PcPME63 is involved in fruit softening during post-cold storage process of European pear (Pyrus communis L.)

Fruit softening is a critical physiological process affecting pear fruit quality, primarily driven by cell wall lysis and remodeling. European pear (Pyrus communis L.) varieties are known for their rapid softening, which can reduce their storage and transportation tolerance. In order to comprehensively examine the potential molecular mechanisms and regulatory networks of fruit softening in European pears, we examined softening characteristics in three European pear varieties, namely 'Abate Fetel', 'Packham's Triumph' and 'Alexandrine Douillard'. Our investigation indicated that fruit firmness values after 2 or 4 d of post-cold storage were significantly lower than those observed 0 d post-cold storage. The process of cell wall depolymerization was found to be particularly significant at 4 d post-cold storage compared to the initial state at 0 d post-cold storage. To gain insights into the molecular changes associated with this softening process, RNA-seq analysis was conducted on three cultivated pear varieties under different storage durations. This analysis identified 721 genes that exhibited differential expression before and after softening. Furthermore, the results of the weighted gene coexpression network analysis (WGCNA) revealed a negative correlation between the expression of pectin methylesterase (PME) 63 and fruit firmness, suggesting a potential role for PME63 in the softening process. Additionally, our further investigation indicated that PcPME63 is localized on the cell membrane. Through transgenic experiments in tomato, the overexpression of PcPME63 was shown to accelerate the ripening process and reduce fruit firmness, providing strong evidence for the regulatory role of this gene in fruit softening. Collectively, the findings presented in this study lay a solid foundation for future research aimed at unraveling the genetic and molecular mechanisms governing the softening of European pears.