Identification of novel sesquiterpene synthase genes that mediate the biosynthesis of valerianol, which was an unknown ingredient of tea.

Seven cDNA clones encoding terpene synthases (TPSs), their structures closely related to each other, were isolated from the flower of Camellia hiemalis ('Kantsubaki'). Their putative TPS proteins were phylogenetically positioned in a sole clade with the TPSs of other Camellia species. The obtained Tps genes, one of which was designated ChTps1 (ChTps1a), were introduced into mevalonate-pathway-engineered Escherichia coli, which carried the genes for utilizing acetoacetate as a substrate, and cultured in a medium including lithium acetoacetate. Volatile products generated in the E. coli cells transformed with ChTps1 were purified from the cell suspension culture, and analyzed by NMR. Consequently, the predominant product with ChTPS1 was identified as valerianol, indicating that the ChTps1 gene codes for valerianol synthase. This is the first report on a gene that can mediate the synthesis of valerianol. We next synthesized a Tps ortholog encoding ChTPS1variant R477H (named CsiTPS8), whose sequence had been isolated from a tea tree (Camellia sinensis), carried out similar culture experiment with the E. coli transformant including CsiTps8, and consequently found valerianol production equally. Furthermore, GC-MS analysis of several teas revealed that valerianol had been an unknown ingredient in green tea and black tea.

Identification of a novel hedycaryol synthase gene isolated from Camellia brevistyla flowers and floral scent of Camellia cultivars.

MAIN CONCLUSION: A novel terpene synthase (Tps) gene isolated from Camellia brevistyla was identified as hedycaryol synthase, which was shown to be expressed specifically in flowers. Camellia plants are very popular because they bloom in winter when other plants seldom flower. Many ornamental cultivars of Camellia have been bred mainly in Japan, although the fragrance of their flowers has not been studied extensively. We analyzed floral scents of several Camellia cultivars by gas chromatography-mass spectrometry (GC-MS) and found that Camellia brevistyla produced various sesquiterpenes in addition to monoterpenes, whereas Camellia japonica and its cross-lines produced only monoterpenes, including linalool as the main product. From a flower of C. brevistyla, we isolated one cDNA encoding a terpene synthase (TPS) comprised of 554 amino acids, which was phylogenetically positioned to a sole gene clade. The cDNA, designated CbTps1, was expressed in mevalonate-pathway-engineered Escherichia coli, which carried the Streptomyces mevalonate-pathway gene cluster in addition to the acetoacetate-CoA ligase gene. A terpene product was purified from recombinant E. coli cultured with lithium acetoacetate, and analyzed by (1)H-nulcear magnetic resonance spectroscopy ((1)H-NMR) and GC-MS. It was shown that a sesquiterpene hedycaryol was produced, because (1)H-NMR signals of the purified product were very broad, and elemol, a thermal rearrangement product from hedycaryol, was identified by GC-MS analysis. Spectroscopic data of elemol were also determined. These results indicated that the CbTps1 gene encodes hedycaryol synthase. Expression analysis of CbTps1 showed that it was expressed specifically in flowers, and hedycaryol is likely to be one of the terpenes that attract insects for pollination of C. brevistyla. A linalool synthase gene, which was isolated from a flower of Camellia saluenensis, is also described.