Molecular cloning and functional characterization of α-humulene synthase, a possible key enzyme of zerumbone biosynthesis in shampoo ginger (Zingiber zerumbet Smith)

Shampoo ginger (Zingiber zerumbet Smith) has a high content and large variety of terpenoids in the essential oil of its rhizome. Here, we report on the isolation of a cDNA clone (ZSS1) encoding α-humulene synthase, a possible key enzyme of zerumbone biosynthesis. This clone contains an open reading frame of 1,644 bp and is predicted to encode a protein of 548 amino acids with a calculated molecular mass of 64.5 kDa. The deduced amino acid sequence shows 34–63% identity with known sesquiterpene synthases of other angiosperm species. Based on exon-intron organization, ZSS1 is classified as the terpene synthase-III (TPS-III) subfamily. When expressed in Escherichia coli, the recombinant enzyme catalyzed the formation of a major product, α-humulene (95%) and a minor by-product, β-caryophyllene (5%). Introduction of ZSS1 and the foreign mevalonate pathway involved in FPP synthesis into E. coli results in in vivo production of α-humulene. Transcript of ZSS1 was detected almost exclusively in rhizomes and was up-regulated in both leaves and rhizomes after treatment with methyl jasmonate (MeJA), suggesting its ecological function in shampoo ginger.