山崎 真巳

White Kwao Krua (Pueraria candollei var. mirifica), a Thai medicinal plant, is a rich source of phytoestrogens, especially isoflavonoids and chromenes. These phytoestrogens are well known; however, their biosynthetic genes remain largely uncharacterized. Cytochrome P450 (P450) is a large protein family that plays a crucial role in the biosynthesis of various compounds in plants, including phytoestrogens. Thus, we focused on P450s involved in the isoflavone hydroxylation that potentially participates in the biosynthesis of miroestrol. Three candidate P450s were isolated from the transcriptome libraries by considering the phylogenetic and expression data of each tissue of P. mirifica. The candidate P450s were functionally characterized both in vitro and in planta. Accordingly, the yeast microsome harboring PmCYP81E63 regiospecifically exhibited either 2' or 3' daidzein hydroxylation and genistein hydroxylation. Based on in silico calculation, PmCYP81E63 had higher binding energy with daidzein than with genistein, which supported the in vitro result of the isoflavone specificity. To confirm in planta function, the candidate P450s were then transiently co-expressed with isoflavone-related genes in Nicotiana benthamiana. Despite no daidzein in the infiltrated N. benthamiana leaves, genistein and hydroxygenistein biosynthesis were detectable by liquid Chromatography with tandem mass spectrometry (LC-MS/MS). Additionally, we demonstrated that PmCYP81E63 interacted with several enzymes related to isoflavone biosynthesis using bimolecular fluorescence complementation studies and a yeast two-hybrid analysis, suggesting a scheme of metabolon formation in the pathway. Our findings provide compelling evidence regarding the involvement of PmCYP81E63 in the early step of the proposed miroestrol biosynthesis in P. mirifica.

High-throughput RNA sequencing (RNA-seq) analysis of samples from Mallotus japonicus, a traditional medicinal plant, yielded two novel RNA viruses tentatively named Mallotus japonicus virus A (MjVA) and Mallotus japonicus virus B (MjVB). The MjVA and MjVB genomes encode proteins showing amino acid sequence similarities to those of poleroviruses (the genus Polerovirus, the family Solemoviridae) and amalgaviruses (the genus Amalgavirus, the family Amalgaviridae), respectively. The MjVA genome contains seven highly overlapping open reading frames, which are translated to seven proteins through various translational mechanisms, including -1 programmed ribosomal frameshifting (PRF) at the slippery motif GGGAAAC, non-AUG translational initiation, and stop codon readthrough. The MjVB genome encodes two proteins; one of which is translated by +1 PRF mechanism at the slippery motif UUUCGN. The abundance analysis of virus-derived RNA fragments revealed that MjVA is highly concentrated in plant parts with well-developed phloem tissues as previously demonstrated in other poleroviruses, which are transmitted by phloem feeders, such as aphids. MjVB, an amalgavirus generally transmitted by seeds, is distributed in all samples at low concentrations. Thus, this study demonstrates the effectiveness and usefulness of RNA-seq analysis of plant samples for the identification of novel RNA viruses and analysis of their tissue distribution. Keywords: Polerovirus; Amalgavirus; Mallotus japonicus; RNA virus; viral genome; programmed ribosomal frameshifting.

A high-quality genome assembly is imperative to explore the evolutionary basis of characteristic attributes that define chemotype and provide essential resources for a molecular breeding strategy for enhanced production of medicinal metabolites. Here, using single-molecule high-fidelity (HiFi) sequencing reads, we report chromosome-scale genome assembly for Chinese licorice (Glycyrrhiza uralensis), a widely used herbal and natural medicine. The entire genome assembly was achieved in eight chromosomes, with contig and scaffold N50 as 36.02 and 60.2 Mb, respectively. With only 17 assembly gaps and half of the chromosomes having no or one assembly gap, the presented genome assembly is among the best plant genomes to date. Our results showed an advantage of using highly accurate long-read HiFi sequencing data for assembling a highly heterozygous genome including its complexed repeat content. Additionally, our analysis revealed that G. uralensis experienced a recent whole-genome duplication at approximately 59.02 million years ago post a gamma (γ) whole-genome triplication event, which contributed to its present chemotype features. The metabolic gene cluster analysis identified 355 gene clusters, which included the entire biosynthesis pathway of glycyrrhizin. The genome assembly and its annotations provide an essential resource for licorice improvement through molecular breeding and the discovery of valuable genes for engineering bioactive components and understanding the evolution of specialized metabolites biosynthesis.

Marasmin [S-(methylthiomethyl)-L-cysteine-4-oxide] is a pharmaceutically valuable sulfur-containing compound produced by the traditional medicinal plant, Tulbaghia violacea. Here, we report the identification of an S- oxygenase, TvMAS1, that produces marasmin from its corresponding sulfide, S-(methylthiomethyl)-L-cysteine. The amino acid sequence of TvMAS1 showed high sequence similarity to known flavin-containing S-oxygenating monooxygenases in plants. Recombinant TvMAS1 catalyzed regiospecific S-oxygenation at S4 of S-(methylthiomethyl)-L-cysteine to yield marasmin, with an apparent Km value of 0.55 mM. TvMAS1 mRNA accumulated with S-(methylthiomethyl)-L-cysteine and marasmin in various organs of T. violacea. Our findings suggest that TvMAS1 catalyzes the S-oxygenation reaction during the last step of marasmin biosynthesis in T. violacea.

S-Alk(en)ylcysteine sulfoxides (CSOs), such as methiin, alliin, and isoalliin, are health-beneficial natural products biosynthesized in the genus Allium. Here, we report the induction of multiple callus tissue lines from three Allium vegetables, onion (A. cepa), Welsh onion (A. fistulosum), and Chinese chive (A. tuberosum), and their ability to accumulate CSOs. Callus tissues were initiated and maintained in the presence of picloram and 2-isopentenyladenine as auxin and cytokinin, respectively. For all plant species tested, the callus tissues almost exclusively accumulated methiin as CSO, while the intact plants contained a substantial amount of isoalliin together with methiin. These results suggest that the cellular developmental conditions and the regulatory mechanisms required for the biosynthesis of methiin are different from those of alliin and isoalliin. The methiin content in the callus tissues of onion and Welsh onion was much higher compared to that in the intact plants, and its cellular concentration could be estimated as 1.9-21.7 mM. The activity of alliinase that degrades CSOs in the callus tissues was much lower than that of the intact plants for onion and Welsh onion, but at similar levels as in the intact plants for Chinese chive. Our findings that the callus tissues of onion and Welsh onion showed high methiin content and low alliinase activity highlighted their potential as a plant-based system for methiin production.

Mallotus japonicus is a valuable traditional medicinal plant in East Asia for applications as a gastrointestinal drug. However, the molecular components involved in the biosynthesis of bioactive metabolites have not yet been explored, primarily due to a lack of omics resources. In this study, we established metabolome and transcriptome resources for M. japonicus to capture the diverse metabolite constituents and active transcripts involved in its biosynthesis and regulation. A combination of untargeted metabolite profiling with data-dependent metabolite fragmentation and metabolite annotation through manual curation and feature-based molecular networking established an overall metabospace of M. japonicus represented by 2129 metabolite features. M. japonicus de novo transcriptome assembly showed 96.9% transcriptome completeness, representing 226,250 active transcripts across seven tissues. We identified specialized metabolites biosynthesis in a tissue-specific manner, with a strong correlation between transcripts expression and metabolite accumulations in M. japonicus. The correlation- and network-based integration of metabolome and transcriptome datasets identified candidate genes involved in the biosynthesis of key specialized metabolites of M. japonicus. We further used phylogenetic analysis to identify 13 C-glycosyltransferases and 11 methyltransferases coding candidate genes involved in the biosynthesis of medicinally important bergenin. This study provides comprehensive, high-quality multi-omics resources to further investigate biological properties of specialized metabolites biosynthesis in M. japonicus.

Plant genomes remain highly fragmented and are often characterized by hundreds to thousands of assembly gaps. Here, we report chromosome-level reference and phased genome assembly of Ophiorrhiza pumila, a camptothecin-producing medicinal plant, through an ordered multi-scaffolding and experimental validation approach. With 21 assembly gaps and a contig N50 of 18.49 Mb, Ophiorrhiza genome is one of the most complete plant genomes assembled to date. We also report 273 nitrogen-containing metabolites, including diverse monoterpene indole alkaloids (MIAs). A comparative genomics approach identifies strictosidine biogenesis as the origin of MIA evolution. The emergence of strictosidine biosynthesis-catalyzing enzymes precede downstream enzymes' evolution post γ whole-genome triplication, which occurred approximately 110 Mya in O. pumila, and before the whole-genome duplication in Camptotheca acuminata identified here. Combining comparative genome analysis, multi-omics analysis, and metabolic gene-cluster analysis, we propose a working model for MIA evolution, and a pangenome for MIA biosynthesis, which will help in establishing a sustainable supply of camptothecin.

Cornus officinalis, an important traditional medicinal plant, is used as major constituents of tonics, analgesics, and diuretics. While several studies have focused on its characteristic bioactive compounds, little is known on their biosynthesis. In this study, we performed LC-QTOF-MS-based metabolome and RNA-seq-based transcriptome profiling for seven tissues of C. officinalis. Untargeted metabolome analysis assigned chemical identities to 1,215 metabolites and showed tissue-specific accumulation for specialized metabolites with medicinal properties. De novo transcriptome assembly established for C. officinalis showed 96% of transcriptome completeness. Co-expression analysis identified candidate genes involved in the biosynthesis of iridoids, triterpenoids, and gallotannins, the major group of bioactive metabolites identified in C. officinalis. Integrative omics analysis identified 45 cytochrome P450s genes correlated with iridoids accumulation in C. officinalis. Network-based integration of genes assigned to iridoids biosynthesis pathways with these candidate CYPs further identified seven promising CYPs associated with iridoids' metabolism. This study provides a valuable resource for further investigation of specialized metabolites' biosynthesis in C. officinalis.

Preasperterpenoid A, featuring a 5/7/(3)6/5 pentacyclic structure, is a C25 sesterterpenoid produced by Penicillium verruculosum. The results of density functional calculations on putative biosynthetic carbocation cyclization/rearrangements leading to preasperterpenoid A revealed a highly concerted four-step cyclization mechanism. Interestingly, two secondary carbocation structures were obtained as minima, but appeared almost as shoulders in the energy profile, and may represent essentially transient structures during the highly concerted reaction.

BACKGROUND: Pueraria candollei var. mirifica, a Thai medicinal plant used traditionally as a rejuvenating herb, is known as a rich source of phytoestrogens, including isoflavonoids and the highly estrogenic miroestrol and deoxymiroestrol. Although these active constituents in P. candollei var. mirifica have been known for some time, actual knowledge regarding their biosynthetic genes remains unknown. RESULTS: Miroestrol biosynthesis was reconsidered and the most plausible mechanism starting from the isoflavonoid daidzein was proposed. A de novo transcriptome analysis was conducted using combined P. candollei var. mirifica tissues of young leaves, mature leaves, tuberous cortices, and cortex-excised tubers. A total of 166,923 contigs was assembled for functional annotation using protein databases and as a library for identification of genes that are potentially involved in the biosynthesis of isoflavonoids and miroestrol. Twenty-one differentially expressed genes from four separate libraries were identified as candidates involved in these biosynthetic pathways, and their respective expressions were validated by quantitative real-time reverse transcription polymerase chain reaction. Notably, isoflavonoid and miroestrol profiling generated by LC-MS/MS was positively correlated with expression levels of isoflavonoid biosynthetic genes across the four types of tissues. Moreover, we identified R2R3 MYB transcription factors that may be involved in the regulation of isoflavonoid biosynthesis in P. candollei var. mirifica. To confirm the function of a key-isoflavone biosynthetic gene, P. candollei var. mirifica isoflavone synthase identified in our library was transiently co-expressed with an Arabidopsis MYB12 transcription factor (AtMYB12) in Nicotiana benthamiana leaves. Remarkably, the combined expression of these proteins led to the production of the isoflavone genistein. CONCLUSIONS: Our results provide compelling evidence regarding the integration of transcriptome and metabolome as a powerful tool for identifying biosynthetic genes and transcription factors possibly involved in the isoflavonoid and miroestrol biosyntheses in P. candollei var. mirifica.

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 mu m 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.

This review describes the application of computational chemistry to plant secondary metabolism, focusing on the biosynthetic mechanisms of terpene/terpenoid, alkaloid, flavonoid, and lignin as representative examples. Through these biosynthetic studies, we exhibit several computational methods, including density functional theory (DFT) calculations, theozyme calculation, docking simulation, molecular dynamics (MD) simulation, and quantum mechanics/molecular mechanics (QM/MM) calculation. This review demonstrates how modern computational chemistry can be employed as an effective tool for revealing biosynthetic mechanisms and the potential of computational chemistry-for example, elucidating how enzymes regulate regio- and stereoselectivity, finding the key catalytic residue of an enzyme, and assessing the viability of hypothetical pathways. Furthermore, insights for the next research objective involving application of computational chemistry to plant secondary metabolism are provided herein. This review will be helpful for plant scientists who are not well versed with computational chemistry.

We previously showed that the regio- and stereoselectivity in terpene-forming reactions are determined by the conformations of the carbocation intermediates, which reflect the initial conformation of the substrate, geranylfarnesyl diphosphate (GFPP). However, it remains unclear how the initial conformation of GFPP is controlled, and which part(s) of the GFPP molecule are important for its fixation inside the substrate-binding pocket. Here, we present the first detailed analysis of the inherent atomic mobility in carbocation intermediates during sesterterpene biosynthesis. We identified two methyl groups as the least mobile of all the carbons of the carbocation intermediates in the first half of the cyclization cascade. Our analysis suggests that these two methyl groups are critical for the preorganization of GFPP in the biosynthetic pathways leading to sesterfisherol and quiannulatene.

最近急速に進んだゲノム科学技術の発展により、植物における有用アルカロイド生合成についても、その特異な物質代謝がどのように進化してきたかに関するゲノムレベルでの解明が進んでいる。筆者らが明らかにしてきたアルカロイド生産の方向決定ステップを触媒する酵素の分子進化、ならびに毒性アルカロイドを生産する植物の自己耐性の分子進化について紹介し、今後の新しい生合成のデザインを目指した展開について説明する。

The results of quantum chemical calculations on the mechanism of the carbocation cascade of reactions in the biosynthetic pathways leading to the pentacyclic sesterterpenes quiannulatene and sesterfisherol provide reasonable answers to several persistent mechanistic questions in sesterterpene biosynthesis, including: 1) the reaction pathways of the multicyclic ring system construction and skeletal rearrangements, 2) the mechanism of triquinane skeleton formation, which requires more complicated rearrangements than previously proposed, 3) the stereochemistry of the final carbocation intermediate, and 4) the determining factor of biosynthetic selection for either 5/6/4/6/5 or 5/6/5/5/5 pentacyclic skeleton formation. This in-depth mechanistic study on sesterterpene biosynthesis revealed that the shape of the final product and the type of triquinane skeleton formed are regulated by the stereochemistry and conformation of the common starting material, geranylfarnesyl diphosphate (GFPP).

AndA, an Fe(II)/α-ketoglutarate (αKG)-dependent enzyme, is the key enzyme that constructs the unique and congested bridged-ring system of anditomin (1), by catalyzing consecutive dehydrogenation and isomerization reactions. Although we previously characterized AndA to some extent, the means by which the enzyme facilitates this drastic structural reconstruction have remained elusive. In this study, we have solved three X-ray crystal structures of AndA, in its apo form and in the complexes with Fe(II), αKG, and two substrates. The crystal structures and mutational experiments identified several key amino acid residues important for the catalysis and provided insight into how AndA controls the reaction. Furthermore, computational calculations validated the proposed reaction mechanism for the bridged-ring formation and also revealed the requirement of a series of conformational changes during the transformation.

We analyzed the metabolites and proteins contained in pure intact vacuoles isolated from Arabidopsis suspension-cultured cells using capillary electrophoresis-mass spectrometry (CE-MS), Fourier transform-ion cyclotron resonance (FT-ICR)-MS and liquid chromatography (LC)-MS. We identified 21 amino acids and five organic acids as major primary metabolites in the vacuoles with CE-MS. Further, we identified small amounts of 27 substances including well-known vacuolar molecules, but also some unexpected substances (e.g. organic phosphate compounds). Non-target analysis of the vacuolar sample with FT-ICR-MS suggested that there are 1,106 m/z peaks that could predict the 5,090 molecular formulae, and we have annotated 34 compounds in these peaks using the KNapSAck database. By conducting proteomic analysis of vacuolar sap, we found 186 proteins in the same vacuole samples. Since the vacuole is known as a major degradative compartment, many of these were hydrolases, but we also found various oxidoreductases and transferases. The relationships between the proteins and metabolites in the vacuole are discussed.

The three Forsythia species, F. suspensa, F. viridissima and F. koreana, have been used as herbal medicines in China, Japan and Korea for centuries and they are known to be rich sources of numerous pharmaceutical metabolites, forsythin, forsythoside A, arctigenin, rutin and other phenolic compounds. In this study, de novo transcriptome sequencing and assembly was performed on these species. Using leaf and flower tissues of F. suspensa, F. viridissima and F. koreana, 1.28–2.45-Gbp sequences of Illumina based pair-end reads were obtained and assembled into 81,913, 88,491 and 69,458 unigenes, respectively. Classification of the annotated unigenes in gene ontology terms and KEGG pathways was used to compare the transcriptome of three Forsythia species. The expression analysis of orthologous genes across all three species showed the expression in leaf tissues being highly correlated. The candidate genes presumably involved in the biosynthetic pathway of lignans and phenylethanoid glycosides were screened as co-expressed genes. They express highly in the leaves of F. viridissima and F. koreana. Furthermore, the three unigenes annotated as acyltransferase were predicted to be associated with the biosynthesis of acteoside and forsythoside A from the expression pattern and phylogenetic analysis. This study is the first report on comparative transcriptome analyses of medicinally important Forsythia genus and will serve as an important resource to facilitate further studies on biosynthesis and regulation of therapeutic compounds in Forsythia species.

The secret of chemical diversity and function of specialized metabolites in medicinal plants will be unveiled by study of functional genomics at an unprecedentedly rapid rate in the coming years. This is mostly ascribed to the remarkable advancement in the high-throughput DNA sequencing together with other omics technologies such as metabolomics, in particular, due to drastic reduction in the cost of acquiring, storing and analyzing massive omics datasets. Once the genes involved in a biosynthetic pathway of specialized compounds in plants are elucidated, synthetic biology or genome editing can be applied to produce the target compounds in an engineered organism or to manipulate the pathway in planta. Coupled with these advancements in pathway elucidation approaches, modern plant biotechnology strategies are bound to significantly contribute to the sustainable development goals set by United Nations.

The cyclization mechanisms involved in the biosynthesis of sesterterpenes are not fully understood. For example, there are two plausible reaction pathways for sesterfisherol biosynthesis, which differ in the order of ring cyclization: A-D-B/C (Path a) and A-B-C/D (Path b). It is difficult to capture intermediates of terpene cyclization, which is a complex, domino-type reaction, and so here we employed a combination of experimental and computational methods. Density functional theory calculations revealed unexpected intermediates and transition states, and implied that C-H···π interaction between a carbocation intermediate and an aromatic residue of sesterfisherol synthase (NfSS) plays a critical role, serving to accelerate the 1,2-H shift (thereby preventing triquinane carbocation formation) and to protect reactive carbocation intermediates from bases such as pyrophosphate or water in the active site. Site-directed mutagenesis of NfSS guided by docking simulations confirmed that phenylalanine F191 is a critical amino acid residue for sesterfisherol synthase, as the F191A mutant of NfSS produces novel sesterterpenes, but not sesterfisherol. Although both pathways are energetically viable, on the basis of our computational and experimental results, NfSS-mediated sesterfisherol biosynthesis appears to proceed via Path a. These findings may also provide new insight into the cyclization mechanisms in related sesterterpene synthases.

In the late stage of anthocyanin biosynthesis, dihydroflavonol reductase (DFR) and anthocyanidin synthase (ANS) mediate a formal tautomerization. However, such oxidation/reduction process requires high energy and appears to be unnecessary, as the oxidation state does not change during the transformation. Thus, a non-enzymatic pathway of tautomerization has also been proposed. To resolve the long-standing issue of whether this non-enzymatic pathway is the main contributor for the biosynthesis, we carried out density functional theory (DFT) calculations to examine this non-enzymatic pathway from dihydroflavonol to anthocyanidin. We show here that the activation barriers for the proposed non-enzymatic tautomerization are too high to enable the reaction to proceed under normal aqueous conditions in plants. The calculations also explain the experimentally observed requirement for acidic conditions during the final step of conversion of 2-flaven-3,4-diol to anthocyanidin; a thermodynamically and kinetically favorable concerted pathway can operate under these conditions.

Heterologous expression of four Glade-A bifunctional terpene synthases (BFTSs), giving di/sesterterpenes with unique polycyclic carbon skeletons such as sesterfisherol, enabled the isolation of the sesterterpenes Bm1, Bm2, Bm3, and Ph1. Their structures suggested that formation of the products occurs via various diastereomeric carbocation intermediates, allowing the proposal that dade-A BFTSs catalyze three-step cyclizations using several stereofacial combinations of allylic cation-olefin pairs in the corresponding intermediates to generate various stereoisomers.

Aconitum carmichaelii is an important medicinal herb used widely in China, Japan, India, Korea, and other Asian countries. While extensive research on the characterization of metabolic extracts of A. carmichaelii has shown accumulation of numerous bioactive metabolites including aconitine and aconitine-type diterpene alkaloids, its biosynthetic pathway remains largely unknown. Biosynthesis of these secondary metabolites is tightly controlled and mostly occurs in a tissue-specific manner therefore, transcriptome analysis across multiple tissues is an attractive method to identify the molecular components involved for further functional characterization. In order to understand the biosynthesis of secondary metabolites, Illumina-based deep transcriptome profiling and analysis was performed for four tissues (flower, bud, leaf, and root) of A. carmichaelii, resulting in 5.5 Gbps clean RNA-seq reads assembled into 128,183 unigenes. Unigenes annotated as possible rate-determining steps of an aconitine-type biosynthetic pathway were highly expressed in the root, in accordance with previous reports describing the root as the accumulation site for these metabolites. We also identified 21 unigenes annotated as cytochrome P450s and highly expressed in roots, which represent candidate unigenes involved in the diversification of secondary metabolites. Comparative transcriptome analysis of A. carmichaelii with A. heterophyllum identified 20,232 orthogroups, representing 30,633 unigenes of A. carmichaelii, gene ontology enrichment analysis of which revealed essential biological process together with a secondary metabolic process to be highly enriched. Unigenes identified in this study are strong candidates for aconitine-type diterpene alkaloid biosynthesis, and will serve as useful resources for further validation studies.

Medicinal plants are a rich source of highly diverse specialized metabolites with important pharmacological properties. Until recently, plant biologists were limited in their ability to explore the biosynthetic pathways of these metabolites, mainly due to the scarcity of plant genomics resources. However, recent advances in high-throughput large-scale analytical methods have enabled plant biologists to discover biosynthetic pathways for important plant-based medicinal metabolites. The reduced cost of generating omics datasets and the development of computational tools for their analysis and integration have led to the elucidation of biosynthetic pathways of several bioactive metabolites of plant origin. These discoveries have inspired synthetic biology approaches to develop microbial systems to produce bioactive metabolites originating from plants, an alternative sustainable source of medicinally important chemicals. Since the demand for medicinal compounds are increasing with the world's population, understanding the complete biosynthesis of specialized metabolites becomes important to identify or develop reliable sources in the future. Here, we review the contributions of major omics approaches and their integration to our understanding of the biosynthetic pathways of bioactive metabolites. We briefly discuss different approaches for integrating omics datasets to extract biologically relevant knowledge and the application of omics datasets in the construction and reconstruction of metabolic models.

Ferns are known to produce onoceroids including onoceranes and serratanes having unusual structures among triterpenes. From the fern Lycopodium clavatum, a novel onoceroid synthase gene was cloned that showed high sequence identity with a previously identified alpha-onocerin synthase. Functional analysis by coexpression with pre-alpha-onocerin synthase in yeast led to the production of tohogenol and serratenediol. The result suggested that serratanes are directly biosynthesized from pre-alpha-onocerin and not from alpha-onocerin as previously assumed.

Lonicera japonica is one of the most important medicinal plants with applications in traditional Chinese and Japanese medicine for thousands of years. Extensive studies on the constituents of L. japonica extracts have revealed an accumulation of pharmaceutically active metabolite classes, such as chlorogenic acid, luteolin and other flavonoids, and secoiridoids, which impart characteristic medicinal properties. Despite being a rich source of pharmaceutically active metabolites, little is known about the biosynthetic enzymes involved, and their expression profile across different tissues of L. japonica. In this study, we performed de novo transcriptome assembly for L. japonica, representing transcripts from nine different tissues. A total of 22 Gbps clean RNA-seq reads from nine tissues of L. japonica were used, resulting in 243,185 unigenes, with 99,938 unigenes annotated based on a homology search using blastx against the NCBI-nr protein database. Unsupervised principal component analysis and correlation studies using transcript expression data from all nine tissues of L. japonica showed relationships between tissues, explaining their association at different developmental stages. Homologs for all genes associated with chlorogenic acid, luteolin, and secoiridoid biosynthesis pathways were identified in the L. japonica transcriptome assembly. Expression of unigenes associated with chlorogenic acid was enriched in stems and leaf-2, unigenes from luteolin were enriched in stems and flowers, while unigenes from secoiridoid metabolic pathways were enriched in leaf-1 and shoot apex. Our results showed that different tissues of L. japonica are enriched with sets of unigenes associated with specific pharmaceutically important metabolic pathways and, therefore, possess unique medicinal properties. The present study will serve as a resource for future attempts for functional characterization of enzyme coding genes within key metabolic processes.

Background: Plants produce a vast variety of specialized metabolites which can be a rich source for lead compounds for the development of new drugs. Alkaloids are one the largest groups of plant specialized metabolites important for natural product based pharmaceuticals. Of these, lysine (Lys)-derived alkaloids exhibit a wide range of pharmacological properties which are beneficial for humans. For instance they have anticancer, anti-Alzheimer's disease, anti-inflammatory, hypocholesterolemic and antiarrhtymic effects. Lys-derived alkaloids are widely distributed throughout the plant kingdom: they can be found in various species from clubmosses to flowering plants. Lys is one of the most essential amino acids for humans and livestock and is synthesized in the plastids of land plants. Lys-derived alkaloids can be divided into four major groups including quinolizidine, lycopodium, piperidine, and indolizidine alkaloids. Despite the importance of these compounds, the biosynthetic pathways of Lys-derived alkaloids are not well understood. With the exception of indolizidine alkaloids, Lys decarboxylase (LDC) is the enzyme involved in the first committed step of the biosynthesis by catalyzing the transformation of L-Lys into cadaverine. Cadaverine is then oxidized by copper amine oxidase (CuAO) and spontaneously cyclized to Delta(1) -piperideine Schiff base which is a universal intermediate for the production of various Lys-derived alkaloids. Conclusion: In this review, we briefly summarize the recent understanding about the structures, occurrences, analytical procedures, biosyntheses, and potential health effects and medical applications of Lys-derived alkaloids with emphasis on quinolizidine alkaloids (QAs).

The hairy roots (HR) of Ophiorrhiza pumila produce camptothecin (CPT), a monoterpenoid indole alkaloid used as a precursor in the synthesis of chemotherapeutic drugs. O. pumila HR culture is considered as a promising alternative source of CPT, however, the knowledge about the biosynthetic pathway and regulatory mechanism is still limited. In this study, five genes that encode AP2/ERF transcription factors, namely OpERF1-OpERF5, were isolated from HR of O. pumila. Phylogenetic analysis of AP2/ERF protein sequences suggested the close evolutionary relationship of OpERF1 with stress-responsive ERF factors in Arabidopsis and of OpERF2 with ERF factors reported to regulate alkaloid production, such as ORCA3 in Catharanthus roseus, NIC2 locus ERF in tobacco, and JRE4 in tomato. We generated the transgenic HR lines of O. pumila, ERF1i and ERF2i, in which the expression of OpERF1 and OpERF2, respectively, was suppressed using RNA interference technique. The transcriptome and metabolome of these suppressed HR were analyzed for functional characterization of OpERF1 and OpERF2. Although significant changes were not observed in the metabolome, including CPT and related compounds, the suppression of OpERF2 resulted in reduced expression of genes in the 2-C-methyl-D-erythritol 4-phosphate and secologanin-strictosidine pathways, which supply a precursor, strictosidine, for CPT biosynthesis. Furthermore, while it was not conclusive for OpERF1, enrichment analysis of differentially expressed genes in the suppressed HR showed that the gene ontology terms for oxidation-reduction, presumably involved in secondary metabolite pathways, were enriched in the ERF2i downregulated gene set. These results suggest a positive role of OpERF2 in regulating specialized metabolism in O. pumila.

The genus Physalis in the Solanaceae family contains several species of benefit to humans. Examples include P. alkekengi (Chinese-lantern plant, hozuki in Japanese) used for medicinal and for decorative purposes, and P. peruviana, also known as Cape gooseberry, which bears an edible, vitamin-rich fruit. Members of the Physalis genus are a valuable resource for phytochemicals needed for the development of medicines and functional foods. To fully utilize the potential of these phytochemicals we need to understand their biosynthesis, and for this we need genomic data, especially comprehensive transcriptome datasets for gene discovery We report the de novo assembly of the transcriptome from leaves of P. alkekengi and P. peruviana using Illumina RNA-seq technologies. We identified 75,221 unigenes in P. alkekengi and 54,513 in P. peruviana. All unigenes were annotated with gene ontology (GO), Enzyme Commission (EC) numbers, and pathway information from the Kyoto Encyclopedia of Genes and Genomes (KEGG). We classified unigenes encoding enzyme candidates putatively involved in the secondary metabolism and identified more than one unigenes for each step in terpenoid backbone- and steroid biosynthesis in P. alkekengi and P. peruviana. To measure the variability of the withanolides including physalins and provide insights into their chemical diversity in Physalis, we also analyzed the metabolite content in leaves of P. alkekengi and P. peruviana at five different developmental stages by liquid chromatography-mass spectrometry. We discuss that comprehensive transcriptome approaches within a family can yield a clue for gene discovery in Physalis and provide insights into their complex chemical diversity. The transcriptome information we submit here will serve as an important public resource for further studies of the specialized metabolism of Physalis species.

Here, we report potential transcripts involved in the biosynthesis of therapeutic metabolites in Swertia japonica , the first report of transcriptome assembly, and characterization of the medicinal plant from Swertia genus. Swertia genus, representing over 170 plant species including herbs such as S. chirata, S. hookeri, S. longifolia, S. japonica, among others, have been used as the traditional medicine in China, India, Korea, and Japan for thousands of years. Due to the lack of genomic and transcriptomic resources, little is known about the molecular basis involved in the biosynthesis of characteristic key bioactive metabolites. Here, we performed deep-transcriptome sequencing for the aerial tissues and the roots of S. japonica, generating over 2 billion raw reads with an average length of 101 bps. Using a combined approach of three popular assemblers, de novo transcriptome assembly for S. japonica was obtained, yielding 81,729 unigenes having an average length of 884 bps and N50 value of 1452 bps, of which 46,963 unigenes were annotated based on the sequence similarity against NCBI-nr protein database. Annotation of transcriptome assembly resulted in the identification of putative genes encoding all enzymes from the key therapeutic metabolite biosynthesis pathways. Transcript abundance analysis, gene ontology enrichment analysis, and KEGG pathway enrichment analysis revealed metabolic processes being up-regulated in the aerial tissues with respect to the roots of S. japonica. We also identified 37 unigenes as potential candidates involved in the glycosylation of bioactive metabolites. Being the first report of transcriptome assembly and annotation for any of the Swertia species, this study will be a valuable resource for future investigations on the biosynthetic pathways of therapeutic metabolites and their regulations.

Lycopodium alkaloids (LAs) are derived from lysine (Lys) and are found mainly in Huperziaceae and Lycopodiaceae. LAs are potentially useful against Alzheimer's disease, schizophrenia, and myasthenia gravis. Here, we cloned the bifunctional lysine/ornithine decarboxylase (L/ODC), the first gene involved in LA biosynthesis, from the LA-producing plants Lycopodium clavatum and Huperzia serrata. We describe the in vitro and in vivo functional characterization of the L. clavatum L/ODC (LcL/ODC). The recombinant LcL/ODC preferentially catalyzed the decarboxylation of L-Lys over L-ornithine (L-Orn) by about 5 times. Transient expression of LcL/ODC fused with the amino or carboxyl terminus of green fluorescent protein, in onion (Allium cepa) epidermal cells and Nicotiana benthamiana leaves, showed LcL/ODC localization in the cytosol. Transgenic tobacco (Nicotiana tabacum) hairy roots and Arabidopsis (Arabidopsis thaliana) plants expressing LcL/ODC enhanced the production of a Lys-derived alkaloid, anabasine, and cadaverine, respectively, thus, confirming the function of LcL/ODC in plants. In addition, we present an example of the convergent evolution of plant Lys decarboxylase that resulted in the production of Lys-derived alkaloids in Leguminosae (legumes) and Lycopodiaceae (clubmosses). This convergent evolution event probably occurred via the promiscuous functions of the ancestral Orn decarboxylase, which is an enzyme involved in the primary metabolism of polyamine. The positive selection sites were detected by statistical analyses using phylogenetic trees and were confirmed by site-directed mutagenesis, suggesting the importance of those sites in granting the promiscuous function to Lys decarboxylase while retaining the ancestral Orn decarboxylase function. This study contributes to a better understanding of LA biosynthesis and the molecular evolution of plant Lys decarboxylase.

Catharanthus roseus (L.) G. Don is a medicinal plant well known for producing antitumor drugs such as vinblastine and vincristine, which are classified as terpenoid indole alkaloids (TIAs). The TIA metabolic pathway in C. roseus has been extensively studied. However, the localization of TIA intermediates at the cellular level has not been demonstrated directly. In the present study, the metabolic pathway of TIA in C. roseus was studied with two forefront metabolomic techniques, that is, Imaging mass spectrometry (MS) and live Single-cell MS, to elucidate cell-specific TIA localization in the stem tissue. Imaging MS indicated that most TIAs localize in the idioblast and laticifer cells, which emit blue fluorescence under UV excitation. Single-cell MS was applied to four different kinds of cells [idioblast (specialized parenchyma cell), laticifer, parenchyma, and epidermal cells] in the stem longitudinal section. Principal component analysis of Imaging MS and Single-cell MS spectra of these cells showed that similar alkaloids accumulate in both idioblast cell and laticifer cell. From MS/MS analysis of Single-cell MS spectra, catharanthine, ajmalicine, and strictosidine were found in both cell types in C. roseus stem tissue, where serpentine was also accumulated. Based on these data, we discuss the significance of TIA synthesis and accumulation in the idioblast and laticifer cells of C. roseus stem tissue.

The Panax genus has been a source of natural medicine, benefitting human health over the ages, among which the Panax japonicus represents an important species. Our understanding of several key pathways and enzymes involved in the biosynthesis of ginsenosides, a pharmacologically active class of metabolites and a major chemical constituents of the rhizome extracts from the Panax species, are limited. Limited genomic information, and lack of studies on comparative transcriptomics across the Panax species have restricted our understanding of the biosynthetic mechanisms of these and many other important classes of phytochemicals. Herein, we describe Illumina based RNA sequencing analysis to characterize the transcriptome and expression profiles of genes expressed in the five tissues of P. japonicus, and its comparison with other Panax species. RNA sequencing and de novo transcriptome assembly for P. japonicus resulted in a total of 135,235 unigenes with 78,794 (58.24%) unigenes being annotated using NCBI-nr database. Transcriptome profiling, and gene ontology enrichment analysis for five tissues of P. japonicus showed that although overall processes were evenly conserved across all tissues. However, each tissue was characterized by several unique unigenes with the leaves showing the most unique unigenes among the tissues studied. A comparative analysis of the P. japonicus transcriptome assembly with publically available transcripts from other Panax species, namely, P. ginseng, P. notoginseng, and P. quinquefolius also displayed high sequence similarity across all Panax species, with P. japonicus showing highest similarity with P. ginseng. Annotation of P. japonicus transcriptome resulted in the identification of putative genes encoding all enzymes from the triterpene backbone biosynthetic pathways, and identified 24 and 48 unigenes annotated as cytochrome P450 (CYP) and glycosyltransferases (GT), respectively. These CYPs and GTs annotated unigenes were conserved across all Panax species and co-expressed with other the transcripts involved in the triterpenoid backbone biosynthesis pathways. Unigenes identified in this study represent strong candidates for being involved in the triterpenoid saponins biosynthesis, and can serve as a basis for future validation studies.

Camptothecin is a plant-derived alkaloid and important precursor of clinically used anti-tumor drugs, but little is known about regulatory mechanism of camptothecin production in plants. We show here that a MYB transcription factor, OpMYB1, isolated from Ophiorrhiza pumila is a regulator of camptothecin biosynthesis. OpMYB1 has an EAR-like motif and exhibits a transcriptional repression activity in an in vivo assay using Arabidopsis thaliana leaves. Overexpression of OpMYB1 in hairy roots of O. pumila resulted in reduced production of camptothecin and reduced expression of OpTDC encoding triptophane decarboxylase catalyzing the earliest step in camptothecin biosynthesis. From the deep transcriptome analysis, GO enrichment in secondary (specialized) metabolisms, especially in phenylpropanoid pathway was observed in the hairy roots over-expressing OpMYB1. Furthuremore, gene suppression by OpMYB1 was revealed in biosynthetic pathways of seco-iridoids, monoterpene indole alkaloids, anthraquinone and chlorogenic acid. These results suggested that OpMYB1 is a negative regulator to fine-tune the general specialized metabolisms in O. pumila.

Onocerin is known for its unusual structure among triterpenoids, with a symmetrical structure that is formed by cyclizations at the both termini of dioxidosqualene. The nature of the enzyme catalyzing these unusual cyclizations has remained elusive for decades. Here, we report the cloning of genes responsible for these reactions; they exhibited unprecedented substrate specificities among oxidosqualene cyclase family members. Two genes, LCC and LCD, were identified from the fern Lycopodium clavatum. Expression in yeast revealed that both were required to produce -onocerin. LCC, the first dioxidosqualene cyclase, catalyzed the production of a novel intermediate pre--onocerin from only dioxidosqualene as a substrate; LCD catalyzed the second half of the cyclization, exclusively from pre--onocerin. These results demonstrated that these two most unusual oxidosqualene cyclases were involved in onocerin biosynthesis.

Study on transcriptome, the entire pool of transcripts in an organism or single cells at certain physiological or pathological stage, is indispensable in unraveling the connection and regulation between DNA and protein. Before the advent of deep sequencing, microarray was the main approach to handle transcripts. Despite obvious shortcomings, including limited dynamic range and difficulties to compare the results from distinct experiments, microarray was widely applied. During the past decade, next-generation sequencing (NGS) has revolutionized our understanding of genomics in a fast, high-throughput, cost-effective, and tractable manner. By adopting NGS, efficiency and fruitful outcomes concerning the efforts to elucidate genes responsible for producing active compounds in medicinal plants were profoundly enhanced. The whole process involves steps, from the plant material sampling, to cDNA library preparation, to deep sequencing, and then bioinformatics takes over to assemble enormous yet fragmentary data from which to comb and extract information. The unprecedented ly rapid development of such technologies provides so many choices to facilitate the task, which can cause confusion when choosing the suitable methodology for specific purposes. Here, we review the general approaches for deep transcriptome analysis and then focus on their application in discovering biosynthetic pathways of medicinal plants that produce important secondary metabolites.