Characterization of two monoterpene synthases involved in floral scent formation in Hedychium coronarium

Hedychium coronarium, a perennial herb belonging to the family Zingiberaceae, is cultivated as a garden plant or cut flower as well as for medicine and aromatic oil. Its flowers emit a fresh and inviting scent, which is mainly because of monoterpenes present in the profile of the floral volatiles. However, fragrance produced as a result of monoterpenes has not been well studied. In the present study, two novel terpene synthase (TPS) genes (HcTPS7 and HcTPS8) were isolated to study the biosynthesis of monoterpenes in H. coronarium. In vitro characterization showed that the recombinant HcTPS7 was capable of generating sabinene as its main product, in addition to nine sub-products from geranyl diphosphate (GPP). Recombinant HcTPS8 almost specifically catalyzed the formation of linalool from GPP, while it converted farnesyl diphosphate (FPP) to α-bergamotene, cis-α-bisabolene, β-farnesene and other ten sesquiterpenes. Subcellular localization experiments revealed that HcTPS7 and HcTPS8 were located in plastids. Real-time PCR analyses showed that HcTPS7 and HcTPS8 genes were highly expressed in petals and sepals, but were almost undetectable in vegetative organs. The changes of their expression levels in petals were positively correlated with the emission patterns of sabinene and linalool, respectively, during flower development. The results indicated that HcTPS7 and HcTPS8 were involved in the biosynthesis of sabinene and linalool in H. coronarium flowers. Results on these two TPSs first characterized from H. coronarium provide new insights into molecular mechanisms of terpene biosynthesis in this species and also lay the basis for biotechnological modification of floral scent profile in Hedychium.