Cloning and expression analysis of polygalacturonase and pectin methylesterase genes during softening in apricot (Prunus armeniaca L.) fruit

Apricot softening is an important physiological process that influences fruit quality and postharvest life. Polygalacturonase (PG; EC 3.2.1.6.9) and pectin methylesterase (PME; EC 3.1.11) are two important cell wall hydrolases that have been widely studied during fruit softening. However, the roles of PG and PME genes in apricot softening remain unclear. In the present study, PaPG1 and PaPME1 from the apricot fruit were cloned and characterized. Moreover, the effects of 1-methylcyclopropene (1-MCP) treatment on firmness, ethylene production, PaPG1 and PaPME1 expression levels as well as PG and PME activities in apricots during storage at 4 ℃ were investigated, and the quality traits of apricot fruit during shelf life at 25 ℃ after cold storage were analyzed. Results showed that the application of 1-MCP significantly inhibited the decrease in fruit firmness as well as the increase in ethylene production, and markedly suppressed the expression levels of PaPG1 and PaPME1 and the increases in PG and PME activities of the apricots during cold storage. In addition, the 1-MCP treated apricots exhibited higher firmness, titratable acid (TA) content as well as lower ethylene production, respiration rate and weight loss compared to the control during shelf life at 25 ℃. These results suggested that 1-MCP treatment delayed the softening and ripening of the apricots during cold storage, and maintained better quality and consumer acceptability of the apricots during shelf life. PG and PME genes might play crucial roles in the development of apricot softening during cold storage.