Citrus fruit flavor and aroma biosynthesis: isolation, functional characterization, and developmental regulation of Cstps1, a key gene in the production of the sesquiterpene aroma compound valencene.
ABSTRACT Citrus fruits possess unique aromas rarely found in other fruit species. While fruit flavor is composed of complex combinations of soluble and volatile compounds, several low-abundance sesquiterpenes, such as valencene, nootkatone, alpha-sinensal, and beta-sinensal, stand out in citrus as important flavor and aroma compounds. The profile of terpenoid volatiles in various citrus species and their importance as aroma compounds have been studied in detail, but much is still lacking in our understanding of the physiological, biochemical, and genetic regulation of their production. Here, we report on the isolation, functional expression, and developmental regulation of Cstps1, a sesquiterpene synthase-encoding gene, involved in citrus aroma formation. The recombinant enzyme encoded by Cstps1 was shown to convert farnesyl diphosphate to a single sesquiterpene product identified as valencene by gas chromatography-mass spectrometry (GC-MS). Phylogenetic analysis of plant terpene synthase genes localized Cstps1 to the group of angiosperm sesquiterpene synthases. Within this group, Cstps1 belongs to a subgroup of citrus sesquiterpene synthases. Cstps1 was found to be developmentally regulated: transcript was found to accumulate only towards fruit maturation, corresponding well with the timing of valencene accumulation in fruit. Although citrus fruits are non-climacteric, valencene accumulation and Cstps1 expression were found to be responsive to ethylene, providing further evidence for the role of ethylene in the final stages of citrus fruit ripening. Isolation of the gene encoding valencene synthase provides a tool for an in-depth study of the regulation of aroma compound biosynthesis in citrus and for metabolic engineering for fruit flavor characteristics.
Article: Influence of processing steps and fruit maturity on volatile concentrations in juices from clementine, mandarin, and their hybrids[show abstract] [hide abstract]
ABSTRACT: During growth, ripening, and post-harvest, the quality of fruits can be modified by various stresses. Ample maturation allows prolonged storage and increases the quality of citrus fruits. The eight major volatile compounds in fresh juices from mandarin (Citrus reticulata Blanco var. Willow Leaf), clementine (Citrus reticulata×Citrus sinensis var. Commune), and their six cross-pollinated hybrids were quantified by gas chromatography. Mandarin juice contained the highest volatile concentration (2177.6±110.6mgL−1), whereas the total aromatic compounds of the hybrid and clementine juices were lower (1060.6±81.6–1724.2±138.5mgL−1 and 864.8±67.8mgL−1, respectively). Limonene was the major compound (667.3±53.7–1259.9±98.4mgL−1) in all juices. We observed significant differences according to the process of juice extraction used (with and without peel). The relative volatile concentration was higher when the juice was extracted with peel, and the juicing process induced differences in the relative volatile concentrations of between 20 and 40%. The levels of volatile compounds in the juice changed according to the degree of fruit maturity. The concentrations of the eight major juice components increased during ripening and until the commercial maturity stage when the juice was obtained from peeled fruits, whereas their concentrations increased until the post-maturation stage when the juices were produced from whole fruits. These two factors determined the contributions of these compounds to the characteristic aromas of Citrus juices. Keywords Citrus juices-Hybrids-Aroma-Juice processing-Fruit maturity-HS-SPMEEuropean Food Research and Technology 04/2012; 231(3):379-386. · 1.57 Impact Factor
Article: Plant volatile terpenoid metabolism: biosynthetic genes, transcriptional regulation and subcellular compartmentation.[show abstract] [hide abstract]
ABSTRACT: Volatile terpenoids released from different plant parts play crucial roles in pollinator attraction, plant defense, and interaction with the surrounding environment. Two distinct pathways localized in different subcellular compartments are responsible for the biosynthesis of these compounds. Recent advances in the characterization of genes and enzymes responsible for substrate and end product biosynthesis as well as efforts in metabolic engineering have revealed new aspects of volatile terpenoid biosynthesis. This review summarizes recent progress in the characterization of volatile terpenoid biosynthetic genes, their spatio-temporal expression patterns and subcellular localization of corresponding proteins. In addition, recent information obtained from metabolic engineering is discussed.FEBS letters 07/2010; 584(14):2965-73. · 3.54 Impact Factor