The tomato terpene synthase gene family

Isolation and characterisation of sesquiterpene synthase from aromatic orchid Phalaenopsis bellina (Rchb.f.) Christenson

BACKGROUND

Phalaenopsis bellina, an orchid native to Borneo, is renowned for its unique appearance. It releases distinct fragrances, which have been linked to the presence of terpenoids. However, the identification and study of sesquiterpene synthase in P. bellina remain limited. In this study, we examines the functional characterisation of terpene synthase (TPS) from P. bellina, known as PbTS, through recombinant protein expression and its manifestation in the flower.

METHODS AND RESULTS

Gene annotation of PbTS revealed that the inferred peptide sequence of PbTS comprises 1,680 bp nucleotides encoding 559 amino acids with an estimated molecular mass of 65.2 kDa and a pI value of 5.4. A similarity search against GenBank showed that PbTS shares similarities with the previously published partial sequence of P. bellina (ABW98504.1) and Phalaenopsis equestris (XP_020597359.1 and ABW98503.1). Intriguingly, the phylogenetic analysis places the PbTS gene within the TPS-a group. In silico analysis of PbTS demonstrated stable interactions with farnesyl pyrophosphate (FPP), geranyl pyrophosphate (GPP), and geranylgeranyl pyrophosphate (GGPP). To verify this activity, an in vitro enzyme assay was performed on the PbTS recombinant protein, which successfully converted FPP, GPP, and GGPP into acyclic sesquiterpene β-farnesene, yielding approximately 0.03 mg/L. Expressional analysis revealed that the PbTS transcript was highly expressed in P. bellina, but its level did not correlate with β-farnesene levels across various flowering time points and stages.

CONCLUSION

The insights gained from this study will enhance the understanding of terpenoid production in P. bellina and aid in the discovery of novel fragrance-related genes in other orchid species.

Pangenome Identification and Analysis of Terpene Synthase Gene Family Members in Gossypium

Terpene synthases (TPSs), key gatekeepers in the biosynthesis of herbivore-induced terpenes, are pivotal in the diversity of terpene chemotypes across and within plant species. Here, we constructed a gene-based pangenome of the Gossypium genus by integrating the genomes of 17 diploid and 10 tetraploid species. Within this pangenome, 208 TPS syntelog groups (SGs) were identified, comprising 2 core SGs (TPS5 and TPS42) present in all 27 analyzed genomes, 6 softcore SGs (TPS11, TPS12, TPS13, TPS35, TPS37, and TPS47) found in 25 to 26 genomes, 131 dispensable SGs identified in 2 to 24 genomes, and 69 private SGs exclusive to a single genome. The mutational load analysis of these identified TPS genes across 216 cotton accessions revealed a great number of splicing variants and complex splicing patterns. The nonsynonymous/synonymous Ka/Ks value for all 52 analyzed TPS SGs was less than one, indicating that these genes were subject to purifying selection. Of 208 TPS SGs encompassing 1795 genes, 362 genes derived from 102 SGs were identified as atypical and truncated. The structural analysis of TPS genes revealed that gene truncation is a major mechanism contributing to the formation of atypical genes. An integrated analysis of three RNA-seq datasets from cotton plants subjected to herbivore infestation highlighted nine upregulated TPSs, which included six previously characterized TPSs in G. hirsutum (AD1_TPS10, AD1_TPS12, AD1_TPS40, AD1_TPS42, AD1_TPS89, and AD1_TPS104), two private TPSs (AD1_TPS100 and AD2_TPS125), and one atypical TPS (AD2_TPS41). Also, a TPS-associated coexpression module of eight genes involved in the terpenoid biosynthesis pathway was identified in the transcriptomic data of herbivore-infested G. hirsutum. These findings will help us understand the contributions of TPS family members to interspecific terpene chemotypes within Gossypium and offer valuable resources for breeding insect-resistant cotton cultivars.

From sequences to sustainability: Exploring dipterocarp genomes for oleoresin production, timber quality, and conservation

Dipterocarp species dominate tropical forest ecosystems and provide key ecological and economic value through their use of aromatic resins, medicinal chemicals, and high-quality timber. However, habitat loss and unsustainable logging have endangered many Dipterocarpaceae species. Genomic strategies provide new opportunities for both elucidating the molecular pathways underlying these desirable traits and informing conservation efforts for at-risk taxa. This review summarizes the progress in dipterocarp genomics analysis and applications. We describe 16 recently published Dipterocarpaceae genome sequences, representing crucial genetic blueprints. Phylogenetic comparisons delineate evolutionary relationships among species and provide frameworks for pinpointing functional changes underlying specialized metabolism and wood development patterns. We also discuss connections revealed thus far between specific gene families and both oleoresin biosynthesis and wood quality traits-including the identification of key terpenoid synthases and cellulose synthases likely governing pathway flux. Moreover, the characterization of adaptive genomic markers offers vital resources for supporting conservation practices prioritizing resilient genotypes displaying valuable oleoresin and timber traits. Overall, progress in dipterocarp functional and comparative genomics provides key tools for addressing the intertwined challenges of preserving biodiversity in endangered tropical forest ecosystems while sustainably deriving aromatic chemicals and quality lumber that support diverse human activities.

The synthesis of papaya fruit flavor-related linalool was regulated by CpTPS18 and CpNAC56

Papaya is a tropical fruit crop renowned for its rich nutrition, particularly pro-vitamin A. Aroma substances are a major component of fruit quality. While extensive research has been conducted on papaya aroma, there has been a notable lack of in-depth research into a specific class of substances. To bridge this gap, our study focused on analyzing the aroma components of various papaya varieties and their biosynthesis pathways. We compared the volatile components of three papaya varieties with distinct flavors at various ripeness stages. A continuous accumulation of linalool, a volatile compound, in the 'AU9' fruit was detected as it matured. The linalool content reached 56% of the total volatile components upon full ripening. Notably, this percentage was significantly higher than that observed in the other two varieties, 'ZhongBai' and 'Malaysian 7', indicating that linalool serves as the primary component influencing the papaya's odor. Subsequently, we identified CpTPS18, a gene associated with linalool biosynthesis, and demonstrated its ability to catalyze linalool production from GPP and enhance its accumulation through overexpression in papaya fruits, both in vivo and in vitro. Based on transcriptomic analysis, it was predicted that CpMYB56 and CpNAC56 may transcriptionally activate the expression of CpTPS18. Subsequent yeast one-hybrid assay and dual luciferase analysis revealed that CpNAC56 activates the transcription of CpTPS18. Transient overexpression in vivo demonstrated that this gene could upregulate the expression of CpTPS18 and promote linalool accumulation. These results uncovered the primary volatile molecule responsible for papaya fruit odor and identified two major genes influencing its biosynthesis. The genomic resources and information obtained from this study will expedite papaya improvement for fruit quality.

Identification and characterization of a key LcTPS in the biosynthesis of volatile monoterpenes and sesquiterpenes in Litchi fruit

Litchi (Litchi chinensis Sonn.) has a desirable sweet taste and exotic aroma, making it popular in the markets. However, the biosynthesis of aroma volatiles in litchi fruit has rarely been investigated. In this study, the content and composition of volatile compounds were determined during litchi fruit ripening. In the mature green and mature red stages of litchi, 49 and 45 volatile compounds were detected, respectively. Monoterpenes were found to be the most abundant volatile compounds in mature red fruit, and their contents significantly increased compared to green fruit, mainly including citronellol, geraniol, myrcene, and D-limonene, which contributed to the aroma in litchi fruit. By comparing the expression profiles of the genes involved in the terpene synthesis pathway during fruit development, a terpene synthesis gene (LcTPS1-2) was identified and characterized as a major player in the synthesis of monoterpenes and sesquiterpenes. A subcellular localization analysis found LcTPS1-2 to be present in the plastid and cytoplasm. The recombinant LcTPS1-2 enzyme was able to catalyze the formation of three monoterpenes, myrcene, geraniol and citral, from geranyl pyrophosphate (GPP) and to convert farnesyl diphosphate (FPP) to a sesquiterpene, caryophyllene in vitro. Transgenic Arabidopsis thaliana plants overexpressing LcTPS1-2 exclusively released one monoterpene D-limonene, and three sesquiterpenes cis-thujopsene, (E)-β-famesene and trans-β-ionone. These results indicate that LcTPS1-2 plays an important role in the production of major volatile terpenes in litchi fruit and provides a basis for future investigations of terpenoid biosynthesis in litchi and other horticultural crops.

Multiplex Expression Cassette Assembly: A flexible and versatile method for building complex genetic circuits in conventional vectors

The manipulation of multiple transcription units for simultaneous and coordinated expression is not only key to building complex genetic circuits to accomplish diverse functions in synthetic biology, but is also important in crop breeding for significantly improved productivity and overall performance. However, building constructs with multiple independent transcription units for fine-tuned and coordinated regulation is complicated and time-consuming. Here, we introduce the Multiplex Expression Cassette Assembly (MECA) method, which modifies canonical vectors compatible with Golden Gate Assembly, and then uses them to produce multi-cassette constructs. By embedding the junction syntax in primers that are used to amplify functional elements, MECA is able to make complex constructs using only one intermediate vector and one destination vector via two rounds of one-pot Golden Gate assembly reactions, without the need for dedicated vectors and a coherent library of standardized modules. As a proof-of-concept, we modified eukaryotic and prokaryotic expression vectors to generate constructs for transient expression of green fluorescent protein and β-glucuronidase in Nicotiana benthamiana, genome editing to block monoterpene metabolism in tomato glandular trichomes, production of betanin in tobacco and synthesis of β-carotene in Escherichia coli. Additionally, we engineered the stable production of thymol and carvacrol, bioactive compounds from Lamiaceae family plants, in glandular trichomes of tobacco. These results demonstrate that MECA is a flexible, efficient and versatile method for building complex genetic circuits, which will not only play a critical role in plant synthetic biology, but also facilitate improving agronomic traits and pyramiding traits for the development of next-generation elite crops.

Nitrogen-mediated volatilisation of defensive metabolites in tomato confers resistance to herbivores

Plants synthesise a vast array of volatile organic compounds (VOCs), which serve as chemical defence and communication agents in their interactions with insect herbivores. Although nitrogen (N) is a critical resource in the production of plant metabolites, its regulatory effects on defensive VOCs remain largely unknown. Here, we investigated the effect of N content in tomato (Solanum lycopersicum) on the tobacco cutworm (Spodoptera litura), a notorious agricultural pest, using biochemical and molecular experiments in combination with insect behavioural and performance analyses. We observed that on tomato leaves with different N contents, S. litura showed distinct feeding preference and growth and developmental performance. Particularly, metabolomics profiling revealed that limited N availability conferred resistance upon tomato plants to S. litura is likely associated with the biosynthesis and emission of the volatile metabolite α-humulene as a repellent. Moreover, exogenous application of α-humulene on tomato leaves elicited a significant repellent response against herbivores. Thus, our findings unravel the key factors involved in N-mediated plant defence against insect herbivores and pave the way for innovation of N management to improve the plant defence responses to facilitate pest control strategies within agroecosystems.

Sesquiterpene Cyclase BcBOT2 Promotes the Unprecedented Wagner-Meerwein Rearrangement of the Methoxy Group

Presilphiperfolan-8β-ol synthase (BcBOT2), a substrate-promiscuous sesquiterpene cyclase (STC) of fungal origin, is capable of converting two new farnesyl pyrophosphate (FPP) derivatives modified at C7 of farnesyl pyrophosphate (FPP) bearing either a hydroxymethyl group or a methoxymethyl group. These substrates were chosen based on a computationally generated model. Biotransformations yielded five new oxygenated terpenoids. Remarkably, the formation of one of these tricyclic products can only be explained by a cationically induced migration of the methoxy group, presumably via a Meerwein-salt intermediate, unprecedented in synthetic chemistry and biosynthesis. The results show the great principle and general potential of terpene cyclases for mechanistic studies of unusual cation chemistry and for the creation of new terpene skeletons.

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.

Gas Chromatography-Mass Spectrometry Metabolites and Transcriptome Profiling Reveal Molecular Mechanisms and Differences in Terpene Biosynthesis in Two Torrya grandis Cultivars during Postharvest Ripening

Terpene aroma compounds are key quality attributes of postharvest Torreya grandis nuts, contributing to their commercial value. However, terpene biosynthesis and regulatory networks in different T. grandis cvs. are still poorly understood. Here, chief cvs. 'Xi Fei' and 'Xiangya Fei' were investigated for their differences in terpene biosynthesis and gene expression levels during postharvest ripening using headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) and transcriptomic datasets. A total of 28 and 22 aroma compounds were identified in 'Xi Fei' and 'Xiangya Fei', respectively. Interestingly, differences in aroma composition between the two cvs. were mostly attributed to D-limonene and α-pinene levels as key determinants in Torreya nuts' flavor. Further, transcriptome profiling, correlation analysis, and RT-qPCR annotated two novel genes, TgTPS1 in 'Xi Fei' and TgTPS2 in 'Xiangya Fei', involved in terpene biosynthesis. In addition, six transcription factors (TFs) with comparable expression patterns to TgTPS1 and four TFs to TgTPS2 were identified via correlation analysis of a volatile and transcriptome dataset to be involved in terpene biosynthesis. Our study provides novel insight into terpene biosynthesis and its regulation at the molecular level in T. grandis nut and presents a valuable reference for metabolic engineering and aroma improvement in this less explored nut.

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.

Tomato root specialized metabolites evolved through gene duplication and regulatory divergence within a biosynthetic gene cluster

Tremendous plant metabolic diversity arises from phylogenetically restricted specialized metabolic pathways. Specialized metabolites are synthesized in dedicated cells or tissues, with pathway genes sometimes colocalizing in biosynthetic gene clusters (BGCs). However, the mechanisms by which spatial expression patterns arise and the role of BGCs in pathway evolution remain underappreciated. In this study, we investigated the mechanisms driving acylsugar evolution in the Solanaceae. Previously thought to be restricted to glandular trichomes, acylsugars were recently found in cultivated tomato roots. We demonstrated that acylsugars in cultivated tomato roots and trichomes have different sugar cores, identified root-enriched paralogs of trichome acylsugar pathway genes, and characterized a key paralog required for root acylsugar biosynthesis, SlASAT1-LIKE (SlASAT1-L), which is nested within a previously reported trichome acylsugar BGC. Last, we provided evidence that ASAT1-L arose through duplication of its paralog, ASAT1, and was trichome-expressed before acquiring root-specific expression in the Solanum genus. Our results illuminate the genomic context and molecular mechanisms underpinning metabolic diversity in plants.

Exogenous methyl jasmonate treatment induced the transcriptional responses and accumulation of volatile terpenoids in Oenanthe javanica (Blume) DC

Water dropwort is favored by consumers for its unique flavor and medicinal value. Terpenoids were identified as the main volatile compounds related to its flavor. In this study, water dropwort was treated with different concentrations of exogenous methyl jasmonate (MeJA). The contents of volatile terpenoids were determined under various MeJA treatments. The results indicated that 0.1 mM of MeJA most effectively promoted the biosynthesis of flavor-related terpenoids in water dropwort. Terpinolene accounted the highest proportion among terpene compounds in water dropwort. The contents of jasmonates in water dropwort were also increased after exogenous MeJA treatments. Transcriptome analysis indicated that DEGs involved in the terpenoid biosynthesis pathway were upregulated. The TPS family was identified from water dropwort, and the expression levels of Oj0473630, Oj0287510 and Oj0240400 genes in TPS-b subfamily were consistent with the changes of terpene contents under MeJA treatments. Oj0473630 was cloned from the water dropwort and designated as OjTPS3, which is predicted to be related to the biosynthesis of terpinolene in water dropwort. Subcellular localization indicated that OjTPS3 protein was localized in chloroplast. Protein purification and enzyme activity of OjTPS3 protein were conducted. The results showed that the purified OjTPS3 protein catalyzed the biosynthesis of terpinolene by using geranyl diphosphate (GPP) as substrate in vitro. This study will facilitate to further understand the molecular mechanism of terpenoid biosynthesis and provide a strategy to improve the flavor of water dropwort.

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.

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.

Sequence-Structure Analysis Unlocking the Potential Functional Application of the Local 3D Motifs of Plant-Derived Diterpene Synthases

Plant-derived diterpene synthases (PdiTPSs) play a critical role in the formation of structurally and functionally diverse diterpenoids. However, the specificity or functional-related features of PdiTPSs are not well understood. For a more profound insight, we collected, constructed, and curated 199 functionally characterized PdiTPSs and their corresponding 3D structures. The complex correlations among their sequences, domains, structures, and corresponding products were comprehensively analyzed. Ultimately, our focus narrowed to the geometric arrangement of local structures. We found that local structural alignment can rapidly localize product-specific residues that have been validated by mutagenesis experiments. Based on the 3D motifs derived from the residues around the substrate, we successfully searched diterpene synthases (diTPSs) from the predicted terpene synthases and newly characterized PdiTPSs, suggesting that the identified 3D motifs can serve as distinctive signatures in diTPSs (I and II class). Local structural analysis revealed the PdiTPSs with more conserved amino acid residues show features unique to class I and class II, whereas those with fewer conserved amino acid residues typically exhibit product diversity and specificity. These results provide an attractive method for discovering novel or functionally equivalent enzymes and probing the product specificity in cases where enzyme characterization is limited.

Measuring BVOC emissions released by tomato plants grown in a soilless integrated rooftop greenhouse

Urban design is currently promoting the inclusion of plants in buildings. However, plants emit biogenic volatile organic compounds (BVOCs), which alone or in combination with other airborne molecules such as CO2, may result in a general increase in tropospheric pollution. Many studies have documented the effects of biotic and abiotic factors on plant BVOC responses, but few have assessed the contribution of typical CO2 levels found in indoor work and meeting spaces. To answer this question, we monitored CO2 and constitutive (MT-limonene) and induced (LOX-cis-3-hexenal) BVOC emissions of a fully developed tomato crop grown hydroponically inside an integrated rooftop greenhouse (i-RTG) in a Mediterranean climate. Two distinctive CO2 assays were performed at the level of the i-RTG by supplying or not CO2. The impact of CO2 on plant physiological emittance was then assessed, and the resulting BVOC rates were compared with reference to EU-LCI values. MT-limonene was ubiquitous among the assays and the most abundant, while LOX-cis-3-hexenal was detected only under controlled CO2 management. The highest levels detected were below the indicated LCIs and were approximately tenfold lower than the corresponding LCI for MT-limonene (50.88 vs. 5000 μg m-3) and eightfold (6.63 μg m-3) higher than the constitutive emission level for LOX-cis-3-hexenal. Over extended sampling (10 min) findings revealed a general emission decrease and significantly different CO2 concentration between the assays. Despite similar decreasing rates of predicted net photosynthesis (Pn) and stomatal conductance (gs) their correlation with decreasing CO2 under uncontrolled condition indirectly suggested a negative CO2 impact on plant emission activity. Conversely, increasing CO2 under the controlled assay showed a positive correlation with induced emissions but not with constitutive ones. Because of significantly higher levels of relative humidity registered under the uncontrolled condition, this factor was considered to affect more than CO2 the emission response and even its collection. This hypothesis was supported by literature findings and attributed to a common issue related with the sampling in static enclosure. Hence, we suggested a careful monitoring of the sampling conditions or further improvements to avoid bias and underestimation of actual emissions. Based on the main outcomes, we observed no evidence of a hazardous effect of registered CO2 rates on the BVOC emissions of tomato plant. Furthermore, because of the low BVOC levels measured in the i-RTG, we assumed as safe the recirculation of this air along building's indoor environments.

Chemoenzymatic Synthesis of a New Germacrene Derivative Named Germacrene F

The new farnesyl pyrophosphate (FPP) derivative with a shifted olefinic double bond from C6-C7 to C7-C8 is accepted and converted by the sesquiterpene cyclases protoilludene synthase (Omp7) as well as viridiflorene synthase (Tps32). In both cases, a so far unknown germacrene derivative was found to be formed, which we name "germacrene F". Both cases are examples in which a modification around the central olefinic double bond in FPP leads to a change in the mode of initial cyclization (from 1→11 to 1→10). For Omp7 a rationale for this behaviour was found by carrying out molecular docking studies. Temperature-dependent NMR experiments, accompanied by NOE studies, show that germacrene F adopts a preferred mirror-symmetric conformation with both methyl groups oriented in the same directions in the cyclodecane ring.

HrTPS12 gene dramatically enhanced insect resistance of sea buckthorn to infection by fruit fly (Rhagoletis batava obseuriosa Kol.)

BACKGROUND

Terpenoids emitted from plants are important for regulating plant-insect interaction. However, it is still unclear how terpenoids affect the host defense system. There are few reports of terpenoids' involvement in the mechanisms that regulate woody plants' insect resistance.

RESULTS

The (E)-β-ocimene of terpenes was only found in RBO-resist leaves, and its content was higher than that of other type terpenes. Further, we also found (E)-β-ocimene had a significant avoidance effect on RBO and reached 87.5% of the highest avoidance rate. Meanwhile, overexpression of HrTPS12 in Arabidopsis increased the HrTPS12 expression level, (E)-β-ocimene content, and enhanced the defense against RBO. However, silencing HrTPS12 in sea buckthorn revealed that the expression levels of HrTPS12 and (E)-β-ocimene significantly decreased, causing the attraction effect on RBO.

CONCLUSION

HrTPS12 was an up-regulator, which improves sea buckthorn resistance to RBO by regulating the synthesis of volatile (E)-β-ocimene. These results provide in-depth information about the interaction between RBO and sea buckthorn and provide a theoretical basis for developing plant-based insect repellents that can be used to manage RBO. © 2023 Society of Chemical Industry.

Flavonoid production in tomato mediates both direct and indirect plant defences against whiteflies in tritrophic interactions

BACKGROUND

The role of plant flavonoids in direct defences against chewing and sap-sucking herbivorous insects has been extensively characterized. However, little is known about flavonoid-mediated tritrophic interactions between plants, herbivorous insects and natural enemies. In this study, we investigated how flavonoids modulate plant-insect interactions in a tritrophic system involving near-isogenic lines (NILs) of cultivated tomato (Solanum lycopersicum) with high (line NIL-purple hypocotyl [PH]) and low (line NIL-green hypocotyl [GH]) flavonoid levels, with a generalist herbivore whitefly (Bemisia tabaci) and its predatory bug (Orius sauteri).

RESULTS

By contrasting levels of tomato flavonoids (direct defence) while manipulating the presence of predators (indirect defence), we found that high production of flavonoids in tomato was associated with a higher inducibility of direct defences and a stronger plant resistance to whitefly infestation and stimulated the emissions of induced volatile organic compounds, thereby increasing the attractiveness of B. tabaci-infested plants to the predator O. sauteri. Furthermore, suppression of B. tabaci population growth and enhancement of plant growth were mediated directly by the high production of flavonoids and indirectly by the attraction of O. sauteri, and the combined effects were larger than each effect individually.

CONCLUSION

Our results show that high flavonoid production in tomato enhances herbivore-induced direct and indirect defences to better defend against herbivores in tritrophic interactions. Thus, the development of transgenic plants may present an opportunity to utilize the beneficial role of flavonoids in integrated pest management, while simultaneously maintaining or improving resistance against other pests and pathogens. © 2023 Society of Chemical Industry.

The Capsicum terpenoid biosynthetic module is affected by spider-mite herbivory

In response to herbivory, Capsicum annuum leaves adapt their specialized metabolome that may protect the plant against herbivore feeding either directly or indirectly through volatile metabolites acting as cues for natural enemies of the herbivore. The volatile blend of spider-mite infested leaves differs from non-challenged leaves predominantly by a higher contribution of mono- and sesquiterpenes. In addition to these terpenoids released into the headspace, the terpenoid composition of the leaves alters upon herbivory. All this suggests an important role for terpenoids and their biosynthetic machinery in the defence against herbivory. Here, we show that the C. annuum genome contains a terpene synthase (TPS) gene family of 103 putative members of which structural analysis revealed that 27 encode functional enzymes. Transcriptome analysis showed that several TPS loci were differentially expressed upon herbivory in leaves of two C. annuum genotypes, that differ in susceptibility towards spider mites. The relative expression of upstream biosynthetic genes from the mevalonate and the methylerythritol phosphate pathway also altered upon herbivory, revealing a shift in the metabolic flux through the terpene biosynthetic module. The expression of multiple genes potentially acting downstream of the TPSs, including cytochrome P450 monooxygenases, UDP-glucosyl transferases, and transcription factors strongly correlated with the herbivory-induced TPS genes. A selection of herbivory-induced TPS genes was functionally characterized through heterologous expression and the products that these enzymes catalysed matched with the volatile and non-volatile terpenoids induced in response to herbivory.

Secondary Metabolites and Their Role in Strawberry Defense

Strawberry is a high-value commercial crop and a model for the economically important Rosaceae family. Strawberry is vulnerable to attack by many pathogens that can affect different parts of the plant, including the shoot, root, flowers, and berries. To restrict pathogen growth, strawberry produce a repertoire of secondary metabolites that have an important role in defense against diseases. Terpenes, allergen-like pathogenesis-related proteins, and flavonoids are three of the most important metabolites involved in strawberry defense. Genes involved in the biosynthesis of secondary metabolites are induced upon pathogen attack in strawberry, suggesting their transcriptional activation leads to a higher accumulation of the final compounds. The production of secondary metabolites is also influenced by the beneficial microbes associated with the plant and its environmental factors. Given the importance of the secondary metabolite pathways in strawberry defense, we provide a comprehensive overview of their literature and their role in the defense responses of strawberry. We focus on terpenoids, allergens, and flavonoids, and discuss their involvement in the strawberry microbiome in the context of defense responses. We discuss how the biosynthetic genes of these metabolites could be potential targets for gene editing through CRISPR-Cas9 techniques for strawberry crop improvement.

Shifts in carbon partitioning by photosynthetic activity increase terpenoid synthesis in glandular trichomes

Several commercially important secondary metabolites are produced and accumulated in high amounts by glandular trichomes, giving the prospect of using them as metabolic cell factories. Due to extremely high metabolic fluxes through glandular trichomes, previous research focused on how such flows are achieved. The question regarding their bioenergetics became even more interesting with the discovery of photosynthetic activity in some glandular trichomes. Despite recent advances, how primary metabolism contributes to the high metabolic fluxes in glandular trichomes is still not fully elucidated. Using computational methods and available multi-omics data, we first developed a quantitative framework to investigate the possible role of photosynthetic energy supply in terpenoid production and next tested experimentally the simulation-driven hypothesis. With this work, we provide the first reconstruction of specialised metabolism in Type-VI photosynthetic glandular trichomes of Solanum lycopersicum. Our model predicted that increasing light intensities results in a shift of carbon partitioning from catabolic to anabolic reactions driven by the energy availability of the cell. Moreover, we show the benefit of shifting between isoprenoid pathways under different light regimes, leading to a production of different classes of terpenes. Our computational predictions were confirmed in vivo, demonstrating a significant increase in production of monoterpenoids while the sesquiterpenes remained unchanged under higher light intensities. The outcomes of this research provide quantitative measures to assess the beneficial role of chloroplast in glandular trichomes for enhanced production of secondary metabolites and can guide the design of new experiments that aim at modulating terpenoid production.

Comparative Analysis and Identification of Terpene Synthase Genes in Convallaria keiskei Leaf, Flower and Root Using RNA-Sequencing Profiling

The 'Lilly of the Valley' species, Convallaria, is renowned for its fragrant white flowers and distinctive fresh and green floral scent, attributed to a rich composition of volatile organic compounds (VOCs). However, the molecular mechanisms underlying the biosynthesis of this floral scent remain poorly understood due to a lack of transcriptomic data. In this study, we conducted the first comparative transcriptome analysis of C. keiskei, encompassing the leaf, flower, and root tissues. Our aim was to investigate the terpene synthase (TPS) genes and differential gene expression (DEG) patterns associated with essential oil biosynthesis. Through de novo assembly, we generated a substantial number of unigenes, with the highest count in the root (146,550), followed by the flower (116,434) and the leaf (72,044). Among the identified unigenes, we focused on fifteen putative ckTPS genes, which are involved in the synthesis of mono- and sesquiterpenes, the key aromatic compounds responsible for the essential oil biosynthesis in C. keiskei. The expression of these genes was validated using quantitative PCR analysis. Both DEG and qPCR analyses revealed the presence of ckTPS genes in the flower transcriptome, responsible for the synthesis of various compounds such as geraniol, germacrene, kaurene, linalool, nerolidol, trans-ocimene and valencene. The leaf transcriptome exhibited genes related to the biosynthesis of kaurene and trans-ocimene. In the root, the identified unigenes were associated with synthesizing kaurene, trans-ocimene and valencene. Both analyses indicated that the genes involved in mono- and sesquiterpene biosynthesis are more highly expressed in the flower compared to the leaf and root. This comprehensive study provides valuable resources for future investigations aiming to unravel the essential oil-biosynthesis-related genes in the Convallaria genus.

Identification and functional analysis of ZmDLS associated with the response to biotic stress in maize

Terpenes are the main class of secondary metabolites produced in response to pest and germ attacks. In maize (Zea mays L.), they are the essential components of the herbivore-induced plant volatile mixture, which functioned as a direct or indirect defense against pest and germ attacks. In this study, 43 maize terpene synthase gene (ZmTPS) family members were systematically identified and analyzed through the whole genomes of maize. Nine genes, including Zm00001d032230, Zm00001d045054, Zm00001d024486, Zm00001d004279, Zm00001d002351, Zm00001d002350, Zm00001d053916, Zm00001d015053, and Zm00001d015054, were isolated for their differential expression pattern in leaves after corn borer (Ostrinia nubilalis) bite. Additionally, six genes (Zm00001d045054, Zm00001d024486, Zm00001d002351, Zm00001d002350, Zm00001d015053, and Zm00001d015054) were significantly upregulated in response to corn borer bite. Among them, Zm00001d045054 was cloned. Heterologous expression and enzyme activity assays revealed that Zm00001d045054 functioned as d-limonene synthase. It was renamed ZmDLS. Further analysis demonstrated that its expression was upregulated in response to corn borer bites and Fusarium graminearum attacks. The mutant of ZmDLS downregulated the expressions of Zm00001d024486, Zm00001d002351, Zm00001d002350, Zm00001d015053, and Zm00001d015054. It was more attractive to corn borer bites and more susceptible to F. graminearum infection. The yeast one-hybrid assay and dual-luciferase assay showed that ZmMYB76 and ZmMYB101 could upregulate the expression of ZmDLS by binding to the promoter region. This study may provide a theoretical basis for the functional analysis and transcriptional regulation of terpene synthase genes in crops.

Allelic variation of terpene synthases drives terpene diversity in the wild species of the Freesia genus

Terpene synthases (TPSs) play pivotal roles in conferring the structural diversity of terpenoids, which are mainly emitted from flowers, whereas the genetic basis of the release of floral volatile terpenes remains largely elusive. Though quite similar in sequence, TPS allelic variants still function divergently, and how they drive floral terpene diversity in closely related species remains unknown. Here, TPSs responsible for the floral scent of wild Freesia species were characterized, and the functions of their natural allelic variants, as well as the causal amino acid residues, were investigated in depth. Besides the 8 TPSs previously reported in modern cultivars, 7 additional TPSs were functionally evaluated to contribute to the major volatiles emitted from wild Freesia species. Functional characterization of allelic natural variants demonstrated that allelic TPS2 and TPS10 variants changed the enzymatic capacity while allelic TPS6 variants drove the diversity of floral terpene products. Further residue substitution analysis revealed the minor residues determining the enzyme catalytic activity and product specificity. The clarification of TPSs in wild Freesia species reveals that allelic TPS variants evolved differently to determine the interspecific floral volatile terpenes in the genus and might be used for modern cultivar improvement.

Genome-wide identification and expression analysis of terpene synthases in Gossypium species in response to gossypol biosynthesis

Cottonseed is an invaluable resource, providing protein, oil, and abundant minerals that significantly contribute to the well-being and nutritional needs of both humans and livestock. However, cottonseed also contains a toxic substance called gossypol, a secondary metabolite in Gossypium species that plays an important role in cotton plant development and self-protection. Herein, genome-wide analysis and characterization of the terpene synthase (TPS) gene family identified 304 TPS genes in Gossypium. Bioinformatics analysis revealed that the gene family was grouped into six subgroups TPS-a, TPS-b, TPS-c, TPS-e, TPS-f, and TPS-g. Whole-genome, segmental, and tandem duplication contributed to the evolution of TPS genes. According to the analysis of selection pressure, it was predicted that TPS genes experience predominantly negative selection, with positive selection occurring subsequently. RT-qPCR analysis in TM-1 and CRI-12 lines revealed GhTPS48 gene as the candidate gene for silencing experiments. To summarize, comprehensive genome-wide studies, RT-qPCR, and gene silencing experiments have collectively demonstrated the involvement of the TPS gene family in the biosynthesis of gossypol in cotton.

A cytosolic bifunctional geranyl/farnesyl diphosphate synthase provides MVA-derived GPP for geraniol biosynthesis in rose flowers

Geraniol derived from essential oils of various plant species is widely used in the cosmetic and perfume industries. It is also an essential trait of the pleasant smell of rose flowers. In contrast to other monoterpenes which are produced in plastids via the methyl erythritol phosphate pathway, geraniol biosynthesis in roses relies on cytosolic NUDX1 hydrolase which dephosphorylates geranyl diphosphate (GPP). However, the metabolic origin of cytosolic GPP remains unknown. By feeding Rosa chinensis "Old Blush" flowers with pathway-specific precursors and inhibitors, combined with metabolic profiling and functional characterization of enzymes in vitro and in planta, we show that geraniol is synthesized through the cytosolic mevalonate (MVA) pathway by a bifunctional geranyl/farnesyl diphosphate synthase, RcG/FPPS1, producing both GPP and farnesyl diphosphate (FPP). The downregulation and overexpression of RcG/FPPS1 in rose petals affected not only geraniol and germacrene D emissions but also dihydro-β-ionol, the latter due to metabolic cross talk of RcG/FPPS1-dependent isoprenoid intermediates trafficking from the cytosol to plastids. Phylogenetic analysis together with functional characterization of G/FPPS orthologs revealed that the G/FPPS activity is conserved among Rosaceae species. Site-directed mutagenesis and molecular dynamic simulations enabled to identify two conserved amino acids that evolved from ancestral FPPSs and contribute to GPP/FPP product specificity. Overall, this study elucidates the origin of the cytosolic GPP for NUDX1-dependent geraniol production, provides insights into the emergence of the RcG/FPPS1 GPPS activity from the ancestral FPPSs, and shows that RcG/FPPS1 plays a key role in the biosynthesis of volatile terpenoid compounds in rose flowers.

Insights into the convergent evolution of fructan biosynthesis in angiosperms from the highly characteristic chicory genome

Fructans in angiosperms play essential roles in physiological functions and environmental adaptations. As a major source of industrial fructans (especially inulin-type), chicory (Cichorium intybus L.) is a model species for studying fructan biosynthesis. However, the genes underlying this process and their evolutionary history in angiosperms remain elusive. We combined multiple sequencing technologies to assemble and annotate the chicory genome and scan its (epi)genomic features, such as genomic components, DNA methylation, and three-dimensional (3D) structure. We also performed a comparative genomics analysis to uncover the associations between key traits and gene families. We achieved a nearly complete chicory genome assembly and found that continuous bursts of a few highly active retrotransposon families largely shaped the (epi)genomic characteristics. The highly methylated genome with its unique 3D structure potentially influences critical biological processes. Our comprehensive comparative genomics analysis deciphered the genetic basis for the rich sesquiterpene content in chicory and indicated that the fructan-accumulating trait resulted from convergent evolution in angiosperms due to shifts in critical sites of fructan-active enzymes. The highly characterized chicory genome provides insight into Asteraceae evolution and fructan biosynthesis in angiosperms.

Genome-wide identification of terpenoid synthase family genes in Gossypium hirsutum and functional dissection of its subfamily cadinene synthase A in gossypol synthesis

Plant terpenoid synthase (TPS) family genes participate in metabolite synthesis, hormones, gossypol, etc. Here, we genome-widely identified TPS family genes in 12 land plant species. Four hundred and thirty TPS-related genes were divided into seven subfamilies. The TPS-c in Bryophytes was suggested to be the earliest subfamily, followed by the TPS-e/f and TPS-h presence in ferns. TPS-a, the largest number of genes, was derived from monocotyledonous and dicotyledonous plants. Collinearity analysis showed that 38 out of the 76 TPS genes in G. hirsutum were collinear within G. arboreum and G. raimondii. Twenty-one GhTPS-a genes belong to the cadinene synthase (GhCDN) subfamily and were divided into five groups, A, B, C, D, and E. The special cis-elements in the promoters of 12 GhCDN-A genes suggested that the JA and ethylene signaling pathways may be involved in their expression regulation. When 12 GhCDN-A genes were simultaneously silenced through virus-induced gene silencing, the glandular color of GhCDN-A-silenced plants was lighter than that of the control, supported by a gossypol content decrease based on HPLC testing, suggesting that GhCDN-A subgroup genes participate in gossypol synthesis. According to RNA-seq analysis, gossypol synthesis-related genes and disease-resistant genes in the glandular variety exhibited upregulated expression compared to the glandless variety, whereas hormone signaling-related genes were downregulated. All in all, these results revealed plant TPS gene evolution rules and dissected the TPS subfamily, GhCDN-A, function in gossypol synthesis in cotton.

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

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

Genome-Wide Identification and Expression Analysis of TPS Gene Family in Liriodendron chinense

Terpenoids play a key role in plant growth and development, supporting resistance regulation and terpene synthase (TPS), which is the last link in the synthesis process of terpenoids. Liriodendron chinense, commonly called the Chinese tulip tree, is a rare and endangered tree species of the family Magnoliaceae. However, the genome-wide identification of the TPS gene family and its transcriptional responses to development and abiotic stress are still unclear. In the present study, we identified a total of 58 TPS genes throughout the L. chinense genome. A phylogenetic tree analysis showed that they were clustered into five subfamilies and unevenly distributed across six chromosomes. A cis-acting element analysis indicated that LcTPSs were assumed to be highly responsive to stress hormones, such as methyl jasmonate (MeJA) and abscisic acid (ABA). Consistent with this, transcriptome data showed that most LcTPS genes responded to abiotic stress, such as cold, drought, and hot stress, at the transcriptional level. Further analysis showed that LcTPS genes were expressed in a tissue-dependent manner, especially in buds, leaves, and bark. Quantitative reverse transcription PCR (qRT-PCR) analysis confirmed that LcTPS expression was significantly higher in mature leaves compared to young leaves. These results provide a reference for understanding the function and role of the TPS family, laying a foundation for further study of the regulation of TPS in terpenoid biosynthesis in L. chinense.

Plastidial engineering with coupled farnesyl diphosphate pool reconstitution and enhancement for sesquiterpene biosynthesis in tomato fruit

Sesquiterpenes represent a large class of terpene compounds found in plants with broad applications such as pharmaceuticals and biofuels. The plastidial MEP pathway in ripening tomato fruit is naturally optimized to provide the 5-carbon isoprene building blocks of all terpenes for production of the tetraterpene pigment lycopene and other carotenoids, making it an excellent plant system to be engineered for production of high-value terpenoids. We reconstituted and enhanced the pool of sesquiterpene precursor farnesyl diphosphate (FPP) in plastids of tomato fruit by overexpressing the fusion gene DXS-FPPS encoding a fusion protein of 1-deoxy-D-xylulose 5-phosphate synthase (DXS) linked with farnesyl diphosphate synthase (originally called farnesyl pyrophosphate synthase, and abbreviated as FPPS) under the control of fruit-ripening specific polygalacturonase (PG) promoter concomitant with substantial reduction in lycopene content and large production of FPP-derived squalene. The supply of precursors achieved by the fusion gene expression can be harnessed by an engineered sesquiterpene synthase that is retargeted to plastid to engineer high-yield sesquiterpene production in tomato fruit, offering an effective production system for high-value sesquiterpene ingredients.

The genomes of medicinal skullcaps reveal the polyphyletic origins of clerodane diterpene biosynthesis in the family Lamiaceae

The presence of anticancer clerodane diterpenoids is a chemotaxonomic marker for the traditional Chinese medicinal plant Scutellaria barbata, although the molecular mechanisms behind clerodane biosynthesis are unknown. Here, we report a high-quality assembly of the 414.98 Mb genome of S. barbata into 13 pseudochromosomes. Using phylogenomic and biochemical data, we mapped the plastidial metabolism of kaurene (gibberellins), abietane, and clerodane diterpenes in three species of the family Lamiaceae (Scutellaria barbata, Scutellaria baicalensis, and Salvia splendens), facilitating the identification of genes involved in the biosynthesis of the clerodanes, kolavenol, and isokolavenol. We show that clerodane biosynthesis evolved through recruitment and neofunctionalization of genes from gibberellin and abietane metabolism. Despite the assumed monophyletic origin of clerodane biosynthesis, which is widespread in species of the Lamiaceae, our data show distinct evolutionary lineages and suggest polyphyletic origins of clerodane biosynthesis in the family Lamiaceae. Our study not only provides significant insights into the evolution of clerodane biosynthetic pathways in the mint family, Lamiaceae, but also will facilitate the production of anticancer clerodanes through future metabolic engineering efforts.

Functional characterization of a bark-specific monoterpene synthase potentially involved in wounding- and methyl jasmonate-induced linalool emission in rubber (Hevea brasiliensis)

Rubber (Hevea brasiliensis) is a latex-producing plant that often encounters mechanical wounding, as well as pathogen and pest attacks through wound sites during and after tapping. Terpenoids play an important role in the ecological interactions of many plant species, and their diversity is mainly generated by enzymes known as terpene synthases (TPS). In this study, one cDNA sequence encoding a putative terpene synthase, HbTPS20, was obtained from the bark tissues of H. brasiliensis. The encoded protein contains 610 amino acids with a putative N-terminal plastid transit peptide of approximately 70 residues. It belongs to the TPS-b subfamily. Further phylogenetic analysis showed that HbTPS20 formed a separate branch that diverged from the progenitor of all other potentially functional terpene synthases of the rubber TPS-b subfamily. The truncated HbTPS20 without the signal peptide coding sequence was successfully expressed in E. coli and in vitro enzymatic assays with geranyl diphosphate (GPP) or neryl diphosphate (NPP) as a substrate defined HbTPS20 as an active linalool synthase (HbLIS) with the ability to produce linalool as the principal product. RT-qPCR analysis showed that the highest transcript levels of HbTPS20 were found in barks, and this gene was expressed at 2.26- and 250-fold greater levels in the bark tissues of wounded and MeJA-treated plants, respectively, than in those of the control plants. This indicates that this gene may be involved in the induced stress responses of rubber.

Systematic identification of TPS genes in Gossypium and their characteristics in response to flooding stress

Terpene synthases (TPS) is a key enzyme in the synthesis of plant terpenoids. Studies on TPSs have not been reported in Gossypium barbadense and Gossypium arboreum. 260 TPSs were identified in Gossypium, including 71 in Gossypium hirsutum, 75 in Gossypium. barbadense, 60 in Gossypium. arboreum, and 54 in Gossypium raimondii. We systematically analyzed the TPS gene family of Gossypium from three aspects: gene structure, evolutionary process and gene function. (1) Gene structure: Based on the protein structure of two conserved domains (PF01397 and PF03936), the TPS gene family is divided into five clades: TPS -a, -b, -c, -e/f and -g. (2) Evolution: Whole genome duplication and segmental duplication are the main modes of TPS gene amplification. (3) Function: The abundance of cis-acting elements may reveal the functional diversity of TPSs in cotton. TPS gene has tissue specific expression in cotton. The hypomethylation of the exon of TPSs may help to enhance the adaptability of cotton to flooding stress. In conclusion, this study can broaden the understanding of structure-evolution-function of the TPS gene family, and provide reference for the mining and verification of new genes.

Biogenesis of flavor-related linalool is diverged and genetically conserved in tree peony (Paeonia × suffruticosa)

Floral scent is an important and genetically complex trait in horticultural plants. Tree peony (Paeonia × suffruticosa) originates in the Pan-Himalaya and has nine wild species divided into two subsections, Delavayanae and Vaginatae. Their flowers are beloved worldwide for their sweet floral fragrance, yet the flavor-related volatiles and underlying biosynthetic pathways remain unknown. Here, we characterized the volatile blends of all wild tree peony species and found that the flavor-related volatiles were highly divergent, but linalool was a unique monoterpene in subsect. Delavayanae. Further detection of volatiles in 97 cultivars with various genetic backgrounds showed that linalool was also the characteristic aroma component in Paeonia delavayi hybrid progenies, suggesting that linalool was conserved and dominant within subsect. Delavayanae and its hybrids, instead of species and cultivars from subsect. Vaginatae. Global transcriptome analysis of all wild tree peony species and 60 cultivars revealed five candidate genes that may be involved in key steps of linalool biosynthesis; especially the expressions of three TPS genes, PdTPS1, PdTPS2, and PdTPS4, were significantly positively correlated with linalool emissions across tree peony cultivars. Further biochemical evidence demonstrated that PdTPS1 and PdTPS4 were the pivotal genes determining the species-specific and cultivar-specific emission of linalool. This study revealed a new insight into floral scent divergence in tree peony and would greatly facilitate our understanding of the phylogeny and evolution of Paeonia.

Full-length transcriptome analysis of two chemotype and functional characterization of genes related to sesquiterpene biosynthesis in Atractylodes lancea

Atractylodes lancea (Thunb.) DC. is an important medicinal plant mainly distributed in China. A. lancea is rich in volatile oils and has a significant effect on various diseases, including coronavirus disease 2019 (COVID-19). Based on the signature constituents of volatile oils, A. lancea is divided into two chemotypes: the Dabieshan and Maoshan chemotype. Gas chromatography-mass spectrometry (GC-MS) results revealed that the hinesol and β-eudesmol contents in the Dabieshan chemotype were higher than those in the Maoshan chemotype. Next-generation sequencing (NGS) and single-molecule real-time (SMRT) sequencing technologies were combined to investigate the molecular mechanisms of sesquiterpenoid biosynthesis in A. lancea. A total of 42 differentially expressed genes (DEGs) for terpenoid biosynthesis were identified in the two chemotype groups, and nine full-length terpene synthase (TPS) genes were identified. Subcellular localization revealed that AlTPS1 and AlTPS2 proteins were localized in the nucleus and endoplasmic reticulum. They use FPP as a substrate to generate sesquiterpenoids. AlTPS1 catalyzes biosynthesis of elemol while AlTPS2 is observed to perform β-farnesene synthase activity. This study provides information for understanding the differences in the accumulation of terpenoids in two chemotypes of A. lancea and lays a foundation for further elucidation of the molecular mechanism of sesquiterpenoid biosynthesis.

Comprehensive identification of terpene synthase genes and organ-dependent accumulation of terpenoid volatiles in a traditional medicinal plant Angelica archangelica L

Angelica archangelica L. is a traditional medicinal plant of Nordic origin that produces an unusual amount and variety of terpenoids. The unique terpenoid composition of A. archangelica likely arises from the involvement of terpene synthases (TPSs) with different specificities, none of which has been identified. As the first step in identifying TPSs responsible for terpenoid chemodiversity in A. archangelica, we produced a transcriptome catalogue using the mRNAs extracted from the leaves, tap roots, and dry seeds of the plant; 11 putative TPS genes were identified (AaTPS1-AaTPS11). Phylogenetic analysis predicted that AaTPS1-AaTPS5, AaTPS6-AaTPS10, and AaTPS11 belong to the monoterpene synthase (monoTPS), sesquiterpene synthase (sesquiTPS), and diterpene synthase clusters, respectively. We then performed in vivo enzyme assays of the AaTPSs using recombinant Escherichia coli systems to examine their enzymatic activities and specificities. Nine recombinant enzymes (AaTPS2-AaTPS10) displayed TPS activities with specificities consistent with their phylogenetics; however, AaTPS5 exhibited a strong sesquiTPS activity along with a weak monoTPS activity. We also analyzed terpenoid volatiles in the flowers, immature and mature seeds, leaves, and tap roots of A. archangelica using gas chromatography-mass spectrometry; 14 monoterpenoids and 13 sesquiterpenoids were identified. The mature seeds accumulated the highest levels of monoterpenoids, with β-phellandrene being the most prominent. α-Pinene and β-myrcene were abundant in all organs examined. The in vivo assay results suggest that the AaTPSs functionally identified in this study are at least partly involved in the chemodiversity of terpenoid volatiles in A. archangelica.

Transcriptome sequencing and gas chromatography–mass spectrometry analyses provide insights into β-caryophyllene biosynthesis in Brassica campestris

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β-Caryophyllene (BCP) was detected in Brassica campestris.

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BCP content changed in cultivars during developmental stages and MeJA treatment.

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In the phylogenetic analysis, the TPSa gene subfamily was divided into four groups

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The potential regulatory and transporter network of BCP was constructed.

Sesquiterpenes are important defensive secondary metabolites and aroma components. However, limited information is available on the mechanism of sesquiterpene formation and composition in the non-heading Chinese cabbage (NHCC) leaf. Therefore, headspace solid-phase microextraction/gas chromatography–mass spectrometry (HS-SPME/GC–MS) combined with transcriptome analysis was used to study the mechanism of volatile organic compound formation. A total of 26 volatile organic compounds were identified in two NHCC cultivars ‘SZQ’ and ‘XQC’ and their F1 hybrids. Among these, sesquiterpene β-caryophyllene was identified only in ‘XQC’ and F1. Five genes encoding caryophyllene synthase were identified. The candidate β-caryophyllene synthase genes BcTPSa11 and BcTPSa21 had high expression levels only in ‘XQC’ and F1. In addition, several transcription factors of MYB-related, MYB, bHLH, and AP2/ERF families were identified by co-expression, suggesting that they regulate β-caryophyllene biosynthesis. Our results provide a molecular basis for sesquiterpene biosynthesis as well as insights into the regulatory network of β-caryophyllene in NHCC.

Thirteen Dipterocarpoideae genomes provide insights into their evolution and borneol biosynthesis

Dipterocarpoideae, the largest subfamily of the Dipterocarpaceae, is a dominant component of Southeast Asian rainforests and is widely used as a source of wood, damar resin, medicine, and essential oil. However, many Dipterocarpoideae species are currently on the IUCN Red List owing to severe degradation of their habitats under global climate change and human disturbance. Genetic information regarding these taxa has only recently been reported with the sequencing of four Dipterocarp genomes, providing clues to the function and evolution of these species. Here, we report on 13 high-quality Dipterocarpoideae genome assemblies, ranging in size from 302.6 to 494.8 Mb and representing the five most species-rich genera in Dipterocarpoideae. Molecular dating analyses support the Western Gondwanaland origin of Dipterocarpaceae. Based on evolutionary analysis, we propose a three-step chromosome evolution scenario to describe the karyotypic evolution from an ancestor with six chromosomes to present-day species with 11 and 7 chromosomes. We discovered an expansion of genes encoding cellulose synthase (CesA), which is essential for cellulose biosynthesis and secondary cell-wall formation. We functionally identified five bornyl diphosphate synthase (BPPS) genes, which specifically catalyze the biosynthesis of borneol, a natural medicinal compound extracted from damar resin and oils, thus providing a basis for large-scale production of natural borneol in vitro.

Metabolome and transcriptome analysis of terpene synthase genes and their putative role in floral aroma production in Litchi chinensis

Volatile organic compounds (VOCs) are essential traits of flowers since they attract pollinators, aid in seed distribution, protect the plant from internal and external stimuli, and are involved in plant-plant and plant-environment interactions. Apart from their role in plants, VOCs are used in pharmaceuticals, fragrances, cosmetics, and flavorings. Litchi (Litchi chinensis Sonn.) is a popular fruit due to its enticing red appearance, exotic taste, and high nutritional qualities. Litchi flowers bloom as inflorescences primarily on the shoot terminals. There are three distinct flower types, two male and one female, all of which are produced on the same panicle and rely on insect pollination. Herein, we used a comprehensive metabolomic approach to examine the volatile profile of litchi fruit (green pericarp, yellow pericarp, and red pericarp) as well as male and female flowers (bud stage, half open and full bloom). From a quantitative examination of the volatiles in L. chinensis, a total of 19, 22, and 21 VOCs were discovered from female flowers, male flowers, and fruits, with the majority of them belonging to sesquiterpenes. Multivariate analysis revealed that the volatile profiles of fruits differ from those of male and female flowers. Three VOCs were unique to male flowers and ten to the fruit, while eight VOCs were shared by both male and female flowers and eleven by both male and female flowers and the fruit. Furthermore, for the first time, we identified and comprehensively studied the TERPENE SYNTHASE genes (TPS) using the litchi genome and transcriptome database, which revealed 38 TPS genes unevenly distributed across the 15 chromosomes. A phylogenetic study showed that LcTPS were grouped into TPS-b, TPS-c, TPS-e, TPS-f, and TPS-g subfamilies, with TPS-b having the most genes. The conserved motifs (RR_X8 W, NSE/DTE, and DD_XX D) were studied in LcTPSs, and significant variation between subfamilies was discovered. Furthermore, after integrating the metabolome and transcriptome datasets, several VOCs were shown to be development-specific and highly linked with distinct LcTPS genes, making them promising biomarkers. Interestingly, LcTPS17/20/23/24/31 were associated with monoterpene edges, while the rest were connected to sesquiterpene edges, indicating their probable participation in the aroma biosynthesis mechanism of certain compounds.

Genome-wide analysis of terpene synthase gene family to explore candidate genes related to disease resistance in Prunus persica

In plants, a family of terpene synthases (TPSs) is responsible for the biosynthesis of terpenes and contributes to species-specific diversity of volatile organic compounds, which play essential roles in fitness of plants. However, little is known about the TPS gene family in peach and/or nectarine (Prunus persica L.). In this study, we identified 40 PpTPS genes in peach genome v2.0. Although these PpTPSs could be clustered into five classes, they distribute in several gene clusters of three chromosomes, share conserved exon-intron organizations, and code similar protein motifs. Thirty-five PpTPSs, especially PpTPS2, PpTPS23, PpTPS17, PpTPS18, and PpTPS19, altered their transcript levels after inoculation with Botryosphaeria dothidea, a cause of peach gummosis, compared to the mock treatments, which might further affect the contents of 133 terpenoids at 48 hours and/or 84 hours post inoculations in the current-year shoots of 'Huyou018', a highly susceptible nectarine cultivar. Moreover, about fifteen PpTPSs, such as PpTPS1, PpTPS2, PpTPS3, and PpTPS5, showed distinct expression patterns during fruit development and ripening in two peach cultivars, yellow-fleshed 'Jinchun' and white-fleshed 'Hikawa Hakuho'. Among them, the transcription level of chloroplast-localized PpTPS3 was obviously related to the content of linalool in fruit pulps. In addition, elevated concentrations (0.1 g/L to 1.0 g/L) of linalool showed antifungal activities in PDA medium. These results improve our understanding of peach PpTPS genes and their potential roles in defense responses against pathogens.

Targeted approaches to improve tomato fruit taste

Tomato (Solanum lycopersicum) is the most valuable fruit and horticultural crop species worldwide. Compared with the fruits of their progenitors, those of modern tomato cultivars are, however, often described as having unsatisfactory taste or lacking flavor. The flavor of a tomato fruit arises from a complex mix of tastes and volatile metabolites, including sugars, acids, amino acids, and various volatiles. However, considerable differences in fruit flavor occur among tomato varieties, resulting in mixed consumer experiences. While tomato breeding has traditionally been driven by the desire for continual increases in yield and the introduction of traits that provide a long shelf-life, consumers are prepared to pay a reasonable premium for taste. Therefore, it is necessary to characterize preferences of tomato flavor and to define its underlying genetic basis. Here, we review recent conceptual and technological advances that have rendered this more feasible, including multi-omics-based QTL and association analyses, along with the use of trained testing panels, and machine learning approaches. This review proposes how the comprehensive datasets compiled to date could allow a precise rational design of tomato germplasm resources with improved organoleptic quality for the future.

Identification and characterization of three nearly identical linalool/nerolidol synthase from Acorus calamus

Acorus calamus is a perennial aromatic medicinal plant from the Acorusaceae family, known for its pharmaceutical and medicinal value. A combined chemical, biochemical, and molecular study was conducted to evaluate the differential accumulation of volatile organic compounds (VOCs) in rhizomes and leaves of A. calamus essential oil. Here, we performed VOC profiling and transcriptome-based identification and functional characterization of terpene synthase (TPS) genes. A total of 110 VOCs were detected from the rhizomes and leaves of A. calamus, and some VOCs showed significant differences between them. The further transcriptome-based analysis led to the identification of six putative TPSs genes. In phylogenetic analysis, three TPSs belonged to the TPS-g clade, one to each of the TPS-a, TPS-c, and TPS-e clades. The heterologous E. coli-based expression of recombinant TPSs identified three genes (AcTPS3, AcTPS4, and AcTPS5) as bifunctional linalool/nerolidol synthase. The correlation of TPS gene expression and VOC metabolite profiles supported the function of these genes in A. calamus. Our findings provide a roadmap for future efforts to enhance the molecular mechanisms of terpene biosynthesis and our understanding of Acorus-insect interactions.

Genome-wide identification and analysis of terpene synthase (TPS) genes in celery reveals their regulatory roles in terpenoid biosynthesis

Terpenes are an important class of secondary metabolites in celery, which determine its flavor. Terpene synthase (TPS) has been established as a key enzyme in the biosynthesis of terpenes. This study systematically analyzed all members of the TPS gene family of celery (Apium graveolens) based on whole genome data. A total of 39 celery TPS genes were identified, among which TPS-a and TPS-b represented the two largest subfamilies. 77 cis-element types were screened in the promoter regions of AgTPS genes, suggesting the functional diversity of members of this family. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses showed that AgTPS genes were enriched in multiple terpenoid biosynthesis pathways. Transcript abundance analysis and qRT-PCR showed that most AgTPS genes were differentially expressed in different tissues and colors of celery, with AgTPS 6, 9, and 11 expressed differentially in tissues, while AgTPS31, 32, and 38 are expressed differently in colors. More than 70% of the celery volatile compounds identified by HS-SPME-GC/MS were terpene, and the most critical compounds were β-Myrcene, D-Limonene, β-Ocimene and γ-Terpinene. Principal component analysis (PCA) showed that compounds (E)-β-Ocimene, D-Limonene, β-Myrcene and γ-Terpinene predominantly accounted for the variation. Further correlation analysis between gene expression and terpenoid accumulation showed that the four genes AgTPS9, 25, 31 and 38 genes may have positive regulatory effects on the synthesis of D-Limonene and β-Myrcene in celery. Overall, this study identified key candidate genes that regulate the biosynthesis of volatile compounds and provide the foothold for the development and utilization of terpenoids in celery.

A monoterpene synthase gene cluster of tea plant (Camellia sinensis) potentially involved in constitutive and herbivore-induced terpene formation

Monoterpenes and sesquiterpenes are the most abundant volatiles in tea plants and have dual functions in aroma quality formation and defense responses in tea plants. Terpene synthases (TPS) are the key enzymes for the synthesis of terpenes in plants; however, the functions of most of them in tea plants are still unknown. In this study, six putative terpene biosynthesis gene clusters were identified from the tea plant genome. Then we cloned three new TPS-b subfamily genes, CsTPS08, CsTPS10 and CsTPS58. In vitro enzyme assays showed that CsTPS08 and CsTPS58 are two multiple-product terpene synthases, with the former synthesizing linalool as the main product, and β-myrcene, α-phellandrene, α-terpinolene, D-limonene, cis-β-ocimene, trans-β-ocimene and (4E,6Z)-allo-ocimene as minor products are also detected, while the latter catalyzing the formation of α-pinene and D-limonene using GPP as the substrate. No product of CsTPS10 was detected in the prokaryotic expression system, but geraniol production was detected when transiently expressed in tobacco leaves. CsTPS08 and CsTPS10 are two functional members of a monoterpene synthase gene cluster, which were significantly induced during both Ectropis oblique feeding and fresh leaf spreading treatments, suggesting that they have dual functions involved in tea plant pest defense and tea aroma quality regulation. In addition, the differences in their expression levels in different tea plant cultivars provide a possibility for the subsequent screening of tea plant resources with a specific aroma flavor. Our results deepen the understanding of terpenoid synthesis in tea plants.

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.

Genome-wide identification and characterization of terpene synthase genes in Gossypium hirsutum

Terpenoids are widely distributed in plants and play important roles in the regulation of plant growth and development and in the interactions between plants and both the environment and other organisms. However, terpene synthase (TPS) genes have not been systematically investigated in the tetraploid Gossypium hirsutum. In this study, whole genome identification and characterization of the TPS family from G. hirsutum were carried out. Eighty-five TPS genes, including 47 previously unidentified genes, were identified in the G. hirsutum genome and classified into 5 subfamilies according to protein sequence similarities, as follows: 43 GhTPS-a, 29 GhTPS-b, 4 GhTPS-c, 7 GhTPS-e/f, and 2 GhTPS-g members. These 85 TPS genes were mapped onto 19 chromosomes of the G. hirsutum genome. Segmental duplications and tandem duplications contributed greatly to the expansion of TPS genes in G. hirsutum and were followed by intense purifying selection during evolution. Indentification of cis-acting regulatory elements suggest that the expression of TPS genes is regulated by a variety of hormones. RNA sequencing (RNA-seq) expression profile analysis revealed that the TPS genes had distinct spatiotemporal expression patterns, and several genes were highly and preferentially expressed in the leaves of cotton with gossypol glands (glanded cotton) versus a glandless strain. Virus-induced gene silencing (VIGS) of three TPS genes yielded plants characterized by fewer, smaller, and lighter gossypol glands, which indicated that these three genes were responsible for gland activity. Taken together, our results provide a solid basis for further elucidation of the biological functions of TPS genes in relation to gland activity and gossypol biosynthesis to develop cotton cultivars with low cottonseed gossypol contents.

The chromosome-scale assembly of endive (Cichorium endivia) genome provides insights into the sesquiterpenoid biosynthesis

Endive (Cichorium endivia L.) is a leafy vegetable in the Asteraceae family. Sesquiterpene lactones (STLs) in endive leaves bring a bitter taste that varies between varieties. Despite their importance in breeding varieties with unique flavours, sesquiterpenoid biosynthesis pathways in endive are poorly understood. We assembled a chromosome-scale endive genome of 641 Mb with a contig N50 of 5.16 Mb and annotated 46,711 protein-coding genes. Several gene families, especially terpene synthases (TPS) genes, expanded significantly in the C. endivia genome. STLs biosynthesis-related genes and TPS genes in more bitter varieties have shown a higher level of expression, which could be attributed to genomic variations. Our results penetrate the origin and diversity of bitter taste and facilitate the molecular breeding of endive varieties with unique bitter tastes. The high-quality endive assembly would provide a reference genome for studying the evolution and diversity of Asteraceae.