Polyamine oxidase (PAO)–mediated polyamine catabolism plays potential roles in peach (Prunus persica L.) fruit development and ripening

Recently, there is an increased interest in the function of polyamine (PA) catabolism during fruit ripening, but little is known about its role during the ripening of peach (Prunus persica L.). In this study, the contents of both free and conjugated PAs markedly decreased as the peach fruit ripened. However, RNA-seq analysis showed that the transcript levels of PA synthesis–related genes increased, suggesting that the decreasing PA content during peach ripening was associated with PA catabolism. To better understanding the function of PA catabolism in peach ripening, genes encoding potential polyamine oxidases (PAOs), which are involved in PA catabolism, were identified across the peach genome. Four putative PAO genes (PpePAO1-PpePAO4) were identified in peach using the recently released genome database. The mRNA level of PpePAO1 was significantly increased during peach fruit ripening. Detection of free PAs in tobacco leaves transiently over-expressing PpePAO1 suggested that this gene is probably involved in terminal catabolism of PA. Treatment with the PAO inhibitor guazatine significantly reduced ethylene production and flesh softening of peach fruit, decreased the expression levels of fruit ripening-related genes, and significantly decreased the expression level of PpePAO1 and PAO activity, while PA contents were dramatically higher compared to control treatments. Our results suggests that PpePAO1-mediated PA catabolism is associated with decreased PA content during peach fruit ripening. These data provide valuable knowledge for better understanding the roles of PA catabolism in peach development and ripening.