UV-B irradiation differentially regulates terpene synthases and terpene content of peach.

Plants generate protective molecules in response to ultraviolet (UV) light. In laboratory experiments, 48 h UV-B irradiation of peach fruits and leaves reduced the flavour-related monoterpene linalool by 60%. No isoprene was detected, but other terpenoids increased significantly, including a threefold accumulation of the sesquiterpene (E,E)-α-farnesene, which was also increased by jasmonic acid treatment. RNA sequencing revealed altered transcript levels for two terpene synthases (TPSs): PpTPS1, a TPS-g subfamily member, decreased by 86% and PpTPS2, a TPS-b subfamily member, increased 80-fold. Heterologous expression in Escherichia coli and transient overexpression in tobacco and peach fruits showed PpTPS1 was localized in plastids and associated with production of linalool, while PpTPS2 was responsible for (E,E)-α-farnesene biosynthesis in the cytoplasm. Candidate regulatory genes for these responses were identified. Commercial peach production in Asia involves fruit bagging to maintain marketable yield and quality. TPS gene expression and volatile terpenoid production in field experiments, using bags transmitting high UV-B radiation, showed similar effects on peach volatiles to those from laboratory experiments. Bags transmitting less UV-B light ameliorated the reduction in the flavour volatile linalool, indicating that flavour components of peach fruits can be modulated by selecting an appropriate source of environmental screening material.

Glycosidically bound volatiles as affected by ripening stages of Satsuma mandarin fruit.

Composition and changes in free volatiles have been extensively studied in citrus fruit such as mandarin. However, components of glycosidically bound volatiles and changes during fruit ripening have been rarely investigated. A total of 56 glycosidically-bound volatiles were identified in fruit peel at four ripening stages. The highest concentrations in glycosidically-bound volatiles were observed for methyl salicylate in ripening fruit. Concentration of total bound volatiles increased from color conversion stage at 150days after bloom (DAB), peaked at yellow stage (190DAB), followed by a decrease at orange stage (210DAB). Satsuma mandarin fruit at different ripening stages could be separated in a partial least squares-discriminant analysis (PLS-DA) plot using glycosidically bound volatiles as variables. In total 35 glycosidically bound volatiles were identified with variable importance in projection (VIP) score exceeding 1, which may be potential markers for separating fruit at different ripening stages.

Effects of postharvest methyl jasmonate treatment on main health-promoting components and volatile organic compounds in cherry tomato fruits.

Effects of postharvest methyl jasmonate (MeJA) treatment on the contents of ascorbic acid and carotenoids, as well as the compositions and contents of volatile organic compounds (VOCs) in cherry tomato fruits were investigated during 11 days of storage at room temperature (25 °C). The results showed that MeJA treatment significantly increased the contents of ascorbic acid and carotenoids, especially lycopene in postharvest cherry tomato fruits. Moreover, MeJA treatment improved the contents of carotenoids derived VOCs such as 6-methyl-5-hepten-2-one (MHO), while had no effect on firmness, sugars and titratable acidity. All above results suggested that the exogenous MeJA application is potential in enhancement of main health-promoting components and VOCs in postharvest cherry tomato fruits.

Genome-Wide Identification, Expression Patterns, and Functional Analysis of UDP Glycosyltransferase Family in Peach (Prunus persica L. Batsch).

Peach (Prunus persica L. Batsch) is a commercial grown fruit trees, important because of its essential nutrients and flavor promoting secondary metabolites. The glycosylation processes mediated by UDP-glycosyltransferases (UGTs) play an important role in regulating secondary metabolites availability. Identification and characterization of peach UGTs is therefore a research priority. A total of 168 peach UGT genes that distributed unevenly across chromosomes were identified based on their conserved PSPG motifs. Phylogenetic analysis of these genes with plant UGTs clustered them into 16 groups (A-P). Comparison of the patterns of intron-extron and their positions within genes revealed one highly conserved intron insertion event in peach UGTs. Tissue specificity, temporal expression patterns in peach fruit during development and ripening, and in response to abiotic stress UV-B irradiation was investigated using RNA-seq strategy. The relationship between UGTs transcript levels and concentrations of glycosylated volatiles was examined to select candidates for functional analysis. Heterologous expressing these candidate genes in Escherichia coli identified UGTs that were involved in the in vitro volatile glycosylation. Our results provide an important source for the identification of functional UGT genes to potential manipulate secondary biosynthesis in peach.