Cherries are one of the important fruit trees. The growth of cherry is greatly affected by abiotic stresses such as drought, which hinders its development. Chalcone synthase (CHS, EC 2.3.1.74) is a crucial rate-limiting enzyme in the flavonoid biosynthetic pathway that plays an important role in regulating plant growth, development, and abiotic stress tolerance. In the current study, three genes encoding chalcone synthase were identified in the genome of sweet cherry (Prunus avium L.). The three genes contained fewer introns and showed high homology with CHS genes of other Rosaceae members. All members are predicted to localize in the cytoplasm. The conserved catalytic sites may be located at the Cys163, Phe214, His302, and Asn335 residues. These genes were differentially expressed during flower bud dormancy and fruit development. The total flavonoid content of Chinese cherry (Cerasus pseudocerasus Lindl.) was highest in the leaves and slightly higher in the pulp than in the peel. No significant difference in total flavonoid content was detected between aborted kernels and normally developing kernels. Overexpression of Chinese cherry CpCHS1 in tobacco improved the germination frequency of tobacco seeds under drought stress, and the fresh weight of transgenic seedlings under drought stress was higher than that of the wild type, and the contents of SOD, POD, CAT, and Pro in OE lines were significantly increased and higher than WT under drought stress. These results indicate cherry CHS genes are conserved and functionally diverse and will assist in elucidating the functions of flavonoid synthesis pathways in cherry and other Rosaceae species under drought stress.

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Copper amine oxidases (CuAOs) play important roles in PA catabolism, plant growth and development, and abiotic stress response. In order to better understand how PA affects cherry fruit, four potential PavCuAO genes (PavCuAO1–PavCuAO4) that are dispersed over two chromosomes were identified in the sweet cherry genome. Based on phylogenetic analysis, they were classified into three subclasses. RNA-seq analysis showed that the PavCuAO genes were tissue-specific and mostly highly expressed in flowers and young leaves. Many cis-elements associated with phytohormones and stress responses were predicted in the 2 kb upstream region of the promoter. The PavCuAOs transcript levels were increased in response to abscisic acid (ABA) and gibberellin 3 (GA3) treatments, as well as abiotic stresses (NaCl, PEG, and cold). Quantitative fluorescence analysis and high-performance liquid chromatography confirmed that the Put content fell, and the PavCuAO4 mRNA level rose as the sweet cherry fruit ripened. After genetically transforming Arabidopsis with PavCuAO4, the Put content in transgenic plants decreased significantly, and the expression of the ABA synthesis gene NCED was also significantly increased. At the same time, excessive H2O2 was produced in PavCuAO4 transiently expressed tobacco leaves. The above results strongly proved that PavCuAO4 can decompose Put and may promote fruit ripening by increasing the content of ABA and H2O2 while suppressing total free PA levels in the fruit.

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