Volatile Ester Formation in Roses. Identification of an Acetyl-Coenzyme A. Geraniol/Citronellol Acetyltransferase in Developing Rose Petals

Abstract

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 RhAAT1 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 identified in rose scent, and these compounds have been classified into several chemical groups including hydrocarbons, alcohols, esters, aromatic ethers, and "others" (aldehydes such as geranial and nonanal, rose oxide, and norisoprenes such as ␤-ionone; Flament et al., 1993;Weiss, 1997).Volatile esters such as geranyl acetate and 2-phenylethyl acetate are important contributors to the aroma of roses and many other flowers (Knudsen and Tollsten, 1993). Volatile esters also contribute to the unique aroma of fruits such as banana (Musa acuminata), apple (Malus domestica), melon (Cucumis melo), strawberry (Fragaria ananassa), and spice plants such as lavender (Lavandula officinalis; Croteau and Karp, 1991;Ueda et al., 1992). Despite the knowledge of the contribution of volatile acetate esters to the aroma of roses, including the demonstration of the circadian emission of some major volatile acetate esters by flowers of the rose var. "Honesty" (Helsper et al., 1998), little is known about the mechanisms by which these compounds are formed in roses.Acetate esters in plants are normally generated as a result of the action of alcohol acetyltransferase (AAT) enzymes that transfer the acetyl moiety from acetylCoA to an alcoholic substrate ( Fig. 1; Harada et al., 1985;Fellman and Mattheis, 19...

Evaluation of Lavender Varietal Characteristics Using Three Content Ratios between Alcohol-based Fragrance Ingredients and Their Derivatives

“…This showed that the individual reaction of a fragrance ingredient has a specific varietal activity. Shalit et al (2003) reported that acetate esters are produced from alcohol-based compounds by acylation reactions catalyzed by alcohol acetyltransferase (AAT). When AAT obtained from rose petals was added to various types of alcohol-based compounds, all of the compounds showed acylation activity, although the activities differed with the various compounds used.…”

Rosa Damascena—Genetic Resources and Capacity Building for Molecular Breeding

“…In addition a large number of petal expressed cDNAs have been identified and stored in databases (14,23,27,28). Genes involved in scent production were identified: sesquiterpene synthase (23), alcohol acetyl transferase (50), O-methyltransferases (32,48,49). Transciption factors controlling the rose floral development have also been identified and cloned (36).…”

Physiological and Psychological Effects of Rose ‘Wishing’ Flowers and Their Hydrosols on the Human Autonomic Nervous System and Mood State

“…The volatile component compositions were different between fresh rose flowers and hydrosols (Table 1). Fresh flowers contained 3,5-dimethoxy toluene (13.0%, reported as a tea-like odor) (Cherri-Martin et al, 2007) and cis-3-hexenyl acetate (12.5%, reported as a fruity and green-leaves like odor) (Morales and Aparicio, 1999;Shalit et al, 2003) as major components. A high amount of 3,5-dimethoxy toluene has been confirmed in hybrid tea roses (Joichi et al, 2005).…”