Effects of 1-methylcyclopropene (1-MCP) on the expression of genes involved in the chlorophyll degradation pathway of apple fruit during storage

The ripening of the apple (Malus × domestica Borkh.) fruit is regulated by the phytohormone ethylene, where degreening is an important physiological metabolism caused by chlorophyll (Chl) degradation. However, to date, research on how ethylene affects the Chl degradation pathway of apple peel during ripening remains scarce. In this study, the effects of ethylene on the expression of Chl catabolic genes (CCGs) of apple peel during ripening were studied by treating harvested commercial mature apples with 0.5 μL L^-1 1-methylcyclopropene (1-MCP). The results showed that 1-MCP treatment led to a delayed climacteric peak of respiration and ethylene production, exhibiting higher Chl content and hue angle (H˚) compared to untreated fruit during ripening. Lower quantities of pheophorbide a oxygenase (PAO), pheophytinase (PPH) and red Chl catabolite reductase (RCCR) were also observed in peel tissues under 1-MCP treatment during ripening. Further study with quantitative real-time polymerase chain reaction (qPCR) revealed that the expression of CCGs, except for MdNYE1a, increased atdifferentdegrees upon ripening. Meanwhile, the apples treated with 1-MCP presented a downregulated expression of MdRCCR2, MdNYC1, MdNYC3 and MdNOL2 and a fluctuating expression of MdNYE1a, MdPPH1, MdPAO6, MdPAO8 and MdHCAR compared with the controls during ripening. Our results indicated the regulatory role of ethylene in the Chl degradation pathway of apple peel during ripening.