The family of terpene synthases in plants: a mid-size family of genes for specialized metabolism that is highly diversified throughout the kingdom

Comparative investigation on the aroma profiles of edible citrus flowers in the main organs and different developmental stages

Pomelo flowers emit a strong fragrance and give aromatic odors. Volatile compounds from pomelo flowers were analyzed at three developmental stages and in the main organs by molecular sensory science. A total of 134 volatiles including 25 odorants, were analyzed by gas chromatography-mass spectrometry/pulsed flame photometric detector (GC-MS/PFPD) and multidimensional GC-MS/olfactory (MDGC-MS/O). The total volatile content varied among pomelo flowers at different developmental stages (stage-III > stage-II > stage-I) and among different organs of pomelo flowers (petal > pistil > stamen). Linalool was an important odorant with a high OAV, and floral/fruity comprised the predominant aroma profile. Four odorants, ethyl 2-methylbutanoate, linalool, β-myrcene, and 2-butenal, were selected based on variable importance in projection (VIP) values and contributed mainly to the discrimination of pomelo flowers at three different developmental stages. Linalool, β-myrcene, d-limonene, and ethyl hexanoate were potential markers for evaluating flavor differences in pomelo floral organs.

Metabolites-induced co-evolutionary warfare between plants, viruses, and their associated vectors: So close yet so far away

Agriculture and global food security encounter significant challenges due to viral threats. In the following decades, several molecular studies have focused on discovering biosynthetic pathways of numerous defensive and signaling compounds, as key regulators of plant interactions, either with viruses or their associated vectors. Nevertheless, the complexities of specialized metabolites mediated plant-virus-vector tripartite viewpoint and the identification of their co-evolutionary crossroads toward antiviral defense system, remain elusive. The current study reviews the various roles of plant-specialized metabolites (PSMs) and how plants use these metabolites to defend against viruses. It discusses recent examples of specialized metabolites that have broad-spectrum antiviral properties. Additionally, the study presents the co-evolutionary basis of metabolite-mediated plant-virus-insect interactions as a potential bioinspired approach to combat viral threats. The prospects also show promising metabolic engineering strategies aimed at discovering a wide range of PSMs that are effective in fending off viruses and their related vectors. These advances in understanding the potential role of PSMs in plant-virus interactions not only serve as a cornerstone for developing plant antiviral systems, but also highlight essential principles of biological control.

Terpene synthases GhTPS6 and GhTPS47 participate in resistance to Verticillium dahliae in upland cotton

Terpene synthases (TPSs) are enzymes responsible for catalyzing the production of diverse terpenes, the largest class of secondary metabolites in plants. Here, we identified 107 TPS gene loci encompassing 92 full-length TPS genes in upland cotton (Gossypium hirsutum L.). Phylogenetic analysis showed they were divided into six subfamilies. Segmental duplication and tandem duplication events contributed greatly to the expansion of TPS gene family, particularly the TPS-a and TPS-b subfamilies. Expression profile analysis screened out that GhTPSs may mediate the interaction between cotton and Verticillium dahliae. Three-dimensional structures and subcellular localizations of the two selected GhTPSs, GhTPS6 and GhTPS47, which belong to the TPS-a subfamily, demonstrated similarity in protein structures and nucleus and cytoplasm localization. Virus-induced gene silencing (VIGS) of the two GhTPSs yielded plants characterized by increased wilting and chlorosis, more severe vascular browning, and higher disease index than control plants. Additionally, knockdown of GhTPS6 and GhTPS47 led to the down-regulation of cotton terpene synthesis following V. dahliae infection, indicating that these two genes may positively regulate resistance to V. dahliae through the modulation of disease-resistant terpene biosynthesis. Overall, our study represents a comprehensive analysis of the G. hirsutum TPS gene family, revealing their potential roles in defense responses against Verticillium wilt.

Understanding the chemical language mediating maize immunity and environmental adaptation

Diverse networks of specialized metabolites promote plant fitness by mediating beneficial and antagonistic environmental interactions. In maize (Zea mays), constitutive and dynamically formed cocktails of terpenoids, benzoxazinoids, oxylipins, and phenylpropanoids contribute to plant defense and ecological adaptation. Recent research has highlighted the multifunctional nature of many specialized metabolites, serving not only as elaborate chemical defenses that safeguard against biotic and abiotic stress but also as regulators in adaptive developmental processes and microbiome interactions. Great strides have also been made in identifying the modular pathway networks that drive maize chemical diversity. Translating this knowledge into strategies for enhancing stress resilience traits has the potential to address climate-driven yield losses in one of the world's major food, feed, and bioenergy crops.

Plant specialized metabolism: Diversity of terpene synthases and their products

Terpenoids are ubiquitous to all kingdoms of life and are one of the most diverse groups of compounds, both structurally and functionally. Despite being derived from common precursors, isopentenyl diphosphate and dimethylallyl diphosphate, their exceptional diversity is partly driven by the substrate and product promiscuity of terpene synthases that produce a wide array of terpene skeletons. Plant terpene synthases can be subdivided into different subfamilies based on sequence homology and function. However, in many cases, structural architecture of the enzyme is more essential to product specificity than primary sequence alone, and distantly related terpene synthases can often mediate similar reactions. As such, the focus of this brief review is on some of the recent progress in understanding terpene synthase function and diversity.

The genome of Vicia sativa ssp. amphicarpa provides insights into the role of terpenoids in antimicrobial resistance within subterranean fruits

Vicia sativa ssp. amphicarpa is a unique forage crop capable of simultaneously producing fruits above and below ground, representing a typical amphicarpic plant. In this study, we sequenced and assembled seven pseudo-chromosomes of the genome of V. sativa ssp. amphicarpa (n = 7) yielding a genome size of 1.59 Gb, with a total annotation of 48 932 protein-coding genes. Long terminal repeat (LTR) elements constituted 62.28% of the genome, significantly contributing to the expansion of genome size. Phylogenetic analysis revealed that the divergence between V. sativa ssp. amphicarpa and V. sativa was around 0.88 million years ago (MYA). Comparative transcriptomic and metabolomic analysis of aerial and subterranean pod shells showed biosynthesis of terpenoids in the subterranean pod shells indicating a correlation between the antimicrobial activity of subterranean pod shells and the biosynthesis of terpenoids. Furthermore, functional validation indicates that overexpression of VsTPS5 and VsTPS16 enhances terpenoid biosynthesis for antibacterial activity. Metabolomic analysis suggests the involvement of terpenoids in the antimicrobial properties of subterranean pod shells. Deciphering the genome of V. sativa ssp. amphicarpa elucidated the molecular mechanisms behind the antimicrobial properties of subterranean fruits in amphicarpic plants, providing valuable insights for the study of amphicarpic plant biology.

The chromosome-level genome assembly of Cananga odorata provides insights into its evolution and terpenoid biosynthesis

Cananga odorata is known as a natural perfume tree of the Annonaceae family in Magnoliales. However, its phylogenetic position and the molecular mechanisms involved in the biosynthesis of the floral volatile organic compounds (VOCs) remain unclear. Here, by combining a variety of sequencing platforms, we present a telomere-to-telomere (T2T) genome of C. odorata with 735.83 Mb, which represents the highest integrity and assembly quality of genome in magnoliid plants reported to date. Phylogenetic analysis based on multiple datasets and approaches showed that C. odorata, as a member of magnoliids, is sister to eudicots, after their divergence from monocots. Metabolomic of VOCs in the essential oil and flowers scent showed that sesquiterpenes, especially β-caryophyllene, were the major compounds. Two CoTPS21 homologues derived from tandem duplication events were highly expressed during flower development and were identified as the key sesquiterpene synthases for the production of β-caryophyllene. In addition, CoSPL3 and CoSPL9 were considered as potential transcription factors for activating the expression of CoTPS21 homologues. Our results shed light on the molecular mechanisms underlying the biosynthesis of the unique floral fragrance in C. odorata and provide new insights into the phylogenetic position of magnoliids.

Functional characterization of sesquiterpene synthase in Mongolian medicine Syringa oblata in heartwood formation

Lilac (Syringa oblata) is a well-known horticultural plant, and its aromatic heartwood is widely utilized in Traditional Mongolian Medicine for treating angina. However, limited research on the dynamic changes and mechanisms of aromatic substance formation during heartwood development hinders the analysis and utilization of its medicinal components. In this study, volatile metabolome analysis revealed that sesquiterpenes are the primary metabolites responsible for the aroma in heartwood, with cadinane and eremophilane types being the most prevalent. Among the identified sesquiterpene synthases, SoSTPS1-5 exhibited significantly increased expression in heartwood formation and was selected for further investigation. Molecular docking simulations predicted multiple amino acid binding sites and confirmed its ability to catalyze the formation of eremophilane, copaene, cadinane, germacrane, and elemane-type sesquiterpenes from FPP (farnesyl pyrophosphate). Co-expression and promoter analysis suggested a transcriptional regulatory network primarily involving WRKY transcription factors. Additionally, aiotic and biotic stress inducers, such as Ag+, Fusarium oxysporum, and especially MeJA, were found to activate the expression of SoSTPS1-5 and promote sesquiterpene accumulation. This study provides insights into the basis of medicinal substance formation and the potential mechanisms of sesquiterpene accumulation in lilac heartwood, laying a foundation for future research on the biosynthesis and utilization of its medicinal components.

Plant Molecular Phenology and Climate Feedbacks Mediated by BVOCs

Climate change profoundly affects the timing of seasonal activities of organisms, known as phenology. The impact of climate change is not unidirectional; it is also influenced by plant phenology as plants modify atmospheric composition and climatic processes. One important aspect of this interaction is the emission of biogenic volatile organic compounds (BVOCs), which link the Earth's surface, atmosphere, and climate. BVOC emissions exhibit significant diurnal and seasonal variations and are therefore considered essential phenological traits. To understand the dynamic equilibrium arising from the interplay between plant phenology and climate, this review presents recent advances in comprehending the molecular mechanisms underpinning plant phenology and its interaction with climate. We provide an overview of studies investigating molecular phenology, genome-wide gene expression analyses conducted in natural environments, and how these studies revolutionize the concept of phenology, shifting it from observable traits to dynamic molecular responses driven by gene-environment interactions. We explain how this knowledge can be scaled up to encompass plant populations, regions, and even the globe by establishing connections between molecular phenology, changes in plant distribution, species composition, and climate.

Comparative transcriptome profiling reveals distinct regulatory responses of secondary defensive metabolism in Datura species (Solanaceae) under plant development and herbivory-mediated stress

Differential expression of genes is key to mediating developmental and stress-related plant responses. Here, we addressed the regulation of plant metabolic responses to biotic stress and the developmental variation of defense-related genes in four species of the genus Datura with variable patterns of metabolite accumulation and development. We combine transcriptome profiling with phylogenomic techniques to analyze gene expression and coexpression in plants subjected to damage by a specialist folivore insect. We found (1) common overall gene expression in species of similar chemical profiles, (2) species-specific responses of proteins involved in specialized metabolism, characterized by constant levels of gene expression coupled with transcriptional rearrangement, and (3) induction of transcriptional rearrangement of major terpene and tropane alkaloid genes upon herbivory. Our results indicate differential modulation of terpene and tropane metabolism linked to jasmonate signaling and specific transcription factors to regulate developmental variation and stress programs, and suggest plastic adaptive responses to cope with herbivory. The transcriptional profiles of specialized metabolism shown here reveal complex genetic control of plant metabolism and contribute to understanding the molecular basis of adaptations and the physiological variation of significant ecological traits.

Functional identification of specialized diterpene synthases from Chamaecyparis obtusa and C. obtusa var. formosana to illustrate the putative evolution of diterpene synthases in Cupressaceae

Chamaecyparis obtusa and C. obtusa var. formosana of the Cupressaceae family are well known for their fragrance and excellent physical properties. To investigate the biosynthesis of unique diterpenoid compounds, diterpene synthase genes for specialized metabolite synthesis were cloned from C. obtusa and C. obtusa var. formosana. Using an Escherichia coli co-expression system, eight diterpene synthases (diTPSs) were characterized. CoCPS and CovfCPS are class II monofunctional (+)-copalyl diphosphate synthases [(+)-CPSs]. Class I monofunctional CoLS and CovfLS convert (+)-copalyl diphosphate [(+)-CPP] to levopimaradiene, CoBRS, CovfBRS1, and CovfBRS3 convert (+)-CPP to (-)-beyerene, and CovfSDS converts (+)-CPP to (-)-sandaracopimaradiene. These enzymes are all monofunctional diterpene syntheses in Cupressaceae family of gymnosperm, and differ from those in Pinaceae. The discovery of the enzyme responsible for the biosynthesis of tetracyclic diterpene (-)-beyerene was characterized for the first time. Diterpene synthases with different catalytic functions exist in closely related species within the Cupressaceae family, indicating that this group of monofunctional diterpene synthases is particularly prone to the evolution of new functions and development of species-specific specialized diterpenoid constituents.

Chromosome genome assembly of the Camphora longepaniculata (Gamble) with PacBio and Hi-C sequencing data

Introduction

Camphora longepaniculata, a crucial commercial crop and a fundamental component of traditional Chinese medicine, is renowned for its abundant production of volatile terpenoids. However, the lack of available genomic information has hindered pertinent research efforts in the past.

Methods

To bridge this gap, the present study aimed to use PacBio HiFi, short-read, and highthroughput chromosome conformation capture sequencing to construct a chromosome-level assembly of the C. longepaniculata genome.

Results and discussion

With twelve chromosomes accounting for 99.82% (766.69 Mb) of the final genome assembly, which covered 768.10 Mb, it was very complete. Remarkably, the assembly's contig and scaffold N50 values are exceptional as well-41.12 and 63.78 Mb, respectively-highlighting its excellent quality and intact structure. Furthermore, a total of 39,173 protein-coding genes were predicted, with 38,766 (98.96%) of them being functionally annotated. The completeness of the genome was confirmed by the Benchmarking Universal Single-Copy Ortholog evaluation, which revealed 99.01% of highly conserved plant genes. As the first comprehensive assembly of the C. longepaniculata genome, it provides a crucial starting point for deciphering the complex pathways involved in terpenoid production. Furthermore, this excellent genome serves as a vital resource for upcoming research on the breeding and genetics of C. longepaniculata.

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.

An improved genome assembly of Chrysanthemum nankingense reveals expansion and functional diversification of terpene synthase gene family

BACKGROUND

Terpenes are important components of plant aromas, and terpene synthases (TPSs) are the key enzymes driving terpene diversification. In this study, we characterized the volatile terpenes in five different Chrysanthemum nankingense tissues. In addition, genome-wide identification and expression analysis of TPS genes was conducted utilizing an improved chromosome-scale genome assembly and tissue-specific transcriptomes. The biochemical functions of three representative TPSs were also investigated.

RESULTS

We identified tissue-specific volatile organic compound (VOC) and volatile terpene profiles. The improved Chrysanthemum nankingense genome assembly was high-quality, including a larger assembled size (3.26 Gb) and a better contig N50 length (3.18 Mb) compared to the old version. A total of 140 CnTPS genes were identified, with the majority representing the TPS-a and TPS-b subfamilies. The chromosomal distribution of these TPS genes was uneven, and 26 genes were included in biosynthetic gene clusters. Closely-related Chrysanthemum taxa were also found to contain diverse TPS genes, and the expression profiles of most CnTPSs were tissue-specific. The three investigated CnTPS enzymes exhibited versatile activities, suggesting multifunctionality.

CONCLUSIONS

We systematically characterized the structure and diversity of TPS genes across the Chrysanthemum nankingense genome, as well as the potential biochemical functions of representative genes. Our results provide a basis for future studies of terpene biosynthesis in chrysanthemums, as well as for the breeding of improved chrysanthemum varieties.

Identification and functional analysis of floral terpene synthase genes in Curcuma alismatifolia

MAIN CONCLUSION

CaTPS2 and CaTPS3 were significantly expressed in flowers of Curcuma alismatifolia 'Shadow' and demonstrated bifunctional enzyme activity, CaTPS2 generated linalool and nerolidol as products, and CaTPS3 catalyzed β-myrcene and β-farnesene formation. This study presents the discovery and functional characterization of floral terpene synthase (TPS) genes in Curcuma alismatifolia 'Shadow', a cultivar renowned for its unique fragrance. Addressing the gap in understanding the genetic basis of floral scent in this species, we identified eight TPS genes through comprehensive transcriptome sequencing. Among these, CaTPS2 and CaTPS3 were significantly expressed in floral tissues and demonstrated bifunctional enzyme activity corresponding to the major volatile compounds detected in 'Shadow'. Functional analyses, including in vitro assays complemented with rigorous controls and alternative identification methods, elucidated the roles of these TPS genes in terpenoid biosynthesis. In vitro studies were conducted via heterologous expression in E. coli, followed by purification of the recombinant protein using affinity chromatography, enzyme assays were performed with GPP/FPP as the substrate, and volatile products were inserted into the GC-MS for analysis. Partially purified recombinant protein of CaTPS2 catalyzed GPP and FPP to produce linalool and nerolidol, respectively, while partially purified recombinant protein of CaTPS3 generated β-myrcene and β-farnesene with GPP and FPP as substrates, respectively. Real-time quantitative PCR further validated the expression patterns of these genes, correlating with terpenoid accumulation in different plant tissues. Our findings illuminate the molecular mechanisms underpinning floral fragrance in C. alismatifolia and provide a foundation for future genetic enhancements of floral scent in ornamental plants. This study, therefore, contributes to the broader understanding of terpenoid biosynthesis in plant fragrances, paving the way for biotechnological applications in horticulture plant breeding.

Integrated Metabolomics and Transcriptomics Analysis Reveals New Insights into Triterpene Biosynthesis in Rosa rugosa

Rosa rugosa is highly regarded for its aesthetic and therapeutic qualities. In particular, R. rugosa's flowers are known to produce essential oils containing a mixture of volatile terpenes, phenylpropanoids, and other compounds. Despite this, extensive research exists on volatile terpenes in flowers, while the knowledge of non-volatile terpenes in distinct tissues is still limited. Using UPLC-ESI-MS/MS, a comprehensive analysis of the terpene metabolites in five different tissues of R. rugosa was conducted. These metabolites accumulated in distinct tissues, and the majority of them were triterpenoids. Transcriptome data were collected from five tissues using RNA-seq. Transcriptomics and metabolomics were utilized to evaluate the triterpene biosynthesis pathway, resulting in new insights into its regulation and biosynthesis. The RrOSC10 was identified as a key enzyme in converting 2,3-oxidosqualene into α-amyrin, potentially contributing to the triterpene biosynthesis pathway. Furthermore, the expression of the RrOSC10 gene was upregulated by salinity for 0.5 h and 1 h, with subsequent downregulation at 2 h. This study lays a foundation for future research on the biosynthesis and accumulation of triterpenes in R. rugosa.

Chemical and transcriptomic analyses of leaf trichomes from Cistus creticus subsp. creticus reveal the biosynthetic pathways of certain labdane-type diterpenoids and their acetylated forms

Labdane-related diterpenoids (LRDs), a subgroup of terpenoids, exhibit structural diversity and significant commercial and pharmacological potential. LRDs share the characteristic decalin-labdanic core structure that derives from the cycloisomerization of geranylgeranyl diphosphate (GGPP). Labdanes derive their name from the oleoresin known as 'Labdanum', 'Ladano', or 'Aladano', used since ancient Greek times. Acetylated labdanes, rarely identified in plants, are associated with enhanced biological activities. Chemical analysis of Cistus creticus subsp. creticus revealed labda-7,13(E)-dien-15-yl acetate and labda-7,13(E)-dien-15-ol as major constituents. In addition, novel labdanes such as cis-abienol, neoabienol, ent-copalol, and one as yet unidentified labdane-type diterpenoid were detected for the first time. These compounds exhibit developmental regulation, with higher accumulation observed in young leaves. Using RNA-sequencing (RNA-seq) analysis of young leaf trichomes, it was possible to identify, clone, and eventually functionally characterize labdane-type diterpenoid synthase (diTPS) genes, encoding proteins responsible for the production of labda-7,13(E)-dien-15-yl diphosphate (endo-7,13-CPP), labda-7,13(E)-dien-15-yl acetate, and labda-13(E)-ene-8α-ol-15-yl acetate. Moreover, the reconstitution of labda-7,13(E)-dien-15-yl acetate and labda-13(E)-ene-8α-ol-15-yl acetate production in yeast is presented. Finally, the accumulation of LRDs in different plant tissues showed a correlation with the expression profiles of the corresponding genes.

Engineering Sclareol Production on the Leaf Surface of Nicotiana tabacum

Sclareol, a diterpene alcohol, is the most common starting material for the synthesis of ambrox, which serves as a sustainable substitute for ambergris, a valuable fragrance secreted by sperm whales. Sclareol has also been proposed to possess antibacterial, antifungal, and anticancer activities. However, in nature, sclareol is only produced by a few plant species, including Cistus creticus, Cleome spinosa, Nicotiana glutinosa, and Salvia sclarea, which limits its commercial application. In this study, we cloned the two genes responsible for sclareol biosynthesis in S. sclarea, labda-13-en-8-ol diphosphate synthase (LPPS) and sclareol synthase (SS), and overexpressed them in tobacco (Nicotiana tabacum L.). The best transgenic tobacco lines accumulated 4.1 μg/cm2 of sclareol, which is comparable to the sclareol production of N. glutinosa, a natural sclareol producer. Thus, sclareol synthesis in tobacco represents a potential alternative means for the production of this high-value compound.

Identification and functional analysis of a deduced geraniol synthase from Camphora officinarum

The market demand for essential oil containing citral is increasing. Our research group identified a rare chemotype of Camphora officinarum whose leaves are high in citral content by examining over 1000 wild trees across the entire native distribution area of C. officinarum in China. Because C. officinarum is suitable for large-scale cultivation, it is therefore seen as a promising source of natural citral. However, the molecular mechanism of citral biosynthesis in C. officinarum is poorly understood. In this study, transcriptomic analyses of C. officinarum with different citral contents revealed a strong positive correlation between the expression of a putative geraniol synthase gene (CoGES) and citral content. The CoGES cDNA was cloned, and the CoGES protein shared high similarity with other monoterpene synthases. Enzymatic assays of CoGES with geranyl diphosphate (GPP) as substrate yielded geraniol as the single product, which is the precursor of citral. Further transient expression of CoGES in Nicotiana benthamiana resulted in a higher relative content of geranial and the appearance of a new substance, neral. These findings indicate that CoGES is a geraniol synthase-encoding gene, and the encoded protein can catalyze the transformation of GPP into geraniol, which is further converted into geranial and neral through an unknown mechanism in vivo. These findings expand our understanding of citral biosynthesis in Lauraceae plants.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01463-4.

Identification of key genes controlling monoterpene biosynthesis of Citral-type Cinnamomum bodinieri Levl. Based on transcriptome and metabolite profiling

The citral-type is the most common chemotype in Cinnamomum bodinieri Levl (C. bodinieri), which has been widely used in the daily necessities, cosmetics, biomedicine, and aromatic areas due to their high citral content. Despite of this economic prospect, the possible gene-regulatory roles of citral biosynthesis in the same geographic environment remains unknown. In this study, the essential oils (EOs) of three citral type (B1, B2, B3) and one non-citral type (B0) varieties of C. bodinieri were identified by GC-MS after hydrodistillation extraction in July. 43 components more than 0.10% were identified in the EOs, mainly composed of monoterpenes (75.8-91.84%), and high content citral (80.63-86.33%) were identified in citral-type. Combined transcriptome and metabolite profiling analysis, plant-pathogen interaction(ko04626), MAPK signaling pathway-plant(ko04016), starch and sucrose metabolism(ko00500), plant hormone signal transduction(ko04075), terpenoid backbone biosynthesis (ko00900) and monoterpenoid biosynthesis (ko00902) pathways were enriched significantly. The gene expression of differential genes were linked to the monoterpene content, and the geraniol synthase (CbGES), alcohol dehydrogenase (CbADH), geraniol 8-hydroxylase-like (CbCYP76B6-like) and 8-hydroxygeraniol dehydrogenase (Cb10HGO) were upregulated in the citral-type, indicating that they were associated with high content of geraniol and citral. The activities of CbGES and CbADH in citral type were higher than in non-citral type, which was corroborated by enzyme-linked immunosorbent assay (ELISA). This study on the accumulation mechanism of citral provides a theoretical basis for the development of essential oil of C. bodinieri.

Stability trends in carbocation intermediates stemming from germacrene A and hedycaryol

In the current work, we analyzed the origin of difference in stabilities among the germacrene A and hedycaryol-derived carbocations. This study focused on twelve hydrocarbons derived from germacrene A and twelve from hedycaryol, which can be divided into three groups: four molecules containing 6-6 bicyclic rings, four 5-7 bicyclic compounds with the carbocation being on the seven-membered ring and the remaining four 5-7 bicyclic compounds with the carbocation on the five-membered ring. The variations in energy within the groups of carbocations (i.e., 6-6 and two kinds of 5-7 bicyclic carbocations) can be ascribed to intramolecular repulsion interactions, as seen from non-covalent interactions plots. Despite the structural similarities between germacrene A and hedycaryol cations, they possess a somewhat different stability trend. These differences are attributed to C+···OH intramolecular interactions present in some hedycaryol cations, which are absent in the carbocations derived from germecrene A.

Exploring Chemical Variability in the Essential Oils of the Thymus Genus

Thyme remains an indispensable herb today, finding its place in gastronomy, medicine, cosmetics, and gardens worldwide. It is highly valued in herbal remedies and pharmaceutical formulations for its antibacterial, antifungal, and antioxidant properties derived from the richness of its essential oil, which comprises various volatile components. However, climate change poses a significant challenge today, potentially affecting the quality of thyme, particularly the extracted essential oil, along with other factors such as biotic influences and the plant's geographical distribution. Consequently, complex diversity in essential oil composition was observed, also influenced by genetic diversity within the same species, resulting in distinct chemotypes. Other factors contributing to this chemodiversity include the chosen agrotechnology and processing methods of thyme, the extraction of the essential oil, and storage conditions. In this review, we provide the latest findings on the factors contributing to the chemovariability of thyme essential oil.

Ancestral terpene cyclases: From fundamental science to applications in biosynthesis

Terpenes constitute one of the largest family of natural products with potent applications as renewable platform chemicals and medicines. The low activity, selectivity and stability displayed by terpene biosynthetic machineries can constitute an obstacle towards achieving expedient biosynthesis of terpenoids in processes that adhere to the 12 principles of green chemistry. Accordingly, engineering of terpene synthase enzymes is a prerequisite for industrial biotechnology applications, but obstructed by their complex catalysis that depend on reactive carbocationic intermediates that are prone to undergo bifurcation mechanisms. Rational redesign of terpene synthases can be tedious and requires high-resolution structural information, which is not always available. Furthermore, it has proven difficult to link sequence space of terpene synthase enzymes to specific product profiles. Herein, the author shows how ancestral sequence reconstruction (ASR) can favorably be used as a protein engineering tool in the redesign of terpene synthases without the need of a structure, and without excessive screening. A detailed workflow of ASR is presented along with associated limitations, with a focus on applying this methodology on terpene synthases. From selected examples of both class I and II enzymes, the author advocates that ancestral terpene cyclases constitute valuable assets to shed light on terpene-synthase catalysis and in enabling accelerated biosynthesis.

Functional characterization of terpene synthases SmTPS1 involved in floral scent formation in Salvia miltiorrhiza

Plants attract beneficial insects and promote pollination by releasing floral scents. Salvia miltiorrhiza, as an insect-pollinated flowering plant, which has been less studied for its floral aroma substances. This study revealed that S. miltiorrhiza flowers produce various volatile terpenoids, including five monoterpenes and ten sesquiterpenes, with the sesquiterpene compound (E)-β-caryophyllene being the most abundant, accounting for 28.1% of the total volatile terpenoids. Y-tube olfactometer experiments were conducted on the primary pollinator of S. miltiorrhiza, the Apis ceranas. The results indicated that (E)-β-caryophyllene compound had an attractive effect on the Apis ceranas. By comparing the homologous sequences with the genes of (E)-β-caryophyllene terpene synthases in other plants, the SmTPS1 gene was selected for further experiment. Subcellular localization experiments showed SmTPS1 localized in the cytoplasm, and its in vitro enzyme assay revealed that it could catalyze FPP into β-Elemene, (E)-β-caryophyllene and α-Humulene. Overexpression of SmTPS1 in S. miltiorrhiza resulted in a 5.29-fold increase in gene expression. The GC-MS analysis revealed a significant increase in the concentration of (E)-β-caryophyllene in the transgenic plants, with levels 2.47-fold higher compared to the empty vector plants. Furthermore, Y-tube olfactometer experiments showed that the transgenic plants were significantly more attractive to Apis ceranas compared to the empty vector plants. Co-expression analysis suggested that four SmMYCs (SmMYC1, SmMYC5, SmMYC10, and SmMYC11) may be involved in the transcriptional regulation of SmTPS1. The yeast one-hybrid screen and the Dual luciferase assay indicated that SmMYC10 positively regulates the expression of SmTPS1. In conclusion, this study lays a foundation for the functional analysis and transcriptional regulation of terpene synthase genes in S. miltiorrhiza.

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.

Comparative physiological, biochemical, metabolomic, and transcriptomic analyses reveal the formation mechanism of heartwood for Acacia melanoxylon

Acacia melanoxylon is well known as a valuable commercial tree species owing to its high-quality heartwood (HW) products. However, the metabolism and regulatory mechanism of heartwood during wood development remain largely unclear. In this study, both microscopic observation and content determination proved that total amount of starches decreased and phenolics and flavonoids increased gradually from sapwood (SW) to HW. We also obtained the metabolite profiles of 10 metabolites related to phenolics and flavonoids during HW formation by metabolomics. Additionally, we collected a comprehensive overview of genes associated with the biosynthesis of sugars, terpenoids, phenolics, and flavonoids using RNA-seq. A total of ninety-one genes related to HW formation were identified. The transcripts related to plant hormones, programmed cell death (PCD), and dehydration were increased in transition zone (TZ) than in SW. The results of RT-PCR showed that the relative expression level of genes and transcription factors was also high in the TZ, regardless of the horizontal or vertical direction of the trunk. Therefore, the HW formation took place in the TZ for A. melanoxylon from molecular level, and potentially connected to plant hormones, PCD, and cell dehydration. Besides, the increased expression of sugar and terpenoid biosynthesis-related genes in TZ further confirmed the close connection between terpenoid biosynthesis and carbohydrate metabolites of A. melanoxylon. Furthermore, the integrated analysis of metabolism data and RNA-seq data showed the key transcription factors (TFs) regulating flavonoids and phenolics accumulation in HW, including negative correlation TFs (WRKY, MYB) and positive correlation TFs (AP2, bZIP, CBF, PB1, and TCP). And, the genes and metabolites from phenylpropanoid and flavonoid metabolism and biosynthesis were up-regulated and largely accumulated in TZ and HW, respectively. The findings of this research provide a basis for comprehending the buildup of metabolites and the molecular regulatory processes of HW formation in A. melanoxylon.

LaMYC7, a positive regulator of linalool and caryophyllene biosynthesis, confers plant resistance to Pseudomonas syringae

Linalool and caryophyllene are the main monoterpene and sesquiterpene compounds in lavender; however, the genes regulating their biosynthesis still remain many unknowns. Here, we identified LaMYC7, a positive regulator of linalool and caryophyllene biosynthesis, confers plant resistance to Pseudomonas syringae. LaMYC7 was highly expressed in glandular trichomes, and LaMYC7 overexpression could significantly increase the linalool and caryophyllene contents and reduce susceptibility to P. syringae in Nicotiana. In addition, the linalool possessed antimicrobial activity against P. syringae growth and acted dose-dependently. Further analysis demonstrated that LaMYC7 directly bound to the promoter region of LaTPS76, which encodes the terpene synthase (TPS) for caryophyllene biosynthesis, and that LaTPS76 was highly expressed in glandular trichomes. Notably, the LaMYC7 promoter contained hormone and stress-responsive regulatory elements and responded to various treatments, including ultraviolet, low temperature, salt, drought, methyl jasmonate, and P. syringae infection treatments. Under these treatments, the changes in the linalool and caryophyllene contents were similar to those in LaMYC7 transcript abundance. Based on the results, LaMYC7 could respond to P. syringae infection in addition to being involved in linalool and caryophyllene biosynthesis. Thus, the MYC transcription factor gene LaMYC7 can be used in the breeding of high-yielding linalool and caryophyllene lavender varieties with pathogen resistance.

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.

Populus MYC2 orchestrates root transcriptional reprogramming of defence pathway to impair Laccaria bicolor ectomycorrhizal development

The jasmonic acid (JA) signalling pathway plays an important role in the establishment of the ectomycorrhizal symbiosis. The Laccaria bicolor effector MiSSP7 stabilizes JA corepressor JAZ6, thereby inhibiting the activity of Populus MYC2 transcription factors. Although the role of MYC2 in orchestrating plant defences against pathogens is well established, its exact contribution to ECM symbiosis remains unclear. This information is crucial for understanding the balance between plant immunity and symbiotic relationships. Transgenic poplars overexpressing or silencing for the two paralogues of MYC2 transcription factor (MYC2s) were produced, and their ability to establish ectomycorrhiza was assessed. Transcriptomics and DNA affinity purification sequencing were performed. MYC2s overexpression led to a decrease in fungal colonization, whereas its silencing increased it. The enrichment of terpene synthase genes in the MYC2-regulated gene set suggests a complex interplay between the host monoterpenes and fungal growth. Several root monoterpenes have been identified as inhibitors of fungal growth and ECM symbiosis. Our results highlight the significance of poplar MYC2s and terpenes in mutualistic symbiosis by controlling root fungal colonization. We identified poplar genes which direct or indirect control by MYC2 is required for ECM establishment. These findings deepen our understanding of the molecular mechanisms underlying ECM symbiosis.

Integrative multiomics profiling of passion fruit reveals the genetic basis for fruit color and aroma

Passion fruit (Passiflora edulis) possesses a complex aroma and is widely grown in tropical and subtropical areas. Here, we conducted the de novo assembly, annotation, and comparison of PPF (P. edulis Sims) and YPF (P. edulis f. flavicarpa) reference genomes using PacBio, Illumina, and Hi-C technologies. Notably, we discovered evidence of recent whole-genome duplication events in P. edulis genomes. Comparative analysis revealed 7.6∼8.1 million single nucleotide polymorphisms, 1 million insertions/deletions, and over 142 Mb presence/absence variations among different P. edulis genomes. During the ripening of yellow passion fruit, metabolites related to flavor, aroma, and color were substantially accumulated or changed. Through joint analysis of genomic variations, differentially expressed genes, and accumulated metabolites, we explored candidate genes associated with flavor, aroma, and color distinctions. Flavonoid biosynthesis pathways, anthocyanin biosynthesis pathways, and related metabolites are pivotal factors affecting the coloration of passion fruit, and terpenoid metabolites accumulated more in PPF. Finally, by heterologous expression in yeast (Saccharomyces cerevisiae), we functionally characterized 12 terpene synthases. Our findings revealed that certain TPS homologs in both YPF and PPF varieties produce identical terpene products, while others yield distinct compounds or even lose their functionality. These discoveries revealed the genetic and metabolic basis of unique characteristics in aroma and flavor between the 2 passion fruit varieties. This study provides resources for better understanding the genome architecture and accelerating genetic improvement of passion fruits.

A diterpene synthase from the sandfly Lutzomyia longipalpis produces the pheromone sobralene

The phlebotomine sandfly, Lutzomyia longipalpis, a major vector of the Leishmania parasite, uses terpene pheromones to attract conspecifics for mating. Examination of the L. longipalpis genome revealed a putative terpene synthase (TPS), which-upon heterologous expression in, and purification from, Escherichia coli-yielded a functional enzyme. The TPS, termed LlTPS, converted geranyl diphosphate (GPP) into a mixture of monoterpenes with low efficiency, of which β-ocimene was the major product. (E,E)-farnesyl diphosphate (FPP) principally produced small amounts of (E)-β-farnesene, while (Z,E)- and (Z,Z)-FPP yielded a mixture of bisabolene isomers. None of these mono- and sesquiterpenes are known volatiles of L. longipalpis. Notably, however, when provided with (E,E,E)-geranylgeranyl diphosphate (GGPP), LlTPS gave sobralene as its major product. This diterpene pheromone is released by certain chemotypes of L. longipalpis, in particular those found in the Ceará state of Brazil. Minor diterpene components were also seen as products of the enzyme that matched those seen in a sandfly pheromone extract.

Bioinformatic analysis of microbial type terpene synthase genes in plants

Plants are prolific producers of terpenoids. Terpenoid biosynthesis is initiated by terpene synthases (TPS). In plants, two types of terpenes synthase genes are recognized: typical plant TPS genes and microbial-terpene synthase like-genes (MTPSL). While TPS genes are ubiquitous in land plants, MTPSL genes appear to be restricted to non-seed land plants. Evolutionarily, TPS genes are specific to land plants, whereas MTPSL genes have related counterparts in other organisms, especially fungi and bacteria. The presence of microbial type TPS in plants, fungi and bacteria, with the latter two often being associated with plants, poses a challenge in accurately identifying bona fide MTPSL genes in plants. In this chapter, we present bioinformatic procedures designed to identify MTPSL genes in sequenced plant genomes and/or transcriptomes. Additionally, we outline validation methods for confirming the identified microbial-type TPS genes as genuine plant genes. The method described in this chapter can also be adopted to analyze microbial type TPS in organisms other than plants.

Insights into taxadiene synthase catalysis and promiscuity facilitated by mutability landscape and molecular dynamics

MAIN CONCLUSION

Protein modeling, carbocation docking, and molecular dynamics along with structure-based mutability landscapes provided insight into taxadiene synthase catalysis (first step of the anticancer Taxol biosynthesis), protein structure-function correlations, and promiscuity. Plant terpenes belong to one of the largest and most diverse classes of natural products. This diversity is driven by the terpene synthase enzyme family which comprises numerous different synthases, several of which are promiscuous. Taxadiene synthase (TXS) is a class I diterpene synthase that catalyzes the first step in the biosynthesis pathway of the diterpene Taxol, an anticancer natural product produced by the Taxus plant. Exploring the molecular basis of TXS catalysis and its promiscuous potential garnered interest as a necessary means for understanding enzyme evolution and engineering possibilities to improve Taxol biosynthesis. A catalytically active closed conformation TXS model was designed using the artificial intelligence system, AlphaFold, accompanied by docking and molecular dynamics simulations. In addition, a mutability landscape of TXS including 14 residues was created to probe for structure-function relations. The mutability landscape revealed no mutants with improved catalytic activity compared to wild-type TXS. However, mutations of residues V584, Q609, V610, and Y688 showed high degree of promiscuity producing cembranoid-type and/or verticillene-type major products instead of taxanes. Mechanistic insights into V610F, V584M, Q609A, and Y688C mutants compared to the wild type revealed the trigger(s) for product profile change. Several mutants spanning residues V584, Q609, Y688, Y762, Q770, and F834 increased production of taxa-4(20),11(12)-diene which is a more favorable substrate for Taxol production compared to taxa-4(5),11(12)-diene. Finally, molecular dynamics simulations of the TXS reaction cascade revealed residues involved in ionization, carbocation stabilization, and cyclization ushering deeper understanding of the enzyme catalysis mechanism.

Plant-derived monoterpene S-linalool and β-ocimene generated by CsLIS and CsOCS-SCZ are key chemical cues for attracting parasitoid wasps for suppressing Ectropis obliqua infestation in Camellia sinensis L

Insect-induced plant volatile organic compounds (VOCs) may function as either direct defence molecules to deter insects or indirect defence signals to attract the natural enemies of the invading insects. Tea (Camellia sinensis L.), an important leaf-based beverage crop, is mainly infested by Ectropis obliqua which causes the most serious damage. Here, we report a mechanistic investigation of tea plant-derived VOCs in an indirect defence mechanism against E. obliqua. Parasitoid wasp Parapanteles hyposidrae, a natural enemy of E. obliqua, showed strong electrophysiological response and selection behaviour towards S-linalool and β-ocimene, two monoterpenes with elevated emission from E. obliqua-damaged tea plants. Larvae frass of E. obliqua, which also released S-linalool and β-ocimene, was found to attract both mated female or male Pa. hyposidrae according to gas chromatography-electroantennogram detection and Y-tube olfactometer assays. In a field setting, both S-linalool and β-ocimene were effective in recruiting both female and male Pa. hyposidrae wasps. To understand the molecular mechanism of monoterpenes-mediated indirect defence in tea plants, two novel monoterpene synthase genes, CsLIS and CsOCS-SCZ, involved in the biosynthesis of S-linalool or β-ocimene, respectively, were identified and biochemically characterised. When the expression of these two genes in tea plants was inhibited by antisense oligodeoxynucleotide, both volatile emission and attraction of wasps were reduced. Furthermore, gene expression analysis suggested that the expression of CsLIS and CsOCS-SCZ is regulated by the jasmonic acid signalling pathway in the tea plant.

Molecular cloning and characterization of farnesyl diphosphate synthase from Rosa rugosa Thunb associated with salinity stress

Rosa rugosa, a renowned ornamental plant, is cultivated for its essential oil containing valuable monoterpenes, sesquiterpenes, and other compounds widely used in the floriculture industry. Farnesyl diphosphate synthase (FPPS) is a key enzyme involved in the biosynthesis of sesquiterpenes and triterpenes for abiotic or biotic stress. In this study, we successfully cloned and characterized a full-length FPPS- encoding cDNA identified as RrFPPS1 using RT-PCR from R. rugosa. Phylogenetic analysis showed that RrFPPS1 belonged to the angiosperm-FPPS clade. Transcriptomic and RT-qPCR analyses revealed that the RrFPPS1 gene had tissue-specific expression patterns. Subcellular localization analysis using Nicotiana benthamiana leaves showed that RrFPPS1 was a cytoplasmic protein. In vitro enzymatic assays combined with GC-MS analysis showed that RrFPPS1 produced farnesyl diphosphate (FPP) using isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) as substrates to provide a precursor for sesquiterpene and triterpene biosynthesis in the plant. Additionally, our research found that RrFPPS1 was upregulated under salt treatment. These substantial findings contribute to an improved understanding of terpene biosynthesis in R. rugosa and open new opportunities for advancements in horticultural practices and fragrance industries by overexpression of the RrFPPS1 gene in vivo increased FPP production and subsequently led to elevated sesquiterpene yields in the future. The knowledge gained from this study can potentially lead to the development of enhanced varieties of R. rugosa with improved aroma, medicinal properties, and resilience to environmental stressors.

Comparative Analysis of Metabolome and Transcriptome in Different Tissue Sites of Aquilaria sinensis (Lour.) Gilg

The resinous stem of Aquilaria sinensis (Lour.) Gilg is the sole legally authorized source of agarwood in China. However, whether other tissue parts can be potential substitutes for agarwood requires further investigation. In this study, we conducted metabolic analysis and transcriptome sequencing of six distinct tissues (root, stem, leaf, seed, husk, and callus) of A. sinensis to investigate the variations in metabolite distribution characteristics and transcriptome data across different tissues. A total of 331 differential metabolites were identified by chromatography-mass spectrometry (GC-MS), of which 22.96% were terpenoids. The differentially expressed genes (DEGs) in RNA sequencing were enriched in sesquiterpene synthesis via the mevalonate pathway. The present study establishes a solid foundation for exploring potential alternatives to agarwood.

Alcohol dehydrogenases regulated by a MYB44 transcription factor underlie Lauraceae citral biosynthesis

Lineage-specific terpenoids have arisen throughout the evolution of land plants and are believed to play a role in interactions between plants and the environment. Species-specific gene clusters in plants have provided insight on the evolution of secondary metabolism. Lauraceae is an ecologically important plant family whose members are also of considerable economic value given their monoterpene contents. However, the gene cluster responsible for the biosynthesis of monoterpenes remains yet to be elucidated. Here, a Lauraceae-specific citral biosynthetic gene cluster (CGC) was identified and investigated using a multifaceted approach that combined phylogenetic, collinearity, and biochemical analyses. The CGC comprises MYB44 as a regulator and 2 alcohol dehydrogenases (ADHs) as modifying enzymes, which derived from species-specific tandem and proximal duplication events. Activity and substrate divergence of the ADHs has resulted in the fruit of mountain pepper (Litsea cubeba), a core Lauraceae species, consisting of more than 80% citral. In addition, MYB44 negatively regulates citral biosynthesis by directly binding to the promoters of the ADH-encoding genes. The aggregation of citral biosynthetic pathways suggests that they may form the basis of important characteristics that enhance adaptability. The findings of this study provide insights into the evolution of and the regulatory mechanisms involved in plant terpene biosynthesis.

Full-Length Transcriptome Sequencing and RNA-Seq Analysis Offer Insights into Terpenoid Biosynthesis in Blumea balsamifera (L.) DC

Blumea balsamifera (L.) DC., an important economic and medicinal herb, has a long history of being used as a traditional Chinese medicine. Its leaves have always been used as a raw material for the extraction of essential oils, comprising large amounts of terpenoids, which have good therapeutic effects on many diseases, such as eczema, bacterial infection, and hypertension. However, the genetic basis of terpenoid biosynthesis in this plant is virtually unknown on account of the lack of genomic data. Here, a combination of next-generation sequencing (NGS) and full-length transcriptome sequencing was applied to identify genes involved in terpenoid biosynthesis at five developmental stages. Then, the main components of essential oils in B. balsamifera were identified using GC-MS. Overall, 16 monoterpenoids and 20 sesquiterpenoids were identified and 333,860 CCS reads were generated, yielding 65,045 non-redundant transcripts. Among these highly accurate transcripts, 59,958 (92.18%) transcripts were successfully annotated using NR, eggNOG, Swissprot, KEGG, KOG, COG, Pfam, and GO databases. Finally, a total of 56 differently expressed genes (DEGs) involved in terpenoid biosynthesis were identified, including 38 terpenoid backbone genes and 18 TPSs, which provide a significant amount of genetic information for B. balsamifera. These results build a basis for resource protection, molecular breeding, and the metabolic engineering of this plant.

Chemically Mediated Plant-Plant Interactions: Allelopathy and Allelobiosis

Plant-plant interactions are a central driver for plant coexistence and community assembly. Chemically mediated plant-plant interactions are represented by allelopathy and allelobiosis. Both allelopathy and allelobiosis are achieved through specialized metabolites (allelochemicals or signaling chemicals) produced and released from neighboring plants. Allelopathy exerts mostly negative effects on the establishment and growth of neighboring plants by allelochemicals, while allelobiosis provides plant neighbor detection and identity recognition mediated by signaling chemicals. Therefore, plants can chemically affect the performance of neighboring plants through the allelopathy and allelobiosis that frequently occur in plant-plant intra-specific and inter-specific interactions. Allelopathy and allelobiosis are two probably inseparable processes that occur together in plant-plant chemical interactions. Here, we comprehensively review allelopathy and allelobiosis in plant-plant interactions, including allelopathy and allelochemicals and their application for sustainable agriculture and forestry, allelobiosis and plant identity recognition, chemically mediated root-soil interactions and plant-soil feedback, and biosynthesis and the molecular mechanisms of allelochemicals and signaling chemicals. Altogether, these efforts provide the recent advancements in the wide field of allelopathy and allelobiosis, and new insights into the chemically mediated plant-plant interactions.

LiNAC100 contributes to linalool biosynthesis by directly regulating LiLiS in Lilium 'Siberia'

MAIN CONCLUSION

The transcription factor LiNAC100 has a novel function of regulating floral fragrance by directly regulating linalool synthase gene LiLiS. Lilium 'Siberia', an Oriental hybrid, is renowned as both a cut flower and garden plant, prized for its color and fragrance. The fragrance comprises volatile organic compounds (VOCs), primarily monoterpenes found in the plant. While the primary terpene synthases in Lilium 'Siberia' were identified, the transcriptional regulation of these terpene synthase (TPS) genes remains unclear. Thus, understanding the regulatory mechanisms of monoterpene biosynthesis is crucial for breeding flower fragrance, thereby improving ornamental and commercial values. In this study, we isolated a nuclear-localized LiNAC100 transcription factor from Lilium 'Siberia'. The virus-induced gene silencing (VIGS) of LiNAC100 was found to down-regulate the expression of linalool synthase gene (LiLiS) and significantly inhibit linalool synthesis. Conversely, transient overexpression of LiNAC100 produced opposite effects. Additionally, yeast one-hybrid and dual-luciferase assays confirmed that LiNAC100 directly activates LiLiS expression. Our findings reveal that LiNAC100 plays a key role in monoterpene biosynthesis in Lilium 'Siberia', promoting linalool synthesis through the activation of LiLiS expression. These results offer insights into the molecular mechanisms of terpene biosynthesis in Lilium 'Siberia' and open avenues for biotechnological enhancement of floral scent.

Discovery of Diverse Sesquiterpenoids from Crossiella cryophila through Genome Mining and NMR Tracking

Terpenoids, the largest and most structurally diverse natural product family, are predominantly found in fungi and plants, with bacterial terpenoids forming a minor fraction. Here, we established an efficient platform that integrates genome mining and NMR-tracking for prioritizing strains and tracking bacterial terpenoids. By employing this platform, we selected Crossiella cryophila for a comprehensive investigation of its capacity for terpenoid production, resulting in the characterization of 15 sesquiterpenoids. These compounds comprise nine new sesquiterpenoids (1-9), along with six known analogs (10-15), which are categorized into five distinctive carbon skeletons: bicyclogermacrane, maaliane, cadinane, eudesmane, and nor-eudesmane. Their chemical structures were determined through a combination of spectroscopic analysis, single-crystal X-ray diffraction, and quantum chemical calculations. Notably, the absolute configurations of compounds 1, 2, 5-7, 9, and 13-15 were determined via single-crystal X-ray diffraction analyses. The selected compounds were evaluated for their anticancer, antimicrobial, and anti-inflammatory bioactivities; however, none of these compounds displayed any significant bioactivity. This study enriches the repertoire of bacterial terpenoids, offers a practical process for prioritizing strains for bacterial terpenoids discovery, and establishes a foundation for exploring terpenoid biosynthesis.

Biochemical analysis of the TPS-a subfamily in Medicago truncatula

Terpenes are important mediators of plant chemical response to environmental cues. Here, we describe the genome-wide identification and biochemical characterization of TPS-a members in Medicago truncatula, a model legume crop. Genome mining identified thirty-nine full-length terpene synthases with a significant number predicted to produce monoterpenes and sesquiterpenes. Biochemical characterization of the TPS-a subfamily associated with sesquiterpene biosynthesis revealed such compounds, that exhibit substantial biological activity in other plants. Gene expression analysis using qPCR and the Medicago gene atlas illustrated distinct tissue and time-based variation in expression in leaves and roots. Together our work establishes the gene-to-metabolite relationships for sesquiterpene synthases in M. truncatula. Understanding the biosynthetic capacity is a foundational step to defining the ecological roles of this important family of compounds.

Analysis of root volatiles and functional characterization of a root-specific germacrene A synthase in Artemisia pallens

MAIN CONCLUSION

The study demonstrated that Artemisia pallens roots can be a source of terpene-rich essential oil and root-specific ApTPS1 forms germacrene A contributing to major root volatiles. Davana (Artemisia pallens Bess) is a valuable aromatic herb within the Asteraceae family, highly prized for its essential oil (EO) produced in the aerial parts. However, the root volatile composition, and the genes responsible for root volatiles have remained unexplored until now. Here, we show that A. pallens roots possess distinct oil bodies and yields ~ 0.05% of EO, which is primarily composed of sesquiterpenes β-elemene, neryl isovalerate, β-selinene, and α-selinene, and trace amounts of monoterpenes β-myrcene, D-limonene. This shows that, besides aerial parts, roots of davana can also be a source of unique EO. Moreover, we functionally characterized a terpene synthase (ApTPS1) that exhibited high in silico expression in the root transcriptome. The recombinant ApTPS1 showed the formation of β-elemene and germacrene A with E,E-farnesyl diphosphate (FPP) as a substrate. Detailed analysis of assay products revealed that β-elemene was the thermal rearrangement product of germacrene A. The functional expression of ApTPS1 in Saccharomyces cerevisiae confirmed the in vivo germacrene A synthase activity of ApTPS1. At the transcript level, ApTPS1 displayed predominant expression in roots, with significantly lower level of expression in other tissues. This expression pattern of ApTPS1 positively correlated with the tissue-specific accumulation level of germacrene A. Overall, these findings provide fundamental insights into the EO profile of davana roots, and the contribution of ApTPS1 in the formation of a major root volatile.

Integrated transcriptomics and metabolomics analysis provides insights into aromatic volatiles formation in Cinnamomum cassia bark at different harvesting times

BACKGROUND

Cinnamomum cassia Presl, classified in the Lauraceae family, is widely used as a spice, but also in medicine, cosmetics, and food. Aroma is an important factor affecting the medicinal and flavoring properties of C. cassia, and is mainly determined by volatile organic compounds (VOCs); however, little is known about the composition of aromatic VOCs in C. cassia and their potential molecular regulatory mechanisms. Here, integrated transcriptomic and volatile metabolomic analyses were employed to provide insights into the formation regularity of aromatic VOCs in C. cassia bark at five different harvesting times.

RESULTS

The bark thickness and volatile oil content were significantly increased along with the development of the bark. A total of 724 differentially accumulated volatiles (DAVs) were identified in the bark samples, most of which were terpenoids. Venn analysis of the top 100 VOCs in each period showed that twenty-eight aromatic VOCs were significantly accumulated in different harvesting times. The most abundant VOC, cinnamaldehyde, peaked at 120 months after planting (MAP) and dominated the aroma qualities. Five terpenoids, α-copaene, β-bourbonene, α-cubebene, α-funebrene, and δ-cadinene, that peaked at 240 MAP could also be important in creating C. cassia's characteristic aroma. A list of 43,412 differentially expressed genes (DEGs) involved in the biosynthetic pathways of aromatic VOCs were identified, including phenylpropanoids, mevalonic acid (MVA) and methylerythritol phosphate (MEP). A gene-metabolite regulatory network for terpenoid and phenylpropanoid metabolism was constructed to show the key candidate structural genes and transcription factors involved in the biosynthesis of terpenoids and phenylpropanoids.

CONCLUSIONS

The results of our research revealed the composition and changes of aromatic VOCs in C. cassia bark at different harvesting stages, differentiated the characteristic aroma components of cinnamon, and illuminated the molecular mechanism of aroma formation. These foundational results will provide technical guidance for the quality breeding of C. cassia.

Maize terpene synthase 1 impacts insect behavior via the production of monoterpene volatiles β-myrcene and linalool

Plant-derived volatiles are important mediators of plant-insect interactions as they can provide cues for host location and quality, or act as direct or indirect defense molecules. The volatiles produced by Zea mays (maize) include a range of terpenes, likely produced by several of the terpene synthases (TPS) present in maize. Determining the roles of specific terpene volatiles and individual TPSs in maize-insect interactions is challenging due to the promiscuous nature of TPSs in vitro and their potential for functional redundancy. In this study, we used metabolite GWAS of a sweetcorn diversity panel infested with Spodoptera frugiperda (fall armyworm) to identify genetic correlations between TPSs and individual volatiles. This analysis revealed a correlation between maize terpene synthase 1 (ZmTPS1) and emission of the monoterpene volatiles linalool and β-myrcene. Electroantennogram assays showed gravid S. frugiperda could detect both linalool and β-myrcene. Quantification of headspace volatiles in a maize tps1 loss-of-function mutant confirmed that ZmTPS1 is an important contributor to linalool and β-myrcene emission in maize. Furthermore, pairwise choice assays between tps1 mutant and wild-type plants showed that ZmTPS1, and by extension its volatile products, aid host location in the chewing insect S. frugiperda, yet repel the sap-sucking pest, Rhopalosiphum maidis (corn leaf aphid). On the other hand, ZmTPS1 had no impact on indirect defense via the recruitment of the parasitoid Cotesia marginiventris. ZmTPS1 is therefore an important mediator of the interactions between maize and its insect pests.

Chromosomal-scale genomes of two Rosa species provide insights into genome evolution and ascorbate accumulation

Rosa roxburghii and Rosa sterilis, two species belonging to the Rosaceae family, are widespread in the southwest of China. These species have gained recognition for their remarkable abundance of ascorbate in their fresh fruits, making them an ideal vitamin C resource. In this study, we generated two high-quality chromosome-scale genome assemblies for R. roxburghii and R. sterilis, with genome sizes of 504 and 981.2 Mb, respectively. Notably, we present a haplotype-resolved, chromosome-scale assembly for diploid R. sterilis. Our results indicated that R. sterilis originated from the hybridization of R. roxburghii and R. longicuspis. Genome analysis revealed the absence of recent whole-genome duplications in both species and identified a series of duplicated genes that possibly contributing to the accumulation of flavonoids. We identified two genes in the ascorbate synthesis pathway, GGP and GalLDH, that show signs of positive selection, along with high expression levels of GDP-d-mannose 3', 5'-epimerase (GME) and GDP-l-galactose phosphorylase (GGP) during fruit development. Furthermore, through co-expression network analysis, we identified key hub genes (MYB5 and bZIP) that likely regulate genes in the ascorbate synthesis pathway, promoting ascorbate biosynthesis. Additionally, we observed the expansion of terpene synthase genes in these two species and tissue expression patterns, suggesting their involvement in terpenoid biosynthesis. Our research provides valuable insights into genome evolution and the molecular basis of the high concentration of ascorbate in these two Rosa species.

Identification of Volatile Compounds and Terpene Synthase (TPS) Genes Reveals ZcTPS02 Involved in β-Ocimene Biosynthesis in Zephyranthes candida

Zephyranthes candida is a frequently cultivated ornamental plant containing several secondary metabolites, including alkaloids, flavonoids, and volatile organic compounds (VOCs). However, extensive research has been conducted only on non-VOCs found in the plant, whereas the production of VOCs and the molecular mechanisms underlying the biosynthesis of terpenes remain poorly understood. In this study, 17 volatile compounds were identified from Z. candida flowers using gas chromatography-mass spectrometry (GC-MS), with 16 of them being terpenoids. Transcriptome sequencing resulted in the identification of 17 terpene synthase (TPS) genes; two TPS genes, ZcTPS01 and ZcTPS02, had high expression levels. Biochemical characterization of two enzymes encoded by both genes revealed that ZcTPS02 can catalyze geranyl diphosphate (GPP) into diverse products, among which is β-ocimene, which is the second most abundant compound found in Z. candida flowers. These results suggest that ZcTPS02 plays a vital role in β-ocimene biosynthesis, providing valuable insights into terpene biosynthesis pathways in Z. candida. Furthermore, the expression of ZcTPS02 was upregulated after 2 h of methyl jasmonate (MeJA) treatment and downregulated after 4 h of the same treatment.

Terpene Synthase Gene Family in Chinese Chestnut (Castanea mollissima BL.) Harbors Two Sesquiterpene Synthase Genes Implicated in Defense against Gall Wasp Dryocosmus kuriphilus

Chinese chestnut (Castanea mollissima BL.) is a well-known fruit tree that has been cultivated in East Asia for millennia. Leaves and buds of the plant can become seriously infested by the gall wasp Dryocosmus kuriphilus (GWDK), which results in gall formation and associated significant losses in fruit production. Herbivore-induced terpenes have been reported to play an important role in plant-herbivory interactions, and in this study, we show that upon herbivory by GWDK, four terpene-related compounds were significantly induced, while the concentrations of these four compounds in intact buds were relatively low. Among these compounds, (E)-nerolidol and (E, E)-α-farnesene have frequently been reported to be involved in plant herbivory defenses, which suggests direct and/or indirect functions in chestnut GWDK defenses. Candidate terpene synthase (TPS) genes that may account for (E)-nerolidol and (E, E)-α-farnesene terpene biosynthesis were characterized by transcriptomics and phylogenetic approaches, which revealed altered transcript levels for two TPSs: CmAFS, a TPS-g subfamily member, and CmNES/AFS, a TPS-b clade member. Both genes were dramatically upregulated in gene expression upon GWDK infestation. Furthermore, Agrobacterium tumefaciens-mediated transient overexpression in Nicotiana benthamiana showed that CmAFS catalyzed the formation of (E, E)-α-farnesene, while CmNES/AFS showed dual (E)-nerolidol and (E, E)-α-farnesene synthase activity. Biochemical assays of the recombinant CmAFS and CmNES/AFS proteins confirmed their catalytic activity in vitro, and the enzymatic products were consistent with two of the major volatile compounds released upon GWDK-infested chestnut buds. Subcellular localization demonstrated that CmAFS and CmNES/AFS were both localized in the cytoplasm, the primary compartment for sesquiterpene synthesis. In summary, we show that two novel sesquiterpene synthase genes CmAFS and CmNES/AFS are inducible by herbivory and can account for the elevated accumulation of (E, E)-α-farnesene and (E)-nerolidol upon GWDK infestation and may be implicated in chestnut defense against GWDK herbivores.

Transcriptome Analysis Provides Insights into Catalpol Biosynthesis in the Medicinal Plant Rehmannia glutinosa and the Functional Characterization of RgGES Genes

Rehmannia glutinosa, a member of the Scrophulariaceae family, has been widely used in traditional Chinese medicine since ancient times. The main bioactive component of R. glutinosa is catalpol. However, the biogenesis of catalpol, especially its downstream pathway, remains unclear. To identify candidate genes involved in the biosynthesis of catalpol, transcriptomes were constructed from R. glutinosa using the young leaves of three cultivars, Beijing No. 3, Huaifeng, and Jin No. 9, as well as the tuberous roots and adventitious roots of the Jin No. 9 cultivar. As a result, 71,142 unigenes with functional annotations were generated. A comparative analysis of the R. glutinosa transcriptomes identified over 200 unigenes of 13 enzymes potentially involved in the downstream steps of catalpol formation, including 9 genes encoding UGTs, 13 for aldehyde dehydrogenases, 70 for oxidoreductases, 44 for CYP450s, 22 for dehydratases, 30 for decarboxylases, 19 for hydroxylases, and 10 for epoxidases. Moreover, two novel genes encoding geraniol synthase (RgGES), which is the first committed enzyme in catalpol production, were cloned from R. glutinosa. The purified recombinant proteins of RgGESs effectively converted GPP to geraniol. This study is the first to discover putative genes coding the tailoring enzymes mentioned above in catalpol biosynthesis, and functionally characterize the enzyme-coding gene in this pathway in R. glutinosa. The results enrich genetic resources for engineering the biosynthetic pathway of catalpol and iridoids.