The molecular and biochemical basis for varietal variation in sesquiterpene content in melon (Cucumis melo L.) rinds.
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. CmTpsNY was mostly expressed in 'Noy Yizre'el' rind while CmTpsDul expression was specific to 'Dulce' rind. None of these genes was expressed in rinds of the non-climacteric 'Tam Dew' cultivar. 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. The genes are differentially transcriptionally regulated during fruit development and according to variety and are likely to be associated with chemical differences responsible for the unique aromas of melon varieties.
Portnoy
Vitaly
V
Institute of Plant Sciences, Newe Ya'ar Research Center, Agricultural Research Organization, P.O. Box 1021, Ramat Yishay 30095, Israel.
Benyamini
Yael
Y
Bar
Einat
E
Harel-Beja
Rotem
R
Gepstein
Shimon
S
Giovannoni
James J
JJ
Schaffer
Arthur A
AA
Burger
Joseph
J
Tadmor
Yaakov
Y
Lewinsohn
Efraim
E
Katzir
Nurit
N
D000595:Amino Acid Sequence; D015152:Blotting, Northern; D019755:Carbon-Carbon Lyases / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D028463:Cucumis melo / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D000081223:Polycyclic Sesquiterpenes; D016133:Polymerase Chain Reaction; D011994:Recombinant Proteins / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D012717:Sesquiterpenes / Q000737:chemistry / Q000378:metabolism*; D052617:Solid Phase Microextraction; D013045:Species Specificity
D010940:Plant Proteins; D000081223:Polycyclic Sesquiterpenes; D011994:Recombinant Proteins; D012717:Sesquiterpenes; C054278:gamma-cadinene; C062672:alpha-farnesene; D019755:Carbon-Carbon Lyases; C051130:trichodiene synthetase