A Geranylfarnesyl Diphosphate Synthase Provides the Precursor for Sesterterpenoid (C25) Formation in the Glandular Trichomes of the Mint Species Leucosceptrum canum

From Monocyclization to Pentacyclization: A Versatile Plant Cyclase Produces Diverse Sesterterpenes with Anti-Liver Fibrosis Potential

A prolific multi-product sesterterpene synthase CbTPS1 is characterized from the medicinal Brassicaceae plant Capsella bursa-pastoris. Twenty different sesterterpenes including 16 undescribed compounds, possessing 10 different mono-/di-/tri-/tetra-/penta-carbocyclic skeletons, including the unique 15-membered macrocyclic and 24(15→14)-abeo-capbuane scaffolds, are isolated and structurally elucidated from engineered Escherichia coli strains expressing CbTPS1. Site-directed mutagenesis assisted by molecular dynamics simulations resulted in the variant L354M with up to 13.2-fold increased sesterterpene production. These structurally diverse products suggest a comprehensive cyclization mechanism for plant sesterterpenes and provide compelling evidence for the initial cyclization of geranylfarnesyl diphosphate via a crucial 15-membered monocyclic carbocation. The activities of these sesterterpenes against liver fibrosis is inferred from the inhibition of the transforming growth factor-β/Smad signaling pathway and collagen synthesis. These findings greatly expand the chemical space and biological functions of sesterterpenes and provide new insights into the catalytic mechanism of terpene synthases.

Qualitative Profiling, Antioxidant and Antimicrobial Activities of Polar and Nonpolar Basil Extracts

Basil (Ocimum basilicum L.) is a widely used culinary herb. In this study, ethanol, dichloromethane, and sunflower oil were used separately as solvents with distinct polarities for the extraction of basil aerial parts to simulate the different polarity conditions in domestic food processing. The oil extract (OE) was re-extracted with acetonitrile, and the chemical composition, antioxidant potential, and antimicrobial activities of the ethanol (EE), dichloromethane (DCME), and acetonitrile (ACNE) extracts were determined. A total of 109 compounds were tentatively identified in EE, DCME, and ACNE by HPLC-DAD/ESI-ToF-MS. Fatty acids were present in all extracts. Phenolic acids and flavonoids dominated in EE. DCME was characterised by triterpenoid acids, while diterpenoids were mainly found in ACNE. The extracts were analysed for their antioxidant capacity using the 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) assay. EE and DCME showed significant radical scavenging potential. Antimicrobial activity was explored in eight bacterial, two yeast, and one fungal species. All extracts exhibited high antifungal activity, comparable to or better than that of the commercial drug nistatin. Antibacterial activities were notable for EE and ACNE, while DCME showed no activity against bacteria in the applied concentration ranges. The different polarities of the solvents led to distinctive phytochemical compositions and bioactivities in the extracts.

Immunosuppressive leucosesterterpane and penta-nor-leucosesterterpane sesterterpenoids from Leucosceptrum canum

Five undescribed leucosesterterpane sesterterpenoids, leucosceptrines A-E, two undescribed penta-nor-leucosesterterpane (C20) sesterterpenoids, nor-leucosceptrines A and B, and three known analogues, were obtained from the aerial parts of Leucosceptrum canum of Chinese origin. Leucosceptrines A-C are the first examples of leucosesterterpane-type sesterterpenoids with unclosed dihydropyran rings and reverse configurations at chiral centers C-4 and/or C-12. Nor-leucosceptrines A and B possesses an unusual penta-nor-leucosesterterpane skeleton. Their structures were unambiguously elucidated through comprehensive spectroscopic analyses and single-crystal X-ray diffraction. A plausible biogenetic pathway for these sesterterpenoids was proposed. The immunosuppressive effects of these isolates on the secretion of the cytokine IFN-γ by T cells stimulated with anti-CD3/CD28 monoclonal antibodies were observed with different potencies.

Plant terpenoid biosynthetic network and its multiple layers of regulation

Terpenoids constitute one of the largest and most chemically diverse classes of primary and secondary metabolites in nature with an exceptional breadth of functional roles in plants. Biosynthesis of all terpenoids begins with the universal five‑carbon building blocks, isopentenyl diphosphate (IPP) and its allylic isomer dimethylallyl diphosphate (DMAPP), which in plants are derived from two compartmentally separated but metabolically crosstalking routes, the mevalonic acid (MVA) and methylerythritol phosphate (MEP) pathways. Here, we review the current knowledge on the terpenoid precursor pathways and highlight the critical hidden constraints as well as multiple regulatory mechanisms that coordinate and homeostatically govern carbon flux through the terpenoid biosynthetic network in plants.

Isoprenyl diphosphate synthases of terpenoid biosynthesis in rose-scented geranium (Pelargonium graveolens)

The essential oil of Pelargonium graveolens (rose-scented geranium), an important aromatic plant, comprising mainly mono- and sesqui-terpenes, has applications in food and cosmetic industries. This study reports the characterization of isoprenyl disphosphate synthases (IDSs) involved in P. graveolens terpene biosynthesis. The six identified PgIDSs belonged to different classes of IDSs, comprising homomeric geranyl diphosphate synthases (GPPSs; PgGPPS1 and PgGPPS2), the large subunit of heteromeric GPPS or geranylgeranyl diphosphate synthases (GGPPSs; PgGGPPS), the small subunit of heteromeric GPPS (PgGPPS.SSUI and PgGPPS.SSUII), and farnesyl diphosphate synthases (FPPS; PgFPPS).All IDSs exhibited maximal expression in glandular trichomes (GTs), the site of aroma formation, and their expression except PgGPPS.SSUII was induced upon treatment with MeJA. Functional characterization of recombinant proteins revealed that PgGPPS1, PgGGPPS and PgFPPS were active enzymes producing GPP, GGPP/GPP, and FPP respectively, whereas both PgGPPS.SSUs and PgGPPS2 were inactive. Co-expression of PgGGPPS (that exhibited bifunctional G(G)PPS activity) with PgGPPS.SSUs in bacterial expression system showed lack of interaction between the two proteins, however, PgGGPPS interacted with a phylogenetically distant Antirrhinum majus GPPS.SSU. Further, transient expression of AmGPPS.SSU in P. graveolens leaf led to a significant increase in monoterpene levels. These findings provide insight into the types of IDSs and their role in providing precursors for different terpenoid components of P. graveolens essential oil.

The Chemical Ecology of Plant Natural Products

Plants are excellent chemists with an impressive capability of biosynthesizing a large variety of natural products (also known as secondary or specialized metabolites) to resist various biotic and abiotic stresses. In this chapter, 989 plant natural products and their ecological functions in plant-herbivore, plant-microorganism, and plant-plant interactions are reviewed. These compounds include terpenoids, phenols, alkaloids, and other structural types. Terpenoids usually provide direct or indirect defense functions for plants, while phenolic compounds play important roles in regulating the interactions between plants and other organisms. Alkaloids are frequently toxic to herbivores and microorganisms, and can therefore also provide defense functions. The information presented should provide the basis for in-depth research of these plant natural products and their natural functions, and also for their further development and utilization.

Defensive furofuran lignans localized to the oil cells of Neocinnamomum delavayi and their metabolism by a specialist insect

Neocinnamomum delavayi (Lauraceae) leaves with abundant oil cells are seldom attacked by insects, but their chemical constituent and biological function remain obscure. Three furofuran lignans, including (+)-eudesmin (3), (+)-magnolin (4), and demethoxyaschantin (5), were identified to be the major specialized metabolites in the oil cells of N. delavayi leaves through laser microdissection coupled with NMR analysis. Compounds 3 and 4 exhibited obvious antifeedant activity against a generalist insect Spodoptera exigua, and their natural contents in the leaves could effectively defend against generalist insects. Intriguingly, three specific metabolites 9-11, the O-demethylation derivates of compounds 3-5, were identified from a native specialist insect Dindica polyphaenaria feeding with N. delavayi leaves, implying an adaptation mechanism of specialist insects to plant defensive compounds. The results revealed a chemical connection between plants and insects, which would contribute to our understanding of plant-insect interaction and insect management.

Natural Sesquiterpene Lactone as Source of Discovery of Novel Fungicidal Candidates: Structural Modification and Antifungal Activity Evaluation of Xanthatin Derived from Xanthium strumarium L

As part of our ongoing efforts to discover novel agricultural fungicidal candidates from natural sesquiterpene lactones, in the present work, sixty-three xanthatin-based derivatives containing a arylpyrazole, arylimine, thio-acylamino, oxime, oxime ether, or oxime ester moiety were synthesized. Their structures were well characterized by ¹H and ¹³C nuclear magnetic resonance and high-resolution mass spectrometry, while the absolute configurations of compounds 5' and 6a were further determined by single-crystal X-ray diffraction. Meanwhile, the antifungal activities of the prepared compounds against several phytopathogenic fungi were investigated using the spore germination method and the mycelium growth rate method in vitro. The bioassay results illustrated that compounds 5, 5', and 15 exhibited excellent inhibitory activity against the tested fungal spores and displayed remarkable inhibitory effects on fungal mycelia. Compounds 5 and 5' exhibited more potent inhibitory activity (IC₅₀ = 1.1 and 24.8 μg/mL, respectively) against the spore of Botrytis cinerea than their precursor xanthatin (IC₅₀ = 37.6 μg/mL), wherein the antifungal activity of compound 5 was 34-fold higher than that of xanthatin and 71-fold higher than that of the positive control, difenoconazole (IC₅₀ = 78.5 μg/mL). Notably, compound 6'a also demonstrated broad-spectrum inhibitory activity against the four tested fungal spores. Meanwhile, compounds 2, 5, 8, and 15 showed prominent inhibitory activity against the mycelia of Cytospora mandshurica with the EC₅₀ values of 2.3, 11.7, 11.1, and 3.0 μg/mL, respectively, whereas the EC₅₀ value of xanthatin was 14.8 μg/mL. Additionally, compounds 5' and 15 exhibited good in vivo therapeutic and protective effects against B. cinerea with values of 55.4 and 62.8%, respectively. The preliminary structure-activity relationship analysis revealed that the introduction of oxime, oxime ether, or oxime ester structural fragment at the C-4 position of xanthatin or the introduction of a chlorine atom at the C-3 position of xanthatin might be significantly beneficial to antifungal activity. In conclusion, the comprehensive investigation indicated that partial xanthatin-based derivatives from this study could be considered for further exploration as potential lead structures toward developing novel fungicidal candidates for crop protection.

The functional evolution of architecturally different plant geranyl diphosphate synthases from geranylgeranyl diphosphate synthase

Terpenoids constitute the largest class of plant primary and secondary metabolites with a broad range of biological and ecological functions. They are synthesized from isopentenyl diphosphate and dimethylallyl diphosphate, which in plastids are condensed by geranylgeranyl diphosphate synthases (GGPPSs) to produce GGPP (C20) for diterpene biosynthesis and by geranyl diphosphate synthases (GPPSs) to form GPP (C10) for monoterpene production. Depending on the plant species, unlike homomeric GGPPSs, GPPSs exist as homo- and heteromers, the latter of which contain catalytically inactive GGPPS-homologous small subunits (SSUs) that can interact with GGPPSs. By combining phylogenetic analysis with functional characterization of GGPPS homologs from a wide range of photosynthetic organisms, we investigated how different GPPS architectures have evolved within the GGPPS protein family. Our results reveal that GGPPS gene family expansion and functional divergence began early in nonvascular plants, and that independent parallel evolutionary processes gave rise to homomeric and heteromeric GPPSs. By site-directed mutagenesis and molecular dynamics simulations, we also discovered that Leu-Val/Val-Ala pairs of amino acid residues were pivotal in the functional divergence of homomeric GPPSs and GGPPSs. Overall, our study elucidated an evolutionary path for the formation of GPPSs with different architectures from GGPPSs and uncovered the molecular mechanisms involved in this differentiation.

Heteromerization of short-chain trans-prenyltransferase controls precursor allocation within a plastidial terpenoid network

Terpenes are the largest and most diverse class of plant specialized metabolites. Sesterterpenes (C25), which are derived from the plastid methylerythritol phosphate pathway, were recently characterized in plants. In Arabidopsis thaliana, four genes encoding geranylfarnesyl diphosphate synthase (GFPPS) (AtGFPPS1 to 4) are responsible for the production of GFPP, which is the common precursor for sesterterpene biosynthesis. However, the interplay between sesterterpenes and other known terpenes remain elusive. Here, we first provide genetic evidence to demonstrate that GFPPSs are responsible for sesterterpene production in Arabidopsis. Blockage of the sesterterpene pathway at the GFPPS step increased the production of geranylgeranyl diphosphate (GGPP)-derived terpenes. Interestingly, co-expression of sesterTPSs in GFPPS-OE (overexpression) plants rescued the phenotypic changes of GFPPS-OE plants by restoring the endogenous GGPP. We further demonstrated that, in addition to precursor (DMAPP/IPP) competition by GFPPS and GGPP synthase (GGPPS) in plastids, GFPPS directly decreased the activity of GGPPS through protein-protein interaction, ultimately leading to GGPP deficiency in planta. Our study provides a new regulatory mechanism of the plastidial terpenoid network in plant cells.

A new sesquiterpene synthase catalyzing the formation of (R)-β-bisabolene from medicinal plant Colquhounia coccinea var. mollis and its anti-adipogenic and antibacterial activities

The sesquiterpene β-bisabolene possessing R and S configurations is commonly found in plant essential oils with antimicrobial and antioxidant activities. Here, we report the cloning and functional characterization of a (R)-β-bisabolene synthase gene (CcTPS2) from a Lamiaceae medicinal plant Colquhounia coccinea var. mollis. The biochemical function of CcTPS2 catalyzing the cyclization of farnesyl diphosphate to form a single product (R)-β-bisabolene was characterized through an engineered Escherichia coli producing diverse polyprenyl diphosphate precursors and in vitro enzyme assay, indicating that CcTPS2 was a high-fidelity (R)-β-bisabolene synthase. The production of (R)-β-bisabolene in an engineered E. coli strain harboring the exogenous mevalonate pathway, farnesyl diphosphate synthase and CcTPS1 genes was 17 mg/L under shaking flask conditions. Ultimately, 120 mg of purified (R)-β-bisabolene was obtained from the engineered E. coli, and its structure was elucidated by detailed spectroscopic analyses (including 1D and 2D NMR, and specific rotation). Four chimeric enzymes were constructed through domain swapping, which altered the product outcome, indicating the region important for substrate and product specificity. In addition, (R)-β-bisabolene exhibited anti-adipogenic activity in the model organism Caenorhabditis elegans and antibacterial activity selectively against Gram-positive bacteria.

Labdane diterpenoids from the heartwood of Leucosceptrum canum that impact on root growth and seed germination of Arabidopsis thaliana

Eleven undescribed diterpenoids possessing labdane, 3,18-cyclo-labdane, 19 (4 → 3)-labdane and 12-nor-labdane skeletons, named leucolactones A-K, were isolated from the heartwood of a large woody Lamiaceae plant, Leucosceptrum canum. Their structures were determined by NMR, MS, and in the case of leucolactones A by single crystal X-ray diffraction analysis. Plausible biosynthetic pathway of leucolactones were proposed. Leucolactones showed significant inhibitory effects against seed germination and root elongation of Arabidopsis thaliana in the Petri dish bioassay. Among them, the diastereomeric leucolactones G and H were the most potent, with EC₅₀ values for root elongation of 6.53 ± 1.35 and 9.75 ± 1.25 μM, respectively. The preliminary structure-activity relationship of leucolactones was discussed. The increase of auxin reporter activity in A. thaliana DR5::GUS roots by leucolactone H was observed, indicating that leucolactones altered auxin accumulation and distribution. These findings suggested that leucolactones might be involved in regulation of plant growth and development through altering auxin accumulation and distribution, presumably contributing to the heartwood formation in L. canum.

Essential Oils and Their Compounds as Potential Anti-Influenza Agents

Essential oils (EOs) are chemical substances, mostly produced by aromatic plants in response to stress, that have a history of medicinal use for many diseases. In the last few decades, EOs have continued to gain more attention because of their proven therapeutic applications against the flu and other infectious diseases. Influenza (flu) is an infectious zoonotic disease that affects the lungs and their associated organs. It is a public health problem with a huge health burden, causing a seasonal outbreak every year. Occasionally, it comes as a disease pandemic with unprecedentedly high hospitalization and mortality. Currently, influenza is managed by vaccination and antiviral drugs such as Amantadine, Rimantadine, Oseltamivir, Peramivir, Zanamivir, and Baloxavir. However, the adverse side effects of these drugs, the rapid and unlimited variabilities of influenza viruses, and the emerging resistance of new virus strains to the currently used vaccines and drugs have necessitated the need to obtain more effective anti-influenza agents. In this review, essential oils are discussed in terms of their chemistry, ethnomedicinal values against flu-related illnesses, biological potential as anti-influenza agents, and mechanisms of action. In addition, the structure-activity relationships of lead anti-influenza EO compounds are also examined. This is all to identify leading agents that can be optimized as drug candidates for the management of influenza. Eucalyptol, germacrone, caryophyllene derivatives, eugenol, terpin-4-ol, bisabolene derivatives, and camphecene are among the promising EO compounds identified, based on their reported anti-influenza activities and plausible molecular actions, while nanotechnology may be a new strategy to achieve the efficient delivery of these therapeutically active EOs to the active virus site.

Functional Prediction of trans-Prenyltransferases Reveals the Distribution of GFPPSs in Species beyond the Brassicaceae Clade

Terpenoids are the most diverse class of plant primary and specialized metabolites, and trans-prenyltransferases (trans-PTs) are the first branch point to synthesize precursors of various chain lengths for further metabolism. Whereas the catalytic mechanism of the enzyme is known, there is no reliable method for precisely predicting the functions of trans-PTs. With the exponentially increasing number of available trans-PTs genes in public databases, an in silico functional prediction method for this gene family is urgently needed. Here, we present PTS-Pre, a web tool developed on the basis of the “three floors” model, which shows an overall 86% prediction accuracy for 141 experimentally determined trans-PTs. The method was further validated by in vitro enzyme assays for randomly selected trans-PTs. In addition, using this method, we identified nine new GFPPSs from different plants which are beyond the previously reported Brassicaceae clade, suggesting these genes may have occurred via convergent evolution and are more likely lineage-specific. The high accuracy of our blind prediction validated by enzymatic assays suggests that PTS-Pre provides a convenient and reliable method for genome-wide functional prediction of trans-PTs enzymes and will surely benefit the elucidation and metabolic engineering of terpenoid biosynthetic pathways.

Effects of 5-azaC on Iridoid Glycoside Accumulation and DNA Methylation in Rehmannia glutinosa

Iridoid glycoside is the important secondary metabolite and the main active component in Rehmannia glutinosa. However, the mechanisms that underlie the regulation of iridoid glycoside biosynthesis remain poorly understood in R. glutinosa. Herein, the analysis of RNA-seq data revealed that 3,394 unigenes related to the biosynthesis of secondary metabolites were identified in R. glutinosa. A total of 357 unigenes were involved in iridoid glycoside synthesis, in which the highly conservative genes, such as DXS, DXR, GPPS, G10H, and 10HGO, in organisms were overexpressed. The analysis of the above genes confirmed that the co-occurrence ratio of DXS, DXR, and GPPS was high in plants. Further, our results showed that under normal and 5-azacytidine (5-azaC) treatment, the expression levels of DXS, DXR, GPPS, G10H, and 10HGO were consistent with the iridoid glycoside accumulation in R. glutinosa, in which the application of the different concentrations of 5-azaC, especially 50 μM 5-azaC, could significantly upregulate the expression of five genes above and iridoid glycoside content. In addition, the changes in the spatiotemporal specificity of degree and levels of DNA methylation were observed in R. glutinosa, in which the hemi-methylation was the main reason for the change in DNA methylation levels. Similar to the changes in 5-methyl cytosine (5mC) content, the DNA demethylation could be induced by 5-azaC and responded in a dose-dependent manner to 15, 50, and 100 μM 5-azaC. Taken together, the expression of iridoid glycoside synthesis gene was upregulated by the demethylation in R. glutinosa, followed by triggering the iridoid glycoside accumulation. These findings not only identify the key genes of iridoid glycoside synthesis from R. glutinosa, but also expand our current knowledge of the function of methylation in iridoid glycoside accumulation.

Investigation of the Anti-Inflammatory Activity of Fusaproliferin Analogues Guided by Transcriptome Analysis

Background: Excessive inflammation results in severe tissue damage as well as serious acute or chronic disorders, and extensive research has focused on finding new anti-inflammatory hit compounds with safety and efficacy profiles from natural products. As promising therapeutic entities for the treatment of inflammation-related diseases, fusaproliferin and its analogs have attracted great interest. However, the underlying anti-inflammatory mechanism is still poorly understood and deserves to be further investigated.

Methods: For the estimation of the anti-inflammatory activity of fusaproliferin (1) and its analogs (2-4)in vitro and in vivo, lipopolysaccharide (LPS)-induced RAW264.7 macrophages and zebrafish embryos were employed. Then, transcriptome analysis was applied to guide subsequent western blot analysis of critical proteins in related signaling pathways. Surface plasmon resonance assays (SPR) combined with molecular docking analyses were finally applied to evaluate the affinity interactions between 1-4 and TLR4 and provide a possible interpretation of the downregulation of related signaling pathways.

Results: 1-4 significantly attenuated the production of inflammatory messengers, including nitric oxide (NO), reactive oxygen species (ROS), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and interleukin-1β (IL-1β), as well as nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2), in LPS-induced RAW264.7 macrophages. Transcriptome analyses based on RNA-seq indicated the ability of compound 1 to reverse LPS stimulation and the nuclear factor kappa-B (NF-κB) and mitogen-activated protein kinase (MAPKs) signaling pathways contribute to the anti-inflammatory process. Experimental verification at the protein level revealed that 1 can inhibit the activation of inhibitor of NF-κB kinase (IKK), degradation of inhibitor of NF-κB (IκB), and phosphorylation of NF-κB and reduce nuclear translocation of NF-κB. 1 also decreased the phosphorylation of MAPKs, including p38, extracellular regulated protein kinases (ERK), and c-Jun N-terminal kinase (JNK). SPR assays and molecular docking results indicated that 1-4 exhibited affinity for the TLR4 protein with KD values of 23.5–29.3 μM.

Conclusion: Fusaproliferin and its analogs can be hit compounds for the treatment of inflammation-associated diseases.

Transcriptomic and metabolomic analysis reveals the difference between large and small flower taxa of Herba Epimedii during flavonoid accumulation

Herba Epimedii, as a traditional Chinese herb, is divided into large and small flower taxa, and can invigorate sexuality and strengthen muscles and bones. Herba Epimedii is rich in flavonoids, which largely contribute to its medicinal benefits. In our previous studies, we have found that the flavonoids content was much more in small than large flower taxa. To further identify molecular mechanisms of flavonoids metabolism in Herba Epimedii, combined metabolome and transcriptomic analyses were performed to profile leaves and flowers. Association analysis revealed that the expression of genes involved in flavonoid biosynthesis showed significant differences between small and large flower taxa. Eleven flavonols significantly increased in small compared to large flower taxa. Moreover, genes encoding O-methyltransferase played crucial roles in flavonoids metabolism by an integrated analysis. Taken together, these data highlight the breeding tendency of small flower taxa to improve the quality of Herba Epimedii.

A Monocarbocyclic Sesterterpenoid Biosynthetic Precursor of Leucosceptroids from Leucosceptrum canum and Its Metabolic Isomerization by a Specialist Insect

Pre-leucosceptroid (1), a rare monocarbocyclic sesterterpenoid featuring a cyclopentane ring with a terminal furan moiety, was isolated from the leaves of Leucosceptrum canum. Discovery of 1 suggested a two-step cyclization...

A Cryptic Plant Terpene Cyclase Producing Unconventional 18- and 14-Membered Macrocyclic C25 and C20 Terpenoids with Immunosuppressive Activity

A versatile terpene synthase (LcTPS2) producing unconventional macrocyclic terpenoids was characterized from Leucosceptrum canum. Engineered Escherichia coli and Nicotiana benthamiana expressing LcTPS2 produced six 18-/14-membered sesterterpenoids including five new ones and two 14-membered diterpenoids. These products represent the first macrocyclic sesterterpenoids from plants and the largest sesterterpenoid ring system identified to date. Two variants F516A and F516G producing approximately 3.3- and 2.5-fold, respectively, more sesterterpenoids than the wild-type enzyme were engineered. Both 18- and 14-membered ring sesterterpenoids displayed significant inhibitory activity on the IL-2 and IFN-γ production of T cells probably via inhibition of the MAPK pathway. The findings will contribute to the development of efficient biocatalysts to create bioactive macrocyclic sesterterpenoids, and also herald a new potential in the well-trodden territory of plant terpenoid biosynthesis.

An extremely promiscuous terpenoid synthase from the Lamiaceae plant Colquhounia coccinea var. mollis catalyzes the formation of sester-/di-/sesqui-/mono-terpenoids

Terpenoids are the largest class of natural products with complex structures and extensive bioactivities; their scaffolds are generated by diverse terpenoid synthases (TPSs) from a limited number of isoprenoid diphosphate precursors. Promiscuous TPSs play important roles in the evolution of terpenoid chemodiversity, but they remain largely unappreciated. Here, an extremely promiscuous terpenoid synthase (CcTPS1) of the TPS-b subfamily was cloned and functionally characterized from a leaf-specific transcriptome of the Lamiaceae plant Colquhounia coccinea var. mollis. CcTPS1 is the first sester-/di-/sesqui-/mono-TPS identified from the plant kingdom, accepting C25/C20/C15/C10 diphosphate substrates to generate a panel of sester-/di-/sesqui-/mono-terpenoids. Engineered Escherichia coli expressing CcTPS1 produced three previously unreported terpenoids (two sesterterpenoids and a diterpenoid) with rare cyclohexane-containing skeletons, along with four sesquiterpenoids and one monoterpenoid. Their structures were elucidated by extensive nuclear magnetic resonance spectroscopy. Nicotiana benthamiana transiently expressing CcTPS1 also produced the diterpenoid and sesquiterpenoids, demonstrating the enzyme's promiscuity in planta. Its highly leaf-specific expression pattern combined with detectable terpenoid products in leaves of C. coccinea var. mollis and N. benthamiana expressing CcTPS1 suggested that CcTPS1 was mainly responsible for diterpenoid and sesquiterpenoid biosynthesis in plants. CcTPS1 expression and the terpenoid products could be induced by methyl jasmonate, suggesting their possible role in plant-environment interaction. CcTPS1 was localized to the cytosol and may differ from mono-TPSs in subcellular compartmentalization and substrate tolerance. These findings will greatly aid our understanding of plant TPS evolution and terpenoid chemodiversity; they also highlight the enormous potential of transcriptome mining and heterologous expression for the exploration of unique enzymes and natural products hidden in plants.

Occurrence and biosynthesis of plant sesterterpenes (C25), a new addition to terpene diversity

Terpenes, the largest group of plant-specialized metabolites, have received considerable attention for their highly diverse biological activities. Monoterpenes (C10), sesquiterpenes (C15), diterpenes (C20), and triterpenes (C30) have been extensively investigated at both the biochemical and molecular levels over the past two decades. Sesterterpenes (C25), an understudied terpenoid group, were recently described by plant scientists at the molecular level. This review summarizes the plant species that produce sesterterpenes and describes recent developments in the field of sesterterpene biosynthesis, placing a special focus on the catalytic mechanism and evolution of geranylfarnesyl diphosphate synthase and sesterterpene synthase. Finally, we propose several questions to be addressed in future studies, which may help to elucidate sesterterpene metabolism in plants.

Synthetic Studies toward Leucosceptroid Family of Natural Products

Leucosceptroids are sesterterpenoids with potent antifeedant and antifungal activities. In this paper, efforts on two synthetic strategies toward stereoselective total synthesis of the leucosceptroid family of natural products are reported. Intramolecular addition cyclization strategy could lead to a stereochemically mismatched core structure, while intermolecular addition/ring-closing metathesis cyclization strategy successfully furnished an advanced common intermediate bearing eight contiguous stereogenic centers, including three tetra-substituted ones, which fully matches all the stereochemistry on the tricyclic framework in leucosceptroid H. Late-stage transformation of this intermediate to leucosceptroid H encountered difficulty in oxidizing the secondary hydroxyl group to a carbonyl group in the target. Instead of the desired oxidation, an interesting tricyclic spiral product originating from a C-C bond cleavage was observed.

An update on the function and regulation of methylerythritol phosphate and mevalonate pathways and their evolutionary dynamics

Isoprenoids are among the largest and most chemically diverse classes of organic compounds in nature and are involved in the processes of photosynthesis, respiration, growth, development, and plant responses to stress. The basic building block units for isoprenoid synthesis-isopentenyl diphosphate and its isomer dimethylallyl diphosphate-are generated by the mevalonate (MVA) and methylerythritol phosphate (MEP) pathways. Here, we summarize recent advances on the roles of the MEP and MVA pathways in plant growth, development and stress responses, and attempt to define the underlying gene networks that orchestrate the MEP and MVA pathways in response to developmental or environmental cues. Through phylogenomic analysis, we also provide a new perspective on the evolution of the plant isoprenoid pathway. We conclude that the presence of the MVA pathway in plants may be associated with the transition from aquatic to subaerial and terrestrial environments, as lineages for its core components are absent in green algae. The emergence of the MVA pathway has acted as a key evolutionary event in plants that facilitated land colonization and subsequent embryo development, as well as adaptation to new and varied environments.

Immunosuppressive gentianellane-type sesterterpenoids from the traditional Uighur medicine Gentianella turkestanorum

Whole plants of Gentianella turkestanorum are commonly used as a traditional Uighur medicine. A phytochemical investigation led to the isolation of eight undescribed gentianellane-type sesterterpenoids (18-epi-nitidasin, gentianelloids D-F, and 18-epi-gentianelloids C-F), one undescribed 11,12-seco-gentianellane (18-epi-alborosin), and three known analogs (nitidasin, gentianelloid C and alborosin) among which gentianelloid C was found for the first time from a natural source. The structures of these compounds were elucidated by extensive spectroscopic analyses (including 1D and 2D NMR, HRMS, IR, and specific rotation) and in the case of 18-epi-gentianelloid C by the single-crystal X-ray diffraction analysis. A putative biosynthetic route for these sesterterpenoids was proposed. The immunosuppressive activity of the isolated compounds was also evaluated by their ability to inhibit the proliferation of T cells and T cell cytokine IFN-γ production. Nitidasin suppressed IFN-γ production with an IC₅₀ value of 16.50 μM, while gentianelloid F and alborosin inhibited the proliferation of and IFN-γ production in T cells with IC₅₀ values of 12.40-14.66 μM.

The untapped potential of plant sesterterpenoids: chemistry, biological activities and biosynthesis

Covering: 1969 up to 2021Sesterterpenoids, biosynthetically derived from the precursor, namely geranylfarnesyl diphosphate (GFDP) are amongst the rarest of all isoprenoids with approximately 1300 compounds known. Most sesterterpenoids originate from marine organisms (especially sponges), while only about 15% of these compounds are isolated from several families of plants such as Lamiaceae, Gentianaceae, and Nartheciaceae. Many plant sesterterpenoids possess highly oxygenated and complex cyclic skeletons and exhibit remarkable biological activities involving cytotoxic, anti-inflammatory, antimicrobial, and antifeedant properties. Thus, due to their intrinsic chemical complexity and intriguing biological profiles, plant sesterterpenoids have attracted continuing interest from both chemists and biologists. However, the biosynthesis and distribution of sesterterpenoids in the plant kingdom still remain elusive, although substantial progress has been achieved in recent years. This review provides an overall coverage of sesterterpenoids originating from plant sources, followed by a classification of their chemical skeletons, which summarizes the distribution, chemistry, biological activities, biosynthesis and evolution of plant sesterterpenoids, aiming at strengthening the research efforts toward the untapped great potential of these unique natural product resources.

Evodiamine alleviates lipopolysaccharide-induced pulmonary inflammation and fibrosis by activating apelin pathway

Inflammation can cause a series of inflammatory lung disease, which seriously endangers human health. Pulmonary fibrosis is a kind of inflammatory disease with end-stage lung pathological changes. It has complicated and unknown pathogenesis and is still lack of effective therapeutic drugs. LPS-induced inflammation is a common feature of many infectious inflammations such as pneumonia, bacteremia, glomerulonephritis, etc. Evodiamine, one of the main components of Evodia rutaecarpa, is an alkaloid with excellent antiinflammatory effects. In this study, we evaluated the protective capacities of evodiamine on LPS-induced inflammatory damages in vitro and in vivo. MTT method, flow cytometry, immunofluorescence, and other methods were used for in vitro study to determine the protective capacities of evodiamine. The results suggest that evodiamine can protect murine macrophages from the LPS-nigericin-induced damages by (a) inhibiting cellular apoptosis, (b) inhibiting inflammatory cytokines releasing, and (c) activating the apelin pathway. We also used the exogenous apelin-13 peptide co-cultured with LPS-nigericin in RAW264.7 cells and found that apelin-13 contributes to protecting the effects of evodiamine. In vivo, the ELISA method and immunohistochemistry were used to examine inflammatory cytokines, apelin, and histological changes. BALB/c mice were exposed to LPS and subsequent administration of evodiamine （p.o.）for some time, the results of the alveolar lavage fluid and the tissue slices showed that evodiamine treatment alleviated the pulmonary inflammation and fibrosis, stimulated apelin expression and inhibited the inflammatory cytokines. These results provide a basis for the protective effect and mechanism of evodiamine in LPS-induced inflammation and suggest that it might be potential therapeutics in human pulmonary infections.

Sesterterpenoids: chemistry, biology, and biosynthesis

Covering: July 2012 to December 2019Over the last seven years, expanding research efforts focused on sesterterpenoids has led to the isolation, identification, and characterization of numerous structurally novel and biologically active sesterterpenoids. These newly reported sesterterpenoids provide diverse structures that often incorporate unprecedented ring systems and new carbon skeletons, as well as unusual functional group arrays. Biological activities of potential biomedical importance including suppression of cancer cell growth, inhibition of enzymatic activity, and modulation of receptor signaling, as well as ecologically important functions such as antimicrobial effects and deterrence of herbivorous insects have been associated with a variety of sesterterpenoids. There has also been a rapid growth in our knowledge of the genomics, enzymology, and specific pathways associated with sesterterpene biosynthesis. This has opened up new opportunities for future sesterterpene discovery and diversification through the expression of new cryptic metabolites and the engineered manipulation of associated biosynthetic machinery and processes. In this paper we reviewed 498 new sesterterpenoids, including their structures, source organisms, country of origin, relevant bioactivities, and biosynthesis.

Molecular Basis for Sesterterpene Diversity Produced by Plant Terpene Synthases

Class I terpene synthase (TPS) generates bioactive terpenoids with diverse backbones. Sesterterpene synthase (sester-TPS, C25), a branch of class I TPSs, was recently identified in Brassicaceae. However, the catalytic mechanisms of sester-TPSs are not fully understood. Here, we first identified three nonclustered functional sester-TPSs (AtTPS06, AtTPS22, and AtTPS29) in Arabidopsis thaliana. AtTPS06 utilizes a type-B cyclization mechanism, whereas most other sester-TPSs produce various sesterterpene backbones via a type-A cyclization mechanism. We then determined the crystal structure of the AtTPS18-FSPP complex to explore the cyclization mechanism of plant sester-TPSs. We used structural comparisons and site-directed mutagenesis to further elucidate the mechanism: (1) mainly due to the outward shift of helix G, plant sester-TPSs have a larger catalytic pocket than do mono-, sesqui-, and di-TPSs to accommodate GFPP; (2) type-A sester-TPSs have more aromatic residues (five or six) in their catalytic pocket than classic TPSs (two or three), which also determines whether the type-A or type-B cyclization mechanism is active; and (3) the other residues responsible for product fidelity are determined by interconversion of AtTPS18 and its close homologs. Altogether, this study improves our understanding of the catalytic mechanism of plant sester-TPS, which ultimately enables the rational engineering of sesterterpenoids for future applications.

Gymnosperm glandular trichomes: expanded dimensions of the conifer terpenoid defense system

Glandular trichomes (GTs) are defensive structures that produce and accumulate specialized metabolites and protect plants against herbivores, pathogens, and abiotic stress. GTs have been extensively studied in angiosperms for their roles in defense and biosynthesis of high-value metabolites. In contrast, trichomes of gymnosperms have been described in fossilized samples, but have not been studied in living plants. Here, we describe the characterization of GTs on young stems of a hybrid white spruce. Metabolite and histological analysis of spruce GTs support a glandular function with accumulation of a diverse array of mono-, sesqui- and diterpenes including diterpene methylesters. Methylated diterpenes have previously been associated with insect resistance in white spruce. Headspeace analysis of spruce GTs showed a profile of volatiles dominated by monoterpenes and a highly diverse array of sesquiterpenes. Spruce GTs appear early during shoot growth, prior to the development of a lignified bark and prior to accumulation of terpenes in needles. Spruce GTs may provide an early, terpene-based chemical defense system at a developmental stage when young shoots are particularly vulnerable to foliage and shoot feeding insects, and before the resin duct system characteristic of conifers has fully developed.

A plastid-localized bona fide geranylgeranyl diphosphate synthase plays a necessary role in monoterpene indole alkaloid biosynthesis in Catharanthus roseus

In plants, geranylgeranyl diphosphate (GGPP, C₂₀ ) synthesized by GGPP synthase (GGPPS) serves as precursor for vital metabolic branches including specialized metabolites. Here, we report the characterization of a GGPPS (CrGGPPS2) from the Madagascar periwinkle (Catharanthus roseus) and demonstrate its role in monoterpene (C₁₀ )-indole alkaloids (MIA) biosynthesis. The expression of CrGGPPS2 was not induced in response to methyl jasmonate (MeJA), and was similar to the gene encoding type-I protein geranylgeranyltransferase_β subunit (CrPGGT-I_β), which modulates MIA formation in C. roseus cell cultures. Recombinant CrGGPPS2 exhibited a bona fide GGPPS activity by catalyzing the formation of GGPP as the sole product. Co-localization of fluorescent protein fusions clearly showed CrGGPPS2 was targeted to plastids. Downregulation of CrGGPPS2 by virus-induced gene silencing (VIGS) significantly decreased the expression of transcription factors and pathway genes related to MIA biosynthesis, resulting in reduced MIA. Chemical complementation of CrGGPPS2-vigs leaves with geranylgeraniol (GGol, alcoholic form of GGPP) restored the negative effects of CrGGPPS2 silencing on MIA biosynthesis. In contrast to VIGS, transient and stable overexpression of CrGGPPS2 enhanced the MIA biosynthesis. Interestingly, VIGS and transgenic-overexpression of CrGGPPS2 had no effect on the main GGPP-derived metabolites, cholorophylls and carotenoids in C. roseus leaves. Moreover, silencing of CrPGGT-I_β, similar to CrGGPPS2-vigs, negatively affected the genes related to MIA biosynthesis resulting in reduced MIA. Overall, this study demonstrated that plastidial CrGGPPS2 plays an indirect but necessary role in MIA biosynthesis. We propose that CrGGPPS2 might be involved in providing GGPP for modifying proteins of the signaling pathway involved in MIA biosynthesis.

Stereoselective Construction of the Highly Congested Tricyclic Core Structure in Leucosceptroid H

Leucosceptroids are sesterterpenoids with potent antifeedant and antifungal activities. An efficient stereoselective construction of the highly congested [5,6,5] tricyclic framework of leucosceptroid H is presented. This framework bearing eight contiguous stereogenic centers, including three tetrasubstituted ones, could serve as a common intermediate for the collective total synthesis of the leucosceptroid family of natural products.

More is better: the diversity of terpene metabolism in plants

All plants synthesize a diverse array of terpenoid metabolites. Some are common to all, but many are synthesized only in specific taxa and presumably evolved as adaptations to specific ecological conditions. While the basic terpenoid biosynthetic pathways are common in all plants, recent discoveries have revealed many variations in the way plants synthesized specific terpenes. A major theme is the much greater number of substrates that can be used by enzymes belonging to the terpene synthase (TPS) family. Other recent discoveries include non-TPS enzymes that catalyze the formation of terpenes, and novel transport mechanisms.

Leucosceptroid B from glandular trichomes of Leucosceptrum canum reduces fat accumulation in Caenorhabditis elegans through suppressing unsaturated fatty acid biosynthesis

Obesity that is highly associated with numerous metabolic diseases has become a global health issue nowdays. Plant sesterterpenoids are an important group of natural products with great potential; thus, their bioactivities deserve extensive exploration. RNA-seq analysis indicated that leucosceptroid B, a sesterterpenoid previously discovered from the glandular trichomes of Leucosceptrum canum, significantly regulated the expression of 10 genes involved in lipid metabolism in Caenorhabditis elegans. Furthermore, leucosceptroid B was found to reduce fat storage, and downregulate the expression of two stearoyl-CoA desaturase (SCD) genes fat-6 and fat-7, and a fatty acid elongase gene elo-2 in wild-type C. elegans. In addition, leucosceptroid B significantly decreased fat accumulation in both fat-6 and fat-7 mutant worms but did not affect the fat storage of fat-6; fat-7 double mutant. These findings indicated that leucosceptroid B reduced fat storage depending on the downregulated expression of fat-6, fat-7 and elo-2 and thereby inhibiting the biosynthesis of the corresponding unsaturated fatty acid. These findings provide new insights into the development and utilization of plant sesterterpenoids as potential antilipemic agents.

Production of the Inaccessible Sesquiterpene (-)-5-Epieremophilene by Metabolically Engineered Escherichia coli

(-)-5-Epieremophilene, an epimer of the versatile sesquiterpene (+)-valencene, is an inaccessible natural product catalyzed by three sesquiterpene synthases (SmSTPSs1-3) of the Chinese medicinal herb Salvia miltiorrhiza, and its biological activity remains less explored. In this study, three metabolically engineered Escherichia coli strains were constructed for (-)-5-epieremophilene production with yields of 42.4-76.0 mg/L in shake-flask culture. Introducing an additional copy of farnesyl diphosphate synthase (FDPS) gene through fusion expression of SmSTPS1-FDPS or dividing the FDP synthetic pathway into two modules resulted in significantly improved production, and ultimately 250 mg of (-)-5-epieremophilene were achieved. Biological assay indicated that (-)-5-epieremophilene showed significant antifeedant activity against Helicoverpa armigera (EC₅₀ =1.25 μg/cm² ), a common pest of S. miltiorrhiza, implying its potential defensive role in the plant. The results provided an ideal material supply for studying other potential biological activities of (-)-5-epieremophilene, and also a strategy for manipulating terpene production in engineered E. coli using synthetic biology.

Advances in biosynthesis, regulation, and metabolic engineering of plant specialized terpenoids

Plant specialized terpenoids are natural products that have no obvious role in growth and development, but play many important functional roles to improve the plant's overall fitness. Besides, plant specialized terpenoids have immense value to humans due to their applications in fragrance, flavor, cosmetic, and biofuel industries. Understanding the fundamental aspects involved in the biosynthesis and regulation of these high-value molecules in plants not only paves the path to enhance plant traits, but also facilitates homologous or heterologous engineering for overproduction of target molecules of importance. Recent developments in functional genomics and high-throughput analytical techniques have led to unraveling of several novel aspects involved in the biosynthesis and regulation of plant specialized terpenoids. The knowledge thus derived has been successfully utilized to produce target specialized terpenoids of plant origin in homologous or heterologous host systems by metabolic engineering and synthetic biology approaches. Here, we provide an overview and highlights on advances related to the biosynthetic steps, regulation, and metabolic engineering of plant specialized terpenoids.

Nerylneryl diphosphate is the precursor of serrulatane, viscidane and cembrane-type diterpenoids in Eremophila species

BACKGROUND

Eremophila R.Br. (Scrophulariaceae) is a diverse genus of plants with species distributed across semi-arid and arid Australia. It is an ecologically important genus that also holds cultural significance for many Indigenous Australians who traditionally use several species as sources of medicines. Structurally unusual diterpenoids, particularly serrulatane and viscidane-types, feature prominently in the chemical profile of many species and recent studies indicate that these compounds are responsible for much of the reported bioactivity. We have investigated the biosynthesis of diterpenoids in three species: Eremophila lucida, Eremophila drummondii and Eremophila denticulata subsp. trisulcata.

RESULTS

In all studied species diterpenoids were localised to the leaf surface and associated with the occurrence of glandular trichomes. Trichome-enriched transcriptome databases were generated and mined for candidate terpene synthases (TPS). Four TPSs with diterpene biosynthesis activity were identified: ElTPS31 and ElTPS3 from E. lucida were found to produce (3Z,7Z,11Z)-cembratrien-15-ol and 5-hydroxyviscidane, respectively, and EdTPS22 and EdtTPS4, from E. drummondii and E. denticulata subsp. trisulcata, respectively, were found to produce 8,9-dihydroserrulat-14-ene which readily aromatized to serrulat-14-ene. In all cases, the identified TPSs used the cisoid substrate, nerylneryl diphosphate (NNPP), to form the observed products. Subsequently, cis-prenyl transferases (CPTs) capable of making NNPP were identified in each species.

CONCLUSIONS

We have elucidated two biosynthetic steps towards three of the major diterpene backbones found in this genus. Serrulatane and viscidane-type diterpenoids are promising candidates for new drug leads. The identification of an enzymatic route to their synthesis opens up the possibility of biotechnological production, making accessible a ready source of scaffolds for further modification and bioactivity testing.

Combined Metabolome and Transcriptome Analyses Reveal the Effects of Mycorrhizal Fungus Ceratobasidium sp. AR2 on the Flavonoid Accumulation in Anoectochilus roxburghii during Different Growth Stages

Anoectochilus roxburghii is a traditional Chinese herb with high medicinal value, with main bioactive constituents which are flavonoids. It commonly associates with mycorrhizal fungi for its growth and development. Moreover, mycorrhizal fungi can induce changes in the internal metabolism of host plants. However, its role in the flavonoid accumulation in A. roxburghii at different growth stages is not well studied. In this study, combined metabolome and transcriptome analyses were performed to investigate the metabolic and transcriptional profiling in mycorrhizal A. roxburghii (M) and non-mycorrhizal A. roxburghii (NM) growth for six months. An association analysis revealed that flavonoid biosynthetic pathway presented significant differences between the M and NM. Additionally, the structural genes related to flavonoid synthesis and different flavonoid metabolites in both groups over a period of six months were validated using quantitative real-time polymerase chain reaction (qRT-PCR) and high-performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS). The results showed that Ceratobasidium sp. AR2 could increase the accumulation of five flavonol-glycosides (i.e., narcissin, rutin, isorhamnetin-3-O-beta-d-glucoside, quercetin-7-O-glucoside, and kaempferol-3-O-glucoside), two flavonols (i.e., quercetin and isorhamnetin), and two flavones (i.e., nobiletin and tangeretin) to some degrees. The qRT-PCR showed that the flavonoid biosynthetic genes (PAL, 4CL, CHS, GT, and RT) were significantly differentially expressed between the M and NM. Overall, our findings indicate that AR2 induces flavonoid metabolism in A. roxburghii during different growth stages, especially in the third month. This shows great potential of Ceratobasidium sp. AR2 for the quality improvement of A. roxburghii.

Detoxification of Plant Aromatic Abietanoids via Cleavage of the Benzene Ring into 11,12-Seco-diterpene Polyenes by a Specialist Insect of Leucosceptrum canum

Leaves of Leucosceptrum canum harbor abundant toxic aromatic abietanoids, and they are rarely attacked by insect herbivores, except for the larvae of Nacna malachitis. The excrements of the insect that fed on L. canum leaves were investigated, leading to the isolation and identification of two unprecedented 11,12-seco-abietane diterpene polyenes: nacnabietanins A (1) and B (2). This discovery heralds a unique detoxification mechanism of plant aromatic abietanoids by insects through enzymatic cleavage of stable benzene rings into more easily degraded polyenes.

Characterization of a sesquiterpene cyclase from the glandular trichomes of Leucosceptrum canum for sole production of cedrol in Escherichia coli and Nicotiana benthamiana

Cedrol is an extremely versatile sesquiterpene alcohol that was approved by the Food and Drug Administration of the United States as a flavoring agent or adjuvant and has been commonly used as a flavoring ingredient in cosmetics, foods and medicine. Furthermore, cedrol possesses a wide range of pharmacological properties including sedative, anti-inflammatory and cytotoxic activities. Commercial production of cedrol relies on fractional distillation of cedar wood oils, followed by recrystallization, and little has been reported about its biosynthesis and aspects of synthetic biology. Here, we report the cloning and functional characterization of a cedrol synthase gene (Lc-CedS) from the transcriptome of the glandular trichomes of a woody Lamiaceae plant Leucosceptrum canum. The recombinant Lc-CedS protein catalyzed the in vitro conversion of farnesyl diphosphate into the single product cedrol, suggesting that Lc-CedS is a high-fidelity terpene synthase. Co-expression of Lc-CedS, a farnesyl diphosphate synthase gene and seven genes of the mevalonate (MVA) pathway responsible for converting acetyl-CoA into farnesyl diphosphate in Escherichia coli afforded 363 μg/L cedrol as the sole product under shaking flask conditions. Transient expression of Lc-CedS in Nicotiana benthamiana also resulted in a single product cedrol with a production level of 3.6 μg/g fresh weight. The sole production of cedrol by introducing of Lc-CedS in engineered E. coli and N. benthamiana suggests now alternative production systems using synthetic biology approaches that would better address sufficient supply of cedrol.

Non-volatile natural products in plant glandular trichomes: chemistry, biological activities and biosynthesis

The investigation methods, chemistry, bioactivities, and biosynthesis of non-volatile natural products involving 489 compounds in plant glandular trichomes are reviewed.

Diversified abietane family diterpenoids from the leaves of Leucosceptrum canum and their cytotoxic activity

Twenty-four diterpenoids of abietane family, including thirteen undescribed compounds and eleven known ones, were isolated from the leaves of Leucosceptrum canum. Their structures were elucidated by comprehensive spectroscopic analyses (including 1D and 2D-NMR and HRMS), and in the case of 15-hydroxy-abieta-8,11,13-trien-3-one by single-crystal X-ray diffraction. Their frameworks are highly diversified, involving normal abietane, 9,10-epoxy-9,10-seco-abietane, 18(4 → 3)-abeo-abietane, 3,4-seco-18(4 → 3)-abeo-abietane, and 16-nor-abietane. Selected compounds were evaluated for their cytotoxic activity against three human tumor cell lines, NCI-H1975, HepG2 and MCF-7. Among them, 3β-hydroxy-abieta-8,13-diene, 3β-hydroxy-abieta-8,11,13,15-tetraene, and 3β-hydroxy-9,10-epoxy-9,10-seco-abieta-8,11,13-triene exhibited moderate cytotoxicity against all three cell lines with IC₅₀ values ranging from 8.11 to 50.73 μM, while 3α-hydroxy-abieta-8,11,13,15-tetraene, 3β-hydroxy-abieta-8,11,13,15-tetraen-7-one, and 15-hydroxy-18(4 → 3)-abeo-abieta-3,8,11,13-tetraene were selectively active with IC₅₀ values ranging from 28.80 to 71.29 μM.

My Way: Noncanonical Biosynthesis Pathways for Plant Volatiles

Plant volatiles are crucial for various interactions with other organisms and their surrounding environment. A large number of these volatiles belong to the terpenoid and benzenoid/phenylpropanoid classes, which have long been considered to be exclusively synthesized from a few canonical pathways. However, several alternative pathways producing these plant volatiles have been discovered recently. This review summarizes the current knowledge about new pathways for these two major groups of plant volatiles, which open new perspectives for applications in metabolic engineering.