Copper Amine Oxidase (CuAO)-Mediated Polyamine Catabolism Plays Potential Roles in Sweet Cherry ( L.) Fruit Development and Ripening.

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 genes (-) 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 genes were tissue-specific and mostly highly expressed in flowers and young leaves. Many -elements associated with phytohormones and stress responses were predicted in the 2 kb upstream region of the promoter. The transcript levels were increased in response to abscisic acid (ABA) and gibberellin 3 (GA) 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 mRNA level rose as the sweet cherry fruit ripened. After genetically transforming with , the Put content in transgenic plants decreased significantly, and the expression of the ABA synthesis gene was also significantly increased. At the same time, excessive HO was produced in transiently expressed tobacco leaves. The above results strongly proved that can decompose Put and may promote fruit ripening by increasing the content of ABA and HO while suppressing total free PA levels in the fruit.