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

Biosynthesis of Haloterpenoids in Red Algae via Microbial-like Type I Terpene Synthases

Red algae or seaweeds produce highly distinctive halogenated terpenoid compounds, including the pentabromochlorinated monoterpene halomon that was once heralded as a promising anticancer agent. The first dedicated step in the biosynthesis of these natural product molecules is expected to be catalyzed by terpene synthase (TS) enzymes. Recent work has demonstrated an emerging class of type I TSs in red algal terpene biosynthesis. However, only one such enzyme from a notoriously haloterpenoid-producing red alga (Laurencia pacifica) has been functionally characterized and the product structure is not related to halogenated terpenoids. Herein, we report 10 new type I TSs from the red algae Portieria hornemannii, Plocamium pacificum, L. pacifica, and Laurencia subopposita that produce a diversity of halogenated mono- and sesquiterpenes. We used a combination of genome sequencing, terpenoid metabolomics, in vitro biochemistry, and bioinformatics to establish red algal TSs in all four species, including those associated with the selective production of key halogenated terpene precursors myrcene, trans-β-ocimene, and germacrene D-4-ol. These results expand on a small but growing number of characterized red algal TSs and offer insight into the biosynthesis of iconic halogenated algal compounds that are not without precedence elsewhere in biology.

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.

The haplotype-resolved genome assembly of autotetraploid rhubarb Rheum officinale provides insights into its genome evolution and massive accumulation of anthraquinones

Rheum officinale, a member of the Polygonaceae family, is an important medicinal plant that is widely used in traditional Chinese medicine. Here, we report a 7.68-Gb chromosome-scale assembly of R. officinale with a contig N50 of 3.47 Mb, which was clustered into 44 chromosomes across four homologous groups. Comparative genomics analysis revealed that transposable elements have made a significant contribution to its genome evolution, gene copy number variation, and gene regulation and expression, particularly of genes involved in metabolite biosynthesis, stress resistance, and root development. We placed the recent autotetraploidization of R. officinale at ∼0.58 mya and analyzed the genomic features of its homologous chromosomes. Although no dominant monoploid genomes were observed at the overall expression level, numerous allele-differentially-expressed genes were identified, mainly with different transposable element insertions in their regulatory regions, suggesting that they functionally diverged after polyploidization. Combining genomics, transcriptomics, and metabolomics, we explored the contributions of gene family amplification and tetraploidization to the abundant anthraquinone production of R. officinale, as well as gene expression patterns and differences in anthraquinone content among tissues. Our report offers unprecedented genomic resources for fundamental research on the autopolyploid herb R. officinale and guidance for polyploid breeding of herbs.

Exploring the versatility of sesquiterpene biosynthesis in guava plants: a comparative genome-wide analysis of two cultivars

Psidium guajava L., a fruit crop belonging to the Myrtaceae family, is highly valued for its nutritional and medicinal properties. The family exhibits a diverse chemical profile of essential oils and serves as a valuable resource due to its ecological interactions, adaptability, and dispersal capacity. The Myrtaceae family has been extensively studied for its terpenoids. Genetic studies have focused on foliar terpene yield in species from the Eucalypteae and Melaleucaceae tribes. To understand the evolutionary trends in guava breeding, this study predicted terpene synthase genes (TPS) from different cultivars. Through this analysis, 43 full-length TPS genes were identified, and approximately 77% of them exhibited relative expression in at least one of the five investigated plant tissues (root, leaf, bud, flower, and fruit) of two guava cultivars. We identified intra-species variation in the terpene profile and single nucleotide polymorphisms (SNPs) in twelve TPS genes, resulting in the clustering of 62 genotypes according to their essential oil chemotypes. The high concentration of sesquiterpenes is supported by the higher number of TPS-a genes and their expression. The expansion for TPS sub-families in P. guajava occurred after the expansion of other rosids species. Providing insight into the origin of structural diversification and expansion in each clade of the TPS gene family within Myrtaceae. This study can provide insights into the diversity of genes for specialized metabolites such as terpenes, and their regulation, which can lead to a diverse chemotype of essential oil in different tissues and genotypes. This suggests a mode of enzymatic evolution that could lead to high sesquiterpene production, act as a chemical defense and contribute to the adaptive capacity of this species to different habitats.

The telomere-to-telomere (T2T) genome of Peucedanum praeruptorum Dunn provides insights into the genome evolution and coumarin biosynthesis

BACKGROUND

Traditional Chinese medicine has used Peucedanum praeruptorum Dunn (Apiaceae) for a long time. Various coumarins, including the significant constituents praeruptorin (A-E), are the active constituents in the dried roots of P. praeruptorum. Previous transcriptomic and metabolomic studies have attempted to elucidate the distribution and biosynthetic network of these medicinal-valuable compounds. However, the lack of a high-quality reference genome impedes an in-depth understanding of genetic traits and thus the development of better breeding strategies.

RESULTS

A telomere-to-telomere (T2T) genome was assembled for P. praeruptorum by combining PacBio HiFi, ONT ultra-long, and Hi-C data. The final genome assembly was approximately 1.798 Gb, assigned to 11 chromosomes with genome completeness >98%. Comparative genomic analysis suggested that P. praeruptorum experienced 2 whole-genome duplication events. By the transcriptomic and metabolomic analysis of the coumarin metabolic pathway, we presented coumarins' spatial and temporal distribution and the expression patterns of critical genes for its biosynthesis. Notably, the COSY and cytochrome P450 genes showed tandem duplications on several chromosomes, which may be responsible for the high accumulation of coumarins.

CONCLUSIONS

A T2T genome for P. praeruptorum was obtained, providing molecular insights into the chromosomal distribution of the coumarin biosynthetic genes. This high-quality genome is an essential resource for designing engineering strategies for improving the production of these valuable compounds.

Complete pathway elucidation and heterologous reconstitution of (+)-nootkatone biosynthesis from Alpinia oxyphylla

(+)-Nootkatone is a natural sesquiterpene ketone widely used in food, cosmetics, pharmaceuticals, and agriculture. It is also regarded as one of the most valuable terpenes used commercially. However, plants contain trace amounts of (+)-nootkatone, and extraction from plants is insufficient to meet market demand. Alpinia oxyphylla is a well-known medicinal plant in China, and (+)-nootkatone is one of the main components within the fruits. By transcriptome mining and functional screening using a precursor-providing yeast chassis, the complete (+)-nootkatone biosynthetic pathway in Alpinia oxyphylla was identified. A (+)-valencene synthase (AoVS) was identified as a novel monocot-derived valencene synthase; three (+)-valencene oxidases AoCYP6 (CYP71BB2), AoCYP9 (CYP71CX8), and AoCYP18 (CYP701A170) were identified by constructing a valencene-providing yeast strain. With further characterisation of a cytochrome P450 reductase (AoCPR1) and three dehydrogenases (AoSDR1/2/3), we successfully reconstructed the (+)-nootkatone biosynthetic pathway in Saccharomyces cerevisiae, representing a basis for its biotechnological production. Identifying the biosynthetic pathway of (+)-nootkatone in A. oxyphylla unravelled the molecular mechanism underlying its formation in planta and also supported the bioengineering production of (+)-nootkatone. The highly efficient yeast chassis screening method could be used to elucidate the complete biosynthetic pathway of other valuable plant natural products in future.

Integrative metabolome and transcriptome analyses reveal the differences in flavonoid and terpenoid synthesis between Glycyrrhiza uralensis (licorice) leaves and roots

Licorice from Glycyrrhiza uralensis roots is used in foods and medicines. Although we are aware that licorice roots and leaves have distinct material compositions, the specific reasons for these differences remain unknown. Comparison of the metabolomes and transcriptomes between the leaves and roots revealed flavonoids and triterpenoid saponins were significantly different. Isoflavones were enriched in roots because of upregulation of genes encoding chalcone isomerase and flavone synthase, which are involved in isoflavone synthesis. Six triterpenoid saponins were significantly enriched only in the roots. The leaves did not accumulate glycyrrhetinic acid because of low expression levels of genes involved in its synthesis. A gene encoding a UDP glycosyltransferase, which likely catalyzes the key step in the transformation of glycyrrhetinic acid to glycyrrhizin, was screened. Our results provide information about the differences in flavonoid and triterpenoid synthesis between roots and leaves, and highlight targets for genetic engineering.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-023-01467-y.

Reference genome of the nutrition-rich orphan crop chia (Salvia hispanica) and its implications for future breeding

Chia (Salvia hispanica L.) is one of the most popular nutrition-rich foods and pseudocereal crops of the family Lamiaceae. Chia seeds are a rich source of proteins, polyunsaturated fatty acids (PUFAs), dietary fibers, and antioxidants. In this study, we present the assembly of the chia reference genome, which spans 303.6 Mb and encodes 48,090 annotated protein-coding genes. Our analysis revealed that ~42% of the chia genome harbors repetitive content, and identified ~3 million single nucleotide polymorphisms (SNPs) and 15,380 simple sequence repeat (SSR) marker sites. By investigating the chia transcriptome, we discovered that ~44% of the genes undergo alternative splicing with a higher frequency of intron retention events. Additionally, we identified chia genes associated with important nutrient content and quality traits, such as the biosynthesis of PUFAs and seed mucilage fiber (dietary fiber) polysaccharides. Notably, this is the first report of in-silico annotation of a plant genome for protein-derived small bioactive peptides (biopeptides) associated with improving human health. To facilitate further research and translational applications of this valuable orphan crop, we have developed the Salvia genomics database (SalviaGDB), accessible at https://salviagdb.org.

Multiomics Analysis Reveals the Genetic Basis of Volatile Terpenoid Formation in Oolong Tea

Oolong tea has gained great popularity in China due to its pleasant floral and fruity aromas. Although numerous studies have investigated the aroma differences across various tea cultivars, the genetic mechanism is unclear. This study performed multiomics analysis of three varieties suitable for oolong tea and three others with different processing suitability. Our analysis revealed that oolong tea varieties contained higher levels of cadinane sesquiterpenoids. PanTFBS was developed to identify variants of transcription factor binding sites (TFBSs). We found that the CsDCS gene had two TFBS variants in the promoter sequence and a single nucleotide polymorphism (SNP) in the coding sequence. Integrating data on genetic variations, gene expression, and protein-binding sites indicated that CsDCS might be a pivotal gene involved in the biosynthesis of cadinane sesquiterpenoids. These findings advance our understanding of the genetic factors involved in the aroma formation of oolong tea and offer insights into the enhancement of tea aroma.

Chemistry, biosynthesis and biology of floral volatiles: roles in pollination and other functions

Covering: 2010 to 2023Floral volatiles are a chemically diverse group of plant metabolites that serve multiple functions. Their composition is shaped by environmental, ecological and evolutionary factors. This review will summarize recent advances in floral scent research from chemical, molecular and ecological perspectives. It will focus on the major chemical classes of floral volatiles, on notable new structures, and on recent discoveries regarding the biosynthesis and the regulation of volatile emission. Special attention will be devoted to the various functions of floral volatiles, not only as attractants for different types of pollinators, but also as defenses of flowers against enemies. We will also summarize recent findings on how floral volatiles are affected by abiotic stressors, such as increased temperatures and drought, and by other organisms, such as herbivores and flower-dwelling microbes. Finally, this review will indicate current research gaps, such as the very limited knowledge of the isomeric pattern of chiral compounds and its importance in interspecific interactions.

LcMYB106 suppresses monoterpene biosynthesis by negatively regulating LcTPS32 expression in Litsea cubeba

Litsea cubeba, the core species of the Lauraceae family, is valuable for the production of essential oils due to its high concentration of monoterpenes (90%). The key monoterpene synthase and metabolic regulatory network of monoterpene biosynthesis have provided new insights for improving essential oil content. However, there are few studies on the regulation mechanism of monoterpenes in L. cubeba. In this study, we investigated LcTPS32, a member of the TPS-b subfamily, and identified its function as an enzyme for the synthesis of monoterpenes, including geraniol, α-pinene, β-pinene, β-myrcene, linalool and eucalyptol. The quantitative real-time PCR analysis showed that LcTPS32 was highly expressed in the fruits of L. cubeba and contributed to the characteristic flavor of its essential oil. Overexpression of LcTPS32 resulted in a significant increase in the production of monoterpenes in L. cubeba by activating both the MVA and MEP pathways. Additionally, the study revealed that LcMYB106 played a negative regulatory role in monoterpenes biosynthesis by directly binding to the promoter of LcTPS32. Our study indicates that LcMYB106 could serve as a crucial target for metabolic engineering endeavors, aiming at enhancing the monoterpene biosynthesis in L. cubeba.

Subcellular compartmentalization in the biosynthesis and engineering of plant natural products

Plant natural products (PNPs) are specialized metabolites with diverse bioactivities. They are extensively used in the pharmaceutical, cosmeceutical and food industries. PNPs are synthesized in plant cells by enzymes that are distributed in different subcellular compartments with unique microenvironments, such as ions, co-factors and substrates. Plant metabolic engineering is an emerging and promising approach for the sustainable production of PNPs, for which the knowledge of the subcellular compartmentalization of their biosynthesis is instrumental. In this review we describe the state of the art on the role of subcellular compartments in the biosynthesis of major types of PNPs, including terpenoids, phenylpropanoids, alkaloids and glucosinolates, and highlight the efforts to target biosynthetic pathways to subcellular compartments in plants. In addition, we will discuss the challenges and strategies in the field of plant synthetic biology and subcellular engineering. We expect that newly developed methods and tools, together with the knowledge gained from the microbial chassis, will greatly advance plant metabolic engineering.

Characterization of SchTPSs Enables Construction of Yeast for the Bioproduction of α-Cadinol and the Related Sesquiterpenes

Plant volatile sesquiterpenes (PVSs) play important roles in chemical plant defense. However, it is difficult to isolate sufficient PVSs for deep investigations due to their low contents and chemical and physical properties close to those of other lipids. The extracts of Stellera chamaejasme L. exhibit insecticidal, fungicidal, and allelopathic activities. In this study, we identified three sesquiterpene synthase genes (SchTPS5, SchTPS6, and SchTPS7) from S. chamaejasme L. SchTPS7 is an α-farnesene synthase. SchTPS5 and SchTPS6 are two catalytically promiscuous sesquiterpene synthases, and α-cadinol and τ-muurolol are the predominant products for both of them in Saccharomyces cerevisiae. This study, for the first time, reports plant sesquiterpene synthases capable of producing α-cadinol and/or τ-muurolol in a heterologous host. More intriguingly, seven out of eight products of SchTPS6 in S. cerevisiae possess various insecticidal, fungicidal, and herbicidal activities. Building on this finding, we used SchTPS6 to construct an engineered S. cerevisiae for the production of these sesquiterpenes. The titers of two major products α-cadinol and τ-muurolol, respectively, reached 46.2 ± 4.0 and 11.2 ± 1.4 mg/L in a flask. This study lays a foundation for the development of new agrochemical mixtures.

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.

Genome Assembly of Cordia subcordata, a Coastal Protection Species in Tropical Coral Islands

Cordia subcordata trees or shrubs, belonging to the Boraginaceae family, have strong resistance and have adapted to their habitat on a tropical coral island in China, but the lack of genome information regarding its genetic background is unclear. In this study, the genome was assembled using both short/long whole genome sequencing reads and Hi-C reads. The assembled genome was 475.3 Mb, with 468.7 Mb (99.22%) of the sequences assembled into 16 chromosomes. Repeat sequences accounted for 54.41% of the assembled genome. A total of 26,615 genes were predicted, and 25,730 genes were functionally annotated using different annotation databases. Based on its genome and the other 17 species, phylogenetic analysis using 336 single-copy genes obtained from ortholog analysis showed that C. subcordata was a sister to Coffea eugenioides, and the divergence time was estimated to be 77 MYA between the two species. Gene family evolution analysis indicated that the significantly expanded gene families were functionally related to chemical defenses against diseases. These results can provide a reference to a deeper understanding of the genetic background of C. subcordata and can be helpful in exploring its adaptation mechanism on tropical coral islands in the future.

Insights on Juniperus phoenicea Essential Oil as Potential Anti-Proliferative, Anti-Tyrosinase, and Antioxidant Candidate

In this study, the anti-cancer, anti-tyrosinase, and antioxidant activities of essential oils (EOs) of berries and leaves of Juniperus phoenicea grown wild in North of Tunisia were investigated. The EO yields from leaves and berries were 1.69% and 0.45%, respectively. GC-MS analysis revealed that α-pinene is the predominant component in both EOs (44.17 and 83.56%, respectively). Leaves essential oil presented high levels of β-phellandrene (18%) and camphene (15%). The EOs displayed cytotoxic effects against MCF-7 breast cancer cell, HT-29 colon cancer, and the normal cells H9C2 cardiomyoblasts. Leaves oil strongly inhibited colon cell line proliferation (IC50 of 38 µg/mL), while berries essential oil was more potent against breast cancerous cells MCF-7 (IC50 of 60 µg/mL). Interestingly, berries essential oil exhibited high ability to inhibit melanin synthesis by inhibiting enzyme mono and diphenolase activities. Overall, the results suggested that the two oils are significant sources of healthy natural chemicals.

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.

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.

Neither lysigenous nor just oil: Demystifying myrtaceous secretory cavities

PREMISE

Leaf subepidermal secretory cavities are a notable trait in Myrtaceae, but their formation is still controversial because of the lack of consensus on their ontogeny among authors. Knowledge about the compounds present in these cavities has grown over the last few years, demonstrating that terpenoid-rich oils are not their unique content. These two points are the focus of this study on the ontogeny, structure, and contents of secretory cavities in neotropical Myrtaceae.

METHODS

We used histochemical tests and Raman analysis to verify the basic chemical composition of the cavity contents of nine species. We studied the ontogeny of glands in one species, comparing aldehyde-fixed tissues and fresh sections mounted in an inert medium.

RESULTS

We observed schizogenous development and appearance of the secretory cavities and found that sample processing may induce cell breakdown, which can be misinterpreted as lysigeny. The content of these cavities contains putative terpenes, resins, carbonyl groups, and flavonoids.

CONCLUSIONS

Our findings support the hypothesis that the lysigenous appearance of the oil glands is a technical artifact. These tissue distortions must be considered when interpreting the development of this type of secretory structure. Moreover, the basic analyses of chemical constituents show for the first time that the glands of neotropical Myrtaceae are potential reservoirs of some compounds such as flavonoids previously reported as novelties for a few other myrtaceous species. Because some of them are non-lipid compounds, the idea that the glands are just oil repositories is no longer applicable.

Unraveling the terpene synthase family and characterization of BsTPS2 contributing to (S)-( +)-linalool biosynthesis in Boswellia

Boswellia tree bark exudes oleo-gum resin in response to wounding, which is rich in terpene volatiles. But, the molecular and biochemical basis of wound-induced formation of resin volatiles remains poorly understood. Here, we combined RNA-sequencing (RNA-seq) and metabolite analysis to unravel the terpene synthase (TPS) family contributing to wound-induced biosynthesis of resin volatiles in B. serrata, an economically-important Boswellia species. The analysis of large-scale RNA-seq data of bark and leaf samples representing more than 600 million sequencing reads led to the identification of 32 TPSs, which were classified based on phylogenetic relationship into various TPSs families found in angiosperm species such as TPS-a, b, c, e/f, and g. Moreover, RNA-seq analysis of bark samples collected at 0-24 h post-wounding shortlisted 14 BsTPSs that showed wound-induced transcriptional upregulation in bark, suggesting their important role in wound-induced biosynthesis of resin volatiles. Biochemical characterization of a bark preferentially-expressed and wound-inducible TPS (BsTPS2) in vitro and in planta assays revealed its involvement in resin terpene biosynthesis. Bacterially-expressed recombinant BsTPS2 catalyzed the conversion of GPP and FPP into (S)-( +)-linalool and (E)-(-)-nerolidol, respectively, in vitro assays. However, BsTPS2 expression in Nicotiana benthamiana found that BsTPS2 is a plastidial linalool synthase. In contrast, cytosolic expression of BsTPS2 did not form any product. Overall, the present work unraveled a suite of TPSs that potentially contributed to the biosynthesis of resin volatiles in Boswellia and biochemically characterized BsTPS2, which is involved in wound-induced biosynthesis of (S)-( +)-linalool, a monoterpene resin volatile with a known role in plant defense.

The endomembrane system: how does it contribute to plant secondary metabolism?

New organelle acquisition through neofunctionalization of the endomembrane system (ES) with respect to plant secondary metabolism is a key evolutionary strategy for plant adaptation, which is overlooked due to the complexity of angiosperms. Bryophytes produce a broad range of plant secondary metabolites (PSMs), and their simple cellular structures, including unique organelles, such as oil bodies (OBs), highlight them as suitable model to investigate the contribution of the ES to PSMs. In this opinion, we review latest findings on the contribution of the ES to PSM biosynthesis, with a specific focus on OBs, and propose that the ES provides organelles and trafficking routes for PSM biosynthesis, transportation, and storage. Therefore, future research on ES-derived organelles and trafficking routes will provide essential knowledge for synthetic applications.

Functional Characterization of ent-Copalyl Diphosphate Synthase and Kaurene Synthase Genes from Coffea arabica L

The biochemical profile of coffee beans translates directly into quality traits, nutraceutical and health promoting properties of the coffee beverage. Ent-kaurene is the ubiquitous precursor for gibberellin biosynthesis in plants, but it also serves as an intermediate in specialized (i.e., secondary) diterpenoid metabolism that leads to a diversity of more than 1,000 different metabolites. Nutraceutical effects on human health attributed to diterpenes include antioxidant, anticarcinogenic, and anti-inflammatory properties. Cafestol (CAF) and kahweol (KAH) are two diterpenes found exclusively in the Coffea genus. Our objective was to identify and functionally characterize genes involved in the central step of ent-kaurene production. We identified 17 putative terpene synthase genes in the transcriptome of Coffea arabica. Two ent-copalyl diphosphate synthase (CaCPS) and three kaurene synthase (CaKS) were selected and manually annotated. Transcript expression profiles of CaCPS1 and CaKS3 best matched the CAF and KAH metabolite profiles in different tissues. CaCPS1 and CaKS3 proteins were heterologously expressed and functionally characterized. CaCPS1 catalyzes the cyclization of geranylgeranyl diphosphate (GGPP) to ent-copalyl diphosphate (ent-CPP), which is converted to ent-kaurene by CaKS3. Knowledge about the central steps of diterpene formation in coffee provides a foundation for future characterization of the subsequent enzymes involved in CAF and KAH biosynthesis.

Ralstonia solanacearum Suppresses Tomato Root Growth by Downregulation of a Wall-Associated Receptor Kinase

The root architecture of a range of host plants is altered in response to Ralstonia solanacearum infection. This work aimed to identify host genes involved in root development during R. solanacearum infection. A deficient mutant of the type III secretion system regulator hrpB was created in R. solanacearum GMI1000. The hrpB mutant was impaired in virulence but showed a similar suppressive effect as wild-type GMI1000 on tomato root development. Based on comparative transcriptome analysis, 209 genes were found that showed the same changed expression pattern in GMI1000 and hrpB mutant infected roots relative to uninoculated roots. Among them, the wall-associated receptor kinase WAKL20 was substantially downregulated in GMI1000 and hrpB mutant infected roots. Knockdown of WAKL20 led to a shorter primary root length and fewer lateral roots in tomato as well as in Nicotiana benthamiana. The WAKL20 is a pivotal target suppressed by R. solanacearum to shape the altered root development during infection.

Comparative Metabolomics and Transcriptome Analysis Reveal the Fragrance-Related Metabolite Formation in Phoebe zhennan Wood

Nanmu (Phoebe zhennan) has a unique fragrance and is a high-quality tree species for forest conservation. The types and contents of volatile compounds in different tissues of nanmu wood are different, and the study of its volatile metabolites can help us to understand the source of its fragrance and functions. In order to explore the metabolites related to the wood fragrance of nanmu and to find out the unique volatile substances in the heartwood, gas chromatography-mass spectrometry (GC-MS) was performed to analyze the non-targeted metabolomics in five radial tissues from the sapwood to the heartwood of nanmu. A total of 53 volatile metabolites belonging to 11 classes were detected in all tissues, including terpenes, aromatic hydrocarbons, organoheterocyclics, phenols, esters, organic acids, alcohols, alkaloids, alkane, indoles derivatives, and others. And most of the volatile metabolites were identified for the first time in nanmu wood. Among them, terpenes and aromatic hydrocarbons were the main volatile components. In addition, 22 differential metabolites were screened from HW and SW, HW, and TZ via metabolomic analysis. Among these DAMs, three volatile metabolites (cadinene, a sesquiterpenoid; p-cymene, a monoterpenoid; 1,3,5-triisopropylbenzene, an aromatic hydrocarbon) contributed heavily to the characteristic fragrance of the heartwood. Additionally, the expression of transcripts showed that the unigenes in the terpenoid biosynthesis pathway were especially up-regulated in the SW. Therefore, we speculated that fragrance-related metabolites were synthesized in SW and then deposited in heartwood during sapwood transformed to heartwood. The expression levels of transcription factors (e.g., WRKY, C2H2, NAC) acted as the major regulatory factors in the synthesis of terpenoid. The results lay the foundations for further studies on the formation mechanism of fragrance components in nanmu wood and also provide a reference for the further development and utilization of nanmu wood.

Unraveling the evolutionary dynamics of the TPS gene family in land plants

Terpenes and terpenoids are key natural compounds for plant defense, development, and composition of plant oil. The synthesis and accumulation of a myriad of volatile terpenoid compounds in these plants may dramatically alter the quality and flavor of the oils, which provide great commercial utilization value for oil-producing plants. Terpene synthases (TPSs) are important enzymes responsible for terpenic diversity. Investigating the differentiation of the TPS gene family could provide valuable theoretical support for the genetic improvement of oil-producing plants. While the origin and function of TPS genes have been extensively studied, the exact origin of the initial gene fusion event - it occurred in plants or microbes - remains uncertain. Furthermore, a comprehensive exploration of the TPS gene differentiation is still pending. Here, phylogenetic analysis revealed that the fusion of the TPS gene likely occurred in the ancestor of land plants, following the acquisition of individual C- and N- terminal domains. Potential mutual transfer of TPS genes was observed among microbes and plants. Gene synteny analysis disclosed a differential divergence pattern between TPS-c and TPS-e/f subfamilies involved in primary metabolism and those (TPS-a/b/d/g/h subfamilies) crucial for secondary metabolites. Biosynthetic gene clusters (BGCs) analysis suggested a correlation between lineage divergence and potential natural selection in structuring terpene diversities. This study provides fresh perspectives on the origin and evolution of the TPS gene family.

Tandem duplication and sub-functionalization of clerodane diterpene synthase originate the blooming of clerodane diterpenoids in Scutellaria barbata

Scutellaria barbata is a traditional Chinese herb medicine and a major source of bioactive clerodane diterpenoids. However, barely clerodanes have been isolated from the closely related S. baicalensis. Here we assembled a chromosome-level genome of S. barbata and identified three class II clerodane diterpene synthases (SbarKPS1, SbarKPS2 and SbaiKPS1) from these two organisms. Using in vitro and in vivo assays, SbarKPS1 was characterized as a monofunctional (-)-kolavenyl diphosphate synthases ((-)-KPS), while SbarKPS2 and SbaiKPS1 produced major neo-cleroda-4(18),13E-dienyl diphosphate with small amount of (-)-KPP. SbarKPS1 and SbarKPS2 shared a high protein sequence identity and formed a tandem gene pair, indicating tandem duplication and sub-functionalization probably led to the evolution of monofunctional (-)-KPS in S. barbata. Additionally, SbarKPS1 and SbarKPS2 were primarily expressed in the leaves and flowers of S. barbata, which was consistent with the distribution of major clerodane diterpenoids scutebarbatine A and B. In contrast, SbaiKPS1 was barely expressed in any tissue of S. baicalensis. We further explored the downstream class I diTPS by functional characterizing of SbarKSL3 and SbarKSL4. Unfortunately, no dephosphorylated product was detected in the coupled assays with SbarKSL3/KSL4 and four class II diTPSs (SbarKPS1, SbarKPS2, SbarCPS2 and SbarCPS4) when a phosphatase inhibitor cocktail was included. Co-expression of SbarKSL3/KSL4 with class II diTPSs in yeast cells did not increase the yield of the corresponding dephosphorylated products, either. Together, these findings elucidated the involvement of two class II diTPSs in clerodane biosynthesis in S. barbata, while the class I diTPS is likely not responsible for the subsequent dephosphorylation step.

Essential Oils of Artemisia frigida Plants (Asteraceae): Conservatism and Lability of the Composition

Plants of arid regions have adapted to harsh environments during the long span of their evolution and have developed a set of features necessary for their survival in water-limited conditions. Artemisia frigida Willd. (Asteraceae) is a widely distributed species possessing significant cenotic value in steppe ecosystems due to its high frequency and abundance. This study examines different patterns of formation of essential oil composition in A. frigida plants under the influence of heterogeneous factors, including climate and its integral characteristics (HTC, Cextr, SPEI and others). The work is based on the results of our research conducted in Russia (Republic of Buryatia, Irkutsk region), Mongolia, and China, from 1998 to 2021. A total of 32 constant compounds have been identified in the essential oil of A. frigida throughout its habitat range in Eurasia, from Kazakhstan to Qinghai Province, China. Among them, camphor, 1,8-cineol and bornyl acetate are the dominant components, contained in 93-95% of the samples. Among the sesquiterpenoids, germacrene D is the dominant component in 67% of the samples. The largest variability within the composition of the essential oils of A. frigida is associated with significant differences in the climatic parameters when plants grow in high-altitude and extrazonal conditions.

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.

Monoterpene synthases contribute to the volatile production in tana (Zanthoxylum ailanthoides) through indigenous cultivation practices

Tana (Zanthoxylum ailanthoides), a perennial deciduous species in the Rutaceae family, possesses leaves with a unique fragrance that indigenous peoples incorporate into their traditional cuisine. In Kalibuan, the cultivated tana trees were pruned repeatedly to maintain a shorter height, which led to the growth of new leaves that were spicier and pricklier. Tana leaves contain a range of volatile terpenoids, and the pungent aroma may arise from the presence of monoterpenoids. To gain insight into the biosynthetic pathway, five candidate monoterpene synthase genes were cloned and characterized using a purified recombinant protein assay. The main product of Za_mTPS1, Za_mTPS2, and Za_mTPS5 is sabinene, geraniol, and (E)-β-ocimene, respectively. The main product of Za_mTPS3 and Za_mTPS4 is linalool. Real-time PCR analysis revealed that Za_mTPS1 and Za_mTPS5 are expressed at higher levels in prickly leaves of cultivated tana, suggesting that they may contribute to the distinctive aroma of this plant.

Metabolic engineering of a 1,8-cineole synthase enhances aphid repellence and increases trichome density in transgenic tobacco (Nicotiana tabacum L.)

BACKGROUND

The green peach aphid (Myzus persicae Sulzer) is a harmful agricultural pest that causes severe crop damage by directly feeding or indirectly vectoring viruses. 1,8-cineole synthase (CINS) is a multiproduct enzyme that synthesizes monoterpenes, with 1,8-cineole dominating the volatile organic compound profile. However, the relationship between aphid preference and CINS remains elusive.

RESULTS

Here, we present evidence that SoCINS, a protein from garden sage (Salvia officinalis), enhanced aphid repellence and increased trichome density in transgenic tobacco. Our results demonstrated that overexpression of SoCINS (SoCINS-OE) led to the emission of 1,8-cineole at a level of up to 181.5 ng per g fresh leaf. Subcellular localization assay showed that SoCINS localized to chloroplasts. A Y-tube olfactometer assay and free-choice assays revealed that SoCINS-OE plants had a repellent effect on aphids, without incurring developmental or fecundity-related penalties. Intriguingly, the SoCINS-OE plants displayed an altered trichome morphology, showing increases in trichome density and in the relative proportion of glandular trichomes, as well as enlarged glandular cells. We also found that SoCINS-OE plants had significantly higher jasmonic acid (JA) levels than wild-type plants. Furthermore, application of 1,8-cineole elicited increased JA content and trichome density.

CONCLUSION

Our results demonstrate that SoCINS-OE plants have a repellent effect on aphids, and suggest an apparent link between 1,8-cineole, JA and trichome density. This study presents a viable and sustainable approach for aphid management by engineering the expression of 1,8-cineole synthase gene in plants, and underscores the potential usefulness of monoterpene synthase for pest control. © 2023 Society of Chemical Industry.

Convergent resistance to GABA receptor neurotoxins through plant-insect coevolution

The molecular mechanisms of coevolution between plants and insects remain elusive. GABA receptors are targets of many neurotoxic terpenoids, which represent the most diverse array of natural products known. Over deep evolutionary time, as plant terpene synthases diversified in plants, so did plant terpenoid defence repertoires. Here we show that herbivorous insects and their predators evolved convergent amino acid changing substitutions in duplicated copies of the Resistance to dieldrin (Rdl) gene that encodes the GABA receptor, and that the evolution of duplicated Rdl and terpenoid-resistant GABA receptors is associated with the diversification of moths and butterflies. These same substitutions also evolved in pests exposed to synthetic insecticides that target the GABA receptor. We used in vivo genome editing in Drosophila melanogaster to evaluate the fitness effects of each putative resistance mutation and found that pleiotropy both facilitates and constrains the evolution of GABA receptor resistance. The same genetic changes that confer resistance to terpenoids across 300 Myr of insect evolution have re-evolved in response to synthetic analogues over one human lifespan.

Identification and characterization of novel sesquiterpene synthases TPS9 and TPS12 from Aquilaria sinensis

Sesquiterpenes are characteristic components and important quality criterions for agarwood. Although sesquiterpenes are well-known to be biosynthesized by sesquiterpene synthases (TPSs), to date, only a few TPS genes involved in agarwood formation have been reported. Here, two new TPS genes, namely, TPS9 and TPS12, were isolated from Aquilaria sinensis (Lour.) Gilg, and their functions were examined in Escherichia coli BL21(DE3), with farnesyl pyrophosphate (FPP) and geranyl pyrophosphate (GPP) as the substrate of the corresponding enzyme activities. They were both identified as a multiproduct enzymes. After incubation with FPP, TPS9 liberated β-farnesene and cis-sesquisabinene hydrate as main products, with cedrol and another unidentified sesquiterpene as minor products. TPS12 catalyzes the formation of β-farnesene, nerolidol, γ-eudesmol, and hinesol. After incubation with GPP, TPS9 generated citronellol and geraniol as main products, with seven minor products. TPS12 converted GPP into four monoterpenes, with citral as the main product, and three minor products. Both TPS9 and TPS12 showed much higher expression in the two major tissues emitting floral volatiles: flowers and agarwood. Further, RT-PCR analysis showed TPS9 and TPS12 are typical genes mainly expressed during later stages of stress response, which is better known than that of chromone derivatives. This study will advance our understanding of agarwood formation and provide a solid theoretical foundation for clarifying its mechanism in A. sinensis.

Promoter characterization of a citrus linalool synthase gene mediating interspecific variation in resistance to a bacterial pathogen

BACKGROUND

Terpenoids play essential roles in plant defense against biotic stresses. In Citrus species, the monoterpene linalool mediates resistance against citrus canker disease caused by the gram-negative bacteria Xanthomonas citri subsp. citri (Xcc). Previous work had associated linalool contents with resistance; here we characterize transcriptional responses of linalool synthase genes.

RESULTS

Leaf linalool contents are highly variable among different Citrus species. "Dongfang" tangerine (Citrus reticulata), a species with high linalool levels was more resistant to Xcc than "Shatian" pummelo (C. grandis) which accumulates only small amounts of linalool. The coding sequences of the major leaf-expressed linalool synthase gene (STS4) are highly conserved, while transcript levels differ between the two Citrus species. To understand this apparent differential transcription, we isolated the promoters of STS4 from the two species, fused them to a GUS reporter and expressed them in Arabidopsis. This reporter system revealed that the two promoters have different constitutive activities, mainly in trichomes. Interestingly, both linalool contents and STS4 transcript levels are insensitive to Xcc infestation in citrus plants, but in these transgenic Arabidopsis plants, the promoters are activated by challenge of a bacterial pathogen Pseudomonas syringae, as well as wounding and external jasmonic acid treatment.

CONCLUSIONS

Our study reveals variation in linalool and resistance to Xcc in citrus plants, which may be mediated by different promoter activities of a terpene synthase gene in different Citrus species.

as a Versatile and Predictable Chiral Stationary Phase for the Resolution of Racemic Mixtures

Metal-organic frameworks (MOFs) have become promising materials for multiple applications due to their controlled dimensionality and tunable properties. The incorporation of chirality into their frameworks opens new strategies for chiral separation, a key technology in the pharmaceutical industry as each enantiomer of a racemic drug must be isolated. Here, we describe the use of a combination of computational modeling and experiments to demonstrate that high-performance liquid chromatography (HPLC) columns packed with TAMOF-1 as the chiral stationary phase are efficient, versatile, robust, and reusable with a wide array of mobile phases (polar and non-polar). As proof of concept, in this article, we report the resolution with TAMOF-1 HPLC columns of nine racemic mixtures with different molecular sizes, geometries, and functional groups. Initial in silico studies allowed us to predict plausible separations in chiral compounds from different families, including terpenes, calcium channel blockers, or P-stereogenic compounds. The experimental data confirmed the validity of the models and the robust performance of TAMOF-1 columns. The added value of in silico screening is an unprecedented achievement in chiral chromatography.

Transcriptome Analyses Reveal the Aroma Terpeniods Biosynthesis Pathways of Primula forbesii Franch. and the Functional Characterization of the PfDXS2 Gene

Primula forbesii Franch. is a unique biennial herb with a strong floral fragrance, making it an excellent material for studying the aroma characteristics of the genus Primula. The floral scent is an important ornamental trait that facilitates fertilization. However, the molecular mechanism regulating the floral scent in Primula is unknown. In order to better understand the biological mechanisms of floral scents in this species, this study used RNA sequencing analysis to discuss the first transcriptome sequence of four flowering stages of P. forbesii, which generated 12 P. forbesii cDNA libraries with 79.64 Gb of clean data that formed 51,849 unigenes. Moreover, 53.26% of the unigenes were annotated using public databases. P. forbesii contained 44 candidate genes covering all known enzymatic steps for the biosynthesis of volatile terpenes, the major contributor to the flower's scent. Finally, 1-deoxy-d-xylulose 5-phosphate synthase gene of P. forbesii (PfDXS2, MK370094), the first key enzyme gene in the 2-c-methyl-d-erythritol 4-phosphate (MEP) pathway of terpenoids, was cloned and functionally verified using virus-induced gene silencing (VIGs). The results showed that PfDXS2-silencing significantly reduced the relative concentrations of main volatile terpenes. This report is the first to present molecular data related to aroma metabolites biosynthesis pathways and the functional characterization of any P. forbesii gene. The data on RNA sequencing provide comprehensive information for further analysis of other plants of the genus Primula.

CsTPS21 encodes a jasmonate-responsive monoterpene synthase producing β-ocimene in citrus against Asian citrus psyllid

Huanglongbing (HLB), spread by the Asian citrus psyllid (ACP), is a widespread, devastating disease that causes significant losses in citrus production. Therefore, controlling the ACP infestation and HLB infection is very important for citrus production. The aim of our study was to identify any citrus volatile which could be used as a repellent or less attractant towards ACP, and to envisage the potential of this strategy to control HLB spread. The present study identified a terpene synthase (TPS)-encoding gene CsTPS21 in citrus plants, and this gene was predicted to encode a monoterpene synthase and had an amino acid sequence similar to β-ocimene synthase. CsTPS21 was significantly upregulated by ACP infestation and methyl jasmonic acid (MeJA) treatment but downregulated by salicylic acid (SA). Further heterologous gene expression studies in yeast cells and tobacco plants indicated that the protein catalyzed the formation of β-ocimene, which acted as an ACP repellent. Detailed analysis of tobacco overexpressing CsTPS21 showed that CsTPS21 synthesizing β-ocimene regulated jasmonic acid (JA)-associated pathways by increasing the JA accumulation and inducing the JA biosynthetic gene expression to defend against insect infestation. These findings provide a basis to plan strategies to manage HLB in the field using β-ocimene and CsTPS21 as candidates.

French Guiana honeys from the Amazon biome: First description of volatile fraction and antioxidant capacity

Various honeys from French Guiana were collected and analyzed to investigate their volatile fraction composition and antioxidant activity. Volatile composition was assessed using HS-SPME/GC, GC-MS technique. Oxygenated monoterpenes like hotrienol (0.5-45.3%) were found as major molecules, followed by non terpenic compounds like phenylacetaldehyde (0.8-18.2%) or 3-hydroxy-4-phenyl-2-butanone (0.1-29.3%). Three chemical groups using statistical analysis were classified within investigated honey samples: norisoprenoids/shikimates, mevalonate and their combination. Total phenolics content (TPC) was determined by Folin-Ciocalteu method. Antioxidant activity was assessed by oxygen radical absorbance capacity (ORAC) and 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (ABTS) assays. TPC and anti-radical activity were compared with multifloral honeys from neighboring regions, indicating the possible presence of compounds from the polyphenol family. These results are promising for further biological studies involving honeys from French Guiana.

Molecular characterization of a moss isoprene synthase provides insight into its evolution

This is the first report on the molecular characterization of isoprene synthase (ISPS) from the moss Calohypnum plumiforme. After isoprene emission from C. plumiforme was confirmed, the cDNA encoding C. plumiforme ISPS (CpISPS) was narrowed down using a genome database associated with protein structure prediction, and a CpISPS gene was identified. The recombinant CpISPS, produced in Escherichia coli, converted dimethylallyl diphosphate to isoprene. Phylogenetic analysis indicated similarity between the amino acid sequences of CpISPS and moss diterpene cyclases (DTCs) but not ISPSs of higher plants, implying that CpISPS is derived from moss DTCs and is evolutionarily unrelated to canonical ISPSs of higher plants. CpISPS is a novel class I cyclase of the terpene synthase-c subfamily harboring αβ domains. This study will help further study of isoprene biosynthesis and the physiological functions of isoprene in mosses.

Characterization of sandalwood (E,E)-α-farnesene synthase whose overexpression enhances cold tolerance through jasmonic acid biosynthesis and signaling in Arabidopsis

MAIN CONCLUSION

Santalum album (E,E)-α-farnesene synthase catalyzes FPP into (E,E)-α-farnesene. Overexpression of the SaAFS gene positively improved cold stress tolerance through JA biosynthesis and signaling pathways in Arabidopsis. Volatile terpenoids are released from plants that suffer negative effects following exposure to various biotic and abiotic stresses. Recent studies revealed that (E,E)-α-farnesene synthase (AFS) plays a significant role in a plant's defence against biotic attack. However, little is known about whether AFS contributes to plant resistance to cold stress. In this study, a SaAFS gene was isolated from Indian sandalwood (Santalum album L.) and functionally characterized. The SaAFS protein mainly converts farnesyl diphosphate to (E,E)-α-farnesene. SaAFS was clustered into the AFS clade from angiosperms, suggesting a highly conserved enzyme. SaAFS displayed a significant response to cold stress and methyl jasmonate. SaAFS overexpression (OE) in Arabidopsis enhanced cold tolerance by increasing proline content, reducing malondialdehyde content, electrolyte leakage, and accumulating reactive oxygen species. Transcriptomic analysis revealed that upregulated genes related to stress response and JA biosynthesis and signaling were detected in SaAFS-OE lines compared with wild type plants that were exposed to cold stress. Endogenous JA and jasmonoyl-isoleucine content increased significantly in SaAFS-OE lines exposed to cold stress. Collectively considered, these results suggest that the SaAFS gene is a positive regulator during cold stress tolerance via JA biosynthesis and signaling pathways.

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.

Heterologous Production of Artemisinin in Physcomitrium patens by Direct in vivo Assembly of Multiple DNA Fragments

The sesquiterpene lactone compound artemisinin is a natural medicinal product of commercial importance. This Artemisia annua-derived secondary metabolite is well known for its antimalarial activity and has been studied in several other biological assays. However, the major shortcoming in its production and commercialization is its low accumulation in the native plant. Moreover, the chemical synthesis of artemisinin is difficult and expensive due to its complex structure. Hence, an alternative and sustainable production system of artemisinin in a heterologous host is required. Previously, heterologous production of artemisinin was achieved by Agrobacterium-mediated transformation. However, this requires extensive bioengineering of modified Nicotiana plants. Recently, a technique involving direct in vivo assembly of multiple DNA fragments in the moss, P. patens, has been successfully established. We utilized this technique to engineer artemisinin biosynthetic pathway genes into the moss, and artemisinin was obtained without further modifications with high initial production. Here, we provide protocols for establishing moss culture accumulating artemisinin, including culture preparation, transformation method, and compound detection via HS-SPME, UPLC-MRM-MS, and LC-QTOF-MS. The bioengineering of moss opens up a more sustainable, cost effective, and scalable platform not only in artemisinin production but also other high-value specialized metabolites in the future.

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.

Advances in the Biosynthesis of Terpenoids and Their Ecological Functions in Plant Resistance

Secondary metabolism plays an important role in the adaptation of plants to their environments, particularly by mediating bio-interactions and protecting plants from herbivores, insects, and pathogens. Terpenoids form the largest group of plant secondary metabolites, and their biosynthesis and regulation are extremely complicated. Terpenoids are key players in the interactions and defense reactions between plants, microorganisms, and animals. Terpene compounds are of great significance both to plants themselves and the ecological environment. On the one hand, while protecting plants themselves, they can also have an impact on the environment, thereby affecting the evolution of plant communities and even ecosystems. On the other hand, their economic value is gradually becoming clear in various aspects of human life; their potential is enormous, and they have broad application prospects. Therefore, research on terpenoids is crucial for plants, especially crops. This review paper is mainly focused on the following six aspects: plant terpenes (especially terpene volatiles and plant defense); their ecological functions; their biosynthesis and transport; related synthesis genes and their regulation; terpene homologues; and research and application prospects. We will provide readers with a systematic introduction to terpenoids covering the above aspects.

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.

Aromatic Terpenes and Their Biosynthesis in Dendrobium, and Conjecture on the Botanical Perfumer Mechanism

This review presents a systematic analysis of the studies on volatiles in Dendrobium. Among the various components, aromatic terpenes are a crucial component in the development of the aromatic characteristics of Dendrobium and other plants. Recent advancements in detection and sequencing technology have resulted in a considerable rise in research on the biosynthetic processes of aromatic terpenes in Dendrobium and other flowering plants. Nevertheless, the inquiry into the precise means by which plants regulate the proportion of diverse aromatic terpenes in their floral scent, thereby preserving their olfactory traits, requires further investigation. A conjecture on the botanical perfumer mechanism, which condensed the findings of earlier studies, was put forward to address this area of interest. Specific transcription factors likely govern the coordinated expression of multiple key terpene synthase (TPS) genes during the flowering stage of plants, thereby regulating the proportional biosynthesis of diverse aromatic terpenes and sustaining the distinctive aromatic properties of individual plants. This review serves as a significant theoretical reference for further investigations into aromatic volatile compounds in Dendrobium.

Chemical profile and analysis of biosynthetic pathways and genes of volatile terpenes in Pityopsis ruthii, a rare and endangered flowering plant

It is critical to gather biological information about rare and endangered plants to incorporate into conservation efforts. The secondary metabolism of Pityopsis ruthii, an endangered flowering plant that only occurs along limited sections of two rivers (Ocoee and Hiwassee) in Tennessee, USA was studied. Our long-term goal is to understand the mechanisms behind P. ruthii's adaptation to restricted areas in Tennessee. Here, we profiled the secondary metabolites, specifically in flowers, with a focus on terpenes, aiming to uncover the genomic and molecular basis of terpene biosynthesis in P. ruthii flowers using transcriptomic and biochemical approaches. By comparative profiling of the nonpolar portion of metabolites from various tissues, P. ruthii flowers were rich in terpenes, which included 4 monoterpenes and 10 sesquiterpenes. These terpenes were emitted from flowers as volatiles with monoterpenes and sesquiterpenes accounting for almost 68% and 32% of total emission of terpenes, respectively. These findings suggested that floral terpenes play important roles for the biology and adaptation of P. ruthii to its limited range. To investigate the biosynthesis of floral terpenes, transcriptome data for flowers were produced and analyzed. Genes involved in the terpene biosynthetic pathway were identified and their relative expressions determined. Using this approach, 67 putative terpene synthase (TPS) contigs were detected. TPSs in general are critical for terpene biosynthesis. Seven full-length TPS genes encoding putative monoterpene and sesquiterpene synthases were cloned and functionally characterized. Three catalyzed the biosynthesis of sesquiterpenes and four catalyzed the biosynthesis of monoterpenes. In conclusion, P. ruthii plants employ multiple TPS genes for the biosynthesis of a mixture of floral monoterpenes and sesquiterpenes, which probably play roles in chemical defense and attracting insect pollinators alike.

The genome of Acorus deciphers insights into early monocot evolution

Acorales is the sister lineage to all the other extant monocot plants. Genomic resource enhancement of this genus can help to reveal early monocot genomic architecture and evolution. Here, we assemble the genome of Acorus gramineus and reveal that it has ~45% fewer genes than the majority of monocots, although they have similar genome size. Phylogenetic analyses based on both chloroplast and nuclear genes consistently support that A. gramineus is the sister to the remaining monocots. In addition, we assemble a 2.2 Mb mitochondrial genome and observe many genes exhibit higher mutation rates than that of most angiosperms, which could be the reason leading to the controversies of nuclear genes- and mitochondrial genes-based phylogenetic trees existing in the literature. Further, Acorales did not experience tau (τ) whole-genome duplication, unlike majority of monocot clades, and no large-scale gene expansion is observed. Moreover, we identify gene contractions and expansions likely linking to plant architecture, stress resistance, light harvesting, and essential oil metabolism. These findings shed light on the evolution of early monocots and genomic footprints of wetland plant adaptations.

Differential RNA-Seq Analysis Predicts Genes Related to Terpene Tailoring in Caryopteris × clandonensis

Enzymatic terpene functionalization is an essential part of plant secondary metabolite diversity. Within this, multiple terpene-modifying enzymes are required to enable the chemical diversity of volatile compounds essential in plant communication and defense. This work sheds light on the differentially transcribed genes within Caryopteris × clandonensis that are capable of functionalizing cyclic terpene scaffolds, which are the product of terpene cyclase action. The available genomic reference was subjected to further improvements to provide a comprehensive basis, where the number of contigs was minimized. RNA-Seq data of six cultivars, Dark Knight, Grand Bleu, Good as Gold, Hint of Gold, Pink Perfection, and Sunny Blue, were mapped on the reference, and their distinct transcription profile investigated. Within this data resource, we detected interesting variations and additionally genes with high and low transcript abundancies in leaves of Caryopteris × clandonensis related to terpene functionalization. As previously described, different cultivars vary in their modification of monoterpenes, especially limonene, resulting in different limonene-derived molecules. This study focuses on predicting the cytochrome p450 enzymes underlying this varied transcription pattern between investigated samples. Thus, making them a reasonable explanation for terpenoid differences between these plants. Furthermore, these data provide the basis for functional assays and the verification of putative enzyme activities.

Chromosome-level genome and multi-omics analyses provide insights into the geo-herbalism properties of Alpinia oxyphylla

Introduction

Alpinia oxyphylla Miquel (A. oxyphylla), one of the "Four Famous South Medicines" in China, is an essential understory cash crop that is planted widely in the Hainan, Guangdong, Guangxi, and Fujian provinces. Particularly, A. oxyphylla from Hainan province is highly valued as the best national product for geo-herbalism and is an important indicator of traditional Chinese medicine efficacy. However, the molecular mechanism underlying the formation of its quality remains unspecified.

Methods

To this end, we employed a multi-omics approach to investigate the authentic quality formation of A. oxyphylla.

Results

In this study, we present a high-quality chromosome-level genome assembly of A. oxyphylla, with contig N50 of 76.96 Mb and a size of approximately 2.08Gb. A total of 38,178 genes were annotated, and the long terminal repeats were found to have a high frequency of 61.70%. Phylogenetic analysis demonstrated a recent whole-genome duplication event (WGD), which occurred before A. oxyphylla's divergence from W. villosa (~14 Mya) and is shared by other species from the Zingiberaceae family (Ks, ~0.3; 4DTv, ~0.125). Further, 17 regions from four provinces were comprehensively assessed for their metabolite content, and the quality of these four regions varied significantly. Finally, genomic, metabolic, and transcriptomic analyses undertaken on these regions revealed that the content of nootkatone in Hainan was significantly different from that in other provinces.

Discussion

Overall, our findings provide novel insights into germplasm conservation, geo-herbalism evaluation, and functional genomic research for the medicinal plant A. oxyphylla.

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.