Concise Biosynthesis of Tropone-Containing Spiromaterpenes by a Sesquiterpene Cyclase and a Multifunctional P450 from a Deep-Sea-Derived Spiromastix sp. Fungus

Spiromaterpenes are a group of rare tropone-containing sesquiterpenes with antineuroinflammatory activity. Herein, we elucidate their biosynthetic pathway in a deep-sea-derived Spiromastix sp. fungus by heterologous expression, biochemical characterization, and incubation experiments. The sesquiterpene cyclase SptA was first characterized to catalyze the production of guaia-1(5),6-diene, and a multifunctional cytochrome P450 catalyzed the tropone ring formation. These results provide important clues for the rational mining of bioactive guaiane-type sesquiterpenes and expand the repertoire of P450 activities to synthesize unique building blocks of natural products.

Taxonomic Insights and Its Type Cyclization Correlation of Volatile Sesquiterpenes in Vitex Species and Potential Source Insecticidal Compounds: A Review

Sesquiterpenes (SS) are secondary metabolites formed by the bonding of 3 isoprene (C5) units. They play an important role in the defense and signaling of plants to adapt to the environment, face stress, and communicate with the outside world, and their evolutionary history is closely related to their physiological functions. This review considers their presence and extensively summarizes the 156 sesquiterpenes identified in Vitextaxa, emphasizing those with higher concentrations and frequency among species and correlating with the insecticidal activities and defensive responses reported in the literature. In addition, we classify the SS based on their chemical structures and addresses cyclization in biosynthetic origin. Most relevant sesquiterpenes of the Vitex genus are derived from the germacredienyl cation mainly via bicyclogermacrene and germacrene C, giving rise to aromadrendanes, a skeleton with the highest number of representative compounds in this genus, and 6,9-guaiadiene, respectively, indicating the production of 1.10-cyclizing sesquiterpene synthases. These enzymes can play an important role in the chemosystematics of the genus from their corresponding routes and cyclizations, constituting a new approach to chemotaxonomy. In conclusion, this review is a compilation of detailed information on the profile of sesquiterpene in the Vitex genus and, thus, points to new unexplored horizons for future research.

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.

High Level Production of δ-Guaiene, a Bicyclic Sesquiterpene Accumulated in Agarwood, by Co-expression of δ-Guaiene Synthase and Farnesyl Diphosphate Synthase Genes in Tobacco BY-2 Cells

Two genes encoding δ-guaiene synthase ( GS) and farnesyl diphosphate synthase ( FPS) involved in δ-guaiene biosynthesis in Aquilaria microcarpa were co-expressed in tobacco ( Nicotiana tabacum) BY-2 cells by Agrobacterium -mediated transformation. GC-MS analysis revealed that the transformed tobacco cells liberated δ-guaiene, and the compound was found in the headspace of the culture but not accumulated either in the medium or in the cells. Tobacco cells transformed by solely GS produced 0.2 mg δ-guaiene /L culture, however, concentration of the compound elevated to 0.6 – 5.9 mg/L when GS and FPS were co-expressed in the cells. The stirring efficiency of the cell suspension was improved by the reduction of the culture volume in the vials, and this resulted in an appreciable increase in δ-guaiene content to the level of 102 mg/L culture. Addition of mevalonolactone as the precursor markedly activated δ-guaiene production, and content of the compound elevated to more than 400 mg/L culture. These results strongly suggested that tobacco BY-2 is a suitable host to construct the bio-production system of sesquiterpene compounds, and co-expression of FPS and appropriate sesquiterpene synthase genes in the cells should be the good strategy to establish the highly productive platform of this class of compounds.

Enhanced Production of δ-Guaiene, a Bicyclic Sesquiterpene Accumulated in Agarwood, by Coexpression of δ-Guaiene Synthase and Farnesyl Diphosphate Synthase Genes in Escherichia coli

Two genes involved in δ-guaiene biosynthesis in Aquilaria microcarpa, δ-guaiene synthase (GS) and farnesyl diphosphate synthase (FPS), were overexpressed in Escherichia coli cells. Immunoblot analysis revealed that the concentration of GS-translated protein was rather low in the cells transformed by solely GS while appreciable accumulation of the recombinant protein was observed when GS was coexpressed with FPS GS-transformed cells liberated only a trace amount of δ-guaiene (0.004 μg/mL culture), however, the concentration of the compound elevated to 0.08 μg/mL culture in the cells transformed by GS plus FPS δ-Guaiene biosynthesis was markedly activated when E. coli cells coexpressing GS and FPS were incubated in enriched Terrific broth, and the content of the compound increased to approximately 0.6 μg/mL culture. These results suggest that coexpression of FPS and GS in E. coli is required for efficient 6-guaiene production in the bacterial cells, and the sesquiterpene-producing activity of the transformant is appreciably enhanced in the nutrients-enriched medium.

The Biosynthetic Activities of Primary and Secondary Metabolites in Suspension Cultures of Aquilaria microcarpa

Two types of suspension-cultured Aquilaria microcarpa cells, friable and aggregated, were selectively generated. The biosynthetic activities of primary and secondary metabolites in target cells were detected using laser scanning microscopy (LSM) imaging with diphenylboric acid 2-amino ethyl ester (DPBA) and 9-diethylamino-5H-benzo[alpha]phenoxazine-5-one (Nile red) staining. Scanned friable cells produced weakly fluorescent images revealing low productivity of metabolites. On the other hand, scanning of aggregated cells produced clear fluorescent images depicting the accumulations of flavonoids and lipids. Furthermore, abundant deposition of an unknown resinous compound in extracellular portion of aggregated cells could be visualized. The resinous compound was white to whitish-gray in color and highly sedimented in the medium. Based on these observations, we focused our investigation of metabolite productivity on aggregated suspension cells. Some prominent extracellular compounds were detected in the used liquid medium, as well as in the resinous residue within the medium. The characteristics of these metabolites were investigated in detail via gas chromatography-mass spectrometry (GC-MS) analysis.