| Summary: | 碩士 === 國立成功大學 === 生命科學系 === 105 === Plant secondary metabolites are the major nature products, the emitted volatile compounds as a means of attracting pollinators or defense function, including terpenoids, phenylpropenoids, benzeniods, and fatty acid derivatives. Phalaenopsis bellina is a scent orchid with the main floral compounds of monoterpenes for linalool, geraniol and their derivatives. The enzymes catalyzing the formation of terpenes from geranyl diphosphate (GDP) are terpene synthase (TPS). Based on the sequences, TPSs can be divided into eight subfamilies, TPS-a, -b, -c, -d, -e/f, -g, and -h. To analyze the evolution of TPS genes in Orchidaceae, 10, 14, 35 and 19 TPS genes were first identified from the whole genome sequences of Apostasia shenzhenica, Vanilla fragrans, Dendrobium catenatum and Phalaenopsis equestris, respectively distributing among three subfamilies of Orchidaceae. Phylogenetic relationship of these genes was analyzed, and functional gene clusters were built to assess whether duplication events have occurred with tandem or non-tandem duplication. To functionally characterize the floral scent related monoterpene synthase (MTPS) genes in P. bellina, PbTPS5 and PbTPS10 classified in TPS-b subfamily were cloned. Transient overexpression of these genes in both Nicotiana tabacum and P. I-Hsin Venus was performed. The volatiles emitted from the transient overexpressing plants were collected and analyzed by using GC-MS. Tetrahydromyrcenol was the major product from overexpression of both PbTPS5 and PbTPS10 in N. tabacum. In contrast, linalool production was highly increased for the overexpression of PbTPS10 in P. I-Hsin Venus, about four-fold higher than the overexpression of PbTPS5. However, in vitro enzyme assay of PbTPS5 showed the production of geraniol after fed with geranyl diphosphate (GDP). Taken together, the knowledge gained from this study will enhance our knowledge evolution of TPS gene in Orchidaceae as well as the monoterpene biosynthesis in P. bellina. In future, transgenic plants ecotopically expressing MTPS can be generated to modify the scentless orchids to scent one by introducing MTPS genes.
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