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 (alpha-guaiene, alpha-humulene, and delta-guaiene) could be induced by methyl jasmonate (MJ), and showed that cloned delta-guaiene synthase from MJ-treated cells is involved in the synthesis of these three compounds, although only very small amounts of alpha-humulene are produced. In the present study, cDNAs encoding alpha-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 delta-guaiene synthases. The recombinant enzymes catalyzed the formation of alpha-humulene as a major product. Expression of transcripts of the alpha-humulene synthase and delta-guaiene synthase genes in cultured cells increased after treatment with MJ. These results revealed that these alpha-humulene and delta-guaiene synthases are involved in the synthesis of three sesquiterpenes induced by MJ treatment.