Submitted to: Plant Molecular Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/28/2008
Publication Date: 7/6/2008
Citation: Portnoy, V., Benyamini, Y., Giovannoni, J.J., Schaffer, A., Tadmor, Y., Lewinshon, E., Katzir, N. 2008. The Molecular and Biochemical Basis for Varietal Variation in Sesquiterpene Content in Melon (Cucumis melo L.) Rinds. Plant Molecular Biology. 66:647-661. Interpretive Summary: Melons (Cucumis melo L., Cucurbitaceae) comprise a broad array of wild and cultivated genotypes differing in many traits such as climactericity during fruit ripening, the patterns of sugar and acid accumulation, as well as in the content and composition of secondary metabolites associated with color, taste and aroma. The aroma of melons, as is the case with most fruits, consists of complex mixtures of volatile compounds. Different cultivars display different aromas, and this is reflected in their volatile compositions. Sesquiterpenes are fifteen-carbon compounds found in the majority of plant species and serve diverse roles in communication and defense. Sesquiterpenes are derived from farnesyl diphosphate by a group of enzymes termed sesquiterpene synthases, and encoded by members of the Tps gene family. Many sesquiterpene synthase genes have been described in plants. Here we describe the identification, characterization and molecular regulation of two novel members of the Tps family that are primarily expressed in ripe melon rind tissues: CmTpsNY and CmTpsDul. This work is another step towards the understanding of the factors that contribute to the formation of aroma compounds in melon fruits as part of a larger program aimed at the molecular and biochemical characterization of traits determining fruit quality and diversity.
Technical Abstract: A combined chemical, biochemical and molecular study was conducted to understand the differential accumulation of volatile sesquiterpenes in melon fruits. Sesquiterpenes were present mainly in the rinds of climacteric varieties, and a great diversity in their composition was found among varieties. Sesquiterpenes were generally absent in non-climacteric varieties. Two climacteric melon varieties, the green-fleshed 'Noy Yizre'el', and the orange-fleshed 'Dulce' were further examined. In 'Noy Yizre'el' the main sesquiterpenes accumulated are delta-cadinene, gamma-cadinene and alpha-copaene, while alpha-farnesene is the main sesquiterpene in 'Dulce'. Sesquiterpene synthase activities, mainly restricted to rinds of mature fruits, were shown to generate different sesquiterpenes in each variety according to the compositions found in rinds. EST melon database mining yielded two novel cDNAs coding for members of the Tps gene family termed CmTpsNY and CmTpsDul respectively, that are 43.2 % similar. Heterologous expression in E. coli of CmTpsNY produced mainly delta- copaene, alpha-copaene, beta-caryophyllene, germacrene D, alpha-muurolene, gamma-cadinene, delta- cadinene, and alpha-cadinene, while CmTpsDul produced alpha-farnesene only. Our results indicate that different sesquiterpene synthases encoded by different members of the Tps gene family are active in melon varieties and this specificity modulates the accumulation of sesquiterpenes.