Molecular cloning and characterization of a new linalool synthase

Biosynthesis of monoterpenoid and sesquiterpenoid as natural flavors and fragrances

Terpenoids are a large class of plant-derived compounds, that constitute the main components of essential oils and are widely used as natural flavors and fragrances. The biosynthesis approach presents a promising alternative route in terpenoid production compared to plant extraction or chemical synthesis. In the past decade, the production of terpenoids using biotechnology has attracted broad attention from both academia and the industry. With the growing market of flavor and fragrance, the production of terpenoids directed by synthetic biology shows great potential in promoting future market prospects. Here, we reviewed the latest advances in terpenoid biosynthesis. The engineering strategies for biosynthetic terpenoids were systematically summarized from the enzyme, metabolic, and cellular dimensions. Additionally, we analyzed the key challenges from laboratory production to scalable production, such as key enzyme improvement, terpenoid toxicity, and volatility loss. To provide comprehensive technical guidance, we collected milestone examples of biosynthetic mono- and sesquiterpenoids, compared the current application status of chemical synthesis and biosynthesis in terpenoid production, and discussed the cost drivers based on the data of techno-economic assessment. It is expected to provide critical insights into developing translational research of terpenoid biomanufacturing.

Design of Four Small-Molecule-Inducible Systems in the Yeast Chromosome, Applied to Optimize Terpene Biosynthesis

The optimization of cellular functions often requires the balancing of gene expression, but the physical construction and screening of alternative designs are costly and time-consuming. Here, we construct a strain of Saccharomyces cerevisiae that contains a "sensor array" containing bacterial regulators that respond to four small-molecule inducers (vanillic acid, xylose, aTc, IPTG). Four promoters can be independently controlled with low background and a 40- to 5000-fold dynamic range. These systems can be used to study the impact of changing the level and timing of gene expression without requiring the construction of multiple strains. We apply this approach to the optimization of a four-gene heterologous pathway to the terpene linalool, which is a flavor and precursor to energetic materials. Using this approach, we identify bottlenecks in the metabolic pathway. This work can aid the rapid automated strain development of yeasts for the bio-manufacturing of diverse products, including chemicals, materials, fuels, and food ingredients.

Characterization of a new (Z)-3:(E)-2-hexenal isomerase from tea (Camellia sinensis) involved in the conversion of (Z)-3-hexenal to (E)-2-hexenal

Two major green leaf volatiles (GLVs) in tea that contribute greatly to tea aroma, particularly the green odor, are (E)-2-hexenal and (Z)-3-hexenal. Until now, their formation and related mechanisms during tea manufacture have remained unclear. Our data showed that the contents of (E)-2-hexenal and (Z)-3-hexenal increased more than 1000-fold after live tea leaves were torn. Subsequently, a new (Z)-3:(E)-2-hexenal isomerase (CsHI) was identified in Camellia sinensis. CsHI irreversibly catalyzed the conversion of (Z)-3-hexenal to (E)-2-hexenal. Abiotic stresses including low temperature, dehydration, and mechanical wounding, did not influence the (E)-2-hexenal content in intact tea leaves during withering, but regulated the proportions of (Z)-3-hexenal and (E)-2-hexenal in torn leaves by modulating CsHI at the transcript level. For the first time, this work reveals the formation of (E)-2-hexenal during tea processing and suggests that CsHI may play a pivotal role in tea flavor development as well as in plant defense against abiotic stresses.

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

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

De novo transcriptome sequencing assisted identification of terpene synthases from black pepper (Piper nigrum) berry

Though the volatile profiles of black pepper have been reported already, the information on terpene synthase family genes is not known. In this study, using a combinatorial approach, the berry hybrid transcriptome assembly of llumina and nanopore sequencing, the entire terpene synthase family responsible for the biosynthesis of the flavor-imparting volatiles in black pepper berries was profiled. The profile shows 98 terpene synthases from various terpene synthesis pathways. Three important monoterpene synthases were also validated by targeted amplification, sequencing and homology modeling. This study provides the first of its kind information on the terpene synthase family profile in Piper nigrum, which is potentially a major step for further characterization of the functional terpene synthase genes in black pepper.

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The online version contains supplementary material available at 10.1007/s12298-021-00986-4.

Volatile metabolic profiling and functional characterization of four terpene synthases reveal terpenoid diversity in different tissues of Chrysanthemum indicum L

Chrysanthemum indicum has long been used in traditional Chinese medicine for its health-promoting benefits. Studies on C. indicum have mainly focused on the flowers. Terpenoid distribution in various parts of the plant and characterization of terpene synthases remain unclear. In this study, volatile metabolic profiling was performed to compare the composition and quantity of terpenoids distributed in the root, stem, leaf, flower bud and flower of C. indicum. The potential for extracting active ingredients from the root, stem, and leaf was also examined. In total, 17 monoterpenoids and 27 sesquiterpenoids were identified. Transcriptome data were used to clone two monoterpene synthases and two sesquiterpene synthases highly expressed in the root. The recombinant proteins of full-length and truncated versions of C. indicum terpene synthase (CiTPS1) produced α-pinene, but the truncated one was catalytically more efficient than the full-length version. No product could be detected when full-length version of CiTPS2 was used for catalyzing GPP, but the truncated one can produce a minor amount of α-pinene. CiTPS3 contributed to the production of three sesquiterpenoids, namely β-farnesene, petasitene, and α-bisabolene. CiTPS4 acted as a difunctional enzyme, contributing to the production of four monoterpenoids and three sesquiterpenoids, including petasitene. The evidence suggests that petasitene and the genes responsible for its biosynthesis were first found in the genus Chrysanthemum. The present findings provide insights into the composition, formation, and regulation of these bioactive compounds.

Functional characterization of an Indian sandalwood (Santalum album L.) dual-localized bifunctional nerolidol/linalool synthase gene involved in stress response

Essential oils extracted from the heartwood of Indian sandalwood (Santalum album L.) contain linalool and nerolidol as minor components. However, nerolidol/linalool synthase (NES/LIS), which produce linalool and nerolidol, have yet to be characterized in sandalwood. Using a transcriptomic-based approach, a terpene synthase gene was screened from unigenes of transcriptome data derived from S. album seedlings exposed to low temperature (4 °C). The enzyme encoded by these complementary DNAs belongs to the TPS-b clade. Recombinant SaNES/LIS is a bifunctional enzyme that can catalyze the formation of (E)-nerolidol from farnesyl diphosphate and linalool from geranyl diphosphate, respectively. Whereas SaNES/LIS was primarily localized in chloroplastids, both as granular fluorescence and as diffuse fluorescence, it was also detected in the cytosol of a limited number of cells. Agrobacterium tumefaciens-mediated transient gene expression in planta produced the same terpene products as those obtained in vitro. Real-time PCR analysis showed the highest expression of SaNES/LIS in fruits, with about a three-fold higher level than in leaves, followed by flowers, heartwood and roots. SaNES/LIS transcripts were differentially activated in different tissues in response to methyl jasmonate, cold, high temperature, strong illumination, and drought stress. Our results provide novel insight into the role of sandalwood terpenoids in response to various environmental stresses.

Bioinformatics-aided identification, characterization and applications of mushroom linalool synthases

Enzymes empower chemical industries and are the keystone for metabolic engineering. For example, linalool synthases are indispensable for the biosynthesis of linalool, an important fragrance used in 60-80% cosmetic and personal care products. However, plant linalool synthases have low activities while expressed in microbes. Aided by bioinformatics analysis, four linalool/nerolidol synthases (LNSs) from various Agaricomycetes were accurately predicted and validated experimentally. Furthermore, we discovered a linalool synthase (Ap.LS) with exceptionally high levels of selectivity and activity from Agrocybe pediades, ideal for linalool bioproduction. It effectively converted glucose into enantiopure (R)-linalool in Escherichia coli, 44-fold and 287-fold more efficient than its bacterial and plant counterparts, respectively. Phylogenetic analysis indicated the divergent evolution paths for plant, bacterial and fungal linalool synthases. More critically, structural comparison provided catalytic insights into Ap.LS superior specificity and activity, and mutational experiments validated the key residues responsible for the specificity.

Stereospecific linalool production utilizing two-phase cultivation system in Pantoea ananatis

Linalool is a monoterpene alcohol, which imparts floral scents to a variety of plants and is extensively used in various kinds of products, such as processed foods and beverages for fragrances and flavors. However, linalool from natural resources is racemate, and production of linalool enantiomers is difficult. To produce stereospecific linalool, we evaluated linalool synthase genes (LINS) from plants, such as Actinidia arguta (AaLINS) and Coriandrum sativum (CsLINS) for (S)-specific LINS and a gram-positive bacterium Streptomyces clavuligerus (ScLINS) for (R)-specific LINS, with Pantoea ananatis strain as the host. Among the 16 LINS examined, AaLINS and ScLINS showed the best (S)-linalool production and (R)-linalool production, respectively, with 100 % enantio excess. Co-expression of the mutated farnesyl diphosphate synthase gene, ispA* (S80 F), from Escherichia coli along with the LINS genes also improved linalool production. In order to prevent volatilization and cell toxicity of linalool, two-phase cultivation with isopropyl myristate was done, which had positive effects on linalool production. The carbon flux to the MVA pathway from glucose was increased by inactivating a membrane-bound glucose dehydrogenase. Overall, 5.60 g/L (S)-linalool and 3.71 g/L (R)-linalool were produced from 60.0 g/L glucose by introduction of AaLINS-ispA* and ScLINS-ispA* in P. ananatis, respectively.

Enzyme Catalytic Efficiencies and Relative Gene Expression Levels of (R)-Linalool Synthase and (S)-Linalool Synthase Determine the Proportion of Linalool Enantiomers in Camellia sinensis var. sinensis

Linalool is abundant in tea leaves and contributes greatly to tea aroma. The two isomers of linalool, (R)-linalool and (S)-linalool, exist in tea leaves. Our study found that (R)-linalool was the minor isomer in nine of Camellia sinensis var. sinensis cultivars. The (R)-linalool synthase of tea plant CsRLIS was identified subsequently. It is a chloroplast-located protein and specifically catalyzes the formation of (R)-linalool in vitro and in vivo. CsRLIS was observed to be a stress-responsive gene and caused the accumulation of internal (R)-linalool during oolong tea manufacture, mechanical wounding, and insect attack. Further study demonstrated that the catalytic efficiency of CsRLIS was much lower than that of (S)-linalool synthase CsSLIS, which might explain the lower (R)-linalool proportion in C. sinensis var. sinensis cultivars. The relative expression levels of CsRLIS and CsSLIS may also affect the (R)-linalool proportions among C. sinensis var. sinensis cultivars. This information will help us understand differential distributions of chiral aroma compounds in tea.

Combined transcriptome sequencing and prokaryotic expression to investigate the key enzyme in the 2-C-methylerythritol-4-phosphate pathway of Osmanthus fragrans

Terpenoids are one of the main components of plant aromas. In the present study we investigated these compounds in Osmanthus fragrans Lour., which is a fragrant plant widely used for the production of essential oils. Quantitative real-time PCR (qRT-PCR) results of enzymes associated with the 2-C-methylerythritol-4-phosphate pathway confirmed that the TPS is a key enzyme for terpenoid synthesis in O. fragrans. In a series of experiments, we identified the TPS candidate genes in O. fragrans and revealed the underlying catalytic activity and subcellular localisation of the encoded proteins. Because there is no available O. fragrans reference genome, we sequenced and analysed its transcriptome and identified two putative TPS genes, OfTPS1 and OfTPS2. According to qRT-PCR analysis, both genes were most highly expressed at the full-bloom stage, suggesting that OfTPS1 and OfTPS2 contribute to O. fragrans terpenoid synthesis. To verify this hypothesis, we constructed prokaryotic expression vectors to obtain protein. In order to study the function of OfTPS1 and OfTPS2 in the synthesis of monoterpenes, the obtained proteins were reacted with geranyl pyrophosphate. As a result, two kinds of monoterpenes, (E)-β-ocimene and linalool, were detected from reaction products, respectively. In conclusion, OfTPS1 and OfTPS2 are both monoterpene synthases.

Rahim MH, Sabri S, Lai KS, Song AAL, Abdul Rahim R, Wan Abdullah WMAN, Ong Abdullah J. Functional characterization of a new terpene synthase from Plectranthus amboinicus

Plectranthus amboinicus (Lour.) Spreng is an aromatic medicinal herb known for its therapeutic and nutritional properties attributed by the presence of monoterpene and sesquiterpene compounds. Up until now, research on terpenoid biosynthesis has focused on a few mint species with economic importance such as thyme and oregano, yet the terpene synthases responsible for monoterpene production in P. amboinicus have not been described. Here we report the isolation, heterologous expression and functional characterization of a terpene synthase involved in P. amboinicus terpenoid biosynthesis. A putative monoterpene synthase gene (PamTps1) from P. amboinicus was isolated with an open reading frame of 1797 bp encoding a predicted protein of 598 amino acids with molecular weight of 69.6 kDa. PamTps1 shares 60–70% amino acid sequence similarity with other known terpene synthases of Lamiaceae. The in vitro enzymatic activity of PamTps1 demonstrated the conversion of geranyl pyrophosphate and farnesyl pyrophosphate exclusively into linalool and nerolidol, respectively, and thus PamTps1 was classified as a linalool/nerolidol synthase. In vivo activity of PamTps1 in a recombinant Escherichia coli strain revealed production of linalool and nerolidol which correlated with its in vitro activity. This outcome validated the multi-substrate usage of this enzyme in producing linalool and nerolidol both in in vivo and in vitro systems. The transcript level of PamTps1 was prominent in the leaf during daytime as compared to the stem. Gas chromatography-mass spectrometry (GC-MS) and quantitative real-time PCR analyses showed that maximal linalool level was released during the daytime and lower at night following a diurnal circadian pattern which correlated with the PamTps1 expression pattern. The PamTps1 cloned herein provides a molecular basis for the terpenoid biosynthesis in this local herb that could be exploited for valuable production using metabolic engineering in both microbial and plant systems.

Parallel Transcriptional Regulation of Artemisinin and Flavonoid Biosynthesis

Plants regulate the synthesis of specialized compounds through the actions of individual transcription factors (TFs) or sets of TFs. One such compound, artemisinin from Artemisia annua, is widely used as a pharmacological product in the first-line treatment of malaria. However, the emergence of resistance to artemisinin in Plasmodium species, as well as its low production rates, have required innovative treatments such as exploiting the synergistic effects of flavonoids with artemisinin. We overview current knowledge about flavonoid and artemisinin transcriptional regulation in A. annua, and review the dual action of TFs and structural genes that can regulate both pathways simultaneously. Understanding the concerted action of these TFs and their associated structural genes can guide the development of strategies to further improve flavonoid and artemisinin production.

Functional Expression and Characterization of Trichome-Specific (-)-Limonene Synthase and (+)-α-Pinene Synthase from Cannabis sativa

Two recombinant, stereospecific monoterpene synthases, a (-)-limonene synthase (CsTPS1) and a (+)-α-pinene synthase (CsTPS2), encoded by Cannabis sativa L. cv. ‘Skunk’ trichome mRNA, have been isolated and characterized. Recombinant CsTPS1 showed a Km value of 6.8 μM, a Vmax of 1.1 × 10−4 μmol/min and Vmax/Km of 0.016; the pH optimum was determined at pH 6.5, and a temperature optimum at 40°C. Recombinant CsTPS2 showed a Km value of 10.5 μM, a Vmax of 2.2 × 10−4 μmol/min and Vmax/Km of 0.021; the pH optimum was determined at pH 7.0, and a temperature optimum at 30°C. Phylogenetic analysis showed that both CsTPSs group within the angiosperms and belong to the Tpsb subgroup of monoterpene synthases. The enzymatic products (-)-limonene and (+)-α-pinene were detected as natural products in C. sativa trichomes.

The Biology of Essential Oils in the Pollination of Flowers

Pollination is an essential biological process in higher plant reproduction that involves the transfer of pollen to the female sexual organs of flowers or cones. It plays a critical role in the reproductive success and evolution of most plant species by allowing plants to share genetic material from other members of the same or closely-related species, thus increasing genetic diversity. In many cases, non-plant organisms are involved in carrying out this cross-pollination, including insects, bats, mammals, and birds. In order to attract such pollinators, plants have evolved the ability to produce a mind-boggling array of volatile compounds that have also found abundant use for humans when collected as essential oils. In this review, we focus on the role of essential oil compounds that are produced by flowers as chemical attractants used to draw in their often highly-specific pollinators. We examine in some detail various questions behind the biology of floral scent, including how these compounds are produced in flowers, how they are detected by potential pollinators, and how biotechnology can be used to alter their activity.

Functional characterization and expression analysis of two terpene synthases involved in floral scent formation in Lilium 'Siberia'

Floral scent formation in Lilium 'Siberia' is mainly due to monoterpene presence in the floral profile. LoTPS1 and LoTPS3 are responsible for the formation of (±)-linalool and β-ocimene in Lilium 'Siberia'. Lilium 'Siberia' is a perennial herbaceous plant belonging to Liliaceae family, cultivated both as a cut flower and garden plant. The snowy white flower emits a pleasant aroma which is mainly caused by monoterpenes present in the floral volatile profile. Previously terpene synthase (TPS) genes have been isolated and characterized from various plant species but less have been identified from Liliaceae family. Here, two terpene synthase genes (LoTPS1 and LoTPS3), which are highly expressed in sepals and petals of Lilium 'Siberia' flower were functionally characterized recombinant LoTPS1 specifically catalyzes the formation of (Z)-β-ocimene and (±)-linalool as its main volatile compounds from geranyl pyrophosphate (GPP), whereas LoTPS3 is a promiscuous monoterpene synthase which utilizes both GPP and farnesyl pyrophosphate (FPP) as a substrate to generate (±)-linalool and cis-nerolidol, respectively. Transcript levels of both genes were prominent in flowering parts, especially in sepals and petals which are the main source of floral scent production. The gas chromatography-mass spectrometry (GC-MS) and quantitative real-time PCR analysis revealed that the compounds were emitted throughout the day, prominently during the daytime and lower levels at night following a strong circadian rhythm in their emission pattern. Regarding mechanical wounding, both genes showed considerable involvement in floral defense by inducing the emission of (Z)-β-ocimene and (±)-linalool, elevating the transcript accumulation of LoTPS1 and LoTPS3. Furthermore, the subcellular localization experiment revealed that LoTPS1 was localized in plastids, whilst LoTPS3 in mitochondria. Our findings on these two TPSs characterized from Lilium 'Siberia' provide new insights into molecular mechanisms of terpene biosynthesis in this species and also provide an opportunity for biotechnological modification of floral scent profile of Lilium.

Genome-wide detection of terpene synthase genes in holy basil (Ocimum sanctum L.)

Holy basil (Ocimum sanctum L.) and sweet basil (Ocimum basilicum L.) are the most commonly grown basil species in India for essential oil production and biosynthesis of potentially volatile and non-volatile phytomolecules with commercial significance. The aroma, flavor and pharmaceutical value of Ocimum species is a significance of its essential oil, which contains most of the monoterpenes and sesquiterpenes. A large number of plants have been studied for characterization and identification of terpene synthase genes, involved in terpenoids biosynthesis. The goal of this study is to discover and identify the putative functional terpene synthase genes in O. sanctum. HMMER search was performed by using a set of 13 well sequenced and annotated plant genomes including the newly sequenced genome of O. sanctum with Pfam-A database locally, using HMMER 3.0 hmmsearch for the two Pfam domains (PF01397 and PF03936). Using this search method 81 putative terpene synthases genes (OsaTPS) were identified in O. sanctum; the study further reveals 47 OsaTPS were putatively functional genes, 19 partial OsaTPS, and 15 OsaTPS as probably pseudogenes. All these identified OsaTPS genes were compared with other plant species, and phylogenetic analysis reveals the subfamily classification of OsaTPS in TPS-a, -b, -c, -e, -f and TPS-g subfamilies clusters. This genome-wide identification of OsaTPS genes, their phylogenetic analysis and secondary metabolite pathway mapping predictions together provide a comprehensive understanding of the TPS gene family in Ocimum sanctum and offer opportunities for the characterization and functional validation of numbers of terpene synthase genes.

Industrial brewing yeast engineered for the production of primary flavor determinants in hopped beer

Flowers of the hop plant provide both bitterness and “hoppy” flavor to beer. Hops are, however, both a water and energy intensive crop and vary considerably in essential oil content, making it challenging to achieve a consistent hoppy taste in beer. Here, we report that brewer’s yeast can be engineered to biosynthesize aromatic monoterpene molecules that impart hoppy flavor to beer by incorporating recombinant DNA derived from yeast, mint, and basil. Whereas metabolic engineering of biosynthetic pathways is commonly enlisted to maximize product titers, tuning expression of pathway enzymes to affect target production levels of multiple commercially important metabolites without major collateral metabolic changes represents a unique challenge. By applying state-of-the-art engineering techniques and a framework to guide iterative improvement, strains are generated with target performance characteristics. Beers produced using these strains are perceived as hoppier than traditionally hopped beers by a sensory panel in a double-blind tasting.

Production of aromatic monoterpene molecules in hop flowers is affected by genetic, environmental, and processing factors. Here, the authors engineer brewer’s yeast for the production of linalool and geraniol, and show pilot-scale beer produced by engineered strains reconstitutes some qualities of hop flavor.

Molecular cloning and functional characterization of a monoterpene synthase isolated from the aromatic wild shrub Thymus albicans

The essential oil of Thymus albicans Hoffmanns. & Link, a native shrub from the Iberian Peninsula, is mainly composed of monoterpenes. In this study, a 1,8-cineole synthase was isolated from the 1,8-cineole chemotype. A partial sequence that lacked the complete plastid transit peptide but contained an extended C-terminal when compared to other related terpene synthases was generated by PCR and Rapid Amplification of cDNA Ends (RACE). The predicted mature polypeptide was 593 amino acids in length and shared 78% and 77% sequence similarity with the homologue 1,8-cineole synthase from Rosmarinus officinalis and Salvia officinalis, respectively. The putative protein possessed the characteristic conserved motifs of plant monoterpene synthases including the RRx₈W and DDxxD motifs and phylogenetic analysis indicated that the amplified 1,8-cineole synthase bears greater sequence similarity with other 1,8-cineole synthases from Lamiaceae family relative to the terpene synthases from the genus Thymus. Functional expression of the recombinant protein in Escherichia coli revealed that in the presence of geranyl diphosphate (GPP) 1,8-cineole was the major product but that its production was too low for robust quantification. Other minor conversion products included α-pinene, β-pinene, sabinene and β-myrcene suggesting the isolated 1,8-cineole synthase may be a multi-product enzyme. To our knowledge, this is the first report of a functionally characterized monoterpene synthase from Thymus albicans.

Scent from Jasminum grandiflorum flowers: Investigation of the change in linalool enantiomers at various developmental stages using chemical and molecular methods

Jasminum species are among the most preferred fresh cut flowers in India since ancient times. The plant produces small and fragrant flowers, which are of great demand in the preparation of fragrant garlands and also in perfume industries. Floral volatile of Jasminum grandiflorum L. (Family: Oleaceae) was extracted using solid-phase microextraction and analyzed in enantioselective gas chromatography. Chemical classes of identified volatiles revealed the presence of terpenoids, phenylpropanoids, and fatty acid derivatives. Marker constituent of flower volatiles, linalool was selected for analytical characterization on ethyl- and acetyl-β-cyclodextrin stationary phase. (R)-(-)-Linalool was found as major enantiomer in volatiles of floral buds whereas (S)-(+)-linalool predominated in the volatiles of matured flowers. Simultaneously, a quantitative real-time PCR was performed to find the gene expression of linalool synthase to investigate the mechanism of enantiomeric inversion. The emission pattern of (R)-(-)-linalool at different flower developmental stages was well correlated (P = 0.01) with the gene expression of the cloned linalool synthase from J. grandiflorum. We observed that the successive change in (R)- to (S)-linalool ratio from bud to mature flower was mainly due to the enantio- specific transformation and temporal decline of (R)-linalool producing gene in J. grandiflorum. This enantiomeric change also leads to the difference in flower aroma. Furthermore, this is probably the reason behind consumer's acceptance for jasmine buds rather than bloomed flowers in cut flower segments.

Integrated metabolome and transcriptome analysis of Magnolia champaca identifies biosynthetic pathways for floral volatile organic compounds

Background

Magnolia champaca, commonly known as champak is a well-known tree due to its highly fragrant flowers. Champak floral scent is attributed to a complex mix of volatile organic compounds (VOCs). These aromatic flowers are widely used in flavors and fragrances industry. Despite its commercial importance, the VOC biosynthesis pathways in these flowers are largely unknown. Here, we combine metabolite and RNA sequencing (RNA-seq) analyses of fully opened champak flowers to discover the active VOC biosynthesis pathways as well as floral scent-related genes.

Results

Volatile collection by headspace method and analysis by gas chromatography-mass spectrometry (GC-MS) identified a total of 43 VOCs from fully opened champak flowers, of which 46.9% were terpenoids, 38.9% were volatile esters and 5.2% belonged to phenylpropanoids/benzenoids. Sequencing and de novo assembly of champak flower transcriptome yielded 47,688 non-redundant unigenes. Transcriptome assembly was validated using standard polymerase chain reaction (PCR) based approach for randomly selected unigenes. The detailed profiles of VOCs led to the discovery of pathways and genes involved in floral scent biosynthesis from RNA-seq data. Analysis of expression levels of many floral-scent biosynthesis-related unigenes in flowers and leaves showed that most of them were expressed higher in flowers than in leaf tissues. Moreover, our metabolite-guided transcriptomics, in vitro and in vivo enzyme assays and transgenic studies identified (R)-linalool synthase that is essential for the production of major VOCs of champak flowers, (R)-linalool and linalool oxides.

Conclusion

As our study is the first report on transcriptome analysis of Magnolia champaca, this transcriptome dataset that serves as an important public information for functional genomics will not only facilitate better understanding of ecological functions of champak floral VOCs, but also provide biotechnological targets for sustainable production of champak floral scent.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3846-8) contains supplementary material, which is available to authorized users.

Formation and emission of linalool in tea (Camellia sinensis) leaves infested by tea green leafhopper (Empoasca (Matsumurasca) onukii Matsuda)

Famous oolong tea (Oriental Beauty), which is manufactured by tea leaves (Camellia sinensis) infected with tea green leafhoppers, contains characteristic volatile monoterpenes derived from linalool. This study aimed to determine the formation mechanism of linalool in tea exposed to tea green leafhopper attack. The tea green leafhopper responsible for inducing the production of characteristic volatiles was identified as Empoasca (Matsumurasca) onukii Matsuda. E. (M.) onukii attack significantly induced the emission of linalool from tea leaves (p<0.05) as a result of the up-regulation of the linalool synthases (CsLIS1 and CsLIS2) (p<0.05). Continuous mechanical damage significantly enhanced CsLIS1 and CsLIS2 expression levels and linalool emission (p<0.05). Therefore, continuous wounding was a key factor causing the formation and emission of linalool from tea leaves exposed to E. (M.) onukii attack. This information should prove helpful for the future use of stress responses of plant secondary metabolism to improve quality components of agricultural products.

Production of jet fuel precursor monoterpenoids from engineered Escherichia coli

Monoterpenes (C₁₀ isoprenoids) are the main components of essential oils and are possible precursors for many commodity chemicals and high energy density fuels. Monoterpenes are synthesized from geranyl diphosphate (GPP), which is also the precursor for the biosynthesis of farnesyl diphosphate (FPP). FPP biosynthesis diverts the carbon flux from monoterpene production to C₁₅ products and quinone biosynthesis. In this study, we tested a chromosomal mutation of Escherichia coli's native FPP synthase (IspA) to improve GPP availability for the production of monoterpenes using a heterologous mevalonate pathway. Monoterpene production at high levels required not only optimization of GPP production but also a basal level of FPP to maintain growth. The optimized strains produced two jet fuel precursor monoterpenoids 1,8-cineole and linalool at the titer of 653 mg/L and 505 mg/L, respectively, in batch cultures with 1% glucose. The engineered strains developed in this work provide useful resources for the production of high-value monoterpenes. Biotechnol. Bioeng. 2017;114: 1703-1712. © 2017 Wiley Periodicals, Inc.

Regulation of Floral Terpenoid Emission and Biosynthesis in Sweet Basil (Ocimum basilicum)

Past studies have focused on the composition of essential oil of Ocimum basilicum leaves, but data on composition and regulation of its aerial emissions, especially floral volatile emissions are scarce. We studied the chemical profile, within-flower spatial distribution (sepals, petals, pistils with stamina and pedicels), diurnal emission kinetics and effects of exogenous methyl jasmonate (MeJA) application on the emission of floral volatiles by dynamic headspace collection and identification using gas chromatography-mass spectrometry (GC-MS) and proton transfer reaction mass spectrometry (PTR-MS). We observed more abundant floral emissions from flowers compared with leaves. Sepals were the main emitters of floral volatiles among the flower parts studied. The emissions of lipoxygenase compounds (LOX) and monoterpenoids, but not sesquiterpene emissions, displayed a diurnal variation driven by light. Response to exogenous MeJA treatment of flowers consisted of a rapid stress response and a longer-term acclimation response. The initial response was associated with enhanced emissions of fatty acid derivatives, monoterpenoids, and sesquiterpenoids without variation of the composition of individual compounds. The longer-term response was associated with enhanced monoterpenoid and sesquiterpenoid emissions with profound changes in the emission spectrum. According to correlated patterns of terpenoid emission changes upon stress, highlighted by a hierarchical cluster analysis, candidate terpenoid synthases responsible for observed diversity and complexity of released terpenoid blends were postulated. We conclude that flower volatile emissions differ quantitatively and qualitatively from leaf emissions, and overall contribute importantly to O. basilicum flavor, especially under stress conditions.

Molecular characterization and phylogenetic analysis of two novel regio-specific flavonoid prenyltransferases from Morus alba and Cudrania tricuspidata

Prenylated flavonoids are attractive specialized metabolites with a wide range of biological activities and are distributed in several plant families. The prenylation catalyzed by prenyltransferases represents a Friedel-Crafts alkylation of the flavonoid skeleton in the biosynthesis of natural prenylated flavonoids and contributes to the structural diversity and biological activities of these compounds. To date, all identified plant flavonoid prenyltransferases (FPTs) have been identified in Leguminosae. In the present study two new FPTs, Morus alba isoliquiritigenin 3'-dimethylallyltransferase (MaIDT) and Cudrania tricuspidata isoliquiritigenin 3'-dimethylallyltransferase (CtIDT), were identified from moraceous plants M. alba and C. tricuspidata, respectively. MaIDT and CtIDT shared low levels of homology with the leguminous FPTs. MaIDT and CtIDT are predicted to be membrane-bound proteins with predicted transit peptides, seven transmembrane regions, and conserved functional domains that are similar to other homogentisate prenyltransferases. Recombinant MaIDT and CtIDT were able to regioselectively introduce dimethylallyl diphosphate into the A ring of three flavonoids with different skeleton types (chalcones, isoflavones, and flavones). Phylogenetic analysis revealed that MaIDT and CtIDT are distantly related to their homologs in Leguminosae, which suggests that FPTs in Moraceae and Leguminosae might have evolved independently. MaIDT and CtIDT represent the first two non-Leguminosae FPTs to be identified in plants and could thus lead to the identification of additional evolutionarily varied FPTs in other non-Leguminosae plants and could elucidate the biosyntheses of prenylated flavonoids in various plants. Furthermore, MaIDT and CtIDT might be used for regiospecific prenylation of flavonoids to produce bioactive compounds for potential therapeutic applications due to their high efficiency and catalytic promiscuity.

Characterization of two monoterpene synthases involved in floral scent formation in Hedychium coronarium

Hedychium coronarium, a perennial herb belonging to the family Zingiberaceae, is cultivated as a garden plant or cut flower as well as for medicine and aromatic oil. Its flowers emit a fresh and inviting scent, which is mainly because of monoterpenes present in the profile of the floral volatiles. However, fragrance produced as a result of monoterpenes has not been well studied. In the present study, two novel terpene synthase (TPS) genes (HcTPS7 and HcTPS8) were isolated to study the biosynthesis of monoterpenes in H. coronarium. In vitro characterization showed that the recombinant HcTPS7 was capable of generating sabinene as its main product, in addition to nine sub-products from geranyl diphosphate (GPP). Recombinant HcTPS8 almost specifically catalyzed the formation of linalool from GPP, while it converted farnesyl diphosphate (FPP) to α-bergamotene, cis-α-bisabolene, β-farnesene and other ten sesquiterpenes. Subcellular localization experiments revealed that HcTPS7 and HcTPS8 were located in plastids. Real-time PCR analyses showed that HcTPS7 and HcTPS8 genes were highly expressed in petals and sepals, but were almost undetectable in vegetative organs. The changes of their expression levels in petals were positively correlated with the emission patterns of sabinene and linalool, respectively, during flower development. The results indicated that HcTPS7 and HcTPS8 were involved in the biosynthesis of sabinene and linalool in H. coronarium flowers. Results on these two TPSs first characterized from H. coronarium provide new insights into molecular mechanisms of terpene biosynthesis in this species and also lay the basis for biotechnological modification of floral scent profile in Hedychium.

Transcriptome profiling, and cloning and characterization of the main monoterpene synthases of Coriandrum sativum L

Terpenoids are a large and diverse class of specialized metabolites that are essential for the growth and development of plants, and have tremendous industrial applications. The mericarps of Coriandrum sativum L. (coriander) produce an essential oil (EO) rich in monoterpenes, volatile C10 terpenoids. To investigate EO metabolism, the transcriptome of coriander mericarps, at three developmental stages (early, mid, late) was sequenced via Illumina technology and a transcript library was produced. To validate the usability of the transcriptome sequences, two terpene synthase candidate genes, CsγTRPS and CsLINS, encoding 558 and 562 amino acid proteins were expressed in bacteria, and the recombinant proteins purified by Ni-NTA affinity chromatography. The 65.16 (CsγTRPS) and 65.91 (CsLINS)kDa recombinant proteins catalyzed the conversion of geranyl diphosphate, the precursor to monoterpenes, to γ-terpinene and (S)-linalool, respectively, with apparent Vmax and Km values of 2.24±0.16 (CsγTRPS); 19.63±1.05 (CsLINS)pkat/mg and 66.25±13 (CsγTRPS); 2.5±0.6 (CsLINS)μM, respectively. Together, CsγTRPS and CsLINS account for the majority of EO constituents in coriander mericarps. Investigation of the coriander transcriptome, and knowledge gained from these experiments will facilitate future studies concerning essential and fatty acid oil production in coriander. They also enable efforts to improve the coriander oils through metabolic engineering or plant breeding.

Terpenoid biosynthesis in trichomes--current status and future opportunities

Glandular trichomes are anatomical structures specialized for the synthesis of secreted natural products. In this review we focus on the description of glands that accumulate terpenoid essential oils and oleoresins. We also provide an in-depth account of the current knowledge about the biosynthesis of terpenoids and secretion mechanisms in the highly specialized secretory cells of glandular trichomes, and highlight the implications for metabolic engineering efforts.

Cloning, functional characterization and genomic organization of 1,8-cineole synthases from Lavandula

Several members of the genus Lavandula produce valuable essential oils (EOs) that are primarily constituted of the low molecular weight isoprenoids, particularly monoterpenes. We isolated over 8,000 ESTs from the glandular trichomes of L. x intermedia flowers (where bulk of the EO is synthesized) to facilitate the discovery of genes that control the biosynthesis of EO constituents. The expression profile of these ESTs in L. x intermedia and its parents L. angustifolia and L. latifolia was established using microarrays. The resulting data highlighted a differentially expressed, previously uncharacterized cDNA with strong homology to known 1,8-cineole synthase (CINS) genes. The ORF, excluding the transit peptide, of this cDNA was expressed in E. coli, purified by Ni-NTA agarose affinity chromatography and functionally characterized in vitro. The ca. 63 kDa bacterially produced recombinant protein, designated L. x intermedia CINS (LiCINS), converted geranyl diphosphate (the linear monoterpene precursor) primarily to 1,8-cineole with K ( m ) and k ( cat ) values of 5.75 μM and 8.8 × 10(-3) s(-1), respectively. The genomic DNA of CINS in the studied Lavandula species had identical exon-intron architecture and coding sequences, except for a single polymorphic nucleotide in the L. angustifolia ortholog which did not alter protein function. Additional nucleotide variations restricted to L. angustifolia introns were also observed, suggesting that LiCINS was most likely inherited from L. latifolia. The LiCINS mRNA levels paralleled the 1,8-cineole content in mature flowers of the three lavender species, and in developmental stages of L. x intermedia inflorescence indicating that the production of 1,8 cineole in Lavandula is most likely controlled through transcriptional regulation of LiCINS.

Isolation and characterization of terpene synthases potentially involved in flavor development of ripening olive (Olea europaea) fruits

The flavor and taste of fruits are often determined by terpenes. We identified three cDNAs encoding putative terpene synthases from olive fruits of cv. Frantoio and Grignano. Heterologous expression in a bacterial system demonstrated that one of the terpene synthases, OeGES1, was an active monoterpene synthase that converted geranyl diphosphate to the monoterpene alcohol geraniol. The transcript accumulation pattern of this gene showed a peak during fruit ripening in both genotypes, indicating that the enzyme may be involved in the production of monoterpene flavor compounds in olive fruit. Although the putative terpene synthases OeTPS2 and OeTPS3 clustered with α-farnesene synthases and angiosperm monoterpene synthases, no detectable in vitro activity was found after expression in a bacterial system. Nevertheless, their transcripts sharply accumulated during fruit ripening starting from véraison.

IeCPS2 is potentially involved in the biosynthesis of pharmacologically active Isodon diterpenoids rather than gibberellin

The traditional Chinese medicinal plant, Isodon L., is remarkably rich in pharmacologically active ent-kaurane diterpenoids of diverse carbon skeletons. In an effort to create a resource for gene discovery and elucidate the biosynthesis of Isodonent-kaurane diterpenoids, three cDNAs (named IeCPS1, IeCPS2 and IeCPS2a) were isolated putatively encoding copalyl diphosphate synthases from Isodoneriocalyx leaves. Recombinant proteins of IeCPS1 and IeCPS2 were expressed, respectively, in Escherichia coli, and were shown to specifically convert geranylgeranyl diphosphate to copalyl diphosphate as demonstrated by GC-MS analyses. Based on tissue-specific expression and metabolic localization studies, the IeCPS2 transcripts were detected in young and mature leaves where the dominant ent-kaurane diterpenoid maoecrystal B accumulates, whereas no detectable expression of IeCPS2 was observed in germinating seeds where the gibberellin biosynthetic pathway is usually active. In addition, no evidence for maoecrystal B was found in germinating seeds. On the other hand, IeCPS1 transcripts significantly accumulated in germinating seeds as well as in leaves. The biochemical and molecular genetic evidence thus indicated that IeCPS2 is a copalyl diphosphate synthase potentially involved in the biosynthesis of Isodon diterpenoids in leaves, while IeCPS1 is more probably relevant to gibberellin formation and may, in addition, participate in Isodonent-kaurane diterpenoid production.

Product variability of the 'cineole cassette' monoterpene synthases of related Nicotiana species

Nicotiana species of the section Alatae characteristically emit the floral scent compounds of the 'cineole cassette' comprising 1,8-cineole, limonene, myrcene, α-pinene, β-pinene, sabinene, and α-terpineol. We successfully isolated genes of Nicotiana alata and Nicotiana langsdorfii that encoded enzymes, which produced the characteristic monoterpenes of this 'cineole cassette' with α-terpineol being most abundant in the volatile spectra. The amino acid sequences of both terpineol synthases were 99% identical. The enzymes cluster in a monophyletic branch together with the closely related cineole synthase of Nicotiana suaveolens and monoterpene synthase 1 of Solanum lycopersicum. The cyclization reactions (α-terpineol to 1,8-cineole) of the terpineol synthases of N. alata and N. langsdorfii were less efficient compared to the 'cineole cassette' monoterpene synthases of Arabidopsis thaliana, N. suaveolens, Salvia fruticosa, Salvia officinalis, and Citrus unshiu. The terpineol synthases of N. alata and N. langsdorfii were localized in pistils and in the adaxial and abaxial epidermis of the petals. The enzyme activities reached their maxima at the second day after anthesis when flowers were fully opened and the enzyme activity in N. alata was highest at the transition from day to night (diurnal rhythm).

Molecular cloning and characterization of a linalool synthase from lemon myrtle

Using a homology-based PCR strategy, we identified a cDNA with sequence similarity to linalool synthase from lemon myrtle. Functional expression of the cDNA (designated BcLS) gene in Escherichia coli yielded an active enzyme capable of catalyzing the conversion of geranyl diphosphate to (-)-linalool, i.e., an acyclic monoterpene alcohol, and to lesser amounts of cyclic monoterpenes. The kinetic parameters of BcLS were similar to those of synthases producing cyclic monoterpenes. PCR analysis revealed that the BcLS gene transcript was ubiquitously expressed in lemon myrtle and was upregulated in response to jasmonic acid treatment. Although the physiological role of neryl diphosphate (NPP) dependency of BcLS remains unclear, the cyclization activity of BcLS was enhanced when NPP was used as substrate, resulting in predominant production of cyclic monoterpenes. These findings indicate that BcLS has novel specificity and kinetic parameters, but its physiological responses to stresses such as insect damage appear to be similar to known linalool synthases.

Biocatalytic synthesis of optically active tertiary alcohols

The enzymatic preparation of optically pure tertiary alcohols under sustainable conditions has received much attention. The conventional chemical synthesis of these valuable building blocks is still hampered by the use of harmful reagents such as heavy metal catalysts. Successful examples in biocatalysis used esterases, lipases, epoxide hydrolases, halohydrin dehalogenases, thiamine diphosphate-dependent enzymes, terpene cyclases, -acetylases, and -dehydratases. This mini-review provides an overview on recent developments in the discovery of new enzymes, their functional improvement by protein engineering, the design of chemoenzymatic routes leading to tertiary alcohols, and the discovery of entirely new biotransformations.

Cloning and functional characterization of β-phellandrene synthase from Lavandula angustifolia

En route to building genomics resources for Lavandula, we have obtained over 14,000 ESTs for leaves and flowers of L. angustifolia, a major essential oil crop, and identified a number of previously uncharacterized terpene synthase (TPS) genes. Here we report the cloning, expression in E. coli, and functional characterization of β-phellandrene synthase, LaβPHLS. The ORF--excluding the transit peptide--for this gene encoded a 62.3 kDa protein that contained all conserved motifs present in plant TPSs. Expression in bacteria resulted in the production of a soluble protein that was purified by Ni-NTA agarose affinity chromatography. While the recombinant LaβPHLS did not utilize FPP as a substrate, it converted GPP (the preferred substrate) and NPP into β-phellandrene as the major product, with K (m) and k (cat) of 6.55 μM and 1.75 × 10(-2) s(-1), respectively, for GPP. The LaβPHLS transcripts were highly abundant in young leaves where β-phellandrene is produced, but were barely detectable in flowers and older leaves, where β-phellandrene is not synthesized in significant quantities. This data indicate that β-phellandrene biosynthesis is transcriptionally and developmentally regulated. We also cloned and expressed in E. coli a second TPS-like protein, LaTPS-I, that lacks an internal stretch of 73 amino acids, including the signature DDxxD divalent metal binding motif, compared to other plant TPSs. The recombinant LaTPS-I did not produce detectable products in vitro when assayed with GPP, NPP or FPP as substrates. The lack of activity is most likely due to the absence of catalytically important amino acid residues within the missing region.

Convergent evolution in plant specialized metabolism

Plants synthesize a multitude of compounds that contribute to adaptation to their ecological niches. Such compounds serve as attractants of other living organisms beneficial to the plants or as defense against other biotic as well as abiotic agents. Selection for increased fitness, a never-ending process, has resulted in each plant lineage synthesizing a distinct set of specialized metabolites appropriate for its environment. The total number of specialized metabolites found in the plant kingdom far exceeds the capacity of any one plant genome to encode the necessary enzymes, and just as a plant lineage acquires the ability to make new specialized compounds during evolution, it also loses the ability to make others. Although the ability of plants to make novel, specialized metabolites continues to evolve, there are also many examples in which different plants have independently evolved the ability to make compounds already present in other plant lineages or to make different compounds that fulfill the same role-both are examples of convergent evolution. Here, we discuss many examples of convergent evolution in specialized metabolism. There are many genetic and biochemical mechanisms that can give rise to convergent evolution, and we conclude that, overall, convergent evolution in plant specialized metabolism is surprisingly common.

A genomics resource for investigating regulation of essential oil production in Lavandula angustifolia

We are developing Lavandula angustifolia (lavender) as a model system for investigating molecular regulation of essential oil (a mixture of mono- and sesquiterpenes) production in plants. As an initial step toward building the necessary 'genomics toolbox' for this species, we constructed two cDNA libraries from lavender leaves and flowers, and obtained sequence information for 14,213 high-quality expressed sequence tags (ESTs). Based on homology to sequences present in GenBank, our EST collection contains orthologs for genes involved in the 1-deoxy-D: -xylulose-5-phosphate (DXP) and the mevalonic acid (MVA) pathways of terpenoid biosynthesis, and for known terpene synthases and prenyl transferases. To gain insight into the regulation of terpene metabolism in lavender flowers, we evaluated the transcriptional activity of the genes encoding for 1-deoxy-D: -xylulose-5-phosphate synthase (DXS) and HMG-CoA reductase (HMGR), which represent regulatory steps of the DXP and MVA pathways, respectively, in glandular trichomes (oil glands) by real-time PCR. While HMGR transcripts were barely detectable, DXS was heavily expressed in this tissue, indicating that essential oil constituents are predominantly produced through the DXP pathway in lavender glandular trichomes. As anticipated, the linalool synthase (LinS)-the gene responsible for the production of linalool, a major constituent of lavender essential oil-was also strongly expressed in glands. Surprisingly, the most abundant transcript in floral glandular trichomes corresponded to a sesquiterpene synthase (cadinene synthase, CadS), although sesquiterpenes are minor constituents of lavender essential oils. This result, coupled to the weak activity of the MVA pathway (the main route for sesquiterpene production) in trichomes, indicates that precursor supply may represent a bottleneck in the biosynthesis of sesquiterpenes in lavender flowers.

Monoterpene and sesquiterpene synthases and the origin of terpene skeletal diversity in plants

The multitude of terpene carbon skeletons in plants is formed by enzymes known as terpene synthases. This review covers the monoterpene and sesquiterpene synthases presenting an up-to-date list of enzymes reported and evidence for their ability to form multiple products. The reaction mechanisms of these enzyme classes are described, and information on how terpene synthase proteins mediate catalysis is summarized. Correlations between specific amino acid motifs and terpene synthase function are described, including an analysis of the relationships between active site sequence and cyclization type and a discussion of whether specific protein features might facilitate multiple product formation.

Enantioselective monoterpene alcohol acetylation in Origanum, Mentha and Salvia species

Selected plants within the Origanum, Mentha and Salvia genera, that contain significant amounts of chiral volatile alcohols and their related acetates, exhibit remarkable enantioselectivity of alcohol acetyl transferase (AAT) activity and particularly can discriminate between linalool enantiomers. Origanum dayi AAT produced almost enantiomerically pure (R)-linalyl acetate by enzymatic acetylation of racemic linalool, whereas the closely related O. majorana AAT produced a mixture of (R)- and (S)-linalyl acetate with a ratio of 6:4. V(max) of O. dayi acetylation activity was 30-fold higher for (R)-linalool, whereas in O. majorana no such differences were found.

Two nearly identical terpene synthases catalyze the formation of nerolidol and linalool in snapdragon flowers

Terpenoids emitted from snapdragon flowers include three monoterpenes derived from geranyl diphosphate (GPP), myrcene, (E)-beta-ocimene and linalool, and a sesquiterpene, nerolidol, derived from farnesyl diphosphate (FPP). Using a functional genomics approach, we have isolated and biochemically characterized two nearly identical nerolidol/linalool synthases, AmNES/LIS-1 and AmNES/LIS-2, two enzymes responsible for the terpenoid profile of snapdragon scent remaining to be characterized. The AmNES/LIS-2 protein has an additional 30 amino acids in the N-terminus, and shares 95% amino acid sequence identity with AmNES/LIS-1, with only 23 amino acid substitutions distributed across the homologous regions of the proteins. Although these two terpene synthases have very similar catalytic properties, and synthesize linalool and nerolidol as specific products from GPP and FPP, respectively, they are compartmentally segregated. GFP localization studies and analysis of enzyme activities in purified leucoplasts, together with our previous feeding experiments, revealed that AmNES/LIS-1 is localized in cytosol, and is responsible for nerolidol biosynthesis, whereas AmNES/LIS-2 is located in plastids, and accounts for linalool formation. Our results show that subcellular localization of bifunctional enzymes, in addition to the availability of substrate, controls the type of product formed. By directing nearly identical bifunctional enzymes to more than one cellular compartment, plants extend the range of available substrates for enzyme utilization, thus increasing the diversity of the metabolites produced.

Cloning and functional characterization of three terpene synthases from lavender (Lavandula angustifolia)

The essential oil of lavender (Lavandula angustifolia) is mainly composed of mono- and sesquiterpenes. Using a homology-based PCR strategy, two monoterpene synthases (LaLIMS and LaLINS) and one sesquiterpene synthase (LaBERS) were cloned from lavender leaves and flowers. LaLIMS catalyzed the formation of (R)-(+)-limonene, terpinolene, (1R,5S)-(+)-camphene, (1R,5R)-(+)-alpha-pinene, beta-myrcene and traces of alpha-phellandrene. The proportions of these products changed significantly when Mn(2+) was supplied as the cofactor instead of Mg(2+). The second enzyme LaLINS produced exclusively (R)-(-)-linalool, the main component of lavender essential oil. LaBERS transformed farnesyl diphosphate and represents the first reported trans-alpha-bergamotene synthase. It accepted geranyl diphosphate with higher affinity than farnesyl diphosphate and also produced monoterpenes, albeit at low rates. LaBERS is probably derived from a parental monoterpene synthase by the loss of the plastidial signal peptide and by broadening its substrate acceptance spectrum. The identification and description of the first terpene synthases from L. angustifolia forms the basis for the biotechnological modification of essential oil composition in lavender.

Tomato linalool synthase is induced in trichomes by jasmonic acid

Tomato (Lycopersicon esculentum) plants emit a blend of volatile organic compounds, which mainly consists of terpenes. Upon herbivory or wounding, the emission of several terpenes increases. We have identified and characterized the first two tomato monoterpene synthases, LeMTS1 and LeMTS2. Although these proteins were highly homologous, recombinant LeMTS1 protein produced (R)-linalool from geranyl diphosphate (GPP) and (E)-nerolidol from farnesyl diphosphate (FPP), while recombinant LeMTS2 produced beta-phellandrene, beta-myrcene, and sabinene from GPP. In addition, these genes were expressed in different tissues: LeMTS1 was expressed in flowers, young leaves, stems, and petioles, while LeMTS2 was strongest expressed in stems and roots. LeMTS1 expression in leaves was induced by spider mite-infestation, wounding and jasmonic acid (JA)-treatment, while LeMTS2 did not respond to these stimuli. The expression of LeMTS1 in stems and petioles was predominantly detected in trichomes and could be induced by JA. Because JA treatment strongly induced emission of linalool and overexpression of LeMTS1 in tomato resulted in increased production of linalool, we propose that LeMTS1 is a genuine linalool synthase. Our results underline the importance of trichomes in JA-induced terpene emission in tomato.

Geraniol synthases from perilla and their taxonomical significance

Geraniol synthases were isolated from five pure strains of Perilla citriodora and Perilla frutescens which vary in essential oil type, the main compounds of which were citral, elsholtziaketone, perillaketone, and perillene, respectively. This result supports the putative biosynthetic pathways of these three furylalkenes which are all produced by way of citral. Nucleotide sequences of geraniol synthases from three oil types of P. citriodora were identical, and almost the same as the sequence from P. frutescens, a species with twice the chromosome number of P. citriodora. This identity in sequence between P. citriodora and P. frutescens, together with other previous results, indicates that P. frutescens was formed as an amphidiploid of P. citriodora and an unknown wild species.