA precursor strictosidine and its reactive aglycones has been elucidated, the branch point steps leading to the formation of different classes of MIAs remain poorly characterized. Screening of 3600 ethyl methyl sulfonate mutagenized C. roseus plants using a simple thin-layer chromatography screen yielded a mutant (M2-0754) accumulating high levels of ajmalicine together with significantly lower levels of catharanthine and vindoline. Comparative bioinformatic analyses, virus-induced gene silencing, and biochemical characterization identified geissoschizine synthase, the gateway enzyme that controls flux for the formation of iboga and aspidosperma MIAs. The reduction of geissoschizine synthase transcripts in this high ajmalicine mutant, together with increased transcripts and enzyme activities of strictosidine β-glucosidase and of heteroyohimbine synthase, explains the preferential formation of ajmalicine in the mutant instead of catharanthine and vindoline that accumulates in the wild-type parent. Reciprocal crosses established that that the high ajmalicine phenotype is inherited as a Mendelian recessive trait.

Plant-arthropod interactions: who is the winner?

Herbivorous arthropods have interacted with plants for millions of years. During feeding they release chemical cues that allow plants to detect the attack and mount an efficient defense response. A signaling cascade triggers the expression of hundreds of genes, which encode defensive proteins and enzymes for synthesis of toxic metabolites. This direct defense is often complemented by emission of volatiles that attract beneficial parasitoids. In return, arthropods have evolved strategies to interfere with plant defenses, either by producing effectors to inhibit detection and downstream signaling steps, or by adapting to their detrimental effect. In this review, we address the current knowledge on the molecular and chemical dialog between plants and herbivores, with an emphasis on co-evolutionary aspects.

Herbal genomics as tools for dissecting new metabolic pathways of unexplored medicinal plants and drug discovery

Herbal drugs, on which 80% of the world's population rely, are relatively safe over conventional drugs. Conventional drugs are costly, have serious side effects and hence over the past few decades researchers have focused on drug discovery from herbal medicines or botanical sources. The majority of new herbal drugs have been generated from secondary metabolites (alkaloids, terpenoids and phenolic compounds) of plant metabolism. Till date, only a small fraction of the vast diversity of plant metabolism has been explored for the production of new medicines and other products. The emergence of new herbal genomics research, medicinal plant genomics consortium, together with advances in other omics information may help for the speedy discovery of previously unknown metabolic pathways and enzymes. This review highlights the importance of genomics research in the discovery of some previously unknown enzymes/pathways which may make significant contributions in plant metabolic biology and may be used for the future discovery of many new pharmaceutical agents.

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New herbal drugs generated from secondary metabolites of plant metabolism.

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Genome research can find gene clusters and gene duplication events responsible for specialized metabolism in plants.

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Genome and other omic research helps to find genes to metabolite link.

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This tool could be used for discovery of new pharmaceutical agents.

A tabersonine 3-reductase Catharanthus roseus mutant accumulates vindoline pathway intermediates

Monoterpenoid indole alkaloids (MIAs) have remarkable biological properties that have led to their medical uses for a variety of human diseases. Mutagenesis has been used to generate plants with new alkaloid profiles and a useful screen for rapid comparison of MIA profiles is described. The MIA mutants identified are useful for investigating MIA biosynthesis and for targeted production of these specialised metabolites. The Madagascar periwinkle (Catharanthus roseus) is the sole source of the dimeric anticancer monoterpenoid indole alkaloids (MIAs), 3',4'-anhydrovinblastine and derivatives, which are formed via the coupling of the MIAs, catharanthine and vindoline. While intense efforts to identify parts of the complex pathways involved in the assembly of these dimers have been successful, our understanding of MIA biochemistry in C. roseus remains limited. A simple thin layer chromatography screen of 4000 ethyl methanesulfonate-metagenized M2 plants is described to identify mutant lines with altered MIA profiles. One mutant (M2-1865) accumulated reduced levels of vindoline inside the leaves in favour of high levels of tabersonine-2,3-epoxide and 16-methoxytabersonine-2,3-epoxide on the leaf surface. This MIA profile suggested that changes in tabersonine 3-reductase (T3R) activity might be responsible for the observed phenotype. Molecular cloning of mutant and wild type T3R revealed two nucleotide substitutions at cytosine residues 565 (CAT to TAT) and 903 (ACC to ACA) in the mutant corresponding to substitution (H189Y) and silent (T305T) amino acid mutations, respectively, in the protein. The single amino acid substitution in the mutant T3R protein diminished the biochemical activity of T3R by 95% that explained the reason for the low vindoline phenotype of the mutant. This phenotype was recessive and exhibited standard Mendelian single-gene inheritance. The stable formation and accumulation of epoxides in the M2-1865 mutant provides a dependable biological source of these two MIAs.

MorphDB: Prioritizing Genes for Specialized Metabolism Pathways and Gene Ontology Categories in Plants

Recent times have seen an enormous growth of "omics" data, of which high-throughput gene expression data are arguably the most important from a functional perspective. Despite huge improvements in computational techniques for the functional classification of gene sequences, common similarity-based methods often fall short of providing full and reliable functional information. Recently, the combination of comparative genomics with approaches in functional genomics has received considerable interest for gene function analysis, leveraging both gene expression based guilt-by-association methods and annotation efforts in closely related model organisms. Besides the identification of missing genes in pathways, these methods also typically enable the discovery of biological regulators (i.e., transcription factors or signaling genes). A previously built guilt-by-association method is MORPH, which was proven to be an efficient algorithm that performs particularly well in identifying and prioritizing missing genes in plant metabolic pathways. Here, we present MorphDB, a resource where MORPH-based candidate genes for large-scale functional annotations (Gene Ontology, MapMan bins) are integrated across multiple plant species. Besides a gene centric query utility, we present a comparative network approach that enables researchers to efficiently browse MORPH predictions across functional gene sets and species, facilitating efficient gene discovery and candidate gene prioritization. MorphDB is available at http://bioinformatics.psb.ugent.be/webtools/morphdb/morphDB/index/. We also provide a toolkit, named "MORPH bulk" (https://github.com/arzwa/morph-bulk), for running MORPH in bulk mode on novel data sets, enabling researchers to apply MORPH to their own species of interest.

Expression of tabersonine 16-hydroxylase and 16-hydroxytabersonine-O-methyltransferase in Catharanthus roseus hairy roots

The monoterpene indole alkaloids vindoline and catharanthine, which are exclusively synthesized in the medicinal plant Catharanthus roseus, are the two important precursors for the production of pharmaceutically important anti-cancer medicines vinblastine and vincristine. Hairy root culture is an ideal platform for alkaloids production due to its industrial scalability, genetic and chemical stability, and availability of genetic engineering tools. However, C. roseus hairy roots do not produce vindoline due to the lack of expression of the seven-step pathway from tabersonine to vindoline [Murata & De Luca (2015) Plant Journal, 44, 581-594]. The present study describes the genetic engineering of the first two genes tabersonine 16-hydroxylase (T16H) and 16-O-methyl transferase (16OMT) in the missing vindoline pathway under the control of a glucocorticoid-inducible promoter to direct tabersonine toward vindoline biosynthesis in C. roseus hairy roots. In two transgenic hairy roots, the induced overexpression of T16H and 16OMT resulted in the accumulation of vindoline pathway metabolites 16-hydroxytabersonine and 16-methoxytabersonine. The levels of root-specific alkaloids, including lochnericine, 19-hydroxytabersonine and hörhammericine, significantly decreased in the induced hairy roots in comparison to the uninduced control lines. This suggests tabersonine was successfully channeled to the vindoline pathway away from the roots competing pathway based on the overexpression. Interestingly, another two new metabolites were detected in the induced hairy roots and proposed to be the epoxidized-16-hydroxytabersonine and lochnerinine. Thus, the introduction of vindoline pathway genes in hairy roots can cause unexpected terpenoid indole alkaloids (TIA) profile alterations. Furthermore, we observed complex transcriptional changes in TIA genes and regulators detected by RT-qPCR which highlight the tight regulation of the TIA pathway in response to T16H and 16OMT engineering in C. roseus hairy roots.

The ATP binding cassette transporter, VmTPT2/VmABCG1, is involved in export of the monoterpenoid indole alkaloid, vincamine in Vinca minor leaves

Vinca minor is a herbaceous plant from the Apocynaceae family known to produce over 50 monoterpene indole alkaloids (MIAs). These include several biologically active MIAs that have a range of pharmaceutical activities. The present study shows that the MIAs, vincamine, akuammicine, minovincinine, lochnericine and vincadifformine tend to be secreted on V. minor leaf surfaces. A secretion mechanism of MIAs, previously described for Catharanthus roseus, appears to be mediated by a member (CrTPT2) of the pleiotropic drug resistance ABC transporter subfamily. The molecular cloning of an MIA transporter (VmTPT2/VmABCG1) that is predominantly expressed in V. minor leaves was functionally characterized in yeast and established it as an MIA efflux transporter. The similar function of VmTPT2/VmABCG1 to CrTPT2 increases the likelihood that this MIA transporter family may have co-evolved within members of Apocynaceae family to secrete selected MIAs and to regulate leaf MIA surface chemistry.

Effective Medicinal Plant in Cancer Treatment, Part 2: Review Study

Cancer is the second cause of death after cardiovascular diseases. With due attention to rapid progress in the phytochemical study of plants, they are becoming popular because of their anticancer effects. The aim of this study was to investigate the effective medicinal plants in the treatment of cancer and study their mechanism of action. In order to gather information the keywords “traditional medicine,” “plant compounds,” “medicinal plant,” “medicinal herb,” “toxicity,” “anticancer effect,” “cell line,” and “treatment” were searched in international databases such as ScienceDirect, PubMed, and Scopus and national databases such as Magiran, Sid, and Iranmedex, and a total of 228 articles were collected. In this phase, 49 nonrelevant articles were excluded. Enhancement P53 protein expression, reducing the expression of proteins P27, P21, NFκB expression and induction of apoptosis, inhibition of the PI3K/Akt pathway, and reduction of the level of acid phosphatase and lipid peroxidation are the most effective mechanisms of herbal plants that can inhibit cell cycle and proliferation. Common treatments such as radiotherapy and chemotherapy can cause some complications. According to results of this study, herbal extracts have antioxidant compounds that can induce apoptosis and inhibit cell proliferation by the investigated mechanisms.

Quinolizidine Alkaloid Biosynthesis in Lupins and Prospects for Grain Quality Improvement

Quinolizidine alkaloids (QAs) are toxic secondary metabolites found within the genus Lupinus, some species of which are commercially important grain legume crops including Lupinus angustifolius (narrow-leafed lupin, NLL), L. luteus (yellow lupin), L. albus (white lupin), and L. mutabilis (pearl lupin), with NLL grain being the most largely produced of the four species in Australia and worldwide. While QAs offer the plants protection against insect pests, the accumulation of QAs in lupin grain complicates its use for food purposes as QA levels must remain below the industry threshold (0.02%), which is often exceeded. It is not well understood what factors cause grain QA levels to exceed this threshold. Much of the early work on QA biosynthesis began in the 1970-1980s, with many QA chemical structures well-characterized and lupin cell cultures and enzyme assays employed to identify some biosynthetic enzymes and pathway intermediates. More recently, two genes associated with these enzymes have been characterized, however, the QA biosynthetic pathway remains only partially elucidated. Here, we review the research accomplished thus far concerning QAs in lupin and consider some possibilities for further elucidation and manipulation of the QA pathway in lupin crops, drawing on examples from model alkaloid species. One breeding strategy for lupin is to produce plants with high QAs in vegetative tissues while low in the grain in order to confer insect resistance to plants while keeping grain QA levels within industry regulations. With the knowledge achieved on alkaloid biosynthesis in other plant species in recent years, and the recent development of genomic and transcriptomic resources for NLL, there is considerable scope to facilitate advances in our knowledge of QAs, leading to the production of improved lupin crops.

Folivory elicits a strong defense reaction in Catharanthus roseus: metabolomic and transcriptomic analyses reveal distinct local and systemic responses

Plants deploy distinct secondary metabolisms to cope with environment pressure and to face bio-aggressors notably through the production of biologically active alkaloids. This metabolism-type is particularly elaborated in Catharanthus roseus that synthesizes more than a hundred different monoterpene indole alkaloids (MIAs). While the characterization of their biosynthetic pathway now reaches completion, still little is known about the role of MIAs during biotic attacks. As a consequence, we developed a new plant/herbivore interaction system by challenging C. roseus leaves with Manduca sexta larvae. Transcriptomic and metabolic analyses demonstrated that C. roseus respond to folivory by both local and systemic processes relying on the activation of specific gene sets and biosynthesis of distinct MIAs following jasmonate production. While a huge local accumulation of strictosidine was monitored in attacked leaves that could repel caterpillars through its protein reticulation properties, newly developed leaves displayed an increased biosynthesis of the toxic strictosidine-derived MIAs, vindoline and catharanthine, produced by up-regulation of MIA biosynthetic genes. In this context, leaf consumption resulted in a rapid death of caterpillars that could be linked to the MIA dimerization observed in intestinal tracts. Furthermore, this study also highlights the overall transcriptomic control of the plant defense processes occurring during herbivory.