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

Abstract

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.

Modification of Sugar Profile and Ripening in Atemoya (Annona × atemoya Mabb.) Fruits through Copper Hydroxide Application

“…At 175 days after the first Cu(OH) 2 application (DAFA), atemoya fruits sprayed with different concentrations of Cu(OH) 2 showed higher concentrations of hydrogen peroxide in comparison to T1 (control) ( Figure 1 a), possibly indicating a high activity of copper amine oxidases during ripening, as found in previous studies [ 22 ]. Furthermore, copper as Cu 2+ can inhibit catalase, an enzyme with the ability to directly break H 2 O 2 into H 2 O and O 2 , resulting in high H 2 O 2 concentrations in plant tissue [ 57 , 58 , 59 ], a trend that was also observed in this investigation ( Figure 1 a).…”

“…Different quantities of copper caused a significant concentration of hydrogen peroxide ( Figure 1 a) which may have contributed to the divergence of sugar profiles ( Figure 2 ). This sugar profile alteration was expected because copper participates in the respiration process as a signaling cascade inducer, cofactor of enzymes, and polyamine cofactor [ 19 , 22 , 69 ], and plants were diagnosed with anthracnose. As a result of the high quantity of hydrogen peroxide, carbohydrates may have accumulated and served as signaling molecules.…”

“…When carbohydrates are continuously provided, chlorophyll degradation can be re-strained [ 29 , 77 , 78 ], resulting in a longer shelf life due to a thicker cell wall (skin stiffness) and antioxidant activity [ 25 , 34 ]. As a result, copper is thought to have aided plant defense mechanisms by activating plant-specific genes [ 19 , 22 ]. Sugar in fruits can enhance soluble solids, skin stiffness, catalase, and decrease the action of glucose phosphate isomerase and cytochrome oxidase [ 18 , 34 , 35 ], which could explain why fruits have a longer shelf life ( Figure 3 e).…”

“…Copper is also essential for the ethylene-binding activity of ETR1 (ethylene response 1), a receptor protein [ 20 , 21 ], which is a hormone that causes fruit ripening in climacteric fruits. Copper is also detected in amine oxidases during fruit ripening, where it inhibits putrescine (a competitor of ethylene precursor [ 16 ]) and increases the level of abscisic acid (ABA) and H 2 O 2 [ 22 ]. ABA functions as a ripening promoter [ 23 ].…”

Genome-Wide Identification, Characterization, and Expression Analysis of the Copper-Containing Amine Oxidase Gene Family in Mangrove Kandelia obovata

“…The first group is found within peroxisomes, as shown by the presence of peroxisomal targeting signals. The second group is located outside of the cell, as indicated by the presence of N-terminal signal peptides [4,5]. Previous studies have demonstrated the presence of CuAO members in both peroxisomal and extracellular locations across many species, such as Arabidopsis [6], apple [7], and sweet orange [5].…”