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.

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.

Synthesis of the major glycosylated monoterpene linalool in peach is catalyzed by PpUGT85A2.

Flavonols are a subclass of flavonoids that exhibit a wide array of physiological functions in plants. Commonly found flavonols are synthesized from dihydroflavonols by flavonol synthase (FLS). The genome of Arabidopsis thaliana contains six FLS genes, among which, FLS1, encodes a functional enzyme. Previous work has demonstrated that R2R3-MYB subgroup 7 transcription factors MYB11, MYB12 and MYB111 redundantly regulate flavonol biosynthesis. However, flavonol accumulation in pollen grains was unaffected in the myb11myb12myb111 triple mutant. Here we show that MYB21 and its homologs MYB24 and MYB57, which belong to subgroup 19, promote flavonol biosynthesis through regulation of FLS1 gene expression. A combination of genetic and metabolite analysis is used to identify the role of MYB21 in flavonol biosynthesis regulation through direct binding to the GARE cis-element in the FLS1 promoter. Interestingly, treatment with kaempferol or over-expression of FLS1 rescue stamen defects in the myb21 mutant. We also observed that excess ROS accumulated in myb21 stamen, and that treatment with dipenyleneiodonium chloride (DPI, a ROS inhibitor) can partly rescue the reduced-fertility of a myb21 mutant. Furthermore, drought stress increased ROS abundance and impaired fertility in myb21, myb21myb24myb57 and chs, but not in wild type or myb11myb12myb111. This suggested that pollen-specific flavonol accumulation contributes to drought-induced male fertility by ROS scavenging in Arabidopsis. These are previously unreported insights into the biological function of flavonols in Arabidopsis.

Rapid proliferation and Warburg effect make cancer cells consume plenty of glucose, which induces a low glucose micro-environment within the tumor. Up to date, how cancer cells keep proliferating in the condition of glucose insufficiency still remains to be explored. Recent studies have revealed a close correlation between excessive fructose consumption and breast cancer genesis and progression, but there is no convincing evidence showing that fructose could directly promote breast cancer development. Herein, we found that fructose, not amino acids, could functionally replace glucose to support proliferation of breast cancer cells. Fructose endowed breast cancer cells with the colony formation ability and migratory capacity as effective as glucose. Interestingly, although fructose was readily used by breast cancer cells, it failed to restore proliferation of non-tumor cells in the absence of glucose. These results suggest that fructose could be relatively selectively employed by breast cancer cells. Indeed, we observed that a main transporter of fructose, GLUT5, was highly expressed in breast cancer cells and tumor tissues but not in their normal counterparts. Furthermore, we demonstrated that the fructose diet promoted metastasis of 4T1 cells in the mouse models. Taken together, our data show that fructose can be used by breast cancer cells specifically in glucose-deficiency, and suggest that the high-fructose diet could accelerate the progress of breast cancer in vivo.

Linalool is one of the common flavour-related volatiles across the plant kingdom and plays an essential role in determining consumer liking of plant foods. Although great process has been made in identifying terpene synthase (TPS) genes associated with linalool synthesis, much less is known about regulation of this pathway. We initiated study by identifying PpTPS3 encoding protein catalysing enantiomer (S)-(+)-linalool synthesis, which is a major linalool component (~70%) observed in ripe peach fruit. Overexpression of PpTPS3 led to linalool accumulation, while virus-induced gene silencing of PpTPS3 led to a 66.5% reduction in linalool content in peach fruit. We next identified transcription factor (TF) PpbHLH1 directly binds to E-box (CACATG) in the PpTPS3 promoter and activates its expression based on yeast one-hybrid assay and EMSA analysis. Significantly positive correlation was also observed between PpbHLH1 expression and linalool production across peach cultivars. Peach fruit accumulated more linalool after overexpressing PpbHLH1 in peach fruit and reduced approximately 54.4% linalool production after silencing this TF. DNA methylation analysis showed increased PpTPS3 expression was associated with decreased 5 mC level in its promoter during peach fruit ripening, but no reverse pattern was observed for PpbHLH1. Arabidopsis and tomato fruits transgenic for peach PpbHLH1 synthesize and accumulate higher levels of linalool compared with wild-type controls. Taken together, these results would greatly facilitate efforts to enhance linalool production and thus improve flavour of fruits.

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First purchases of fruit are mainly dependent on aspects of appearance such as color. However, repeat buys of fruit are determined by internal quality traits such as flavor-related volatiles. Differences in volatile profiles in white- and red-fleshed peach fruit are not well understood. In the present study, peach cultivars with white- and red-fleshed fruit were subjected to sensory analysis using electronic nose (e-nose) to evaluate overview volatile profiles. Approximately 97.3% of the total variation in peach color-volatiles was explained by the first principle component 1 (PC1) and PC2. After analyzing sensory differences between peach fruit samples, 50 volatile compounds were characterized based on GC-MS. Multivariate analysis such as partial least squares discriminant analysis (PLS-DA) was applied to identify volatile compounds that contribute to difference in white- and red-fleshed peach fruit cultivars. A total of 18 volatiles that could separate peach fruit cultivars with different colors in flesh during ripening were identified based on variable importance in projection (VIP) score. Fruity note latone γ-hexalactone had higher contents in red-fleshed cultivars, while grassy note C6 compounds such as hexanal, 2-hexenal, (E)-2-hexenal, 1-hexanol, and (Z)-2-hexen-1-ol showed great accumulation in white-fleshed peach fruit.