A cDNA coding for a putative terpene synthase (Grtps) was isolated from `Rio Red' grapefruit (Citrus paradisi Macf.) mature fruit by differential display RT-PCR and the corresponding full-length cDNA and genomic clone were subsequently obtained. The isolated cDNA clone was 1644 bp in length encoding a protein of 548 amino acids with a predicted molecular mass of 64 kDa and of pI 5.38. The genomic clone was 3203 bp in length with 6 introns and 7 exons. This Grtps appears to be a sesquiterpene synthase based on molecular weight, genomic organization, and similarity with the other terpene synthases. Both RT-PCR and Northern blot expression analysis indicated that Grtps is not expressed in immature fruits, roots, or leaves, but only in mature fruits. Southern blot analysis of genomic DNA demonstrated that Grtps is one of the members in the family of terpene synthases.
Ying Jia, Dianren Xia, and E.S. Louzada
H.P.V. Rupasinghe, G. Paliyath, and D.P. Murr
α-Farnesene is an acyclic sesquiterpene hydrocarbon that is a constituent of the volatile components and the surface wax of apples (Malus ×domestica Borkh.). Although oxidation products of α-farnesene have been implicated in the development of superficial scald in apples, the relation between α-farnesene biosynthesis and scald development is not well understood. In vivo labeling studies using isolated tissue segments showed that α-farnesene is derived from trans,trans-[1,2-14Cor 1-3H]-farnesyl pyrophosphate (FPP) mostly in the skin rather than cortex tissue. Among other labeled products, farnesol was >100-fold higher compared to α-farnesene. However, HPLC analysis of hexane-extractable components from apple skin revealed farnesol is not a predominant natural constituent of apple skin tissue. In addition, trans,trans-[1-3H]-farnesol was not converted to α-farnesene by apple skin tissue. Our results indicate that biosynthesis of α-farnesene in apple tissue occurs through the isoprenoid pathway, and the conversion of FPP to α-farnesene is catalyzed by a single sesquiterpene synthase enzyme, trans,trans-α-farnesene synthase, rather than via farnesol as an intermediate. A comparison of α-farnesene biosynthesis between scald-developing and scald-free regions of the same apple showed that incorporation of radiolabel into α-farnesene from trans,trans-[1-3H]-FPP was nearly 3-fold lower in scald-developing skin tissue than in scald-free skin tissue.
H.P.V. Rupasinghe, G. Paliyath, and D.P. Murr
α-Farnesene is an acyclic sesquiterpene hydrocarbon that is a constituent of the surface wax of apples (Malus domestica Borkh.). Although, oxidation products of α-farnesene have been implicated in the development of the physiological disorder superficial scald in apple, the mechanism of α-farnesene biosynthesis has not been studied in detail. We are currently investigating α-farnesene biosynthesis in relation to superficial scald development in apples. Radiolabelled feeding experiments using isolated tissue segments indicated that α-farnesene is derived from trans,trans-farnesyl pyrophosphate (FPP), mainly in the skin rather than cortex. Among the other labeled products detected, farnesol level was over a hundred-fold higher compared to α-farnesene. However, [1-3H] trans,trans-Farnesol was not incorporated into α-farnesene. Feeding radiolabelled FPP to skin tissue segments of scald-developing and normal apples showed differential incorporation of radiolabel into various products. Though the incorporation into α-farnesene was nearly the same, there was higher levels of incorporation into farnesyl esters in normal apples. As well, the levels of radiolabelled in the farnesol fraction was three times higher in scald-developing regions. These results indicate that there are potential difference in the biosynthesis and metabolism of farnesyl components between scald-developing and normal apples. In studies using cell-free extracts, farnesol formation was observed from labeled FPP and was two-fold higher in crude membrane extract compared to crude cytosol. Our results indicate that α-farnesene formation in apple fruit tissue is through FPP and is possibly catalyzed by a single sesquiterpene synthase enzyme. Purification and characterization of this enzyme are in progress.
Ying Kong, Ming Sun, Hui-tang Pan, and Qi-xiang Zhang
into the scent of carnations J. Essential Oil Res. 11 355 359 Degenhardt, J. Köllner, T.G. Gershenzon, J. 2009 Monoterpene and sesquiterpene synthases and the origin of terpene skeletal diversity in plants Phytochemistry 70 1621 1637 Dobson, H
Ying Kong, Jinrong Bai, Lixin Lang, Fang Bao, Xiaoying Dou, Huan Wang, and Hongzhong Shang
Genetic modification in floriculture Crit. Rev. Plant Sci. 26 169 197 De Jong, P.C. 1974 Some notes on the evolution of lilies Lily Yrbk. North Amer. Lily Soc. 27 23 28 Degenhardt, J. Köllner, T.G. Gershenzon, J. 2009 Monoterpene and sesquiterpene
Lynn Maher and Irwin L. Goldman
elucidated in Streptomyces coelicolor , is an Mg 2+ dependent cyclization reaction ( Jiang et al., 2006 ). Geosmin synthase, a unique bifunctional sesquiterpene synthase, first converts farnesyl diphosphate into an 85:15 mix of germacradianol and germacrene