Volatile Ester Formation in Roses Identification of an Acetyl_Coenzyme A. Geraniol Citronellol Acety

Volatile Ester Formation in Roses Identification of an Acetyl_Coenzyme A. Geraniol Citronellol Acety

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Volatile Ester Formation in Roses. Identification of an Acetyl-Coenzyme A. Geraniol/Citronellol Acetyltransferase in Developing Rose Petals 1 Moshe Shalit, Inna Guterman, Hanne Volpin, Einat Bar, Tal Tamari, Naama Menda, Zach Adam, Dani Zamir, Alexander Vainstein, David Weiss, Eran Pichersky, and Efraim Lewinsohn* Department of Vegetable Crops, Newe Ya’ar Research Center, Agricultural Research Organization, P.O. Box 1021, Ramat Yishay 30095, Israel (M.S., E.B., T.T., E.L.); The Institute of Plant Sciences and Genetics in Agriculture, Faculty of Agricultural, Food, and Environmental Quality Sciences, The Hebrew University of Jerusalem, P.O. Box 12, Rehovot 76100, Israel (M.S., I.G., N.M., Z.A., D.Z., A.V., D.W.); Department of Molecular, Cellular, and Developmental Biology, University of Michigan, 830 North University Street, Ann Arbor, Michigan 48109–1048 (E.P.); and Bioinformatics, Department of Genomics, Agricultural Research Organization, Volcani Center, Bet Dagan 50250, Israel (H.V.) The aroma of roses ( Rosa hybrida ) is due to more than 400 volatile compounds including terpenes, esters, and phenolic derivatives. 2-Phenylethyl acetate, cis -3-hexenyl acetate, geranyl acetate, and citronellyl acetate were identified as the main volatile esters emitted by the flowers of the scented rose var. “Fragrant Cloud.” Cell-free extracts of petals acetylated several alcohols, utilizing acetyl-coenzyme A, to produce the corresponding acetate esters. Screening for genes similar to known plant alcohol acetyltransferases in a rose expressed sequence tag database yielded a cDNA ( RhAAT1 ) encoding a protein with high similarity to several members of the BAHD family of acyltransferases. This cDNA was functionally expressed in Escherichia coli , and its gene product displayed acetyl-coenzyme A:geraniol acetyltransferase enzymatic activity in vitro. The RhAAT1 protein accepted other alcohols such as citronellol and 1-octanol as substrates, but 2-phenylethyl alcohol and cis -3-hexen-1-ol were poor substrates, suggesting that additional acetyltransferases are present in rose petals. The RhAAT1 protein is a polypeptide of 458 amino acids, with a calculated molecular mass of 51.8 kD, pI of 5.45, and is active as a monomer. The RhAAT 1 gene was expressed exclusively in floral tissue with maximum transcript levels occurring at stage 4 of flower development, where scent emission is at its peak. Roses ( Rosa hybrida ) are grown as garden plants, for the cut-flower industry, and as a source of natural fragrances. Many modern cut-flower rose cultivars were selected for long vase life, flower shape, and color. Intensive breeding has also generated garden cultivars that have an intense “rose” scent. More than 400 different volatile compounds have been identi- fied in rose scent, and these compounds have been classified into several chemical groups including hy- drocarbons, alcohols, esters, aromatic ethers, and “others” (aldehydes such as geranial and nonanal, rose oxide, and norisoprenes such as b -ionone; Fla- ment et al., 1993; Weiss, 1997).
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Volatile Ester Formation in Roses Identification of an Acetyl_Coenzyme A. Geraniol Citronellol Acety

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