Multi-Substrate Terpene Synthases: Their Occurrence and Physiological Significance

Integrating GC-MS and comparative transcriptome analysis reveals that TsERF66 promotes the biosynthesis of caryophyllene in Toona sinensis tender leaves

Introduction

The strong aromatic characteristics of the tender leaves of Toona sinensis determine their quality and economic value.

Methods and results

Here, GC-MS analysis revealed that caryophyllene is a key volatile compound in the tender leaves of two different T. sinensis varieties, however, the transcriptional mechanisms controlling its gene expression are unknown. Comparative transcriptome analysis revealed significant enrichment of terpenoid synthesis pathway genes, suggesting that the regulation of terpenoid synthesis-related gene expression is an important factor leading to differences in aroma between the two varieties. Further analysis of expression levels and genetic evolution revealed that TsTPS18 is a caryophyllene synthase, which was confirmed by transient overexpression in T. sinensis and Nicotiana benthamiana leaves. Furthermore, we screened an AP2/ERF transcriptional factor ERF-IX member, TsERF66, for the potential regulation of caryophyllene synthesis. The TsERF66 had a similar expression trend to that of TsTPS18 and was highly expressed in high-aroma varieties and tender leaves. Exogenous spraying of MeJA also induced the expression of TsERF66 and TsTPS18 and promoted the biosynthesis of caryophyllene. Transient overexpression of TsERF66 in T. sinensis significantly promoted TsTPS18 expression and caryophyllene biosynthesis.

Discussion

Our results showed that TsERF66 promoted the expression of TsTPS18 and the biosynthesis of caryophyllene in T. sinensis leaves, providing a strategy for improving the aroma of tender leaves.

Enhancing structural diversity of terpenoids by multisubstrate terpene synthases

Terpenoids are one of the largest class of natural products with diverse structures and activities. This enormous diversity is embedded in enzymes called terpene synthases (TSs), which generate diverse terpene skeletons via sophisticated cyclization cascades. In addition to the many highly selective TSs, there are many promiscuous TSs that accept multiple prenyl substrates, or even noncanonical ones, with 6, 7, 8, 11, and 16 carbon atoms, synthesized via chemical approaches, C-methyltransferases, or engineered lepidopteran mevalonate pathways. The substrate promiscuity of TSs not only expands the structural diversity of terpenes but also highlights their potential for the discovery of novel terpenoids via combinatorial biosynthesis. In this review, we focus on the current knowledge on multisubstrate terpene synthases (MSTSs) and highlight their potential applications.

Chemical diversity in angiosperms - monoterpene synthases control complex reactions that provide the precursors for ecologically and commercially important monoterpenoids

Monoterpene synthases (MTSs) catalyze the first committed step in the biosynthesis of monoterpenoids, a class of specialized metabolites with particularly high chemical diversity in angiosperms. In addition to accomplishing a rate enhancement, these enzymes manage the formation and turnover of highly reactive carbocation intermediates formed from a prenyl diphosphate substrate. At each step along the reaction path, a cationic intermediate can be subject to cyclization, migration of a proton, hydride, or alkyl group, or quenching to terminate the sequence. However, enzymatic control of ligand folding, stabilization of specific intermediates, and defined quenching chemistry can maintain the specificity for forming a signature product. This review article will discuss our current understanding of how angiosperm MTSs control the reaction environment. Such knowledge allows inferences about the origin and regulation of chemical diversity, which is pertinent for appreciating the role of monoterpenoids in plant ecology but also for aiding commercial efforts that harness the accumulation of these specialized metabolites for the food, cosmetic, and pharmaceutical industries.

Revelation of enzyme/transporter-mediated metabolic regulatory model for high-quality terpene accumulation in developing fruits of Lindera glauca

Lindera glauca with rich resource and fruit terpene has emerged as potential material for utilization in China, but different germplasms show a variation for essential oil content and volatile profiling. This work aimed to determine key regulators (enzymes or transporters) and unravel mechanism of governing high production of essential oil of L. glauca fruit (EO-LGF). Temporal analysis of fruit growth and EO-LGF accumulation (yield, volatile compounds and contents) during development revealed a notable change in the contents of EO-LGF and its 45 compounds in developing fruits, and the major groups were monoterpene and sesquiterpene, showing good antioxidant and antimicrobial activities. To highlight molecular mechanism that govern such difference in terpene content and compound in developing fruits, Genome-wide assay was used to annotate 104 genes for terpene-synthesis pathway based on recent transcriptome data, and the comparative associations of terpene accumulative amount with gene transcriptional level were conducted on developing fruits to identify some crucial determinants (enzymes and transporters) with metabolic regulation model for high-quality terpene accumulation, involving in carbon allocation (sucrose cleavage, glycolysis and OPP pathway), metabolite transport, isoprene precursor production, C5-unit formation (MEP and MVA pathways), and mono-/sesqui-terpene synthesis. Our findings may present strategy for engineering terpene accumulation for utilization.

The microbial biosynthesis of noncanonical terpenoids

Terpenoids are a class of structurally complex, naturally occurring compounds found predominantly in plant, animal, and microorganism secondary metabolites. Classical terpenoids typically have carbon atoms in multiples of five and follow well-defined carbon skeletons, whereas noncanonical terpenoids deviate from these patterns. These noncanonical terpenoids often result from the methyltransferase-catalyzed methylation modification of substrate units, leading to irregular carbon skeletons. In this comprehensive review, various activities and applications of these noncanonical terpenes have been summarized. Importantly, the review delves into the biosynthetic pathways of noncanonical terpenes, including those with C6, C7, C11, C12, and C16 carbon skeletons, in bacteria and fungi host. It also covers noncanonical triterpenes synthesized from non-squalene substrates and nortriterpenes in Ganoderma lucidum, providing detailed examples to elucidate the intricate biosynthetic processes involved. Finally, the review outlines the potential future applications of noncanonical terpenoids. In conclusion, the insights gathered from this review provide a reference for understanding the biosynthesis of these noncanonical terpenes and pave the way for the discovery of additional unique and novel noncanonical terpenes. KEY POINTS: •The activities and applications of noncanonical terpenoids are introduced. •The noncanonical terpenoids with irregular carbon skeletons are presented. •The microbial biosynthesis of noncanonical terpenoids is summarized.

Discovery of new pyridine-quinoline hybrids as competitive and non-competitive PIM-1 kinase inhibitors with apoptosis induction and caspase 3/7 activation capabilities

New quinoline-pyridine hybrids were designed and synthesised as PIM-1/2 kinase inhibitors. Compounds 5b, 5c, 6e, 13a, 13c, and 14a showed in-vitro low cytotoxicity against normal human lung fibroblast Wi-38 cell line and potent in-vitro anticancer activity against myeloid leukaemia (NFS-60), liver (HepG-2), prostate (PC-3), and colon (Caco-2) cancer cell lines. In addition, 6e, 13a, and 13c significantly induced apoptosis with percentage more than 66%. Moreover, 6e, 13a, and 13c significantly induced caspase 3/7 activation in HepG-2 cell line. Furthermore, 5c, 6e, and 14a showed potent in-vitro PIM-1 kinase inhibitory activity. While, 5b showed potent in-vitro PIM-2 kinase inhibitory activity. Kinetic studies using Lineweaver-Burk double-reciprocal plot indicated that 5b, 5c, 6e, and 14a behaved as competitive inhibitors while 13a behaved as both competitive and non-competitive inhibitor of PIM-1 kinase enzyme. Molecular docking studies indicated that, in-silico affinity came in coherence with the observed in-vitro inhibitory activities against PIM-1/2 kinases.

Stressing the importance of plant specialized metabolites: omics-based approaches for discovering specialized metabolism in plant stress responses

Plants produce a diverse range of specialized metabolites that play pivotal roles in mediating environmental interactions and stress adaptation. These unique chemical compounds also hold significant agricultural, medicinal, and industrial values. Despite the expanding knowledge of their functions in plant stress interactions, understanding the intricate biosynthetic pathways of these natural products remains challenging due to gene and pathway redundancy, multifunctionality of proteins, and the activity of enzymes with broad substrate specificity. In the past decade, substantial progress in genomics, transcriptomics, metabolomics, and proteomics has made the exploration of plant specialized metabolism more feasible than ever before. Notably, recent advances in integrative multi-omics and computational approaches, along with other technologies, are accelerating the discovery of plant specialized metabolism. In this review, we present a summary of the recent progress in the discovery of plant stress-related specialized metabolites. Emphasis is placed on the application of advanced omics-based approaches and other techniques in studying plant stress-related specialized metabolism. Additionally, we discuss the high-throughput methods for gene functional characterization. These advances hold great promise for harnessing the potential of specialized metabolites to enhance plant stress resilience in the future.

An overview of food lipids toward food lipidomics

Increasing evidence regarding lipids' beneficial effects on human health has changed the common perception of consumers and dietary officials about the role(s) of food lipids in a healthy diet. However, lipids are a wide group of molecules with specific nutritional and bioactive properties. To understand their true nutritional and functional value, robust methods are needed for accurate identification and quantification. Specific analytical strategies are crucial to target specific classes, especially the ones present in trace amounts. Finding a unique and comprehensive methodology to cover the full lipidome of each foodstuff is still a challenge. This review presents an overview of the lipids nutritionally relevant in foods and new trends in food lipid analysis for each type/class of lipids. Food lipid classes are described following the LipidMaps classification, fatty acids, endocannabinoids, waxes, C8 compounds, glycerophospholipids, glycerolipids (i.e., glycolipids, betaine lipids, and triglycerides), sphingolipids, sterols, sercosterols (vitamin D), isoprenoids (i.e., carotenoids and retinoids (vitamin A)), quinones (i.e., coenzyme Q, vitamin K, and vitamin E), terpenes, oxidized lipids, and oxylipin are highlighted. The uniqueness of each food group: oil-, protein-, and starch-rich, as well as marine foods, fruits, and vegetables (water-rich) regarding its lipid composition, is included. The effect of cooking, food processing, and storage, in addition to the importance of lipidomics in food quality and authenticity, are also discussed. A critical review of challenges and future trends of the analytical approaches and computational methods in global food lipidomics as the basis to increase consumer awareness of the significant role of lipids in food quality and food security worldwide is presented.

Environmental Factors Affecting Monoterpene Emissions from Terrestrial Vegetation

Monoterpenes are volatile organic compounds that play important roles in atmospheric chemistry, plant physiology, communication, and defense. This review compiles the monoterpene emission flux data reported for different regions and plant species and highlights the role of abiotic environmental factors in controlling the emissions of biogenic monoterpenes and their emission fluxes for terrestrial plant species (including seasonal variations). Previous studies have demonstrated the role and importance of ambient air temperature and light in controlling monoterpene emissions, likely contributing to higher monoterpene emissions during the summer season in temperate regions. In addition to light and temperature dependence, other important environmental variables such as carbon dioxide (CO2), ozone (O3), soil moisture, and nutrient availability are also known to influence monoterpene emissions rates, but the information available is still limited. Throughout the paper, we identify knowledge gaps and provide recommendations for future studies.

Variation in Leaf Volatile Emissions in Potato (Solanum tuberosum) Cultivars with Different Late Blight Resistance

Volatile organic compounds (VOCs) play key roles in plant abiotic and biotic stress resistance, but even for widespread crops, there is limited information on variations in the magnitude and composition of constitutive VOC emissions among cultivars with varying stress resistance. The foliage VOC emissions from nine local and commercial potato cultivars (Alouette, Sarme, Kuras, Ando, Anti, Jõgeva Kollane, Teele, 1681-11, and Reet) with medium to late maturities and varying Phytophthora infestans (the causative agent of late blight disease) resistance backgrounds were analyzed to gain an insight into the genetic diversity of constitutive VOC emissions and to test the hypothesis that cultivars more resistant to Phytophthora infestans have greater VOC emissions and different VOC fingerprints. Forty-six VOCs were identified in the emission blends of potato leaves. The majority of the VOCs were sesquiterpenes (50% of the total number of compounds and 0.5-36.9% of the total emissions) and monoterpenes (30.4% of the total number of compounds and 57.8-92.5% of the total VOC emissions). Qualitative differences in leaf volatiles, mainly in sesquiterpenes, were related to the potato genotype background. Among the volatile groups, the monoterpenes α-pinene, β-pinene, Δ³-carene, limonene, and p-cymene, the sesquiterpenes (E)-β-caryophyllene and α-copaene, and green leaf volatile hexanal were the major volatiles in all cultivars. A higher share of VOCs known to have antimicrobial activities was observed. Interestingly, the cultivars were grouped into high and low resistance categories based on the VOC profiles, and the total terpenoid and total constitutive VOC emission scale positively with resistance. To support and expedite advances in breeding for resistance to diseases such as late blight disease, the plant research community must develop a fast and precise approach to measure disease resistance. We conclude that the blend of emitted volatiles is a fast, non-invasive, and promising indicator to identify cultivars resistant to potato late blight disease.

Impact of heat priming on heat shock responses in Origanum vulgare: Enhanced foliage photosynthetic tolerance and biphasic emissions of volatiles

Climate change enhances the frequency of heatwaves that negatively affect photosynthesis and can alter constitutive volatile emissions and elicit emissions of stress volatiles, but how pre-exposure to mildly warmer temperatures affects plant physiological responses to subsequent severe heat episodes remains unclear, especially for aromatic plants with high and complex volatile defenses. We studied the impact of heat shock (45 °C/5 min) applied alone and after exposure to moderate heat stress (35 °C/1 h, priming) on foliage photosynthesis and volatile emissions in the aromatic plant Origanum vulgare through 72 h recovery period. Heat stress decreased photosynthesis rates and stomatal conductance, whereas the reductions in photosynthesis were primarily due to non-stomatal factors. In non-primed plants, heat shock-induced reductions in photosynthetic activity were the greatest, but photosynthetic activity completely recovered by the end of the experiment. In primed plants, a certain inhibition of photosynthetic activity remained, suggesting a sustained priming effect. Heat shock enhanced the emissions of volatiles including lipoxygenase pathway volatiles, long-chained fatty acid-derived compounds, mono- and sesquiterpenes, geranylgeranyl diphosphate pathway volatiles, and benzenoids, whereas different heat treatments resulted in unique emission blends. In non-primed plants, stress-elicited emissions recovered at 72 h. In primed plants, volatile emissions were multiphasic, the first phase, between 0.5 and 10 h, reflected the primary stress response, whereas the secondary rise, between 24 and 72 h, indicated activations of different defense metabolic pathways. Our results demonstrate that exposure to mild heat leads to a sustained physiological stress memory that enhances plant resistance to subsequent severe heat stress episodes.

Effect of carbon quantum dots derived from extracts of UV-B-exposed Eclipta alba on alcohol-induced liver cirrhosis in Golden Hamster

The Eclipta alba plant is considered hepatoprotective, owing to its phytoconstituents wedelolactone. In the current study, effect of elevated ultraviolet-B (eUV-B) radiation was investigated on biochemical, phytochemical, and antioxidative enzymatic activities of E. alba (Bhringraj) plant. The UV-B exposure resulted in an increase in oxidative stress, which has caused an imbalance in phytochemical, biochemical constituents, and induced antioxidative enzymatic activities. It was observed that the UV-B exposure promoted wedelolactone yield by 23.64%. Further, the leaf extract of UV-B-exposed plants was used for the synthesis of carbon quantum dots (CQDs) using low cost, one-step hydrothermal technique and its biocompatibility was studied using in vitro MTT (3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide) assay on HepG2 liver cell line. It revealed no toxicity in any treatment groups in comparison to the control. Both CQDs and leaf extract were orally administered to the golden hamster suffering from alcohol-induced liver cirrhosis. In the morphometric study, it was clearly observed that a combination of UV-B-exposed leaf extract and synthesized CQDs delivered the best result with maximum recovery of liver tissues. The present study reveals the positive impact of UV-B exposure on the medicinally important plant, increased yield of wedelolactone, and its enhanced hepatoprotective efficacy for the treatment of damaged liver tissues.

Grapevine mono- and sesquiterpenes: Genetics, metabolism, and ecophysiology

Mono- and sesquiterpenes are volatile organic compounds which play crucial roles in human perception of table grape and wine flavour and aroma, and as such their biosynthesis has received significant attention. Here, the biosynthesis of mono- and sesquiterpenes in grapevine is reviewed, with a specific focus on the metabolic pathways which lead to formation of these compounds, and the characterised genetic variation underlying modulation of this metabolism. The bottlenecks for terpene precursor formation in the cytosol and plastid are understood to be the HMG-CoA reductase (HMGR) and 1-deoxy-D-xylylose-5-phosphate synthase (DXS) enzymes, respectively, and lead to the formation of prenyldiphosphate precursors. The functional plasticity of the terpene synthase enzymes which act on the prenyldiphosphate precursors allows for the massive variation in observed terpene product accumulation. This diversity is further enhanced in grapevine by significant duplication of genes coding for structurally diverse terpene synthases. Relatively minor nucleotide variations are sufficient to influence both product and substrate specificity of terpene synthase genes, with these variations impacting cultivar-specific aroma profiles. While the importance of these compounds in terms of grape quality is well documented, they also play several interesting roles in the grapevine's ecophysiological interaction with its environment. Mono- and sesquiterpenes are involved in attraction of pollinators, agents of seed dispersal and herbivores, defence against fungal infection, promotion of mutualistic rhizobacteria interaction, and are elevated in conditions of high light radiation. The ever-increasing grapevine genome sequence data will potentially allow for future breeders and biotechnologists to tailor the aroma profiles of novel grapevine cultivars through exploitation of the significant genetic variation observed in terpene synthase genes.

Addition of Arbuscular Mycorrhizal Fungi Enhances Terpene Synthase Expression in Salvia rosmarinus Cultivars

Culinary herbs are commercially cultivated for their wide range of volatile compounds that give characteristic aromas and tastes. Rosemary (Salvia rosmarinus Spenn.) is an excellent model for assessment of methods improvement of volatile production as cultivars offer a wide variety of aromatic profiles due to the large family of terpene synthase genes. Arbuscular mycorrhizal fungi (AMF) associations have been shown to improve essential oil production in aromatic plants and offer one approach to enhance aroma in commercial herb production. Changes in the expression of seven different terpene synthases were compared in six rosemary cultivars in response to addition of AMF to a peat substrate. Addition of AMF profoundly influenced terpene synthase expression in all cultivars and did so without impacting the optimised plant size and uniformity achieved in these conditions. In addition, two methods for AMF application, developed with the horticultural industry in mind, were tested in this study. Uniform incorporation of AMF mixed into the growing substrate prior to planting of a root plug produced the most consistent root colonisation. Overall, our findings demonstrate the potential for the use of AMF in the improvement of aroma in culinary herbs within a commercial setting but show that outcomes are likely to greatly vary depending on variety.

Volatilomics of raspberry fruit germplasm by combining chromatographic and direct-injection mass spectrometric techniques

The application of direct-injection mass spectrometric (DI-MS) techniques, like Proton Transfer Reaction Time of Flight Mass Spectrometry (PTR-ToF-MS) has been suggested as a reliable phenotyping tool for fruit volatilome assessment in both genetic and quality-related studies. In this study the complexity of raspberry aroma was investigated by a comprehensive untargeted VOC analysis, done by combining SPME-GC-MS and PTR-ToF-MS assessments with multi-block discriminant analysis using the DIABLO mixOmics framework. The aim was to acquire an exhaustive characterization of the raspberry volatilome according to different fruit ripening stages (pink, ripe, and overripe) and genetic variances (50 accessions), as well as to investigate the potential of PTR-ToF-MS as a rapid and high throughput VOC phenotyping tool to address issues related to raspberry fruit quality. Results of this study demonstrated the complementarity between SPME-GC-MS and PTR-ToF-MS techniques to evaluate the raspberry aroma composition. PTR-ToF-MS generates reliable raspberry VOC fingerprints mainly due to a reduced compound fragmentation and precise content estimation. In addition, the high collinearity between isomers of monoterpenes and norisoprenoids, discovered by GC analysis, reduces the main analytic limitation of PTR-ToF-MS of not being able to separate isomeric molecules. The high similarity between the VOC matrices obtained by applying PTR-ToF-MS and SPME-GC-MS confirmed the possibility of using PTR-ToF-MS as a reliable high throughput phenotyping tool for raspberry volatiolome assessment. In addition, results provided by the germplasm collection investigation enabled to distinguish the best performing accessions, based on VOCs composition, to be used as superior parental lines for future breeding programs.

Peltate trichomes in the dormant shoot apex of Metrodorea nigra, a Rutaceae species with rhythmic growth

In Metrodorea nigra, a Rutaceae species with rhythmic growth, the shoot apex in the dormant stage is enclosed by modified stipules. The young organs are fully covered with peltate secretory trichomes, and these structures remain immersed in a hyaline exudate within a hood-shaped structure. Our study focused on the morpho-functional characterization of the peltate trichomes and cytological events associated with secretion. Shoot apices were collected during both dormant and active stages and processed for anatomical, cytochemical and ultrastructural studies. Trichomes initiate secretion early on, remain active throughout leaf development, but collapse as the leaves expand; at which time secretory cavities start differentiation in the mesophyll and secretion increases as the leaf reaches full expansion. The subcellular apparatus of the trichome head cells is consistent with hydrophilic and lipophilic secretion. Secretion involves two vesicle types: the smaller vesicles are PATAg-positive (periodic acid/thiocarbohydrazide/silver proteinate) for carbohydrates and the larger ones are PATAg-negative. In the first phase of secretory activity, the vesicles containing polysaccharides discharge their contents through exocytosis with the secretion accumulating beneath the cuticle, which detaches from the cell wall. Later, a massive discharge of lipophilic substances (lipids and terpenes/phenols) results in their accumulation between the wall and cuticle. Release of the secretions occurs throughout the cuticular microchannels. Continued protection of the leaves throughout shoot development is ensured by replacement of the collapsed secretory trichomes by oil-secreting cavities. Our findings provide new perspectives for understanding secretion regulation in shoot apices of woody species with rhythmic growth.

Genome-wide transcriptome analysis reveals the regulatory network governing terpene trilactones biosynthesis in Ginkgo biloba

Ginkgo biloba L. is currently the only remaining gymnosperm of the Ginkgoaceae Ginkgo genus, and its history can be traced back to the Carboniferous 200 million years ago. Terpene trilactones (TTLs) are one of the main active ingredients in G. biloba, including ginkgolides and bilobalide. They have a good curative effect on cardiovascular and cerebrovascular diseases because of their special antagonistic effect on platelet-activating factors. Therefore, it is necessary to deeply mine genes related to TTLs and to analyze their transcriptional regulation mechanism, which will hold vitally important scientific and practical significance for quality improvement and regulation of G. biloba. In this study, we performed RNA-Seq on the root, stem, immature leaf, mature leaf, microstrobilus, ovulate strobilus, immature fruit and mature fruit of G. biloba. The TTL regulatory network of G. biloba in different organs was revealed by different transcriptomic analysis strategies. Weighted gene co-expression network analysis (WGCNA) revealed that the five modules were closely correlated with organs. The 12 transcription factors, 5 structural genes and 24 Cytochrome P450 (CYP450) were identified as candidate regulators for TTL accumulation by WGCNA and cytoscape visualization. Finally, 6 APETALA2/ethylene response factors, 2 CYP450s and bHLH were inferred to regulate the metabolism of TTLs by correlation analysis. This study is the comprehensive in authenticating transcription factors, structural genes and CYP450 involved in TTL biosynthesis, thereby providing molecular evidence for revealing the comprehensive regulatory network involved in TTL metabolism in G. biloba.

Identification of Genes and Metabolic Pathways Involved in Resin Yield in Masson Pine by Integrative Analysis of Transcriptome, Proteome and Biochemical Characteristics

Masson pine (Pinus massoniana L.) is one of the most important resin-producing tree species in southern China. However, the molecular regulatory mechanisms of resin yield are still unclear in masson pine. In this study, an integrated analysis of transcriptome, proteome, and biochemical characteristics from needles of masson pine with the high and common resin yield was investigated. The results showed that chlorophyll a (Chl a), chlorophyll b (Chl b), total chlorophyll (Chl C), carotenoids (Car), glucose (Glu), gibberellin A9 (GA9), gibberellin A15 (GA15), and gibberellin A53 (GA53) were significantly increased, whereas fructose (Fru), jasmonic acid (JA), jasmonoyl-L-isoleucine (JA-ILE), gibberellin A1 (GA1), gibberellin A3 (GA3), gibberellin A19 (GA19), and gibberellin A24 (GA24) were significantly decreased in the high resin yield in comparison with those in the common one. The integrated analysis of transcriptome and proteome showed that chlorophyll synthase (chlG), hexokinase (HXK), sucrose synthase (SUS), phosphoglycerate kinase (PGK), dihydrolipoamide dehydrogenase (PDH), dihydrolipoamide succinyltransferase (DLST), 12-oxophytodienoic acid reductase (OPR), and jasmonate O-methyltransferases (JMT) were consistent at the transcriptomic, proteomic, and biochemical levels. The pathways of carbohydrate metabolism, terpenoid biosynthesis, photosynthesis, and hormone biosynthesis may play crucial roles in the regulation of resin yield, and some key genes involved in these pathways may be candidates that influence the resin yield. These results provide insights into the molecular regulatory mechanisms of resin yield and also provide candidate genes that can be applied for the molecular-assisted selection and breeding of high resin-yielding masson pine.

Chiral monoterpenes reveal forest emission mechanisms and drought responses

Monoterpenes (C₁₀H₁₆) are emitted in large quantities by vegetation to the atmosphere (>100 TgC year^-1), where they readily react with hydroxyl radicals and ozone to form new particles and, hence, clouds, affecting the Earth's radiative budget and, thereby, climate change^1-3. Although most monoterpenes exist in two chiral mirror-image forms termed enantiomers, these (+) and (-) forms are rarely distinguished in measurement or modelling studies^4-6. Therefore, the individual formation pathways of monoterpene enantiomers in plants and their ecological functions are poorly understood. Here we present enantiomerically separated atmospheric monoterpene and isoprene data from an enclosed tropical rainforest ecosystem in the absence of ultraviolet light and atmospheric oxidation chemistry, during a four-month controlled drought and rewetting experiment⁷. Surprisingly, the emitted enantiomers showed distinct diel emission peaks, which responded differently to progressive drying. Isotopic labelling established that vegetation emitted mainly de novo-synthesized (-)-α-pinene, whereas (+)-α-pinene was emitted from storage pools. As drought progressed, the source of (-)-α-pinene emissions shifted to storage pools, favouring cloud formation. Pre-drought mixing ratios of both α-pinene enantiomers correlated better with other monoterpenes than with each other, indicating different enzymatic controls. These results show that enantiomeric distribution is key to understanding the underlying processes driving monoterpene emissions from forest ecosystems and predicting atmospheric feedbacks in response to climate change.

Overexpression of Terpenoid Biosynthesis Genes Modifies Root Growth and Nodulation in Soybean (Glycine max)

Root nodule formation in many leguminous plants is known to be affected by endogen ous and exogenous factors that affect formation, development, and longevity of nodules in roots. Therefore, it is important to understand the role of the genes which are involved in the regulation of the nodulation signaling pathway. This study aimed to investigate the effect of terpenoids and terpene biosynthesis genes on root nodule formation in Glycine max. The study aimed to clarify not only the impact of over-expressing five terpene synthesis genes isolated from G. max and Salvia guaranitica on soybean nodulation signaling pathway, but also on the strigolactones pathway. The obtained results revealed that the over expression of GmFDPS, GmGGPPS, SgGPS, SgFPPS, and SgLINS genes enhanced the root nodule numbers, fresh weight of nodules, root, and root length. Moreover, the terpene content in the transgenic G. max hairy roots was estimated. The results explored that the monoterpenes, sesquiterpenes and diterpenes were significantly increased in transgenic soybean hairy roots in comparison with the control. Our results indicate the potential effects of terpenoids and terpene synthesis genes on soybean root growth and nodulation. The study provides novel insights for understanding the epistatic relationship between terpenoids, root development, and nodulation in soybean.

GC-MS-based Fingerprinting Reveals Two Chemotypes in the Leaf Essential Oils from Magnolia grandiflora Trees within The Urban Forestry of a Colombian Andean Plateau

Magnolia grandiflora is an aromatic plant widely distributed around the world. In Colombia, and more specifically in Bogotá, M. grandiflora has been introduced as part of urban forestry programs, and their specimens are therefore subjected to several environments. Nevertheless, there are no previous studies on the chemical composition of such plants. Hence, the characterization of the essential oil from 20 specimens of M. grandiflora from Bogotá, Colombia, by GC-MS was carried out here. Two different chemotypes were found. While one was characterized by monoterpenes α-pinene, β-pinene, and limonene, the other contained mainly sesquiterpenes β-elemene, bicyclogermacrene, and germacrene D. Multivariate statistical analyses confirmed their existence and helped to identify variations within and between chemotypes. Furthermore, differential expression of genes encoding the terpene synthases Mg 25 and Mg 17 could arguably be responsible for the characteristic compositions of both chemotypes, as suggested by rational biosynthetic analysis of the most contrasting metabolites.

Multivariate classification of cannabis chemovars based on their terpene and cannabinoid profiles

Cannabis is used to treat various medical conditions, and lines are commonly classified according to their total concentrations of Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD). Based on their ratio of total THC to total CBD, cannabis cultivars are commonly classified into high-THC, high-CBD, and hybrid classes. While cultivars from the same class have similar compositions of major cannabinoids, their levels of other cannabinoids and their terpene compositions may differ substantially. Therefore, a more comprehensive and accurate classification of medicinal cannabis cultivars, based on a large number of cannabinoids and terpenes is needed. For this purpose, three different chemometric-based classification models were constructed using three sets of chemical profiles. We examined those models to determine which provides the most accurate "chemovar" classification. This was done by analyzing profiles of cannabinoids, terpenes, and the combination of these substances using the partial least square-discriminant analysis multivariate (PLS-DA) technique. The chemical profiles were selected from the three major classes of medicinal cannabis that are most commonly prescribed to patients in Israel: high-THC, high-cannabigerol (CBG), and hybrid. We studied the correlations between cannabinoids and terpenes to identify major bio-indicators representing the plant's terpene and cannabinoid content. All three PLS-DA models provided highly accurate classifications, utilizing six to nine latent variables with an overall accuracy ranging from 2 to 11% CV. The PLS-DA model applied to the combined cannabinoid-and-terpene profile did the best job of differentiating between the chemovars in terms of misclassification error, sensitivity, specificity, and accuracy. The combined cannabinoid-and-terpene PLS-DA profile had cross-validation and prediction misclassification errors of 4% and 0%, respectively. This is the first study to demonstrate the highly accurate classification of samples of medicinal cannabis based on their cannabinoid and terpene profiles, as compared to cannabinoid profiles alone. Furthermore, our correlation analysis indicated that 11 cannabinoids and terpenes might serve as bio-indicators for 32 different active compounds. These findings suggest that the use of multivariate statistics could assist in breeding studies and serve as a tool for minimizing the mislabeling of cannabis inflorescences.

Tomato ARPC1 regulates trichome morphology and density and terpene biosynthesis

Based on transcriptomic analysis of wild-type and mutant tomato plants, ARPC1 was found to be important for trichome formation and development and it plays a key role in terpene synthesis. Trichomes are protruding epidermal cells in plant species. They function as the first defense layer against biotic and abiotic stresses. Despite the essential role of tomato trichomes in defense against herbivores, the understanding of their development is still incomplete. Therefore, the aim of this study was to identify genes involved in trichome formation and morphology and terpene synthesis, using transcriptomic techniques. To achieve this, we examined leaf morphology and compared the expression levels of some putative genes involved in trichome formation between wild-type (WT) and hairless-3 (hl-3) tomato mutant. The hl-3 plants displayed swollen and distorted trichomes and reduced trichome density (type I and IV) and terpene synthesis compared with that of the WT plants. Gene expression analysis showed that Actin-Related Protein Component1 (ARPC1) was expressed more highly in the WT than in the hl-3 mutant, indicating its critical role in trichome morphology and density. Additionally, the expression of MYC1 and several terpene synthase genes (TPS9, 12, 20), which are involved in type VI trichome initiation and terpene synthesis, was lower in the hl-3 mutant than in the WT plants. Moreover, transformation of the hl-3 mutant with WT ARPC1 restored normal trichome structure and density, and terpene synthesis. Structural and amino acid sequence analysis showed that there was a missplicing mutation in the hl-3 mutant, which was responsible for the abnormal trichome structure and density, and impaired terpene synthesis. Overall, the findings of this study demonstrated that ARPC1 is involved in regulating trichome structure and terpene synthesis in tomato.

Caterpillar-Induced Rice Volatile (E)-β-Farnesene Impairs the Development and Survival of Chilo suppressalis Larvae by Disrupting Insect Hormone Balance

Significant research progress has recently been made on establishing the roles of tps46 in rice defense. (E)-β-farnesene (Eβf) is a major product of tps46 activity but its physiological functions and potential mechanisms against Chilo suppressalis have not yet been clarified. In the present study, C. suppressalis larvae were artificially fed a diet containing 0.8 g/kg Eβf and the physiological performance of the larvae was evaluated. In response to Eβf treatment, the average 2nd instar duration significantly increased from 4.78 d to 6.31 d while that of the 3rd instar significantly increased from 5.70 d to 8.00 d compared with the control. There were no significant differences between the control and Eβf-fed 4th and 5th instars in terms of their durations. The mortalities of the 2nd and 3rd Eβf-fed instars were 21.00-fold and 6.39-fold higher, respectively, than that of the control. A comparative transcriptome analysis revealed that multiple differentially expressed genes are involved in insect hormone biosynthesis. An insect hormone assay on the 3rd instars disclosed that Eβf disrupted the balance between the juvenile hormone and ecdysteroid levels. Eβf treatment increased the juvenile hormones titers but not those of the ecdysteroids. The qPCR results were consistent with those of the RNA-Seq. The foregoing findings suggested that Eβf impairs development and survival in C. suppressalis larvae by disrupting their hormone balance. Moreover, Eβf altered the pathways associated with carbohydrate and xenobiotic metabolism as well as those related to cofactors and vitamins in C. suppressalis larvae. The discoveries of this study may contribute to the development and implementation of an integrated control system for C. suppressalis infestations in rice.

Functional Analysis of Two Terpene Synthase Genes Isolated from the Flowers of Hosta ‘So Sweet’

The Hosta hybrid cultivar ‘So Sweet’, an important ornamental and widely used horticultural plant, is noted for its rich, fragrant white flowers. The main aroma components of Hosta flowers are terpenoids, mainly monoterpenes. Until now, the terpene synthases responsible for terpene production in Hosta were not described. In this study, two terpene synthase (TPS) genes (HsTPS1 and HsTPS2) were cloned and characterized to further study their function. Furthermore, the volatile terpenes of Hosta ’So Sweet’ in two flower development stages from two in vitro enzyme tests were analyzed by gas chromatography–mass spectrometry (GC–MS). We analyzed the expression levels of two genes at four different developmental stages using quantitative real-time PCR, while localization was analyzed using Nicotina benthamiana leaves. In vitro, the two proteins were identified to mainly produce linalool and nerol. In addition, the active products of the two recombinant proteins were (E,E)-farnesol and (E,E)-farnesal, respectively, using farnesyl pyrophosphate as a substrate. The high expression of HsTPS1 and HsTPS2 was correlated with the release of components of Hosta flowers. To our knowledge, this is the first time that the terpene synthase genes of Hosta species have been isolated and identified, providing an opportunity to study the terpene metabolic pathways in Hosta species.

Expression and promoter analysis of MEP pathway enzyme-encoding genes in Pinus massoniana Lamb

The methylerythritol phosphate (MEP) pathway provides the universal basic blocks for the biosynthesis of terpenoids and plays a critical role in the growth and development of higher plants. Pinus massoniana is the most valuable oleoresin producer tree with an extensive terrestrial range. It has the potential to produce more oleoresin with commercial value, while being resistant to pine wood nematode (PWN) disease. For this study, eleven MEP pathway associated enzyme-encoding genes and ten promoters were isolated from P. massoniana. Three PmDXS and two PmHDR existed as multi-copy genes, whereas the other six genes existed as single copies. All eleven of these MEP enzymes exhibited chloroplast localization with transient expression. Most of the MEP genes showed higher expression in the needles, while PmDXS2, PmDXS3, and PmHDR1 had high expression in the roots. The expressions of a few MEP genes could be induced under exogenous elicitor conditions. The functional complementation in a dxs-mutant Escherichia coli strain showed the DXS enzymatic activities of the three PmDXSs. High throughput TAIL PCR was employed to obtain the upstream sequences of the genes encoding for enzymes in the MEP pathway, whereby abundant light responsive cis-elements and transcription factor (TF) binding sites were identified within the ten promoters. This study provides a theoretical basis for research on the functionality and transcriptional regulation of MEP enzymes, as well as a potential strategy for high-resin generation and improved genetic resistance in P. massoniana.

Fruity, sticky, stinky, spicy, bitter, addictive, and deadly: evolutionary signatures of metabolic complexity in the Solanaceae

Covering: 2000-2022Plants collectively synthesize a huge repertoire of metabolites. General metabolites, also referred to as primary metabolites, are conserved across the plant kingdom and are required for processes essential to growth and development. These include amino acids, sugars, lipids, and organic acids. In contrast, specialized metabolites, historically termed secondary metabolites, are structurally diverse, exhibit lineage-specific distribution and provide selective advantage to host species to facilitate reproduction and environmental adaptation. Due to their potent bioactivities, plant specialized metabolites attract considerable attention for use as flavorings, fragrances, pharmaceuticals, and bio-pesticides. The Solanaceae (Nightshade family) consists of approximately 2700 species and includes crops of significant economic, cultural, and scientific importance: these include potato, tomato, pepper, eggplant, tobacco, and petunia. The Solanaceae has emerged as a model family for studying the biochemical evolution of plant specialized metabolism and multiple examples exist of lineage-specific metabolites that influence the senses and physiology of commensal and harmful organisms, including humans. These include, alcohols, phenylpropanoids, and carotenoids that contribute to fruit aroma and color in tomato (fruity), glandular trichome-derived terpenoids and acylsugars that contribute to plant defense (stinky & sticky, respectively), capsaicinoids in chilli-peppers that influence seed dispersal (spicy), and steroidal glycoalkaloids (bitter) from Solanum, nicotine (addictive) from tobacco, as well as tropane alkaloids (deadly) from Deadly Nightshade that deter herbivory. Advances in genomics and metabolomics, coupled with the adoption of comparative phylogenetic approaches, resulted in deeper knowledge of the biosynthesis and evolution of these metabolites. This review highlights recent progress in this area and outlines opportunities for - and challenges of-developing a more comprehensive understanding of Solanaceae metabolism.

Characterization of Terpene synthase variation in flowers of wild aquilegia species from Northeastern Asia

There are several causes for the great diversity in floral terpenes. The terpene products are determined by the catalytic fidelity, efficiency and plasticity of the active sites of terpene synthases (TPSs). However, the molecular mechanism of TPS in catalyzing terpene biosynthesis and its evolutionary fate in wild plant species remain largely unknown. In this study, the functionality of terpene synthases and their natural variants were assessed in two Northeastern Asia endemic columbine species and their natural hybrid. Synoptically, TPS7, TPS8, and TPS9 were highly expressed in these Aquilegia species from the Zuojia population. The in vitro and in vivo enzymatic assays revealed that TPS7 and TPS8 mainly produced (+)-limonene and β-sesquiphellandrene, respectively, whereas TPS9 produced pinene, similar to the major components released from Aquilegia flowers. Multiple sequence alignment of Aquilegia TPS7 and TPS8 in the Zuojia population revealed amino acid polymorphisms. Domain swapping and amino acid substitution assays demonstrated that 413A, 503I and 529D had impacts on TPS7 catalytic activity, whereas 420G, 538F and 545 L affected the ratio of β-sesquiphellandrene to β-bisabolene in TPS8. Moreover, these key polymorphic amino acid residues were found in Aquilegia species from the Changbai Mountain population. Interestingly, amino acid polymorphisms in TPSs were present in individuals with low expression levels, and nonsynonymous mutations could impact the catalytic activity or product specificity of these genes. The results of this study will shed new light on the function and evolution of TPS genes in wild plant species and are beneficial to the modification of plant fragrances.

Profiles of Essential Oils and Correlations with Phenolic Acids and Primary Metabolites in Flower Buds of Magnolia heptapeta and Magnolia denudata var. purpurascens

Magnolia flower buds are a source of herbal medicines with various active compounds. In this study, differences in the distribution and abundance of major essential oils, phenolic acids, and primary metabolites between white flower buds of Magnolia heptapeta and violet flower buds of Magnolia denudata var. purpurascens were characterised. A multivariate analysis revealed clear separation between the white and violet flower buds with respect to primary and secondary metabolites closely related to metabolic systems. White flower buds contained large amounts of monoterpene hydrocarbons (MH), phenolic acids, aromatic amino acids, and monosaccharides, related to the production of isoprenes, as MH precursors, and the activity of MH synthase. However, concentrations of β-myrcene, a major MH compound, were higher in violet flower buds than in white flower buds, possibly due to higher threonine levels and low acidic conditions induced by comparatively low levels of some organic acids. Moreover, levels of stress-related metabolites, such as oxygenated monoterpenes, proline, and glutamic acid, were higher in violet flower buds than in white flower buds. Our results support the feasibility of metabolic profiling for the identification of phytochemical differences and improve our understanding of the correlated biological pathways for primary and secondary metabolites.

A Global Metabolic Map Defines the Effects of a Si-Based Biostimulant on Tomato Plants under Normal and Saline Conditions

The ongoing unpredictability of climate changes is exponentially exerting a negative impact on crop production, further aggravating detrimental abiotic stress effects. Several research studies have been focused on the genetic modification of crop plants to achieve more crop resilience against such stress factors; however, there has been a paradigm shift in modern agriculture focusing on more organic, eco-friendly and long-lasting systems to improve crop yield. As such, extensive research into the use of microbial and nonmicrobial biostimulants has been at the core of agricultural studies to improve crop growth and development, as well as to attain tolerance against several biotic and abiotic stresses. However, the molecular mechanisms underlying the biostimulant activity remain enigmatic. Thus, this study is a liquid chromatography-mass spectrometry (LC-MS)-based untargeted metabolomics approach to unravel the hypothetical biochemical framework underlying effects of a nonmicrobial biostimulant (a silicon-based formulation) on tomato plants (Solanum lycopersium) under salinity stress conditions. This metabolomics study postulates that Si-based biostimulants could alleviate salinity stress in tomato plants through modulation of the primary metabolism involving changes in the tricarboxylic acid cycle, fatty acid and numerous amino acid biosynthesis pathways, with further reprogramming of several secondary metabolism pathways such as the phenylpropanoid pathway, flavonoid biosynthesis pathways including flavone and flavanol biosynthesis. Thus, the postulated hypothetical framework, describing biostimulant-induced metabolic events in tomato plants, provides actionable knowledge necessary for industries and farmers to, confidently and innovatively, explore, design, and fully implement Si-based formulations and strategies into agronomic practices for sustainable agriculture and food production.

Predictive Engineering of Class I Terpene Synthases Using Experimental and Computational Approaches

Terpenoids are a highly diverse group of natural products with considerable industrial interest. Increasingly, engineered microbes are used for the production of terpenoids to replace natural extracts and chemical synthesis. Terpene synthases (TSs) show a high level of functional plasticity and are responsible for the vast structural diversity observed in natural terpenoids. Their relatively inert active sites guide intrinsically reactive linear carbocation intermediates along one of many cyclisation paths via exertion of subtle steric and electrostatic control. Due to the absence of a strong protein interaction with these intermediates, there is a remarkable lack of sequence‐function relationship within the TS family, making product‐outcome predictions from sequences alone challenging. This, in combination with the fact that many TSs produce multiple products from a single substrate hampers the design and use of TSs in the biomanufacturing of terpenoids. This review highlights recent advances in genome mining, computational modelling, high‐throughput screening, and machine‐learning that will allow more predictive engineering of these fascinating enzymes in the near future.

Biosynthesis, evolution and ecology of microbial terpenoids

Covering: through June 2021Terpenoids are the largest class of natural products recognised to date. While mostly known to humans as bioactive plant metabolites and part of essential oils, structurally diverse terpenoids are increasingly reported to be produced by microorganisms. For many of the compounds biological functions are yet unknown, but during the past years significant insights have been obtained for the role of terpenoids in microbial chemical ecology. Their functions include stress alleviation, maintenance of cell membrane integrity, photoprotection, attraction or repulsion of organisms, host growth promotion and defense. In this review we discuss the current knowledge of the biosynthesis and evolution of microbial terpenoids, and their ecological and biological roles in aquatic and terrestrial environments. Perspectives on their biotechnological applications, knowledge gaps and questions for future studies are discussed.

Structure, synthesis, biosynthesis, and activity of the characteristic compounds from Ginkgo biloba L

Covering: 1928-2021Ginkgo biloba L. is one of the most distinctive plants to have emerged on earth and has no close living relatives. Owing to its phylogenetic divergence from other plants, G. biloba contains many compounds with unique structures that have served to broaden the chemical diversity of herbal medicine. Examples of such compounds include terpene trilactones (ginkgolides), acylated flavonol glycosides (ginkgoghrelins), biflavones (ginkgetin), ginkgotides and ginkgolic acids. The extract of G. biloba leaf is used to prevent and/or treat cardiovascular diseases, while many ginkgo-derived compounds are currently at various stages of preclinical and clinical trials worldwide. The global annual sales of G. biloba products are estimated to total US$10 billion. However, the content and purity of the active compounds isolated by traditional methods are usually low and subject to varying environmental factors, making it difficult to meet the huge demand of the international market. This highlights the need to develop new strategies for the preparation of these characteristic compounds from G. biloba. In this review, we provide a detailed description of the structures and bioactivities of these compounds and summarize the recent research on the development of strategies for the synthesis, biosynthesis, and biotechnological production of the characteristic terpenoids, flavonoids, and alkylphenols/alkylphenolic acids of G. biloba. Our aim is to provide an important point of reference for all scientists who research ginkgo-related compounds for medicinal or other purposes.

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.

Kinetic studies and homology modeling of a dual-substrate linalool/nerolidol synthase from Plectranthus amboinicus

Linalool and nerolidol are terpene alcohols that occur naturally in many aromatic plants and are commonly used in food and cosmetic industries as flavors and fragrances. In plants, linalool and nerolidol are biosynthesized as a result of respective linalool synthase and nerolidol synthase, or a single linalool/nerolidol synthase. In our previous work, we have isolated a linalool/nerolidol synthase (designated as PamTps1) from a local herbal plant, Plectranthus amboinicus, and successfully demonstrated the production of linalool and nerolidol in an Escherichia coli system. In this work, the biochemical properties of PamTps1 were analyzed, and its 3D homology model with the docking positions of its substrates, geranyl pyrophosphate (C10) and farnesyl pyrophosphate (C15) in the active site were constructed. PamTps1 exhibited the highest enzymatic activity at an optimal pH and temperature of 6.5 and 30 °C, respectively, and in the presence of 20 mM magnesium as a cofactor. The Michaelis-Menten constant (Km) and catalytic efficiency (kcat/Km) values of 16.72 ± 1.32 µM and 9.57 × 10-3 µM-1 s-1, respectively, showed that PamTps1 had a higher binding affinity and specificity for GPP instead of FPP as expected for a monoterpene synthase. The PamTps1 exhibits feature of a class I terpene synthase fold that made up of α-helices architecture with N-terminal domain and catalytic C-terminal domain. Nine aromatic residues (W268, Y272, Y299, F371, Y378, Y379, F447, Y517 and Y523) outlined the hydrophobic walls of the active site cavity, whilst residues from the RRx8W motif, RxR motif, H-α1 and J-K loops formed the active site lid that shielded the highly reactive carbocationic intermediates from the solvents. The dual substrates use by PamTps1 was hypothesized to be possible due to the architecture and residues lining the catalytic site that can accommodate larger substrate (FPP) as demonstrated by the protein modelling and docking analysis. This model serves as a first glimpse into the structural insights of the PamTps1 catalytic active site as a multi-substrate linalool/nerolidol synthase.

Terpene Synthase-b and Terpene Synthase-e/f Genes Produce Monoterpenes for Phalaenopsis bellina Floral Scent

Orchids are the most species-rich plants and highly interactive with pollinators via visual or olfactory cues. Biosynthesis and emission of volatile organic compounds (VOCs) to the atmosphere facilitate the olfactory cues and ensure successful pollination. Phalaenopsis bellina is a scented orchid with monoterpenes as major VOCs, comprising linalool, geraniol, and their derivatives. Comparative transcriptomics analysis identified four terpene synthase-b (TPS-b) genes and two TPS-e/f genes with differential gene expression between scented and scentless Phalaenopsis species. Here, we confirmed their differential expression between scented and scentless Phalaenopsis orchids and excluded one TPS-b candidate. We analyzed the temporal and spatial expression and functionally characterized these TPSs. Both TPS-b and TPS-e/f genes showed an increased expression on blooming day or 3 days post-anthesis (D + 3) before the optimal emission of floral scent on D + 5, with especially high expression of PbTPS5 and PbTPS10. The TPS-b genes are expressed exclusively in reproductive organs, whereas the TPS-e/f genes are expressed in both reproductive and vegetative organs. In planta functional characterization of both PbTPS5 and PbTPS10 in tobacco and scentless Phalaenopsis plants did not produce terpenoids. Further ectopic expression in scented Phalaenopsis cultivar P. I-Hsin Venus showed that linalool was the main product, with PbTPS10 displaying 3-fold higher activity than PbTPS5. On in vitro enzyme assay with purified recombinant TPS-b proteins ectopically expressed in Escherichia coli, geraniol was the product catalyzed by PbTPS5 and PbTPS9. PbTPS3 was a linalool/(β)-cis-ocimene synthase and PbTPS4 a linalool synthase. In conclusion, both TPS-b and TPS-e/f enzymes orchestrated floral monoterpene biosynthesis in P. bellina.

Genome sequence of Apostasia ramifera provides insights into the adaptive evolution in orchids

BACKGROUND

The Orchidaceae family is one of the most diverse among flowering plants and serves as an important research model for plant evolution, especially "evo-devo" study on floral organs. Recently, sequencing of several orchid genomes has greatly improved our understanding of the genetic basis of orchid biology. To date, however, most sequenced genomes are from the Epidendroideae subfamily. To better elucidate orchid evolution, greater attention should be paid to other orchid lineages, especially basal lineages such as Apostasioideae.

RESULTS

Here, we present a genome sequence of Apostasia ramifera, a terrestrial orchid species from the Apostasioideae subfamily. The genomes of A. ramifera and other orchids were compared to explore the genetic basis underlying orchid species richness. Genome-based population dynamics revealed a continuous decrease in population size over the last 100 000 years in all studied orchids, although the epiphytic orchids generally showed larger effective population size than the terrestrial orchids over most of that period. We also found more genes of the terpene synthase gene family, resistant gene family, and LOX1/LOX5 homologs in the epiphytic orchids.

CONCLUSIONS

This study provides new insights into the adaptive evolution of orchids. The A. ramifera genome sequence reported here should be a helpful resource for future research on orchid biology.

Gall- and erineum-forming Eriophyes mites alter photosynthesis and volatile emissions in an infection severity-dependent manner in broad-leaved trees Alnus glutinosa and Tilia cordata

Highly host-specific eriophyoid gall- and erineum-forming mites infest a limited range of broadleaf species, with the mites from the genus Eriophyes particularly widespread on Alnus spp. and Tilia spp. Once infected, the infections can be massive, covering a large part of leaf area and spreading through the plant canopy, but the effects of Eriophyes mite gall formation on the performance of host leaves are poorly understood. We studied the influence of three frequent Eriophyes infections, E. inangulis gall-forming mites on Alnus glutinosa, and E. tiliae gall-forming and E. exilis erineum-forming mites on Tilia cordata, on foliage morphology, chemistry, photosynthetic characteristics, and constitutive and induced volatile emissions. For all types of infections, leaf dry mass per unit area, net assimilation rate per area and stomatal conductance strongly decreased with increasing severity of infection. Mite infections resulted in enhancement or elicitation of emissions of fatty acid-derived volatiles, isoprene, benzenoids and carotenoid breakdown products in an infection severity-dependent manner for all different infections. Monoterpene emissions were strongly elicited in T. cordata mite infections, but these emissions were suppressed in E. inangulis-infected A. glutinosa. Although the overall level of mite-induced emissions was surprisingly low, these results highlight the uniqueness of the volatile profiles and offer opportunities for using volatile fingerprints and overall emission rates to diagnose infections by Eriophyes gall- and erineum-forming mites on temperate trees and assess their impact on the physiology of the affected trees.

Heat priming improved heat tolerance of photosynthesis, enhanced terpenoid and benzenoid emission and phenolics accumulation in Achillea millefolium

The mechanism of heat priming, triggering alteration of secondary metabolite pathway fluxes and pools to enhance heat tolerance is not well understood. Achillea millefolium is an important medicinal herbal plant, rich in terpenoids and phenolics. In this study, the potential of heat priming treatment (35°C for 1 hr) to enhance tolerance of Achillea plants upon subsequent heat shock (45°C for 5 min) stress was investigated through recovery (0.5-72 hr). The priming treatment itself had minor impacts on photosynthesis, led to moderate increases in the emission of lipoxygenase (LOX) pathway volatiles and isoprene, and to major elicitation of monoterpene and benzaldehyde emissions in late stages of recovery. Upon subsequent heat shock, in primed plants, the rise in LOX and reduction in photosynthetic rate (A) was much less, stomatal conductance (g_s ) was initially enhanced, terpene emissions were greater and recovery of A occurred faster, indicating enhanced heat tolerance. Additionally, primed plants accumulated higher contents of total phenolics and condensed tannins at the end of the recovery. These results collectively indicate that heat priming improved photosynthesis upon subsequent heat shock by enhancing g_s and synthesis of volatile and non-volatile secondary compounds with antioxidative characteristics, thereby maintaining the integrity of leaf membranes under stress.

Molecular and Functional Evolution of the Spermatophyte Sesquiterpene Synthases

Sesquiterpenes are important defense and signal molecules for plants to adapt to the environment, cope with stress, and communicate with the outside world, and their evolutionary history is closely related to physiological functions. In this study, the information of plant sesquiterpene synthases (STSs) with identified functions were collected and sorted to form a dataset containing about 500 members. The phylogeny of spermatophyte functional STSs was constructed based on the structural comparative analysis to reveal the sequence–structure–function relationships. We propose the evolutionary history of plant sesquiterpene skeletons, from chain structure to small rings, followed by large rings for the first time and put forward a more detailed function-driven hypothesis. Then, the evolutionary origins and history of spermatophyte STSs are also discussed. In addition, three newly identified STSs CaSTS2, CaSTS3, and CaSTS4 were analyzed in this functional evolutionary system, and their germacrene D products were consistent with the functional prediction. This demonstrates an application of the structure-based phylogeny in predicting STS function. This work will help us to understand evolutionary patterns and dynamics of plant sesquiterpenes and STSs and screen or design STSs with specific product profiles as functional elements for synthetic biology application.

Zucchini Plants Alter Gene Expression and Emission of (E)-β-Caryophyllene Following Aphis gossypii Infestation

Zucchini (Cucurbita pepo L.) is widely cultivated in temperate regions. One of the major production challenges is the damage caused by Aphis gossypii (Homoptera: Aphididae), a polyphagous aphid, which can negatively affect its host plant, both directly by feeding and indirectly by vectoring viruses. To gain insights into the transcriptome events that occur during the zucchini-aphid interaction and to understand the early-to-late defense response through gene expression profiles, we performed RNA-sequencing (RNA-Seq) on zucchini leaves challenged by A. gossypii (24, 48, and 96 h post-infestation; hpi). Data analysis indicated a complex and dynamic pattern of gene expression and a transient transcriptional reconfiguration that involved more than 700 differentially expressed genes (DEGs), including a large number of defense-related genes. The down-regulation of key genes of plant immunity, such as leucine-rich repeat (LRR) protein kinases, transcription factors, and genes associated with direct (i.e., protease inhibitors, cysteine peptidases, etc.) and indirect (i.e., terpene synthase) defense responses, suggests the aphid ability to manipulate plant immune responses. We also investigated the emission of volatile organic compounds (VOCs) from infested plants and observed a reduced emission of (E)-β-caryophyllene at 48 hpi, likely the result of aphid effectors, which reflects the down-regulation of two genes involved in the biosynthesis of terpenoids. We showed that (E)-β-caryophyllene emission was modified by the duration of plant infestation and by aphid density and that this molecule highly attracts Aphidius colemani, a parasitic wasp of A. gossypii. With our results we contributed to the identification of genes involved in cucurbit plant interactions with phloem feeders. Our findings may also help pave the way toward developing tolerant zucchini varieties and to identify molecules for sustainable management of harmful insect populations.

Overexpression of Terpenoid Biosynthesis Genes From Garden Sage (Salvia officinalis) Modulates Rhizobia Interaction and Nodulation in Soybean

In legumes, many endogenous and environmental factors affect root nodule formation through several key genes, and the regulation details of the nodulation signaling pathway are yet to be fully understood. This study investigated the potential roles of terpenoids and terpene biosynthesis genes on root nodule formation in Glycine max. We characterized six terpenoid synthesis genes from Salvia officinalis by overexpressing SoTPS6, SoNEOD, SoLINS, SoSABS, SoGPS, and SoCINS in soybean hairy roots and evaluating root growth and nodulation, and the expression of strigolactone (SL) biosynthesis and early nodulation genes. Interestingly, overexpression of some of the terpenoid and terpene genes increased nodule numbers, nodule and root fresh weight, and root length, while others inhibited these phenotypes. These results suggest the potential effects of terpenoids and terpene synthesis genes on soybean root growth and nodulation. This study provides novel insights into epistatic interactions between terpenoids, root development, and nodulation in soybean root biology and open new avenues for soybean research.

Early transcriptional response of terpenoid metabolism to Colletotrichum gloeosporioides in a resistant wild strawberry Fragaria nilgerrensis

Modern strawberry production is often threatened by microbe pathogens. Anthracnose is among the most prominent fungal disease caused mainly by Colletotrichum gloeosporioides and leads to large-scale losses both in quality and yield. Little is known regarding the mechanisms underlying the genetics in the strawberry-C. gloeosporioides interaction. In the current research, a wild accession 'Fragaria nilgerrensis' is used as a resistant model to study the roles of terpenoid and terpene genes in leaf response to C. gloeosporioides. We found that several terpenoids and terpene genes were up-regulated at early time points after challenged with C. gloeosporioides. Among the metabolites detected, sesquiterpenes were the most significantly accumulated compounds, increasing up to ~12-fold at 18 h post infection (hpi), followed by monoterpenes which showed a slight increase upon infection. Consistently, the time-resolved transcriptome data revealed that genes pertaining to terpenoid metabolism were rapidly up-regulated and co-expressed with signaling pathway genes relevant to defense response. Notably, quantitative real-time PCR confirmed that the expression of five terpene synthase genes (TPS) were greatly enhanced, by a factor of one to three orders of magnitude at 3-6 hpi. Our results reveal a possible link between rapidly induced terpenoid metabolism and the autoimmunity underlying anthracnose resistance in a wild strawberry species.

A Phytochemical Perspective on Plant Defense Against Nematodes

Given the large yield losses attributed to plant-parasitic nematodes and the limited availability of sustainable control strategies, new plant-parasitic nematode control strategies are urgently needed. To defend themselves against nematode attack, plants possess sophisticated multi-layered immune systems. One element of plant immunity against nematodes is the production of small molecules with anti-nematode activity, either constitutively or after nematode infection. This review provides an overview of such metabolites that have been identified to date and groups them by chemical class (e.g., terpenoids, flavonoids, glucosinolates, etc.). Furthermore, this review discusses strategies that have been used to identify such metabolites and highlights the ways in which studying anti-nematode metabolites might be of use to agriculture and crop protection. Particular attention is given to emerging, high-throughput approaches for the identification of anti-nematode metabolites, in particular the use of untargeted metabolomics techniques based on nuclear magnetic resonance (NMR) and mass spectrometry (MS).

Terpenes and Terpenoids in Plants: Interactions with Environment and Insects

The interactions of plants with environment and insects are bi-directional and dynamic. Consequently, a myriad of mechanisms has evolved to engage organisms in different types of interactions. These interactions can be mediated by allelochemicals known as volatile organic compounds (VOCs) which include volatile terpenes (VTs). The emission of VTs provides a way for plants to communicate with the environment, including neighboring plants, beneficiaries (e.g., pollinators, seed dispersers), predators, parasitoids, and herbivores, by sending enticing or deterring signals. Understanding terpenoid distribution, biogenesis, and function provides an opportunity for the design and implementation of effective and efficient environmental calamity and pest management strategies. This review provides an overview of plant-environment and plant-insect interactions in the context of terpenes and terpenoids as important chemical mediators of these abiotic and biotic interactions.

Synthetic biology, combinatorial biosynthesis, and chemo‑enzymatic synthesis of isoprenoids

Isoprenoids are a large class of natural products with myriad applications as bioactive and commercial compounds. Their diverse structures are derived from the biosynthetic assembly and tailoring of their scaffolds, ultimately constructed from two C5 hemiterpene building blocks. The modular logic of these platforms can be harnessed to improve titers of valuable isoprenoids in diverse hosts and to produce new-to-nature compounds. Often, this process is facilitated by the substrate or product promiscuity of the component enzymes, which can be leveraged to produce novel isoprenoids. To complement rational enhancements and even re-programming of isoprenoid biosynthesis, high-throughput approaches that rely on searching through large enzymatic libraries are being developed. This review summarizes recent advances and strategies related to isoprenoid synthetic biology, combinatorial biosynthesis, and chemo-enzymatic synthesis, focusing on the past 5 years. Emerging applications of cell-free biosynthesis and high-throughput tools are included that culminate in a discussion of the future outlook and perspective of isoprenoid biosynthetic engineering.

Isolation and functional characterization of four microbial type terpene synthases from ferns

Typical plant terpene synthases (TPSs) are responsible for the production of terpenes, a major class of plant secondary metabolites. However, various nonseed plants also harbor genes encoding microbial terpene synthase-like (MTPSL) enzymes. Here, a scan of 31 ferns transcriptomes revealed 40 sequences putatively encoding MTPSLs. Two groups of sequences were recognized based on the key conserved motifs. Four representative genes were isolated from each of the four species Adiantum capillus-veneris, Cyclosorus parasiticus, Drynaria bonii and Microlepia platyphylla. Following their heterologous expression in E. coli, the recombinant proteins were tested for monoterpene synthase and sesquiterpene synthase activity. These enzymatic products were typical monoterpenes and sesquiterpenes that have been previous shown to be generated by classical plant TPSs when provided with GPP and FPP as substrates. Subcellular localization experiments in the leaf epidermis of Nicotiana benthamiana and onion (Allium cepa) inner epidermal cells indicated that AcMTPSL1 and DbMTPSL were deposited in both the cytoplasm and nucleus, whereas CpMTPSL1 and MpMTPSL were localized in the cytoplasm, chloroplasts and nucleus. AcMTPSL1 was up-regulated in plants exposed to methyl jasmonate treatment, suggesting a role for this gene in host defense. This study provides more information about the catalytic function of MTPSLs in nonseed plants and for the first time, the subcellular localization of MTPSLs was experimentally characterized.

Functional Characterization of Terpene Synthases Accounting for the Volatilized-Terpene Heterogeneity in Lathyrus odoratus Cultivar Flowers

Lathyrus odoratus (sweet pea) is an ornamental plant with exceptional floral scent, previously used as an experimental organism in the early development of Mendelian genetics. However, its terpene synthases (TPSs), which act as metabolic gatekeepers in the biosynthesis of volatile terpenoids, remain to be characterized. Auto-Headspace Solid-phase Microextraction/Gas chromatography-mass spectrometry analysis of floral volatile terpene constituents from seven sweet pea cultivars identified α-bergamotene, linalool, (-)-α-cubebene, geraniol, β-caryophyllene and β-sesquiphellandrene as the dominant compounds. RNA sequencing was performed to profile the transcriptome of L. odoratus flowers. Bioinformatic analysis identified eight TPS genes (acronymed as LoTPS) that were successfully cloned, heterologously expressed and functionally analyzed. LoTPS4 and LoTPS7, belonging to the TPS-b clade, biochemically catalyzed the formation of monoterpenes and sesquiterpenes. LoTPS3 and LoTPS8, placed in the TPS-a clade, also generated monoterpenes and sesquiterpenes, while LoTPS12 belonging to the TPS-g clade showed linalool/nerolidol synthase activity. Notably, biochemical assays of the recombinant LoTPS proteins revealed their catalytic promiscuity, and the enzymatic products were basically consistent with major volatile compounds released from sweet pea flowers. The data from our study lay the foundation for the chemical ecology, molecular genetics and biotechnological improvement of sweet pea and other legumes (Fabaceae).

Production of multiple terpenes of different chain lengths by subcellular targeting of multi-substrate terpene synthase in plants

Multi-substrate terpene synthases (TPSs) are distinct from typical TPSs that react with a single substrate. Although in vitro activity of few multi-substrate TPSs have been reported, in vivo characterization has not been well investigated for most of them. Here, a new TPS from Cananga odorata, CoTPS5, belonging to TPS-f subfamily was functionally characterized in vitro as well as in vivo. CoTPS5 reacted with multiple prenyl-pyrophosphate substrates of various chain lengths as a multi-substrate TPS. It catalyzed the formation of (E)-β-ocimene, (E,E)-α-farnesene and α-springene from geranyl pyrophosphate, (E,E)-farnesyl pyrophosphate and geranylgeranyl pyrophosphate, respectively. Upon transient expression in Nicotiana benthamiana, CoTPS5 localized to cytosol and produced only (E,E)-α-farnesene. However, expression of plastid-targeted CoTPS5 in N. benthamiana resulted in biosynthesis of all three compounds, (E)-β-ocimene, (E,E)-α-farnesene and α-springene. Similarly, transgenic Arabidopsis plants overexpressing plastid-targeted CoTPS5 showed stable and sustainable production of (E)-β-ocimene, (E,E)-α-farnesene and α-springene. Moreover, their production did not affect the growth and development of transgenic Arabidopsis plants. Our results demonstrate that redirecting multi-substrate TPS to a different intracellular compartment could be an effective way to prove in vivo activity of multi-substrate TPSs and thereby allowing for the production of multiple terpenoids simultaneously in plants.