Functional identification of a Lippia dulcis bornyl diphosphate synthase that contains a duplicated, inhibitory arginine-rich motif

Chemical diversity in angiosperms - monoterpene synthases control complex reactions that provide the precursors for ecologically and commercially important monoterpenoids

Monoterpene synthases (MTSs) catalyze the first committed step in the biosynthesis of monoterpenoids, a class of specialized metabolites with particularly high chemical diversity in angiosperms. In addition to accomplishing a rate enhancement, these enzymes manage the formation and turnover of highly reactive carbocation intermediates formed from a prenyl diphosphate substrate. At each step along the reaction path, a cationic intermediate can be subject to cyclization, migration of a proton, hydride, or alkyl group, or quenching to terminate the sequence. However, enzymatic control of ligand folding, stabilization of specific intermediates, and defined quenching chemistry can maintain the specificity for forming a signature product. This review article will discuss our current understanding of how angiosperm MTSs control the reaction environment. Such knowledge allows inferences about the origin and regulation of chemical diversity, which is pertinent for appreciating the role of monoterpenoids in plant ecology but also for aiding commercial efforts that harness the accumulation of these specialized metabolites for the food, cosmetic, and pharmaceutical industries.

Cyclization mechanism of monoterpenes catalyzed by monoterpene synthases in dipterocarpaceae

Monoterpenoids are typically present in the secretory tissues of higher plants, and their biosynthesis is catalyzed by the action of monoterpene synthases (MTSs). However, the knowledge about these enzymes is restricted in a few plant species. MTSs are responsible for the complex cyclization of monoterpene precursors, resulting in the production of diverse monoterpene products. These enzymatic reactions are considered exceptionally complex in nature. Therefore, it is crucial to understand the catalytic mechanism of MTSs to elucidate their ability to produce diverse or specific monoterpenoid products. In our study, we analyzed thirteen genomes of Dipterocarpaceae and identified 38 MTSs that generate a variety of monoterpene products. By focusing on four MTSs with different product spectra and analyzing the formation mechanism of acyclic, monocyclic and bicyclic products in MTSs, we observed that even a single amino acid mutation can change the specificity and diversity of MTS products, which is due to the synergistic effect between the shape of the active cavity and the stabilization of carbon-positive intermediates that the mutation changing. Notably, residues N340, I448, and phosphoric acid groups were found to be significant contributors to the stabilization of intermediate terpinyl and pinene cations. Alterations in these residues, either directly or indirectly, can impact the synthesis of single monoterpenes or their mixtures. By revealing the role of key residues in the catalytic process and establishing the interaction model between specific residues and complex monoterpenes in MTSs, it will be possible to reasonably design and engineer different catalytic activities into existing MTSs, laying a foundation for the artificial design and industrial application of MTSs.

Comparing genomes of Fructus Amomi-producing species reveals genetic basis of volatile terpenoid divergence

Wurfbainia longiligularis and Wurfbainia villosa are both rich in volatile terpenoids and are 2 primary plant sources of Fructus Amomi used for curing gastrointestinal diseases. Metabolomic profiling has demonstrated that bornyl diphosphate (BPP)-related terpenoids are more abundant in the W. villosa seeds and have a wider tissue distribution in W. longiligularis. To explore the genetic mechanisms underlying the volatile terpenoid divergence, a high-quality chromosome-level genome of W. longiligularis (2.29 Gb, contig N50 of 80.39 Mb) was assembled. Functional characterization of 17 terpene synthases (WlTPSs) revealed that WlBPPS, along with WlTPS 24/26/28 with bornyl diphosphate synthase (BPPS) activity, contributes to the wider tissue distribution of BPP-related terpenoids in W. longiligularis compared to W. villosa. Furthermore, transgenic Nicotiana tabacum showed that the GCN4-motif element positively regulates seed expression of WvBPPS and thus promotes the enrichment of BPP-related terpenoids in W. villosa seeds. Systematic identification and analysis of candidate TPS in 29 monocot plants from 16 families indicated that substantial expansion of TPS-a and TPS-b subfamily genes in Zingiberaceae may have driven increased diversity and production of volatile terpenoids. Evolutionary analysis and functional identification of BPPS genes showed that BPP-related terpenoids may be distributed only in the Zingiberaceae of monocot plants. This research provides valuable genomic resources for breeding and improving Fructus Amomi with medicinal and edible value and sheds light on the evolution of terpenoid biosynthesis in Zingiberaceae.

Genome-wide analyzation and functional characterization on the TPS family provide insight into the biosynthesis of mono-terpenes in the camphor tree

Terpene synthase (TPS) plays an important role in terpenoids biosynthesis. Cinnamomum camphora (camphor tree) contains dozens of terpenoids with medicinal value, especially borneol, which has been widely used since ancient times. However, limited information is available regarding the genome-wide identification and characterization of the TPS family in the C. camphora. In this study, 82 CcTPS genes were identified from the camphor tree genome (CTG). Gene cluster and sequence syntenic analysis suggested that tandem duplication occurred within the TPS family of the CTG, especially for the TPS-b subfamily. The chemotype-specific gene expression analysis showed significantly differential expression patterns among six chemotypes. It is worth noting that three genes (CcTPS26, CcTPS49 and CcTPS72) exhibited relatively high expression in the borneol-type camphor tree, compared to the other five chemotypes. Further functional characterization of them indicated that they were all bornyl diphosphate synthases (BPPSs), which function in catalyzing GPP into BPP and then undergoes dephosphorylation to yield borneol. This is the first report that multiple BPPSs exist within a single species. Intriguingly, CcTPS49 and CcTPS72 lead to the generation of dextral-borneol, while CcTPS26 contributes to the biosynthesis of levo-borneol. In addition, the functional characterization of another six CcTPSs suggested that they are responsible for the biosynthesis of linalool, eucalyptol and several other monoterpenes in camphor tree. In conclusion, these novel results provide a foundation for further exploration of the role of the CcTPS gene family and shed light on a better understanding of the biosynthesis and accumulation of monoterpenes in camphor tree.

Biochemical basis for the formation of organ-specific volatile blends in mint

Above-ground material of members of the mint family is commercially distilled to extract essential oils, which are then formulated into a myriad of consumer products. Most of the research aimed at characterizing the processes involved in the formation of terpenoid oil constituents has focused on leaves. We now demonstrate, by investigating three mint species, peppermint (Mentha ˣ piperita L.), spearmint (Mentha spicata L.) and horsemint (Mentha longifolia (L.) Huds.; accessions CMEN 585 and CMEN 584), that other organs - namely stems, rhizomes and roots - also emit volatiles and that the terpenoid volatile composition of these organs can vary substantially from that of leaves, supporting the notion that substantial, currently underappreciated, chemical diversity exists. Differences in volatile quantities released by plants whose roots had been dipped in a Verticillium dahliae-spore suspension (experimental) or dipped in water (controls) were evident: increases of some volatiles in the root headspace of mint species that are susceptible to Verticillium wilt disease (peppermint and M. longifolia CMEN 584) were detected, while the quantities of certain volatiles decreased in rhizomes of species that show resistance to the disease (spearmint and M. longifolia CMEN 585). To address the genetic and biochemical basis underlying chemical diversity, we took advantage of the newly sequenced M. longifolia CMEN 585 genome to identify candidate genes putatively coding for monoterpene synthases (MTSs), the enzymes that catalyze the first committed step in the biosynthesis of monoterpenoid volatiles. The functions of these genes were established by heterologous expression in Escherichia coli, purification of the corresponding recombinant proteins, and enzyme assays, thereby establishing the existence of MTSs with activities to convert a common substrate, geranyl diphosphate, to (+)-α-terpineol, 1,8-cineole, γ-terpinene, and (-)-bornyl diphosphate, but were not active with other potential substrates. In conjunction with previously described MTSs that catalyze the formation of (-)-β-pinene and (-)-limonene, the product profiles of the MTSs identified here can explain the generation of all major monoterpene skeletons represented in the volatiles released by different mint organs.

Cloning, functional characterization and evaluating potential in metabolic engineering for lavender ( +)-bornyl diphosphate synthase

We isolated and functionally characterized a new ( +)-bornyl diphosphate synthase (( +)-LiBPPS) from Lavandula x intermedia. The in planta functions of ( +)-LiBPPS were evaluated in sense and antisense transgenic plants. The monoterpene ( +)-borneol contributes scent and medicinal properties to some plants. It also is the immediate precursor to camphor, another important determinant of aroma and medicinal properties in many plants. ( +)-Borneol is generated through the dephosphorylation of bornyl diphosphate (BPP), which is itself derived from geranyl diphosphate (GPP) by the enzyme ( +)-bornyl diphosphate synthase (( +)-BPPS). In this study we isolated and functionally characterized a novel ( +)-BPPS cDNA from Lavandula x intermedia. The cDNA excluding its transit peptide was expressed in E. coli, and the corresponding recombinant protein was purified with Ni-NTA agarose affinity chromatography. The recombinant ( +)-LiBPPS catalyzed the conversion of GPP to BPP as a major product, and a few minor products. We also investigated the in planta role of ( +)-LiBPPS in terpenoid metabolism through its overexpression in sense and antisense orientations in stably transformed Lavandula latifolia plants. The overexpression of ( +)-LiBPPS in antisense resulted in reduced production of ( +)-borneol and camphor without compromising plant growth and development. As anticipated, the overexpression of the gene led to enhanced production of borneol and camphor, although growth and development were severely impaired in most transgenic lines strongly and ectopically expressing the ( +)-LiBPPS transgene in sense. Our results demonstrate that LiBPPS would be useful in studies aimed at the production of recombinant borneol and camphor in vitro, and in metabolic engineering efforts aimed at lowering borneol and camphor production in plants. However, overexpression in sense may require a targeted expression of the gene in glandular trichomes using a trichome-specific promoter.

Thirteen Dipterocarpoideae genomes provide insights into their evolution and borneol biosynthesis

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

Artemisia annua L. plants lacking Bornyl diPhosphate Synthase reallocate carbon from monoterpenes to sesquiterpenes except artemisinin

The monoterpene camphor is produced in glandular secretory trichomes of the medicinal plant Artemisia annua, which also produces the antimalarial drug artemisinin. We have found that, depending on growth conditions, camphor can accumulate at levels ranging from 1- 10% leaf dry weight (LDW) in the Artemis F1 hybrid, which has been developed for commercial production of artemisinin at up to 1% LDW. We discovered that a camphor null (camphor-0) phenotype segregates in the progeny of self-pollinated Artemis material. Camphor-0 plants also show reduced levels of other less abundant monoterpenes and increased levels of the sesquiterpene precursor farnesyl pyrophosphate plus sesquiterpenes, including enzymatically derived artemisinin pathway intermediates but not artemisinin. One possible explanation for this is that high camphor concentrations in the glandular secretory trichomes play an important role in generating the hydrophobic conditions required for the non-enzymatic conversion of dihydroartemisinic acid tertiary hydroperoxide to artemisinin. We established that the camphor-0 phenotype associates with a genomic deletion that results in loss of a Bornyl diPhosphate Synthase (AaBPS) gene candidate. Functional characterization of the corresponding enzyme in vitro confirmed it can catalyze the first committed step in not only camphor biosynthesis but also in a number of other monoterpenes, accounting for over 60% of total volatiles in A. annua leaves. This in vitro analysis is consistent with loss of monoterpenes in camphor-0 plants. The AaBPS promoter drives high reporter gene expression in A. annua glandular secretory trichomes of juvenile leaves with expression shifting to non-glandular trichomes in mature leaves, which is consistent with AaBPS transcript abundance.

Genome-Wide Identification of BAHD Superfamily and Functional Characterization of Bornyl Acetyltransferases Involved in the Bornyl Acetate Biosynthesis in Wurfbainia villosa

Bornyl acetate (BA) is known as a natural aromatic monoterpene ester with a wide range of pharmacological and biological activities. Borneol acetyltransferase (BAT), catalyzing borneol and acetyl-CoA to synthesize BA, is alcohol acetyltransferase, which belongs to the BAHD super acyltransferase family, however, BAT, responsible for the biosynthesis of BA, has not yet been characterized. The seeds of Wurfbainia villosa (homotypic synonym: Amomum villosum) are rich in BA. Here we identified 64 members of the BAHD gene family from the genome of W. villosa using both PF02458 (transferase) and PF07247 (AATase) as Hidden Markov Model (HMM) to screen the BAHD genes. A total of sixty-four WvBAHDs are distributed on 14 chromosomes and nine unanchored contigs, clustering into six clades; three WvBAHDs with PF07247 have formed a separated and novel clade: clade VI. Twelve candidate genes belonging to clade I-a, I-b, and VI were selected to clone and characterize in vitro, among which eight genes have been identified to encode BATs acetylating at least one type of borneol to synthesize BA. All eight WvBATs can utilize (-)-borneol as substrates, but only five WvBATs can catalyze (+)-borneol, which is the endogenous borneol substrate in the seeds of W. villosa; WvBAT3 and WvBAT4 present the better catalytic efficiency on (+)-borneol than the others. The temporal and spatial expression patterns of WvBATs indicate that WvBAT3 and WvBAT4 are seed-specific expression genes, and their expression levels are correlated with the accumulation of BA, suggesting WvBAT3 and WvBAT4 might be the two key BATs for BA synthesis in the seeds of W. villosa. This is the first report on BAT responsible for the last biosynthetic step of BA, which will contribute to further studies on BA biosynthesis and metabolism engineering of BA in other plants or heterologous hosts.

Identification of (-)-bornyl diphosphate synthase from Blumea balsamifera and its application for (-)-borneol biosynthesis in Saccharomyces cerevisiae

Borneol is a precious monoterpenoid with two chiral structures, (-)-borneol and (+)-borneol. Bornyl diphosphate synthase is the key enzyme in the borneol biosynthesis pathway. Many (+)-bornyl diphosphate synthases have been reported, but no (-)-bornyl diphosphate synthases have been identified. Blumea balsamifera leaves are rich in borneol, almost all of which is (-)-borneol. In this study, we identified a high-efficiency (-)-bornyl diphosphate synthase (BbTPS3) from B. balsamifera that converts geranyl diphosphate (GPP) to (-)-bornyl diphosphate, which is then converted to (-)-borneol after dephosphorylation in vitro. BbTPS3 exhibited a K_m value of 4.93 ± 1.38 μM for GPP, and the corresponding k_cat value was 1.49 s⁻¹. Multiple strategies were applied to obtain a high-yielding (-)-borneol producing yeast strain. A codon-optimized BbTPS3 protein was introduced into the GPP high-yield strain MD, and the resulting MD-B1 strain produced 1.24 mg·L^-1 (-)-borneol. After truncating the N-terminus of BbTPS3 and adding a Kozak sequence, the (-)-borneol yield was further improved by 4-fold to 4.87 mg·L^-1. Moreover, the (-)-borneol yield was improved by expressing the fusion protein module of ERG20^F96W-N127W-YRSQI-t14-BbTPS3K2, resulting in a final yield of 12.68 mg·L^-1 in shake flasks and 148.59 mg·L^-1 in a 5-L bioreactor. This work is the first reported attempt to produce (-)-borneol by microbial fermentation.

Hernandulcin Production in Cell Suspensions of Phyla Scaberrima: Exploring Hernandulcin Accumulation through Physical and Chemical Stimuli

Hernandulcin (HE) is a non-caloric sweetener synthesized by the Mexican medicinal plant Phyla scaberrima. Herein we present the results of HE production through cell suspensions of P. scaberrima as well as the influence of pH, temperature, biosynthetic precursors and potential elicitors to enhance HE accumulation. The incorporation of mevalonolactone (30-400 mg L^-1 ) farnesol (30-400 mg L^-1 ), AgNO3 (0.025-0.175 M), cellulase (5-60 mg L^-1 ; 0.3 units/mg), chitin (20-140 mg L^-1 ) and (+)-epi-α-bisabolol (300-210 mg L^-1 ) to the cell suspensions, resulted in a differential accumulation of HE and biomass. Among elicitors assayed, chitin, cellulase and farnesol increased HE production from 93.2 to ∼160 mg L^-1 but, (+)-epi-α-bisabolol (obtained by a synthetic biology approach) increased HE accumulation up to 182.7 mg L^-1 . HE produced by the cell suspensions was evaluated against nine strains from six species of gastrointestinal bacteria revealing moderate antibacterial activity (MIC, 214-465 μg mL^-1 ) against Staphylococcus aureus, Escherichia coli and Helicobacter pylori. Similarly, HE showed weak toxicity against Lactobacillus sp. and Bifidobacterium bifidum (>1 mg mL^-1 ), suggesting a selective antimicrobial activity on some species of gut microbiota. According to our results, chitin and (+)-epi-α-bisabolol were the most effective molecules to enhance HE accumulation in cell suspensions of P. scaberrima.

Combining Metabolic and Monoterpene Synthase Engineering for de Novo Production of Monoterpene Alcohols in Escherichia coli

The monoterpene alcohols acyclic nerol and bicyclic borneol are widely applied in the food, cosmetic, and pharmaceutical industries. The emerging synthetic biology enables microbial production to be a promising alternative for supplying monoterpene alcohols in an efficient and sustainable approach. In this study, we combined metabolic and plant monoterpene synthase engineering to improve the de novo production of nerol and borneol in prene-overproducing Escherichia coli. We engineered the growth-orthogonal neryl diphosphate (NPP) as the universal precursor of monoterpene alcohol biosynthesis and coexpressed nerol synthase (GmNES) from Glycine max to generate nerol or coexpressed the truncated bornyl diphosphate synthase (LdtBPPS) from Lippia dulcis for borneol production. Further, through site-directed mutation of LdtBPPS based on the structural simulation, we screened multiple variants that markedly elevated the production of acyclic nerol or bicyclic borneol, of which the LdtBPPSS488T mutant outperformed the wild-type LdtBPPS on borneol synthesis and the LdtBPPSF612A variant was superior to GmNES on nerol production. Subsequently, we overexpressed the endogenous Nudix hydrolase NudJ to facilitate the dephosphorylation of precursors and boosted the production of nerol and borneol from glucose. Finally, after the optimization of the fermentation process, the engineered strain ENO2 produced 966.55 mg/L nerol, and strain ENB57 generated 87.20 mg/L borneol in a shake flask, achieving the highest reported titers of nerol and borneol in microbes to date. This work shows a combinatorial engineering strategy for microbial production of natural terpene alcohols.

Bornyl Diphosphate Synthase From Cinnamomum burmanni and Its Application for (+)-Borneol Biosynthesis in Yeast

(+)-Borneol is a desirable monoterpenoid with effective anti-inflammatory and analgesic effects that is known as soft gold. (+)-bornyl diphosphate synthase is the key enzyme in the (+)-borneol biosynthesis pathway. Despite several reported (+)-bornyl diphosphate synthase genes, relatively low (+)-borneol production hinders the attempts to synthesize it using microbial fermentation. Here, we identified the highly specific (+)-bornyl diphosphate synthase CbTPS1 from Cinnamomum burmanni. An in vitro assay showed that (+)-borneol was the main product of CbTPS1 (88.70% of the total products), and the K _m value was 5.11 ± 1.70 μM with a k _cat value of 0.01 s^-1. Further, we reconstituted the (+)-borneol biosynthetic pathway in Saccharomyces cerevisiae. After tailored truncation and adding Kozak sequences, the (+)-borneol yield was improved by 96.33-fold to 2.89 mg⋅L^-1 compared with the initial strain in shake flasks. This work is the first reported attempt to produce (+)-borneol by microbial fermentation. It lays a foundation for further pathway reconstruction and metabolic engineering production of this valuable natural monoterpenoid.

A Comparison of Two Monoterpenoid Synthases Reveals Molecular Mechanisms Associated With the Difference of Bioactive Monoterpenoids Between Amomum villosum and Amomum longiligulare

The fruits of Amomum villosum and Amomum longiligulare are both used medicinally as Fructus Amomi the famous traditional Chinese medicine, however, the medicinal quality of A. villosum is better than that of A. longiligulare. Volatile terpenoids in the seeds, especially bornyl acetate and borneol, are the medicinal components of Fructus Amomi. The volatile terpenoids and transcriptome of developing seeds of A. villosum and A. longiligulare were compared in this study. The result revealed that the bornyl acetate and borneol contents were higher in A. villosum than in A. longiligulare. Additionally, six terpenoid synthase genes (AlTPS1-AlTPS6) were screened from the transcriptome of A. longiligulare, and AlTPS2 and AlTPS3 were found to share 98 and 83% identity with AvTPS2 and AvBPPS (bornyl diphosphate synthase) from A. villosum, respectively. BPPS is the key enzyme for the biosynthesis of borneol and bornyl acetate. Biochemical assays improved that AlTPS2 had an identical function to AvTPS2 as linalool synthase; however, AlTPS3 produced camphene as the major product and bornyl diphosphate (BPP) as the secondary product, whereas AvBPPS produced BPP as its major product. There was only one different amino acid between AlTPS3 (A496) and AvBPPS (G495) in their conserved motifs, and the site-directed mutation of A496G in DTE motif of AlTPS3 changed the major product from camphene to BPP. Molecular docking suggests that A496G mutation narrows the camphene-binding pocket and decreases the BPP-binding energy, thus increases the product BPP selectivity of enzyme. In addition, the expression level of AvBPPS was significantly higher than that of AlTPS3 in seeds, which was consistent with the related-metabolites contents. This study provides insight into the TPS-related molecular bases for the biosynthesis and accumulation differences of the bioactive terpenoids between A. villosum and A. longiligulare. BPPS, the key gene involved in the biosynthesis of the active compound, was identified as a target gene that could be applied for the quality-related identification and breeding of Fructus Amomi.

Mining of candidate genes involved in the biosynthesis of dextrorotatory borneol in Cinnamomum burmannii by transcriptomic analysis on three chemotypes

Background

Dextrorotatory borneol (D-borneol), a cyclic monoterpene, is widely used in traditional Chinese medicine as an efficient topical analgesic drug. Fresh leaves of Cinnamomum trees, e.g., C. burmannii and C. camphor, are the main sources from which D-borneol is extracted by steam distillation, yet with low yields. Insufficient supply of D-borneol has hampered its clinical use and production of patent remedies for a long time. Biological synthesis of D-borneol offers an additional approach; however, mechanisms of D-borneol biosynthesis remain mostly unresolved. Hence, it is important and necessary to elucidate the biosynthetic pathway of D-borneol.

Results

Comparative analysis on the gene expression patterns of different D-borneol production C. burmannii samples facilitates elucidation on the underlying biosynthetic pathway of D-borneol. Herein, we collected three different chemotypes of C. burmannii, which harbor different contents of D-borneol.A total of 100,218 unigenes with an N50 of 1,128 bp were assembled de novo using Trinity from a total of 21.21 Gb clean bases. We used BLASTx analysis against several public databases to annotate 45,485 unigenes (45.38%) to at least one database, among which 82 unigenes were assigned to terpenoid biosynthesis pathways by KEGG annotation. In addition, we defined 8,860 unigenes as differentially expressed genes (DEGs), among which 13 DEGs were associated with terpenoid biosynthesis pathways. One 1-deoxy-D-xylulose-5-phosphate synthase (DXS) and two monoterpene synthase, designated as CbDXS9, CbTPS2 and CbTPS3, were up-regulated in the high-borneol group compared to the low-borneol and borneol-free groups, and might be vital to biosynthesis of D-borneol in C. burmannii. In addition, we identified one WRKY, two BHLH, one AP2/ERF and three MYB candidate genes, which exhibited the same expression patterns as CbTPS2 and CbTPS3, suggesting that these transcription factors might potentially regulate D-borneol biosynthesis. Finally, quantitative real-time PCR was conducted to detect the actual expression level of those candidate genes related to the D-borneol biosynthesis pathway, and the result showed that the expression patterns of the candidate genes related to D-borneol biosynthesis were basically consistent with those revealed by transcriptome analysis.

Conclusions

We used transcriptome sequencing to analyze three different chemotypes of C. burmannii, identifying three candidate structural genes (one DXS, two monoterpene synthases) and seven potential transcription factor candidates (one WRKY, two BHLH, one AP2/ERF and three MYB) involved in D-borneol biosynthesis. These results provide new insight into our understanding of the production and accumulation of D-borneol in C. burmannii.

An Integrative Volatile Terpenoid Profiling and Transcriptomics Analysis for Gene Mining and Functional Characterization of AvBPPS and AvPS Involved in the Monoterpenoid Biosynthesis in Amomum villosum

Amomum villosum, also known as Fructus Amomi, has been used to treat digestive diseases such as abdominal pain, vomiting, and dysentery. Volatile terpenoids are the active metabolites in the essential oil of Fructus Amomi. Nevertheless, downstream genes responsible for activating metabolites biosynthesis in A. villosum still remain unclear. Here, we report the use of an integrative volatile terpenoid profiling and transcriptomics analysis for mining the corresponding genes involved in volatile terpenoid biosynthesis. Ten terpene synthase (TPS) genes were discovered, and two of them were cloned and functionally characterized. AvTPS1 (AvPS: pinene synthase) catalyzed GPP to form α-pinene and β-pinene; AvTPS3 (AvBPPS: bornyl diphosphate synthase) produced bornyl diphosphate as major product and the other three monoterpenoids as minor products. Metabolite accumulation and gene expression pattern combined with AvPS biochemical characterization suggested that AvPS might play a role in biotic defense. On the other hand, the most active ingredient, bornyl acetate, was highly accumulated in seeds and was consistent with the high expression of AvBPPS, which further indicated that AvBPPS is responsible for the biosynthesis of bornyl acetate, the final metabolite of bornyl diphosphate in A. villosum. This study can be used to improve the quality of A. villosum through metabolic engineering, and for the sustainable production of bornyl acetate in heterologous hosts.