Induction of Sesquiterpenoid Production by Methyl Jasmonate inAquilaria sinensisCell Suspension Culture

Comparative transcriptome analysis reveals the differences in wound-induced agarwood formation between Chi-Nan and ordinary germplasm of Aquilaria sinensis

Agarwood is a rare and valuable heartwood derived from Aquilaria sinensis in China. Compared with ordinary germplasm, Chi-Nan, a special germplasm of A. sinensis, has a better agarwood-producing capacity. However, the mechanisms underlying their different qualities remain poorly characterized. Here, a comparative transcriptome analysis of Chi-Nan and ordinary A. sinensis was carried out to investigate the wound responses of both germplasms. A total of 198.19 Gb of clean data were obtained with an average of 6.61 Gb of clean reads for each sample. By comparing with their control groups, more differentially expressed genes (DEGs) were observed in Chi-Nan germplasm. Kyoto Encyclopedia of Genes and Genomes (KEGG) and expression profile analysis suggested that Chi-Nan possesses a stronger ability to respond to wounding. Furthermore, the enrichment of biosynthetic pathways related to sesquiterpenes and 2-(2-phenylethyl) chromones (PECs) were more significant in Chi-Nan than in ordinary germplasm, and related genes showed significantly higher up-regulation in Chi-Nan after wounding. Sixteen candidate genes presumably involved in biosynthesis of agarwood components were identified and found to exhibit higher up-regulation in Chi-Nan than in ordinary germplasm in response to wounding. Overall, these results are helpful in explaining reasons for the higher agarwood-producing properties of Chi-Nan, and contribute to a further understanding of the mechanism of agarwood formation in A. sinensis.

2-(2-Phenylethyl)chromones increase in Aquilaria sinensis with the formation of agarwood

Obtained from Aquilaria Lam. and Gyrinops Gaertn., agarwood is a prestigious perfume and medicinal material in the world. Its primary chemical constituents and indicators of agarwood's development are 2-(2-phenylethyl)chromones (PECs). However, how PECs affect its quality, accumulation, and transformation pattern is still unclear. The present study investigated this issue by monitoring resin filling in agarwood generated by the whole-tree agarwood-inducing technique over a span of a year, observing the ethanol extract concentration at different sampling times, and statistically examining PECs in agarwood from each sampling period. In agarwood, the resin accumulated over time, except during the 4th-6th month due to the creation of a barrier layer. The relative content of total PECs demonstrated an overall increase throughout the year but a decrease from the 4th month to the 6th month, and the relative content of 19 PECs that persisted throughout the year was positively correlated with the content of ethanol extracts. In addition, the process of chromone accumulation was accompanied by the production and transformation of different types of chromones, with flindersia type 2-(2-phenylethyl)chromones, epoxy-2-(2-phenylethyl)chromones, and diepoxy-2-(2-phenylethyl)chromones being the major chromone components; in addition, the content of 5,6,7,8-tetrahydro-2-(2-phenylethyl)chromones kept increasing after 6 months of agarwood formation. Three main trends were identified from 58 analogs of PECs, each with notable variation. The first type had the highest content at the beginning of resin formation. The second type had the highest content at 6 months and then started to decrease, and the third type had a slowly increasing content. As a whole, this study systematically investigated the accumulation of PECs during injury-induced agarwood production in A. sinensis, which is of scientific significance in resolving the transformation of PECs and revealing the secret of agarwood formation.

Fusarium oxysporum infection-induced formation of agarwood (FOIFA): A rapid and efficient method for inducing the production of high quality agarwood

Agarwood, a non-wood product from the endangered Aquilaria and Gyrinops tress, is highly prized for its use in fragrances and medicines. The special formation process of agarwood is closely related to external injury and fungal infection. In this study, we demonstrate that infection of Aquilaria sinensis by Fusarium oxysporum, a soilborne fungus that causes vascular wilt diseases in diverse plants, induces agarwood formation. Based on these findings, an efficient method, termed F. oxysporum infection-induced formation of agarwood (FOIFA), was developed for the rapid production of quality agarwood. The agarwood formed in response to F. oxysporum infection was similar in structure and chemical composition to wild agarwood according to TLC (Thin-layer chromatography), HPLC (high performance liquid chromatography), and GC-MS (gas chromatography-mass spectrometry) analyses, except that the contents of alcohol-soluble extract, chromones, and essential oils (mainly sesquiterpenes) were higher in the formed agarwood.

Integrating Multiple Omics Identifies Phaeoacremonium rubrigenum Acting as Aquilaria sinensis Marker Fungus to Promote Agarwood Sesquiterpene Accumulation by Inducing Plant Host Phosphorylation

The present study aimed to explore the factors that promote persistent agarwood accumulation. To this end, we first investigated the morphological changes and volatile compound distribution in five layers of "Guan Xiang" agarwood. The agarwood-normal transition layer (TL), an essential layer of persistent agarwood accumulation, showed clear metabolic differences by microscopy and GC-MS analysis. Microbiome analysis revealed that Phaeocremonium rubrigenum was the predominant biomarker fungus in the TL of "Guan Xiang" agarwood samples. Among the seven isolated fungi, P. rubrigenum exhibited a significantly heightened ability to induce the production in Aquilaria sinensis seedlings, especially for sesquiterpene. Tracing the proteome profile changes in P. rubrigenum-induced A. sinensis calli for 18 ds showed that the fungus-induced sesquiterpene biosynthesis increased mainly through the mevalonate (MVA) pathway. Specifically, the phosphorylation modification level, instead of the protein abundance of transcription factors (TFs), showed corresponding changes during sesquiterpene biosynthesis, thus indicating that induced phosphorylation is the key reason for enhanced sesquiterpene production. IMPORTANCE Agarwood is an expensive resinous portion derived from Aquilaria plants and has been widely used as medicine, incense, and perfume. The factors involved in steady agarwood accumulation remain elusive. Our current study suggests that as a TL marker fungus, P. rubrigenum could persistently promote agarwood sesquiterpene accumulation by inducing phosphorylation of the TFs-MVA network in A. sinensis. Moreover, our work provides strategies to improve agarwood industry management and sheds light on the potential molecular mechanisms of plant adaptation to native microbial conditions.

Effects of various artificial agarwood-induction techniques on the metabolome of Aquilaria sinensis

BACKGROUND

Agarwood is a highly sought-after resinous wood for uses in medicine, incense, and perfume production. To overcome challenges associated with agarwood production in Aquilaria sinensis, several artificial agarwood-induction treatments have been developed. However, the effects of these techniques on the metabolome of the treated wood samples are unknown. Therefore, the present study was conducted to evaluate the effects of four treatments: fire drill treatment (F), fire drill + brine treatment (FS), cold drill treatment (D) and cold drill + brine treatment (DS)) on ethanol-extracted oil content and metabolome profiles of treated wood samples from A. sinensis.

RESULTS

The ethanol-extracted oil content obtained from the four treatments differed significantly (F < D < DS < FS). A total of 712 metabolites composed mostly of alkaloids, amino acids and derivatives, flavonoids, lipids, phenolic acids, organic acids, nucleotides and derivatives, and terpenoids were detected. In pairwise comparisons, 302, 155, 271 and 363 differentially accumulated metabolites (DAM) were detected in F_vs_FS, D_vs_DS, F_vs_D and FS_vs_DS, respectively. The DAMs were enriched in flavonoid/flavone and flavonol biosynthesis, sesquiterpenoid and triterpenoid biosynthesis. Generally, addition of brine to either fire or cold drill treatments reduced the abundance of most of the metabolites.

CONCLUSION

The results from this study offer valuable insights into synthetically-induced agarwood production in A. sinensis.

Sustainable utilization of Gyrinops walla Gaetner: in vitro production of sesquiterpenes by chemical and biological elicitation

Background

The recent recovery of Gyrinops walla as a potential producer of market-quality agarwood in mature damaged woods and branches has led to the intense illicit felling and exportation of G. walla leading to the verge of extinction from Sri Lankan flora. The sustainable utilization of G. walla undoubtedly enhances the foreign exchange of the country and the non-destructive utilization through tissue culture–based techniques is the only option available for sustainable exploitation and conservation of the vulnerable species. Healthy calli and cell suspensions were chemically and biologically elicited with salicylic acid (SA) and methyl jasmonate (MJ), and the sterilized fungal homogenate (carbohydrate equivalents) of Fusariym oxysporum, Phaeocremonium parasitica, Aspergillus niger, Trichoderma viride, Penicillium commune and Lasidiplodia theobromae fungal strains, respectively. The elicited calli and cell suspensions were harvested at different time periods to extract sesquiterpenes.

Results

Sesquiterpenes were produced in calli under chemical elicitors with media concentrations of 10 μM SA, 100 μM SA, 10 mM MJ and 1 mM MJ and cell suspensions under 0.5 μM SA and 0.1 mM MJ. Phaeocremonium parasitica, Trichoderma viride and Lasidiplodia theobromae were more effective in the production of sesquiterpenes in G. walla callus and cell suspension by biological elicitation.

Conclusion

The findings of the study led to the conclusion of the possibility of induction of production of sesquiterpenes through elicitation of G. walla calli and cell suspension in an in vitro system for sustainable utilization and conservation endeavours.

Simultaneous determination of multiple active 2-(2-phenylethyl)chromone analogues in agarwood by HPLC, QAMS, and UPLC-MS

INTRODUCTION

Chromones are the major constituents of agarwood and are considered to be directly related to its quality. Agarotetrol, a chromone derivative, is a Chinese Pharmacopoeia content detection index. However, comprehensive high-performance liquid chromatography (HPLC), quantitative analysis of multiple components by a single marker (QAMS), and ultra-performance liquid chromatography mass spectrometry (UPLC-MS) analyses of this pharmacopeial plant material have never been performed. Moreover, reports regarding the separation and detection of multiple active 2-(2-phenylethyl)chromone analogues from this plant material are surprisingly scarce.

OBJECTIVE

To establish a simple, reliable, and effective HPLC method utilising both diode array and MS detection for the simultaneous determination of multiple active chromone analogues in agarwood.

METHODS

Four 2-(2-phenylethyl)chromones were isolated from methanol extracts of agarwood. After optimising the extraction, separation, and analytical conditions, validation of the developed analytical method indicated good linearity, satisfactory precision, and good recovery. On this basis, a method for the quantitative analysis of multiple components by a single marker was established. The four 2-(2-phenylethyl)chromones were identified by nuclear magnetic resonance spectroscopic analysis and UPLC coupled to electrospray ionisation quadrupole-time-of-flight MS.

CONCLUSIONS

The behaviour of the chromones characterised by MS fragmentation indicated a loss of molecular CO and the formation of m/z 121 compounds by the cleavage of CH₂ -CH₂ bonds between the chromone and phenyl moieties. Three detection methods were successfully used in this study for agarwood detection, and this protocol may potentially be used as a tool for the quality control of agarwood.

Germacrene A-A Central Intermediate in Sesquiterpene Biosynthesis

This review summarises known sesquiterpenes whose biosyntheses proceed through the intermediate germacrene A. First, the occurrence and biosynthesis of germacrene A in Nature and its peculiar chemistry will be highlighted, followed by a discussion of 6-6 and 5-7 bicyclic compounds and their more complex derivatives. For each compound the absolute configuration, if it is known, and the reasoning for its assignment is presented.

Methyl jasmonate-induced compositional changes of volatile organic compounds in Polygonum minus leaves

Polygonum minus Huds. is a medicinal aromatic plant rich in terpenes, aldehydes, and phenolic compounds. Methyl jasmonate (MeJA) is a plant signaling molecule commonly applied to elicit stress responses to produce plant secondary metabolites. In this study, the effects of exogenous MeJA treatment on the composition of volatile organic compounds (VOCs) in P. minus leaves were investigated by using a metabolomic approach. Time-course changes in the leaf composition of VOCs on days 1, 3, and 5 after MeJA treatment were analyzed through solid-phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS). The VOCs found in MeJA-elicited leaves were similar to those found in mock-treated leaves but varied in quantity at different time points. We focused our analysis on the content and composition of monoterpenes, sesquiterpenes, and green leaf volatiles (GLVs) within the leaf samples. Our results suggest that MeJA enhances the activity of biosynthetic pathways for aldehydes and terpenes in P. minus. Hence, the production of aromatic compounds in this medicinal herb can be increased by MeJA elicitation. Furthermore, the relationship between MeJA elicitation and terpene biosynthesis in P. minus was shown through SPME-GC-MS analysis of VOCs combined with transcriptomic analysis of MeJA-elicited P. minus leaves from our previous study.

Agarwood Induction: Current Developments and Future Perspectives

Agarwood is a resinous part of the non-timber Aquilaria tree, which is a highly valuable product for medicine and fragrance purposes. To protect the endangered Aquilaria species, mass plantation of Aquilaria trees has become a sustainable way in Asian countries to obtain the highly valuable agarwood. As only physiologically triggered Aquilaria tree can produce agarwood, effective induction methods are long sought in the agarwood industry. In this paper, we attempt to provide an overview for the past efforts toward the understanding of agarwood formation, the evolvement of induction methods and their further development prospects by integrating it with high-throughput omics approaches.

GC-MS Study of the Chemical Components of Different Aquilaria sinensis (Lour.) Gilgorgans and Agarwood from Different Asian Countries

As a traditional medicinal herb and valuable natural spice in China, Aquilaria sinensis (Lour.) Gilg has many significant pharmacological effects. Agarwood is the resinous heartwood acquired from wounded A. sinensis trees, and is widely used in pharmaceuticals owing to its excellent medicinal value. In this study, the chemical composition of volatile components and alcohol extracts from different organs of A. sinensis and agarwoods grown in different regions were investigated using GC-MS. The results showed that Vietnam agarwood had the highest moisture content, which was attributed to the local climate, while the fruit and bark of A. sinensis had higher moisture contents than the other organs. The volatile components of A. sinensis organs included 3-ethyl-5-(2-ethylbutyl)-octadecane, oleic acid 3-(octadecyloxy) propyl ester, and docosanoic acid 1,2,3-propanetriyl ester, while the alcohol extracts of A. sinensis organs contained benzoic acid ethyl ester, hexadecanoic acid ethyl ester, oleic acid, and n-hexadecanoic acid. Furthermore, the main active ingredients in agarwood from different habitats were sesquiterpenoids, aromatic species, and chromone compounds. The role of chromone compound 2-phenylethyl-benzopyran as an elicitor and the mechanism of agarwood formation were also investigated. Antioxidant tests showed that essential oils from agarwood and A. sinensis had antioxidant capacities by comparison with butylated hydroxytoluene and vitamin E. An antibacterial activity test showed that the inhibition effect of the essential oil was better against Gram-positive bacteria than against Gram-negative bacteria.

Incubation of Aquilaria subintegra with Microbial Culture Supernatants Enhances Production of Volatile Compounds and Improves Quality of Agarwood Oil

Incubation with microbial culture supernatants improved essential oil yield from Aquilaria subintegra woodchips. The harvested woodchips were incubated with de man, rogosa and sharpe (MRS) agar, yeast mold (YM) agar medium and six different microbial culture supernatants obtained from Lactobacillus bulgaricus, L. acidophilus, Streptococcus thermophilus, Lactococcus lactis, Saccharomyces carlsbergensis and S. cerevisiae prior to hydrodistillation. Incubation with lactic acid bacteria supernatants provided higher yield of agarwood oil (0.45% w/w) than that obtained from yeast (0.25% w/w), agar media (0.23% w/w) and water (0.22% w/w). The composition of agarwood oil from all media and microbial supernatant incubations was investigated by using gas chromatography-mass spectrometry. Overall, three major volatile profiles were obtained, which corresponded to water soaking (control), as well as, both YM and MRS media, lactic acid bacteria, and yeast supernatant incubations. Sesquiterpenes and their oxygenated derivatives were key components of agarwood oil. Fifty-two volatile components were tentatively identified in all samples. Beta-agarofuran, α-eudesmol, karanone, α-agarofuran and agarospirol were major components present in most of the incubated samples, while S. cerevisiae-incubated A. subintegra provided higher amount of phenyl acetaldehyde. Microbial culture supernatant incubation numerically provided the highest yield of agarwood oil compared to water soaking traditional method, possibly resulting from activity of extracellular enzymes produced by the microbes. Incubation of agarwood with lactic acid bacteria supernatant significantly enhanced oil yields without changing volatile profile/composition of agarwood essential oil, thus this is a promising method for future use.

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.

Fungal and Bacterial Diversity Isolated from Aquilaria malaccensis Tree and Soil, Induces Agarospirol Formation within 3 Months after Artificial Infection

Aquilaria malaccensis Lam, commonly known as Agarwood, is a highly valuable species used in production of agar oil from its infected wood, which is utilized in pharmaceutical and perfumery industry. Agar oil formation in agarwood takes years through the natural process which is induced by natural or artificial injury or microbial infection. The role of soil fungi and bacteria in artificial induction is still an unexplored area. In the present study, we isolated the fungal and bacterial community residing inside the stem of A. malaccensis tree and circumventing soil, samples collected from 21 different sites of the north-eastern state Assam of India and explored their potential in induction of Agarospirol (2-(6,10-Dimethylspiro[4,5]dec-6-en-2-yl)-2-propanol) production by artificially infecting the trees with these microorganisms. A total 340 fungi and 131 bacteria were isolated from 50 stem samples, and 188 fungi and 148 bacteria were isolated from 50 soil samples. Highest Shannon (H′ = 2.43) and Fisher (α = 5.57) diversity index was observed in the stem isolates. The dominant fungal genus was Trichoderma in stem with Pi value of 0.18; while in soil, Aspergillus showed dominance with Pi value 0.73. In bacteria, Bacillus genera showed dominance in both stem and soil samples with Pi = 0.62 and 0.51, respectively. Forty fungal and bacterial isolates were used to assess their potential to induce formation of agarwood in A. malaccensis by artificial infection method. Gas chromatography mass spectroscopy (GC-MS) analysis confirmed development of Agarwood by the presence of Agarospirol compound in samples collected after 3 months of the artificial infection. Only 31% of bacterial and 23% of fungal isolates showed their ability in production of Agarospirol by artificial infection method. Bacteria Pantoea dispersa and fungi Penicillium polonicum showed the highest production in comparison to other isolates.

Characterization of α-humulene synthases responsible for the production of sesquiterpenes induced by methyl jasmonate in Aquilaria cell culture

The resinous portions of Aquilaria and Gyrinops plants are known as 'agarwood' and have a distinctive fragrance. To examine the biosynthesis of these fragrant compounds, we previously established cell cultures of Aquilaria crassna in which the production of three sesquiterpenes (α-guaiene, α-humulene, and δ-guaiene) could be induced by methyl jasmonate (MJ), and showed that cloned δ-guaiene synthase from MJ-treated cells is involved in the synthesis of these three compounds, although only very small amounts of α-humulene are produced. In the present study, cDNAs encoding α-humulene synthases were also isolated. Three putative sesquiterpene synthase clones (AcHS1-3) isolated from the MJ-treated cells had very similar amino acid sequences and shared 52 % identity with δ-guaiene synthases. The recombinant enzymes catalyzed the formation of α-humulene as a major product. Expression of transcripts of the α-humulene synthase and δ-guaiene synthase genes in cultured cells increased after treatment with MJ. These results revealed that these α-humulene and δ-guaiene synthases are involved in the synthesis of three sesquiterpenes induced by MJ treatment.

Identification and Functional Characterization of Sesquiterpene Synthases from Xanthium strumarium

Xanthium strumarium synthesizes various pharmacologically active sesquiterpenes. The molecular characterization of sesquiterpene biosynthesis in X. strumarium has not been reported so far. In this study, the cDNAs coding for three sesquiterpene synthases (designated as XsTPS1, XsTPS2 and XsTPS3) were isolated using the X. strumarium transcriptome that we recently constructed. XsTPS1, XsTPS2 and XsTPS3 were revealed to have primary activities forming germacrene D, guaia-4,6-diene and germacrene A, respectively, by either ectopic expression in yeast cells or purified recombinant protein-based in vitro assays. Quantitative real-time PCRs and metabolite analysis for the different plant parts showed that the transcript abundance of XsTPS1-XsTPS3 is consistent with the accumulation pattern of their enzymatic products, supporting their biochemical functions in vivo. In particular, we discovered that none of the XsTPS2 product, guaia-4,6-diene, can be detected in one of the X. strumarium cultivars used in this study (it was named the Hubei-cultivar), in which a natural deletion of two A bases in the XsTPS2 cDNA disrupts its activity, which further confirmed the proposed biochemical role of XsTPS2 in X. strumarium in vivo.

Jasmonic acid is a crucial signal transducer in heat shock induced sesquiterpene formation in Aquilaria sinensis

Agarwood, a highly valuable resinous and fragrant heartwood of Aquilaria plants, is widely used in traditional medicines, incense and perfume. Only when Aquilaria trees are wounded by external stimuli do they form agarwood sesquiterpene defensive compounds. Therefore, understanding the signaling pathway of wound-induced agarwood formation is important. Jasmonic acid (JA) is a well-characterized molecule that mediates a plant's defense response and secondary metabolism. However, little is known about the function of endogenous JA in agarwood sesquiterpene biosynthesis. Here, we report that heat shock can up-regulate the expression of genes in JA signaling pathway, induce JA production and the accumulation of agarwood sesquiterpene in A. sinensis cell suspension cultures. A specific inhibitor of JA, nordihydroguaiaretic acid (NDGA), could block the JA signaling pathway and reduce the accumulation of sesquiterpene compounds. Additionally, compared to SA and H2O2, exogenously supplied methyl jasmonate has the strongest stimulation effect on the production of sesquiterpene compounds. These results clearly demonstrate the central induction role of JA in heat-shock-induced sesquiterpene production in A. sinensis.

Cytochrome P450 CYP71BE5 in grapevine (Vitis vinifera) catalyzes the formation of the spicy aroma compound (-)-rotundone

(-)-Rotundone is a potent odorant molecule with a characteristic spicy aroma existing in various plants including grapevines (Vitis vinifera). It is considered to be a significant compound in wines and grapes because of its low sensory threshold and aroma properties. (-)-Rotundone was first identified in red wine made from the grape cultivar Syrah and here we report the identification of VvSTO2 as a α-guaiene 2-oxidase which can transform α-guaiene to (-)-rotundone in the grape cultivar Syrah. It is a cytochrome P450 (CYP) enzyme belonging to the CYP 71BE subfamily, which overlaps with the very large CYP71D family and, to the best of our knowledge, this is the first functional characterization of an enzyme from this family. VvSTO2 was expressed at a higher level in the Syrah grape exocarp (skin) in accord with the localization of (-)-rotundone accumulation in grape berries. α-Guaiene was also detected in the Syrah grape exocarp at an extremely high concentration. These findings suggest that (-)-rotundone accumulation is regulated by the VvSTO2 expression along with the availability of α-guaiene as a precursor. VvSTO2 expression during grape maturation was considerably higher in Syrah grape exocarp compared to Merlot grape exocarp, consistent with the patterns of α-guaiene and (-)-rotundone accumulation. On the basis of these findings, we propose that VvSTO2 may be a key enzyme in the biosynthesis of (-)-rotundone in grapevines by acting as a α-guaiene 2-oxidase.

Hydrogen peroxide promotes programmed cell death and salicylic acid accumulation during the induced production of sesquiterpenes in cultured cell suspensions of Aquilaria sinensis

Aquilaria sinensis (Lour.) Gilg produces a highly valuable agarwood characterised by a diverse array of sesquiterpenes and chromone derivatives that can protect wounded trees against potential herbivores and pathogens. A defensive reaction on the part of the plant has been proposed as the key reason for agarwood formation, but the issue of whether programmed cell death (PCD), an important process of plant immune responding, is involved in agarwood formation, still needs to be clarified. In this study, treatment of cultured cell suspensions with hydrogen peroxide (H2O2) induced the production of sesquiterpenes due to endogenous accumulation of salicylic acid (SA) and elevations in the expression of sesquiterpene biosynthetic genes. Moreover, PCD was stimulated by H2O2 in cultured cell suspensions of A. sinensis due to the induction of caspase activity, upregulated expression of metacaspases and cytochrome c, and SA accumulation. Our findings demonstrate for the first time that H2O2 stimulates PCD, SA accumulation and sesquiterpene production in cultured cell suspensions of A. sinensis. Furthermore, results from this study provide a valuable insight into investigations of the potential interactions between sesquiterpene synthesis and PCD during agarwood formation.

Identification of genes related to agarwood formation: transcriptome analysis of healthy and wounded tissues of Aquilaria sinensis

BACKGROUND

Agarwood is an expensive resinous heartwood derived from Aquilaria plants that is widely used in traditional medicines, incense and perfume. Only wounded trees can produce agarwood, and the huge demand for the agarwood products has led all Aquilaria spp. being endangered and listed in the Appendix II of the CITES (http://www.cites.org). The major components of agarwood are sesquiterpenes and phenylethyl chromones. Owing to a lack of genomic information, the molecular basis of wound-induced sesquiterpenes biosynthesis and agarwood formation remains unknown.

RESULTS

To identify the primary genes that maybe related to agarwood formation, we sequenced 2 cDNA libraries generated from healthy and wounded A. sinensis (Lour.) Gilg. A total of 89,137 unigenes with an average length of 678.65 bp were obtained, and they were annotated in detail at bioinformatics levels. Of those associated with agarwood formation, 30 putatively encoded enzymes in the sesquiterpene biosynthesis pathway, and a handful of transcription factors and protein kinases were related to wound signal transduction. Three full-length cDNAs of sesquiterpene synthases (ASS1-3) were cloned and expressed in Escherichia coli, and enzyme assays revealed that they are active enzymes, with the major products being δ-guaiene. A methyl jasmonate (MJ) induction experiment revealed that the expression of ASS was significantly induced by MJ, and the production of sesquiterpenes was elevated accordingly. The expression of some transcription factors and protein kinases, especially MYB4, WRKY4, MPKK2 and MAPK2, was also induced by MJ and coordinated with ASS expression, suggesting they maybe positive regulators of ASS.

CONCLUSIONS

This study provides extensive transcriptome information for Aquilaria spp. and valuable clues for elucidating the mechanism of wound-induced agarwood sesquiterpenes biosynthesis and their regulation.

Selection and validation of reference genes for studying stress-related agarwood formation of Aquilaria sinensis

Agarwood is a high-valued woody material for medicine, perfume, and incense production in Asia, Middle East, and Europe. The wild resources of agarwood-producing tree species, e.g., Aquilaria sinensis have been greatly threatened. The formation of agarwood is considered to be associated with the plant stress and defensive responses, thus it would be urgent and significant to investigate the molecular mechanism of these species responding to a variety of stresses. This is the first report regarding the reference gene selection of Aquilaria species for studying the molecular mechanism of stress-related agarwood production. Candidate reference genes were selected according to previous reports and the sequences were obtained from the 454 EST library of A. sinensis. To obtain the robust genes, we applied three independent programs depending on distinct assumptions and combined these results by a rank aggregation algorithm. The result supports tubulin, ribosomal protein, and glyceraldehyde-3-phosphate dehydrogenase to be the most stable reference genes for quantification of target gene expression in the overall samples examined. Validation of these genes through normalizing the expression of a terpene synthase demonstrated that these three genes are reliable. The selective usage of three algorithms based on their characteristics was underlined. However, more robust genes could be identified if the results of all algorithms were combined by a proper method such as the rank aggregation algorithm.

KEY MESSAGE

Reference genes which are critical in gene expression studies are recommended for future molecular studies of stress response and agarwood production in the endangered Aquilaria and other tree species.

Comparison of compositions and antimicrobial activities of essential oils from chemically stimulated agarwood, wild agarwood and healthy Aquilaria sinensis (Lour.) gilg trees

The composition and antimicrobial activity of the essential oils which were obtained from agarwood originated from Aquilaria sinensis (Lour.) Gilg stimulated by the chemical method (S1) were characterized, taking wild agarwood (S2) and healthy trees (S3) respectively as the positive and negative controls. The chemical composition of S1 was investigated by gas chromatography-mass spectrometry (GC-MS). The essential oil of S1 showed a similar composition to that of S2, being rich in sesquiterpenes and aromatic constituents. However, the essential oil of S3 was abundant in fatty acids and alkanes. Essential oils of S1 and S2 had better inhibition activities towards Bacillus subtilis and Staphyloccus aureus, compared with essential oil of S3. Escherichia coli was not sensitive to any of them.

A Novel Sesquiterpene Alcohol from Fimetariella Rabenhorstii, an Endophytic Fungus of Aquilaria sinensis

A novel sesquiterpene alcohol, named frabenol (1), was isolated from liquid cultures of Fimetariella rabenhorstii A20, an endophytic fungus of the agarwood-forming plant Aquilaria sinensis (Lour.) Gilg. The structure of the new compound was elucidated on the basis of spectroscopic methods. The finding of a sesquiterpenoid compound in F. rabenhorstii A20 implied that endophytic fungi of agarwood-producing plants could also contribute to the generation of fragrant chemicals during the agarwood formation processes.

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.

[Research and educational activities through perspective of pharmacognosy]

The research field of pharmacognosy covers a wide variety of subjects based on a knowledge of natural medicines and extends its influence in all surrounding directions. Pharmacognosy itself is generally regarded as one of the branches of pharmaceutical science although the processes to achieve the objectives are not always analytical as are other branches in this field. The extraordinarily long history and broad view provide researchers opportunities to conduct unique projects which can enhance the perspective of the subject in the future. Fieldwork is one feature of scientific research and is viewed as more valuable to projects in pharmacognosy than to those in other fields of pharmaceutical sciences. The frame of my research has been formed around fieldwork; projects targeted are achieved based on information and samples gathered through this means, and further studies are suggested by the ideas obtained. Some of the results and experiences gathered in these projects are described in this article for discussion of the future image of the pharmacognosial field.