[Functional characterization of ent-kaurane-type diterpenoid synthases from Stellera chamaejasme].

Sequential catalysis by ent-copalyl diphosphate(CPS) and ent-kaurene synthase(KS) is a critical step for plants to initiate the biosynthesis of gibberellin with geranylgeranyl pyrophosphate(GGPP) as the substrate. This study mined the transcriptome data of Stellera chamaejasme and cloned two key diterpene synthase genes, SchCPS and SchKS, involved in the gibberellin pathway. The two genes had the complete open reading frames of 2 595 bp and 1 701 bp, encoding two hydrophilic proteins composed of 864 and 566 amino acid residues and with the relative molecular mass of 97.9 kDa and 64.6 kDa and the theoretical isoelectric points of 5.61 and 6.12, respectively. Sequence comparison and phylogenetic tree showed that SchCPS contained LHS, PNV, and DxDD motifs conserved in the CPS family and was categorized in the TPS-c subfamily, while SchKS contained DDxxD, NSE/DTE and PIx motifs conserved in the KS family and was categorized in the TPS-e subfamily. Functional validation showed that SchCPS catalyzed the protonation and cyclization of GGPP to ent-CPP, while SchKS acted on ent-CPP dephosphorylation and re-cyclization to ent-kaurene. In this study, the full-length sequences of SchCPS and SchKS were cloned and functionally verified for the first time, which not only enriched the existing CPS and KS gene libraries but also laid a foundation for the cloning and biosynthesis pathway analysis of more genes involved in the synthesis of active components in S. chamaejasme.

Molecular evolution and characterization of type III polyketide synthase gene family in Aquilaria sinensis.

2-(2-Phenylethyl) chromone (PEC) and its derivatives are markers of agarwood formation and are also related to agarwood quality. However, the biosynthetic and regulatory mechanisms of PECs still remain mysterious. Several studies suggested that type III polyketide synthases (PKSs) contribute to PEC biosynthesis in Aquilaria sinensis. Furthermore, systematic studies on the evolution of PKSs in A. sinensis have rarely been reported. Herein, we comprehensively analyzed PKS genes from 12 plant genomes and characterized the AsPKSs in detail. A unique branch contained only AsPKS members was identified through evolutionary analysis, including AsPKS01 that was previously indicated to participate in PEC biosynthesis. AsPKS07 and AsPKS08, two tandem-duplicated genes of AsPKS01 and lacking orthologous genes in evolutionary models, were selected for their transient expression in the leaves of Nicotiana benthamiana. Subsequently, PECs were detected in the extracts of N. benthamiana leaves, suggesting that AsPKS07 and AsPKS08 promote PEC biosynthesis. The interaction between the promoters of AsPKS07, AsPKS08 and five basic leucine zippers (bZIPs) from the S subfamily indicated that their transcripts could be regulated by these transcription factors (TFs) and might further contribute to PECs biosynthesis in A. sinensis. Our findings provide valuable insights into the molecular evolution of the PKS gene family in A. sinensis and serve as a foundation for advancing PEC production through the bioengineering of gene clusters. Ultimately, this contribution is expected to shed light on the mechanism underlying agarwood formation.

Identification and characterization of two O-methyltransferases involved in biosynthesis of methylated 2-(2-phenethyl)chromones in agarwood.

The 2-(2-phenethyl)chromones (PECs) are the signature constituents responsible for the fragrance and pharmacological properties of agarwood. O-Methyltransferases (OMTs) are necessary for the biosynthesis of methylated PECs, but there is little known about OMTs in Aquilaria sinensis. In this study, we identified 29 OMT genes from the A. sinensis genome. Expression analysis showed they were differentially expressed in different tissues and responded to drill wounding. Comprehensive analysis of the gene expression and methylated PEC content revealed that AsOMT2, AsOMT8, AsOMT11, AsOMT16, and AsOMT28 could potentially be involved in methylated PECs biosynthesis. In vitro enzyme assays and functional analysis in Nicotiana benthamiana demonstrated that AsOMT11 and AsOMT16 could methylate 6-hydroxy-2-(2-phenylethyl)chromone to form 6-methoxy-2-(2-phenylethyl)chromone. A transient overexpression experiment in the variety 'Qi-Nan' revealed that AsOMT11 and AsOMT16 could significantly promote the accumulation of three major methylated PECs. Our results provide candidate genes for the mass production of methylated PECs using synthetic biology.

Identification of a diarylpentanoid-producing polyketide synthase revealing an unusual biosynthetic pathway of 2-(2-phenylethyl)chromones in agarwood.

2-(2-Phenylethyl)chromones (PECs) are the principal constituents contributing to the distinctive fragrance of agarwood. How PECs are biosynthesized is currently unknown. In this work, we describe a diarylpentanoid-producing polyketide synthase (PECPS) identified from Aquilaria sinensis. Through biotransformation experiments using fluorine-labeled substrate, transient expression of PECPS in Nicotiana benthamiana, and knockdown of PECPS expression in A. sinensis calli, we demonstrate that the C6-C5-C6 scaffold of diarylpentanoid is the common precursor of PECs, and PECPS plays a crucial role in PECs biosynthesis. Crystal structure (1.98 Å) analyses and site-directed mutagenesis reveal that, due to its small active site cavity (247 Å3), PECPS employs a one-pot formation mechanism including a "diketide-CoA intermediate-released" step for the formation of the C6-C5-C6 scaffold. The identification of PECPS, the pivotal enzyme of PECs biosynthesis, provides insight into not only the feasibility of overproduction of pharmaceutically important PECs using metabolic engineering approaches, but also further exploration of how agarwood is formed.

Characterization of Guaiene Synthases from Stellera chamaejasme L. Flowers and Their Application in De novo Production of (-)-Rotundone in Yeast.

Four terpene synthases for the biosynthesis of volatile terpenoids were identified from the transcriptome of Stellera chamaejasme L. flowers, including SchTPS1, SchTPS2, SchTPS3, and SchTPS4. Their functions were characterized by synthetic biology approaches in Escherichia coli and in vitro enzymatic assays. SchTPS1, SchTPS2, and SchTPS3 are guaiene synthases, while SchTPS4 is an (E,E)-geranyl linalool synthase. Next, SchTPS1 and α-guaiene 2-oxidase VvSTO2 were co-expressed in Saccharomyces cerevisiae to reconstruct the biosynthetic pathway of (-)-rotundone, which is a unique aroma compound in fruits, vegetables, and wines. This is the first report for the construction of a (-)-rotundone-producing microbial platform.

Evolutionary analysis and structural characterization of Aquilaria sinensis sesquiterpene synthase in agarwood formation: A computational study.

Agarwood originating from Aquilaria sinensis contains sesquiterpenoids that have tremendous commercial value in the pharmaceutical and fragrance industries. Aquilaria sinensis sesquiterpene synthase (AsSTS) is the key enzyme in the agarwood biosynthesis pathway, and its activity directly affects the chemical composition of agarwood; however, its role in species evolution remains unclear. In this study, we performed an evolutionary analysis based on 68 plant sesquiterpene synthase (STS) genes and further structural characterization of the gene encoding AsSTS to explore its molecular evolution. The phylogenetic tree indicated that these STS genes included three subfamilies. Additionally, 23 positively selected sites were detected, and no influence of recombination was found. Furthermore, the protein structure of AsSTS was characterized using primary sequence and structural analyses as having a functional active site lid domain, a substrate binding site, two post-translational modification sites and four conserved motifs. Finally, most virtual mutations of positively selected sites could be stabilized against thermal denaturation by a decrease in free energy, and three virtual mutations (D403R, G470Q and S538K) were shown to play important roles in the function and stability of AsSTS. The molecular evolutionary analysis of plant STSs provides essential clues for further experimental site-directed mutagenesis and molecular modification of AsSTS.

Identification and characterization of a novel sesquiterpene synthase from Aquilaria sinensis: An important gene for agarwood formation.

Sesquiterpene synthases are key enzymes for biosynthesis of sesquiterpene compounds and are important for agarwood formation in Aquilaria sinensis.The As-sesTPS gene encoding a novel sesquiterpene synthase was expressed in Escherichia coli strain BL21 (DE3) as an inclusion body and purified by Ni affinity chromatography. The molecular weight of the protein was lower than the theoretical value. Amino acid sequencing results indicated that the 27.2kDa-recombinant protein was a truncated sesquiterpene synthase from chemically induced A. sinensis. After refolding, the truncated As-SesTPS protein catalyzed the conversion of farnesyl pyrophosphate (FPP) to nerolidol which is a characteristic component of agarwood. The optimal reaction pH for the As-SesTPS protein was 8.0, and the optimal temperature was 30°C. The values of Km and Vmax of As-SesTPS protein towards FPP were 0.0548mM, 42.83µmol/mg.min, respectively. The results of qPCR and iTRAQ demonstrated the much higher expression level of As-SesTPS gene in agarwood than that in whitewood. This study provides a foundation for elucidating the mechanism of agarwood formation in A. sinensis and the potential of the novel gene for improving the quality of artificial agarwood.

Identification and functional characterization of three type III polyketide synthases from Aquilaria sinensis calli.

Type III polyketide synthases (PKSs) play an important role in biosynthesis of various plant secondary metabolites and plant adaptation to environmental stresses. Aquilaria sinensis (A. sinensis) is the main plant species for production of agarwood, little is known about its PKS family. In this study, AsCHS1 and two new type III PKSs, AsPKS1 and AsPKS2, were isolated and characterized in A. sinensis calli. The comparative sequence and phylogenetic analysis indicated that AsPKS1 and AsPKS2 belonged to non-CHS group different from AsCHS1. The recombinant AsPKS1 and AsPKS2 produced the lactone-type products, suggesting their different enzyme activities from AsCHS1. Three PKS genes had a tissues-specific pattern in A. sinensis. Moreover, we examined the expression profiles of three PKS genes in calli under different abiotic stresses and hormone treatments. AsCHS1 transcript was most significantly induced by salt stress, AsPKS1 abundance was most remarkably enhanced by CdCl2 treatment, while AsPKS2 expression was most significantly induced by mannitol treatment. Furthermore, AsCHS1, AsPKS1 and AsPKS2 expression was enhanced upon gibberellins (GA3), methyl jasmonate (MeJA), or salicylic acid (SA) treatment, while three PKS genes displayed low transcript levels at the early stage under abscisic acid (ABA) treatment. In addition, three GFP:PKSs fusion proteins were localized in the cytoplasm and cell wall in Nicotiana benthamiana cells. These results indicated the multifunctional role of three type III PKSs in polyketide biosynthesis, plant resistance to abiotic stresses and signal transduction.

Relationship between Expression of Chalcone Synthase Genes and Chromones in Artificial Agarwood induced by Formic Acid Stimulation Combined with Fusarium sp. A2 Inoculation.

Agarwood (gaharu) is a fragrant resin produced in the heartwood of resinous Gyrinops and Aquilaria species. Artificial agarwood samples were obtained from Aquilaria sinensis (Lour.) Gilg using formic acid (FA) stimulation combined with Fusarium sp. A2 inoculation. The relationship between the expression of chalcone synthase genes (CHS) and dynamic changes in chromone content was explored in resin-deposited parts of the trunks of A. sinensis. CHS gene expression levels were detected by qRT-PCR analysis. The chemical composition of agarwood obtained from the heartwood of A. sinensis before and within 1 year after induction was determined by GC-MS. After induction with FA stimulation combined with F. sp. A2 inoculation, the CHS1 gene showed relatively high expression, whereas the CHS2 gene showed low expression. The relative gene expression level of CHS1 peaked at 12 months, with a 153.1-fold increase, and the dominant period of the CHS2 gene expression was 10 months with a 14.13-fold increase. Moreover, chromones were not detected until after 2 months, and a large proportion of chromone compounds were detected after 4 months. Chromone content increased with time and peaked at 12 months. CHS1 gene expression was significantly correlated with 6-hydroxy-2-(2-phenylethyl)chromone accumulation, and CHS2 gene expression was significantly correlated with 5-hydroxy-6-methoxy-2-(2-phenylethyl)chromone accumulation. CHS gene expression was extremely sensitive to FA stimulation combined with F. sp. A2 inoculation and responded to late-onset injury. CHS genes expression also preceded the chromone accumulation. This work laid the foundation for studies on the mechanism by which genes regulate chromone biosynthesis pathways during the formation of agarwood resin in A. sinensis.

Molecular cloning, characterization and expression analysis of the gene encoding 1-deoxy-D-xylulose 5-phosphate reductoisomerase from Aquilaria sinensis (Lour.) Gilg.

The major constituents of agarwood oils are sesquiterpenes that are obtained from isoprenoid precursors through the plastidial methylerythritol phosphate (MEP) pathway and the cytosolic mevalonate pathway. In this study, a novel full-length cDNA of 1-deoxy-D-xylulose 5-phosphate reductoisomerase (DXR), which was the second key enzyme in the plastid MEP pathway of sesquiterpenes biosynthesis was isolated from the stem of Aquilaria sinensis (Lour.) Gilg by the methods of reverse transcription polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE) technique for the first time, and named as AsDXR. The full-length cDNA of AsDXR was 1768 bp, containing a 1437 bp open reading frame (ORF) encoding a polypeptide of 478 amino acids with a molecular weight of 51.859 kD and the theoretical isoelectric point of 6.29. Comparative and bioinformatic analysis of the deduced AsDXR protein showed extensive homology with DXRs from other plant species, especially Theobroma cacao and Gossypium barbadense, and contained a conserved transit peptide for plastids, and extended pro-rich region and a highly conserved NADPH-binding motif owned by all plant DXRs. Southern blot analysis indicated that AsDXR belonged to a small gene family. Tissue expression pattern analysis revealed that AsDXR expressed strongly in root and stem, but weakly in leaf. Additionally, AsDXR expression was found to be activated by exogenous elicitor of MeJA (methyl jasmonate). The contents of three sesquiterpenes (α-guaiene, α-humulene and Δ-guaiene) were significantly induced by MeJA. This study enables us to further elucidate the role of AsDXR in the biosynthesis of agarwood sesquiterpenes in A. sinensis at the molecular level.

Rapid preparation of (methyl)malonyl coenzyme A and enzymatic formation of unusual polyketides by type III polyketide synthase from Aquilaria sinensis.

(Methyl)malonyl coenzyme A was rapidly and effectively synthesized by a two-step procedure involving preparation of N-hydroxysuccinimidyl (methyl)malonate from (methyl)Meldrum's acid, and followed by transesterification with coenzyme A. The synthesized (methyl)malonyl coenzyme A could be well accepted and assembled to 4-hydroxy phenylpropionyl coenzyme A by type III polyketide synthase from Aquilaria sinensis to produce dihydrochalcone and 4-hydroxy-3,5-dimethyl-6-(4-hydroxyphenethyl)-2H-pyrone as well as 4-hydroxy-3,5-dimethyl-6-(5-(4-hydroxyphenyl)-3-oxopentan-2-yl)-2H-pyrone.

[Cloning and expression analysis of cinnamate 4-hydroxylase (C4H) reductase gene from Aquilaria sinensis].

The study aimed to clone the open reading frame of cinnamate 4-hydroxylase (C4H) from Aquilaria sinensis and analyze the bioinformatics and expression of the gene. One unique sequence containing C4H domain was discovered in our previous reported wound transcriptome dataset of A. sinensis. The open reading frame of C4H was cloned by RT-PCR strategy with the template of mixed RNA extracted from A. sinensis stem which treated by different wound time. The bioinformatic analysis of this gene and its corresponding protein was performed. C4H expression profiles in responds to MeJA (methyl jasmonate) application were analyzed by real-time PCR. The length of C4H open reading frame (ORF) was 1 515 bp, encoding 514 amino acids. The GenBank accession number is KF134783. Inducible-experiments showed that the genes were induced by mechanical wound as well as MeJA induction, and reached the highest expression level at 8 h and 20 h, respectively. The full-length cDNA of C4H and its expression patterns will provide a foundation for further research on its function in the molecular mechanisms of aromatic compounds and flavonoids biosynthesis.

Molecular cloning and characterization of three cDNAs encoding 1-deoxy-d-xylulose-5-phosphate synthase in Aquilaria sinensis (Lour.) Gilg.

Agarwood is an expensive resinous heartwood derived from Aquilaria plants that is widely used in traditional medicines, incense and perfume. The major constituents of agarwood oils are sesquiterpenes, which are obtained from isopentenyl diphosphate and dimethylallyl diphosphate precursors through the plastidial methylerythritol phosphate (MEP) pathway and/or the cytosolic mevalonate pathway. 1-deoxy-d-xylulose-5-phosphate synthase (DXS) is the first rate-limiting enzyme for sesquiterpene synthesis in the MEP pathway. In this study, 3 cDNAs of DXS genes were cloned and characterized from the Aquilaria sinensis (Lour.) Gilg. These genes represent 3 phylogenetically distinct clades conserved among plants. Functional complementation in a DXS-deficient Escherichia coli strain EcAB4-2 demonstrated that they are active DXS, which rescued the E. coli mutant. Their expression profiles in different tissues and in response to different treatments were analyzed by real-time PCR. All 3 genes are highly expressed in stem, followed by leaf and root. AsDXS1 was significantly stimulated by mechanical, chemical, and H2O2 treatment, whereas AsDXS2 and AsDXS3 only responded to chemical treatment and mechanical treatment, respectively. All three genes were oscillation in respond to MJ treatment, with expression peaks occurring at different time points. Our results suggest the conservation of DXS in evolution and imply their distinct functions in primary and defensive sesquiterpene metabolism in A. sinensis.

[Cloning and gene expression of acetyl-CoA C-acetyl transferase gene (AsAACT) from Aquilaria sinensis].

OBJECTIVE: This study aimed to clone the acetyl-CoA C-acetyl transferase (AACT) gene from Aquilaria sinensis and analyze the bioinformatics and expression of the gene. METHOD: One unique sequence containing partly AACT gene sequence was discovered in our previous transcriptome dataset of A. sinensis. AACT gene was cloned by RT-PCR and RACE strategy with the template of RNA extracted from A. sinensis stem. The bioinformatic analysis of this gene and its corresponding protein was performed. The AsAACT expression in calli was analyzed with GADPH gene as an internal control gene in wounded condition by qRT-PCR technique. RESULT: One unique sequence of AACT, named as AsAACT, was cloned from A. sinensis. The full length of AsAACT cDNA was containing a 1 236 bp ORF that encoded 411 amino acids. The result of qRT-PCR displayed that the highest expression level was at 4 h. which indicated that it was possibly involved in early-stage response to wound. CONCLUSION: Cloning and analyzing AsAACT gene from A. sinensis provided basic information for study the function and expression regulation of AsAACT in terpenoid biosynthesis.

Induction, cloning and functional expression of a sesquiterpene biosynthetic enzyme, δ-guaiene synthase, of Aquilaria microcarpa cell cultures.

A homology-based cloning strategy yielded a cDNA clone presumably encoding δ-guaiene synthase, a sesquiterpene cyclase, from tissue cultures of Aquilaria microcarpa, which were treated with methyl jasmonate. Incubation of cell cultures of the plant with yeast extract also induced transcriptional activation of the sesquiterpene synthase gene. The translated protein of the gene obtained by heterologous expression in Escherichia coli catalyzed the cyclization of farnesyl diphosphate to liberate δ-guaiene with δ-guaiene and germacrene A as the minor products. The results obtained in the present study, together with the previously reported results, suggest that two classes of δ-guaiene synthase occur in Aquilaria; the enzyme proteins from A. microcarpa and A. sinensis liberate germacrene A as a minor product, while the protein from A. crassna generates α-humulene instead of germacrene A.

[Cloning, prokaryotic expression, and functional identification of a sesquiterpene synthase gene (AsSS4) from Aquilaria sinensis].

A sesquiterpene synthase (AsSS4) full-length open reading frame (ORF) cDNA was cloned from wounded stems of Aquilaria sinensis by RT-PCR method. The result showed that the ORF of AsSS4 was 1,698 bp encoding 565 amino acids. Prokaryotic expression vector pET28a-AsSS4 was constructed and transformed into E. coli BL21 (DE3) pLysS. Recombinant AsSS4 protein was obtained after induction by IPTG and SDS-PAGE analysis with a MW of 64 kD. Enzymatic reactions using farnesyl pyrophosphate showed that recombinant AsSS4 protein purified by Ni-agarose gel yielded five sesquiterpene compounds, cyclohexane, 1-ethenyl-1-methyl-2, 4-bis(1-methylethenyl)-, ß-elemene, α-guaiene, α-caryophyllene and δ-guaiene. This paper reported the first cloning and functional characterization of AsSS4 gene from A. sinensis, which will establish a foundation for future studies on the molecular mechanisms of wound-induce agarwood formation in A. sinensis

[Cloning and expression analysis of HMG-CoA reductase from Aquilaria sinensis (Lour.) Gilg].

3-Hydroxy-3-methylglutaryl-coenzyme A reductase (HMGR) is the first rate-limiting enzyme for sesquiterpene synthesis in the mevalonate (MVA) pathway. The specific primers were designed according to the transcript sequence of AsHMGR2 from the Aquilaria sinensis (Lour.) Gilg transcriptome database. The full-length cDNA of AsHMGR2 was cloned by RT-PCR and rapid amplification of cDNA ends (RACE) technology, and was analyzed at bioinformatics levels; AsHMGR2 expression profiles in different tissues and in responds to different treatments were analyzed by real-time PCR. The length of AsHMGR2 Open Reading Frame (ORF) was 1 749 bp, encoding 582 amino acids. The GenBank accession number is KC140287. Tissue expression analysis indicated that AsHMGR2 was mainly expressed in root and shoot tips, followed by stem, and was lowest in leaves. Inducible-experiments showed that the genes were induced by mechanical wound as well as chemical liquid induction, and reached the highest expression level at 6 h and 8 h, separately. The full-length cDNA of AsHMGR2 and its expression patterns will provide a foundation for further research on its function in agarwood sesquiterpene biosynthesis.

[Cloning and bioinformatics analysis of chalcone synthase (AsCHS1) gene in Aquilaria sinensis].

OBJECTIVE: The study aimed to clone the open reading frame of chalcone synthase (CHS) from Aquilaria sinensis and analyze the bioinformatics and expression of the gene. METHOD: One unique sequence containing CHS domain was discovered in our previous reported wound transcriptome dataset of A. sinensis. The open reading frame of CHS was cloned by RT-PCR strategy with the template of mixed RNA extracted from A. sinensis stem which treated by different wound time. The bioinformatic analysis of this gene and its corresponding protein was performed. The AsCHS1 expression in calli was analyzed with histone gene as an internal control gene under wound condition by qRT-PCR technique. RESULT: One unique sequence of CHS, named as AsCHS1, was cloned from A. sinensis. The full length of AsCHS1 cDNA was containing a 1 192 bp ORF that encoded 397 amino acids. The result of qRT-PCR displayed that the highest expression level was at 12 h, which indicated that it was possibly involved in early-stage response to wound. CONCLUSION: Cloning and analyzing AsCHS1 gene from A. sinensis provided basic information for study the function and expression regulation of AsCHS1 in the flavonoids biosynthesis.

[Cloning and expression analysis of farnesyl pyrophosphate synthase from Aquilaria sinensis].

Farnesyl diphosphate synthase (FPS) is one of the key rate-limiting enzymes in the sesquiterpene metabolic pathways. In this study, the open reading frame (ORF) of FPS was cloned by PCR based on the transcript sequence of AsFPS1 from the Aquilaria sinensis transcriptome database and sequenced. Total RNA was extracted from the root, stem and leaves of three-year-old A. sinensis, and from healthy and wounded A. sinensis calli, and then reverse-transcribed into single-stranded cDNA as a template for real-time PCR, to detect the expression specificity of AsFPSI in different tissues and its expression profile in responding to different treatments. The result showed that the full length of AsFPS1 was 1 342 bp with the ORF 1 029 bp, encoding 342 amino acids. Tissue expression analysis indicated that AsFPS1 was mainly expressed in root and stem, and was lower in leaves. Inducible-experiments showed that the genes was induced by mechanical wound as well as chemical liquid induction, and reached the highest expression level at 6 h and 12 h, respectively. The full-length cDNA clone of AsFPSI and its expression patterns analysis will provide a foundation for follow-up study on its biological function and agarwood sesquiterpene biosynthesis mechanism.

Genomic organization of δ-guaiene synthase genes in Aquilaria crassna and its possible use for the identification of Aquilaria species.

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 crassna showed that the production of sesquiterpenes (α-guaiene, α-humulene, and δ-guaiene) was induced by treatment with methyl jasmonate, which led to the cloning of δ-guaiene synthases. In the present study, analyses of genomic organization and Southern blotting of δ-guaiene synthase in A. crassna were performed in order to examine the genomic background of δ-guaiene synthases in Aquilaria plants. Genomic cloning and sequencing revealed five types of sequence in putative δ-guaiene synthases sharing more than 96% identity in exon regions, and that these enzymes belonged to the class III TPS subfamily with seven exons and six introns. Furthermore, Southern blotting revealed that at least five copies of δ-guaiene synthase existed in A. crassna. The hybridization of digested DNA of A. crassna and A. sinensis with probes made with a δ-guaiene synthase cDNA fragment resulted in different banding patterns for these two species. It may be possible to identify Aquilaria species by restriction fragment length polymorphism analyses with δ-guaiene synthase cDNA probes.