The diverse sesquiterpene profile of patchouli, Pogostemon cablin, is correlated with a limited number of sesquiterpene synthases

Intron-containing algal transgenes mediate efficient recombinant gene expression in the green microalga Chlamydomonas reinhardtii

Among green freshwater microalgae, Chlamydomonas reinhardtii has the most comprehensive and developed molecular toolkit, however, advanced genetic and metabolic engineering driven from the nuclear genome is generally hindered by inherently low transgene expression levels. Progressive strain development and synthetic promoters have improved the capacity of transgene expression; however, the responsible regulatory mechanisms are still not fully understood. Here, we elucidate the sequence specific dynamics of native regulatory element insertion into nuclear transgenes. Systematic insertions of the first intron of the ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit 2 (rbcS2i1) throughout codon-optimized coding sequences (CDS) generates optimized algal transgenes which express reliably in C. reinhardtii. The optimal rbcS2i1 insertion site for efficient splicing was systematically determined and improved gene expression rates were shown using a codon-optimized sesquiterpene synthase CDS. Sequential insertions of rbcS2i1 were found to have a step-wise additive effect on all levels of transgene expression, which is likely correlated to a synergy of transcriptional machinery recruitment and mimicking the short average exon lengths natively found in the C. reinhardtii genome. We further demonstrate the value of this optimization with five representative transgene examples and provide guidelines for the design of any desired sequence with this strategy.

Colored shade nets induced changes in growth, anatomy and essential oil of Pogostemon cablin

The purpose of this investigation was to determine the influence of colored shade nets on the growth, anatomy and essential oil content, yield and chemical composition of Pogostemon cablin. The plants were cultivated under full sunlight, black, blue and red nets. The harvesting was performed 5 months after planting and it was followed by the analysis of plant growth parameters, leaf anatomy, essential oil content, yield and chemical composition. The plants grown under red net have produced more leaf, shoot, total dry weight and leaf area. Plants cultivated under colored nets showed differences in morphological features. Plants maintained under red net had a higher leaf blade thickness and polar and equatorial diameter of the stomata ratio. Additionally, higher yield of essential oil in the leaves was observed under red and blue colored shade net. The essential oil of the plants grown under red net showed the highest relative percentage of patchoulol (66.84%). Therefore, it is possible using colored shade nets to manipulate P. cablin growth, as well as its essential oil production with several chemical compositions. The analyses of principal components allowed observing that pogostol has negative correlation with α-guaiene and α-bulnesene. There was difference in total dry weight and patchoulol content when the patchouli is cultured under the red colored shade nets.

Patchoulol Production with Metabolically Engineered Corynebacterium glutamicum

Patchoulol is a sesquiterpene alcohol and an important natural product for the perfume industry. Corynebacterium glutamicum is the prominent host for the fermentative production of amino acids with an average annual production volume of ~6 million tons. Due to its robustness and well established large-scale fermentation, C. glutamicum has been engineered for the production of a number of value-added compounds including terpenoids. Both C40 and C50 carotenoids, including the industrially relevant astaxanthin, and short-chain terpenes such as the sesquiterpene valencene can be produced with this organism. In this study, systematic metabolic engineering enabled construction of a patchoulol producing C. glutamicum strain by applying the following strategies: (i) construction of a farnesyl pyrophosphate-producing platform strain by combining genomic deletions with heterologous expression of ispA from Escherichia coli; (ii) prevention of carotenoid-like byproduct formation; (iii) overproduction of limiting enzymes from the 2-c-methyl-d-erythritol 4-phosphate (MEP)-pathway to increase precursor supply; and (iv) heterologous expression of the plant patchoulol synthase gene PcPS from Pogostemon cablin. Additionally, a proof of principle liter-scale fermentation with a two-phase organic overlay-culture medium system for terpenoid capture was performed. To the best of our knowledge, the patchoulol titers demonstrated here are the highest reported to date with up to 60 mg L^−1 and volumetric productivities of up to 18 mg L^−1 d^−1.

Microbial Cell Factories for the Production of Terpenoid Flavor and Fragrance Compounds

Terpenoid flavor and fragrance compounds are of high interest to the aroma industry. Microbial production offers an alternative sustainable access to the desired terpenoids independent of natural sources. Genetically engineered microorganisms can be used to synthesize terpenoids from cheap and renewable resources. Due to its modular architecture, terpenoid biosynthesis is especially well suited for the microbial cell factory concept: a platform host engineered for a high flux toward the central C₅ prenyl diphosphate precursors enables the production of a broad range of target terpenoids just by varying the pathway modules converting the C₅ intermediates to the product of interest. In this review typical terpenoid flavor and fragrance compounds marketed or under development by biotech and aroma companies are given, and the specificities of the aroma market are discussed. The main part of this work focuses on key strategies and recent advances to engineer microbes to become efficient terpenoid producers.

Purification and biochemical characterization of recombinant Persicaria minor β-sesquiphellandrene synthase

BACKGROUND

Sesquiterpenes are 15-carbon terpenes synthesized by sesquiterpene synthases using farnesyl diphosphate (FPP) as a substrate. Recently, a sesquiterpene synthase gene that encodes a 65 kDa protein was isolated from the aromatic plant Persicaria minor. Here, we report the expression, purification and characterization of recombinant P. minor sesquiterpene synthase protein (PmSTS). Insights into the catalytic active site were further provided by structural analysis guided by multiple sequence alignment.

METHODS

The enzyme was purified in two steps using affinity and size exclusion chromatography. Enzyme assays were performed using the malachite green assay and enzymatic product was identified using gas chromatography-mass spectrometry (GC-MS) analysis. Sequence analysis of PmSTS was performed using multiple sequence alignment (MSA) against plant sesquiterpene synthase sequences. The homology model of PmSTS was generated using I-TASSER server.

RESULTS

Our findings suggest that the recombinant PmSTS is mainly expressed as inclusion bodies and soluble aggregate in the E. coli protein expression system. However, the addition of 15% (v/v) glycerol to the protein purification buffer and the removal of N-terminal 24 amino acids of PmSTS helped to produce homogenous recombinant protein. Enzyme assay showed that recombinant PmSTS is active and specific to the C₁₅ substrate FPP. The optimal temperature and pH for the recombinant PmSTS are 30 °C and pH 8.0, respectively. The GC-MS analysis further showed that PmSTS produces β-sesquiphellandrene as a major product and β-farnesene as a minor product. MSA analysis revealed that PmSTS adopts a modified conserved metal binding motif (NSE/DTE motif). Structural analysis suggests that PmSTS may binds to its substrate similarly to other plant sesquiterpene synthases.

DISCUSSION

The study has revealed that homogenous PmSTS protein can be obtained with the addition of glycerol in the protein buffer. The N-terminal truncation dramatically improved the homogeneity of PmSTS during protein purification, suggesting that the disordered N-terminal region may have caused the formation of soluble aggregate. We further show that the removal of the N-terminus disordered region of PmSTS does not affect the product specificity. The optimal temperature, optimal pH, K_m and k_cat values of PmSTS suggests that PmSTS shares similar enzyme characteristics with other plant sesquiterpene synthases. The discovery of an altered conserved metal binding motif in PmSTS through MSA analysis shows that the NSE/DTE motif commonly found in terpene synthases is able to accommodate certain level of plasticity to accept variant amino acids. Finally, the homology structure of PmSTS that allows good fitting of substrate analog into the catalytic active site suggests that PmSTS may adopt a sesquiterpene biosynthesis mechanism similar to other plant sesquiterpene synthases.

Revisiting the Chemistry of Guaiacwood Oil: Identification and Formation Pathways of 5,11- and 10,11-Epoxyguaianes

Guaiacwood oil from Bulnesia sarmientoi Lorentz ex. Griseb is a common natural ingredient of the perfume industry used in both domestic and luxury fragrances for its highly appreciated woody-rosy odor, as well as its excellent fixative properties. Despite its long and traditional use as a perfume ingredient, guaiacwood oil has not been extensively studied. Thus, the chemical characterization of its constituents by using a full array of GC-hyphenated techniques (GC-MS, GC × GC-MS, and pc-GC) combined with conventional chemical fractionation was undertaken. In the course of this work, 15 new sesquiterpenoids mostly belonging to the 5,11- and 10,11-epoxyguaiane families were identified. Each isolated compound was fully characterized by NMR and MS. Collectively, the specific chemical relationships observed between sesquiterpene oxides and alcohols permitted the formulation of probable formation pathways regarding their presence as natural constituents of guaiacwood extracts.

Taste and smell in aquatic and terrestrial environments

The review summarizes results up to 2017 on chemosensory cues occurring in both aquatic and terrestrial environments.

Aging and/or tissue-specific regulation of patchoulol and pogostone in two Pogostemon cablin (Blanco) Benth. cultivars

In Pogostemon cablin (Blanco) Benth. essential oil, patchoulol and pogostone are the two major bioactive phytochemicals while their in vivo biosynthesis remains largely unknown. In this study, seven genes of the plastidic methylerythritol 4-phosphate pathway (MEP) and three genes of the cytoplasmic mevalonate pathway (MVA) in two cultivars, HN and YN, were isolated. Gene expression and phytochemical profiles across leaves and stems at different developmental stages of the two cultivars were evaluated using quantitative reverse-transcription polymerase chain reaction and gas chromatography-mass spectrometry, respectively. Hierarchical analysis showed that the expression of MVA- and MEP-related genes was clustered similarly in the two cultivars. Phytochemical assay revealed that the contents of patchoulol in leaves and pogostone in stems were regulated in an aging-dependent manner. Pogostone was only detected in stems but not in leaves of the two cultivars. The Pearson correlation analysis suggested that several genes were presumably involved in the biosynthesis of patchoulol and pogostone. In the YN cultivar, the 1-deoxy-d-xylulose-5-phosphate reductoisomerase and isopentenyl pyrophosphate isomerase 2 genes, and 2-C-methyl-d-erythritol 4-phosphate cytidylyltransferase were positively responsible for patchoulol and pogostone biosynthesis, respectively. In the HN cultivar, 3-hydroxy-3-methylglutaryl-coenzyme A reductase and mevalonate diphosphate decarboxylase, and mevalonate kinase expression were positively associated with pogostone and patchoulol biosynthesis, respectively. The genes identified in this study are good candidates for the enhancement of patchoulol content in the leaves or pogostone content in the stems of P. cablin. Taken together, our results lay a solid foundation for better understanding of the mechanism underlying patchoulol and pogostone biosynthesis, which in turn may help to improve their content in P. cablin.

Molecular cloning and functional analysis of a 10-epi-junenol synthase from Inula hupehensis

Junenol based-eudesmanolides have been detected in many compositae plant species and were reported to exhibit various pharmacological activities. So far, the gene encoding junenol synthase has never been isolated. Here we report the molecular cloning and functional analysis of a 10-epi-junenol synthase from Inula hupehensis (designated IhsTPS1). IhsTPS1 converts the substrate farnesyl diphosphate into multiple sesquiterpenes with the product 10-epi-junenol being predominant. The transcript levels of IhsTPS1 correlate well with the accumulation pattern of 10-epi-junenol in I. hupehensis organs, supporting its biochemical roles in vivo.

Molecular Dynamics Simulations Elucidate Conformational Dynamics Responsible for the Cyclization Reaction in TEAS

The Mg-dependent 5-epi-aristolochene synthase from Nicotiana tabacum (called TEAS) could catalyze the linear farnesyl pyrophosphate (FPP) substrate to form bicyclic hydrocarbon 5-epi-aristolochene. The cyclization reaction mechanism of TEAS was proposed based on static crystal structures and quantum chemistry calculations in a few previous studies, but substrate FPP binding kinetics and protein conformational dynamics responsible for the enzymatic catalysis are still unclear. Herein, by elaborative and extensive molecular dynamics simulations, the loop conformation change and several crucial residues promoting the cyclization reaction in TEAS are elucidated. It is found that the unusual noncatalytic NH2-terminal domain is essential to stabilize Helix-K and the adjoining J-K loop of the catalytic COOH-terminal domain. It is also illuminated that the induce-fit J-K/A-C loop dynamics is triggered by Y527 and the optimum substrate binding mode in a "U-shape" conformation. The U-shaped ligand binding pose is maintained well with the cooperative interaction of the three Mg(2+)-containing coordination shell and conserved residue W273. Furthermore, the conserved Arg residue pair R264/R266 and aromatic residue pair Y527/W273, whose spatial orientations are also crucial to promote the closure of the active site to a hydrophobic pocket, as well as to form π-stacking interactions with the ligand, would facilitate the carbocation migration and electrophilic attack involving the catalytic reaction. Our investigation more convincingly proves the greater roles of the protein local conformational dynamics than do hints from the static crystal structure observations. Thus, these findings can act as a guide to new protein engineering strategies on diversifying the sesquiterpene products for drug discovery.

Survey of the genome of Pogostemon cablin provides insights into its evolutionary history and sesquiterpenoid biosynthesis

Pogostemon cablin (Blanco) Benth. (Patchouli) is an important traditional Chinese medicinal plant that has both essential oil value and a broad range of therapeutic effects. Here we report the first de novo assembled 1.15-Gb draft genome sequence for P. cablin from next-generation sequencing technology. Our assembly, with a misassembly rate of <4 bp per 100 kb, is ~73% of the predicted genome size (1.57 Gb). Analysis of whole-genome sequences identified 3,147,333 heterozygous single-nucleotide polymorphisms and 490,407 insertions and deletions, giving an estimated heterozygosity rate of 0.274%. A comprehensive annotation pipeline indicated that repetitive sequences make up 58.55% of the assemblies, and that there are estimated 45,020 genes. Comparative genomics analysis showed that the Phrymaceae and Lamiaceae family split ~62.80 Mya, and the divergence between patchouli and sesame occurred ~52.42 Mya, implying a potentially shared recent whole-genome duplication event. Analysis of gene homologs involved in sesquiterpenoid biosynthesis showed that patchouli contains key genes involved in more sesquiterpenoid types and has more copies of genes for each sesquiterpenoid type than several other related plant species. The patchouli genome will facilitate future research on secondary metabolic pathways and their regulation as well as potential selective breeding of patchouli.

In Vivo Validation of In Silico Predicted Metabolic Engineering Strategies in Yeast: Disruption of α-Ketoglutarate Dehydrogenase and Expression of ATP-Citrate Lyase for Terpenoid Production

Background

Engineering of the central carbon metabolism of Saccharomyces cerevisiae to redirect metabolic flux towards cytosolic acetyl-CoA has become a central topic in yeast biotechnology. A cell factory with increased flux into acetyl-CoA can be used for heterologous production of terpenoids for pharmaceuticals, biofuels, fragrances, or other acetyl-CoA derived compounds. In a previous study, we identified promising metabolic engineering targets in S. cerevisiae using an in silico stoichiometric metabolic network analysis. Here, we validate selected in silico strategies in vivo.

Results

Patchoulol was produced by yeast via a heterologous patchoulol synthase of Pogostemon cablin. To increase the metabolic flux from acetyl-CoA towards patchoulol, a truncated HMG-CoA reductase was overexpressed and farnesyl diphosphate synthase was fused with patchoulol synthase. The highest increase in production could be achieved by modifying the carbon source; sesquiterpenoid titer increased from glucose to ethanol by a factor of 8.4. Two strategies predicted in silico were chosen for validation in this work. Disruption of α-ketoglutarate dehydrogenase gene (KGD1) was predicted to redirect the metabolic flux via the pyruvate dehydrogenase bypass towards acetyl-CoA. The metabolic flux was redirected as predicted, however, the effect was dependent on cultivation conditions and the flux was interrupted at the level of acetate. High amounts of acetate were produced. As an alternative pathway to synthesize cytosolic acetyl-CoA, ATP-citrate lyase was expressed as a polycistronic construct, however, in vivo performance of the enzyme needs to be optimized to increase terpenoid production.

Conclusions

Stoichiometric metabolic network analysis can be used successfully as a metabolic prediction tool. However, this study highlights that kinetics, regulation and cultivation conditions may interfere, resulting in poor in vivo performance. Main sites of regulation need to be released and improved enzymes are essential to meet the required activities for an increased product formation in vivo.

Recent advances in biosynthesis of bioactive compounds in traditional Chinese medicinal plants

Plants synthesize and accumulate large amount of specialized (or secondary) metabolites also known as natural products, which provide a rich source for modern pharmacy. In China, plants have been used in traditional medicine for thousands of years. Recent development of molecular biology, genomics and functional genomics as well as high-throughput analytical chemical technologies has greatly promoted the research on medicinal plants. In this article, we review recent advances in the elucidation of biosynthesis of specialized metabolites in medicinal plants, including phenylpropanoids, terpenoids and alkaloids. These natural products may share a common upstream pathway to form a limited numbers of common precursors, but are characteristic in distinct modifications leading to highly variable structures. Although this review is focused on traditional Chinese medicine, other plants with a great medicinal interest or potential are also discussed. Understanding of their biosynthesis processes is critical for producing these highly value molecules at large scale and low cost in microbes and will benefit to not only human health but also plant resource conservation.

Engineered biosynthesis of natural products in heterologous hosts

Natural products produced by microorganisms and plants are a major resource of antibacterial and anticancer drugs as well as industrially useful compounds. However, the native producers often suffer from low productivity and titers. Here we summarize the recent applications of heterologous biosynthesis for the production of several important classes of natural products such as terpenoids, flavonoids, alkaloids, and polyketides. In addition, we will discuss the new tools and strategies at multi-scale levels including gene, pathway, genome and community levels for highly efficient heterologous biosynthesis of natural products.

Functional characterization of terpene synthases and chemotypic variation in three lavender species of section Stoechas

Lavandula pedunculata (Mill.) Cav. subsp. lusitanica, Lavandula stoechas L. subsp. stoechas and Lavandula viridis l'Hér. are three lavender taxa that belong to the botanical section Stoechas and are widely used as aromatherapy, culinary herb or folk medicine in many Mediterranean regions. The analysis of their bioactive volatile constituents revealed the presence of 124 substances, the most abundant being the bicyclic monoterpenes fenchone, camphor and 1,8-cineole that give these three species their respective chemotypes. Most noteworthy was fenchone which, with its reduced form fenchol, made 48% of the total volatile constituents of L. pedunculata while present at 2.9% in L. stoechas and undetectable in L. viridis. In order to provide a molecular explanation to the differences in volatile compounds of these three species, two monoterpene synthases (monoTPS) and one sesquiterpene synthase (sesquiTPS) were cloned in L. pedunculata and functionally characterized as fenchol synthase (LpFENS), α-pinene synthase (LpPINS) and germacrene A synthase (LpGEAS). The two other lavender species contained a single orthologous gene for each of these three classes of TPS with similar enzyme product specificities. Expression profiles of FENS and PINS genes matched the accumulation profile of the enzyme products unlike GEAS. This study provides one of the rare documented cases of chemotype modification during plant speciation via changes in the level of plant TPS gene expression, and not functionality.

Progressive regulation of sesquiterpene biosynthesis in Arabidopsis and Patchouli (Pogostemon cablin) by the miR156-targeted SPL transcription factors

Plant metabolites vary at different stages of their life cycle. Although it is well documented that environmental factors stimulate biosynthesis of secondary metabolites, the regulation by endogenous developmental cues remains poorly understood. The microRNA156 (miR156)-targeted squamosa promoter binding protein-like (SPL) factors function as a major age cue in regulating developmental phase transition and flowering. We show here that the miR156-targeted SPL transcription factor plays an important role in the spatiotemporal regulation of sesquiterpene biosynthesis. In Arabidopsis thaliana, the miR156-SPL module regulates the formation of (E)-β-caryophyllene in the flowering stage through modulating expression of the sesquiterpene synthase gene TPS21. We demonstrated that SPL9 directly binds to TPS21 promoter and activates its expression. In the perennial fragrant herb Pogostemon cablin, the accumulation of patchouli oil, largely composed of sesquiterpenes dominated by (-)-patchoulol, is also age-regulated, and the SPL promotes biosynthesis of sesquiterpenes in elder plants by upregulating patchoulol synthase (PatPTS) gene expression. As miR156-SPLs are highly conserved in plants, our finding not only uncovers a molecular link between developmental timing and sesquiterpene production but also suggests a new strategy to engineer plants for accelerated growth with enhanced production of terpenoids.

Rapid detection of Fusarium wilt in basil (Ocimum sp.) leaves by desorption electrospray ionization mass spectrometry (DESI MS) imaging

A rapid method to unravel the spatial distribution ofFusarium/other pathogen-contamination in asymptomatic leaves under ambient conditions.

Metabolic engineering of the moss Physcomitrella patens to produce the sesquiterpenoids patchoulol and α/β-santalene

The moss Physcomitrella patens, has been genetically engineered to produce patchoulol and β-santalene, two valuable sesquiterpenoid ingredients in the fragrance industry. The highest yield of patchoulol achieved was 1.34 mg/g dry weight. This was achieved by non-targeted transformation of the patchoulol synthase and either a yeast or P. patens HMGR gene under the control of a 35S promoter. Santalene synthase targeted to the plastids yielded 0.039 mg/g dry weight of α/β santalene; cytosolic santalene synthase and 35S controlled HMGR afforded 0.022 mg/g dry weight. It has been observed that the final yield of the fragrance molecules is dependent on the expression of the synthase. This is the first report of heterologous production of sesquiterpenes in moss and it opens up a promising source for light-driven production of valuable fragrance ingredients.

Intensive sampling identifies previously unknown chemotypes, population divergence and biosynthetic connections among terpenoids in Eucalyptus tricarpa

Australian members of the Myrtaceae produce large quantities of ecologically and economically important terpenes and display abundant diversity in both yield and composition of their oils. In a survey of the concentrations of leaf terpenes in Eucalyptus tricarpa (L.A.S. Johnson) L.A.S. Johnson & K.D. Hill, which were previously known from few samples, exceptional variability was found in composition. The aim was to characterize the patterns of variation and covariation among terpene components in this species and to use this information to enhance our understanding of their biosynthesis. There were marked discontinuities in the distributions of numerous compounds, including the overall proportions of mono- and sesquiterpenes, leading us to delineate three distinct chemotypes. Overall, positive covariation predominated, but negative covariation suggested competitive interactions involved in monoterpene synthesis. Two groups of covarying monoterpenes were found, each of which was positively correlated with a group of sesquiterpenes and negatively correlated with the alternate sesquiterpene group. These results imply substantial cross-talk between mono- and sesquiterpene biosynthesis pathways. However, only those compounds hypothesized to share final carbocation intermediates or post-processing steps were strongly positively correlated within chemotypes. This suggests that the broader patterns of covariation among groups of compounds may result from co-regulation of multiple biosynthetic genes, controlling the complex terpene profiles of the chemotypes of Eucalyptus.

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.

Enantiomeric natural products: occurrence and biogenesis

In nature, chiral natural products are usually produced in optically pure form-however, occasionally both enantiomers are formed. These enantiomeric natural products can arise from a single species or from different genera and/or species. Extensive research has been carried out over the years in an attempt to understand the biogenesis of naturally occurring enantiomers; however, many fascinating puzzles and stereochemical anomalies still remain.

The tomato terpene synthase gene family

Compounds of the terpenoid class play numerous roles in the interactions of plants with their environment, such as attracting pollinators and defending the plant against pests. We show here that the genome of cultivated tomato (Solanum lycopersicum) contains 44 terpene synthase (TPS) genes, including 29 that are functional or potentially functional. Of these 29 TPS genes, 26 were expressed in at least some organs or tissues of the plant. The enzymatic functions of eight of the TPS proteins were previously reported, and here we report the specific in vitro catalytic activity of 10 additional tomato terpene synthases. Many of the tomato TPS genes are found in clusters, notably on chromosomes 1, 2, 6, 8, and 10. All TPS family clades previously identified in angiosperms are also present in tomato. The largest clade of functional TPS genes found in tomato, with 12 members, is the TPS-a clade, and it appears to encode only sesquiterpene synthases, one of which is localized to the mitochondria, while the rest are likely cytosolic. A few additional sesquiterpene synthases are encoded by TPS-b clade genes. Some of the tomato sesquiterpene synthases use z,z-farnesyl diphosphate in vitro as well, or more efficiently than, the e,e-farnesyl diphosphate substrate. Genes encoding monoterpene synthases are also prevalent, and they fall into three clades: TPS-b, TPS-g, and TPS-e/f. With the exception of two enzymes involved in the synthesis of ent-kaurene, the precursor of gibberellins, no other tomato TPS genes could be demonstrated to encode diterpene synthases so far.

Enhanced extraction of patchouli alcohol from Pogostemon cablin by microwave radiation-accelerated ionic liquid pretreatment

A microwave radiation-accelerated ionic liquid pretreatment (MRAILP) was developed to enhance extraction of patchouli alcohol from Pogostemon cablin. 1-N-butyl-3-methylimidazolium chloride ([C(4)mim]Cl) was selected as microwave absorbing and cellulose dissolution medium and microwave was applied to accelerate sample dissolution. The conditions of MRAILP including particle size, solvent, microwave pretreatment time and power and the ratio of ionic liquid (IL) to sample were optimized. Under the optimized conditions, the extraction yield of patchouli alcohol by the MRAILP was 1.94%, which has increased by 166% compared with microwave-assisted extraction. The recovery was in the range of 95.71-103.7% with relative standard deviation lower than 3.0%. It was a novel alternative extraction method for the fast extraction and determination of patchouli alcohol from Pogostemon cablin.

Diversion of flux toward sesquiterpene production in Saccharomyces cerevisiae by fusion of host and heterologous enzymes

The ability to transfer metabolic pathways from the natural producer organisms to the well-characterized cell factory Saccharomyces cerevisiae is well documented. However, as many secondary metabolites are produced by collaborating enzymes assembled in complexes, metabolite production in yeast may be limited by the inability of the heterologous enzymes to collaborate with the native yeast enzymes. This may cause loss of intermediates by diffusion or degradation or due to conversion of the intermediate through competitive pathways. To bypass this problem, we have pursued a strategy in which key enzymes in the pathway are expressed as a physical fusion. As a model system, we have constructed several fusion protein variants in which farnesyl diphosphate synthase (FPPS) of yeast has been coupled to patchoulol synthase (PTS) of plant origin (Pogostemon cablin). Expression of the fusion proteins in S. cerevisiae increased the production of patchoulol, the main sesquiterpene produced by PTS, up to 2-fold. Moreover, we have demonstrated that the fusion strategy can be used in combination with traditional metabolic engineering to further increase the production of patchoulol. This simple test case of synthetic biology demonstrates that engineering the spatial organization of metabolic enzymes around a branch point has great potential for diverting flux toward a desired product.

Characterization of delta-guaiene synthases from cultured cells of Aquilaria, responsible for the formation of the sesquiterpenes in agarwood

The resinous portions of Aquilaria plants, called agarwood, have been used as medicines and incenses. Agarwood contains a great variety of sesquiterpenes, and a study using cultured cells of Aquilaria showed the production of sesquiterpenes (α-guaiene, α-humulene, and δ-guaiene) to be induced by treatment with methyl jasmonate (MJ). In this study, the accumulation and production of sesquiterpenes were quantified. The amounts accumulated and produced reached a maximum at 12 h, and the most abundant product was α-humulene at 6 h and δ-guaiene after 12 h. However, a headspace analysis of the cells revealed that α-humulene is likely to be volatilized; so overall, the most abundant sesquiterpene in the cells was δ-guaiene. A cDNA library from RNA isolated from MJ-treated cells was screened using PCR methodologies to isolate five clones with very similar amino acid sequences. These clones were expressed in Escherichia coli, and enzymatic reactions using farnesyl pyrophosphate revealed that three of the clones yielded the same compounds as extracted from MJ-treated cells, the major product being δ-guaiene. These genes and their encoded enzymes are the first sesquiterpene synthases yielding guaiane-type sesquiterpenes as their major products to be reported. Expression of a fourth terpene synthase gene in bacteria resulted in the accumulation of the protein in insoluble forms. Site-directed mutagenesis of the inactive clone and three-dimensional homology modeling suggested that the structure of the N-terminal domain was important in facilitating proper folding of the protein to form a catalytically active structure.

Volatile Oil Composition of Pogostemon heyneanus and Comparison of its Composition with Patchouli Oil

The volatile oil of the leaves of Pogostemon heyneanus Benth. (Lamiaceae) was analyzed by GC and GC-MS. Twenty-six components representing 96.0% of the oil were identified. The major components of the oil were acetophenone (51.0%), β-pinene (5.3%), ( E)-nerolidol (5.4%), and patchouli alcohol (14.0%). Comparison of the compositions of the oils of P. heyneanus and P. cablin (Blanco) Benth. (Patchouli oil) showed wide variation between them. Though 13 sesquiterpenes and oxygenated sesquiterpenes were detected in both oils, their concentrations in the oils differed widely. Acetophenone, benzoyl acetone and ( E)-nerolidol present in the oil of P. heyneanus were not detected in patchouli oil.

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.