Temporal changes in total flavonoid content (TFC), composition, free radical scavenging activity and metabolism-related gene expression of three Prunus humilis cultivars with distinctively different fruit colors were investigated in this study. The highest fruit TFCs of all three cultivars were observed at the initial sampling stage (young-fruit stage, YFS), which then declined gradually until fruit ripening. The dark-red-fruited cultivar ‘Jinou 1’ had the highest TFC, followed by the yellow-red-fruited cultivar ‘Nongda 3’ and the yellow-fruited cultivar ‘Nongda 5’. Thirteen flavonoid compounds were found in the three cultivars by using high-performance liquid chromatography (HPLC), and the content of most flavonoid compounds gradually decreased throughout the fruit-ripening process, with the exception of cyanidin-3-O-glucoside (C3G). C3G, as the main anthocyanin in P. humilis fruits, increased drastically during the fruit-coloring process of cultivars ‘Jinou 1’ and ‘Nongda 3’, while it was not detected in the developing fruits of cultivar ‘Nongda 5’. The antioxidant activity assay (DPPH, FRAP and ABTS) revealed that fruits of all three cultivars at YFS also had the highest antioxidant activities, and cultivar ‘Jinou 1’ had the highest antioxidant activities. Correlation analysis revealed that the antioxidant activities were significantly positively correlated with the TFCs and contents of the main compounds such as catechin, proanthocyanidin B1 and phloretin-2′,4-O-diglucoside (p < 0.01). Moreover, gene expression analysis showed that the flavonoid biosynthetic genes had different expression patterns in the three cultivars. The expression levels of ChCHS, ChCHI, ChF3H, ChDFR, ChLDOX and ChUFGT increased gradually with fruit ripening in cultivar ‘Jinou 1’, while all flavonoid-related genes in cultivar ‘Nongda 5’ decreased gradually during fruit development. The results from our study could significantly contribute to the deeper understanding of flavonoid accumulation mechanisms in P. humilis fruits and also help facilitate the targeted cultivar development and the utilization as a functional food of this fruit species.

The cuticular wax of ‘Hupingzao,’ an important economic crop in China, not only constitutes a key factor in determining the appearance quality and gloss of the fruit but also plays a vital role in regulating water evaporation and resisting biotic and abiotic stresses. In this study, ‘Hupingzao’ fruit produced during the white−ripe (WR) and full−red (FR) periods were used as study materials. The key genes and components of wax development were screened using a combination of transcriptomics and metabolomics. Enrichment analysis was performed on the differential genes and metabolites, and the fatty acid biosynthesis and elongation pathways were selected for further study. A series of key candidate genes in the de novo synthesis, elongation, and subsequent modification pathways of fatty acids were identified, such as acetyl−CoA carboxylase (ACCase), fabF (β−Ketoacyl−ACP Synthase II), and β−ketoacyl−CoA synthase (KCS). To further explore the mechanism of jujube wax biosynthesis, GC−MS (gas chromatography–mass spectrometry) was used to determine and analyze the content and composition of the wax after it was treated with gibberellin and paclobutrazol. The results showed that spraying the plants with GA₃ significantly upregulated the expression of genes involved in fatty acid de novo synthesis and elongation such as accC (Acetyl−CoA Carboxylase, Biotin Carboxylase Subunit), fabD (Malonyl−CoA:ACP Transacylase), fabG (β−Ketoacyl−ACP Reductase), fabI (Enoyl−ACP Reductase), ACSL (Long−chain Acyl−CoA Synthetase), and KCS and increased the content of dodecanoic acid, behenic acid, lignoceric acid, and hexacosanoic acid. These results suggest that the GA signal may participate in the upregulation of fatty acid synthesis. In this study, we systematically constructed a molecular map of wax fatty acid metabolism during the fruit development stage of the ‘Hupingzao’ variety, providing an important theoretical basis and candidate genes for future directional regulation of wax components via molecular breeding or cultivation measures.