Ethylene altered fruit cuticular wax, the expression of cuticular wax synthesis-related genes and fruit quality during cold storage of apple (Malus domestica Borkh. c.v. Starkrimson) fruit

To investigate the impact of ethylene in regulating wax synthesis-related gene expression and the consequent fruit quality changes during cold storage, four key apple wax synthesis genes from 'Starkrimson' apple, MdCER4, MdCER6, MdWSD1 and MdMAH1, were identified, and their expression levels in response to treatments with ethephon and 1-methylcyclopropene (1-MCP) during cold storage were studied. The fruit quality changes in these two treatments were also determined during cold storage. The results showed that ethephon increased cuticular wax density, accelerated wax crystal melting and fruit senescence during cold storage of 'Starkrimson' apple, while 1-MCP delayed these processes. The results also showed that ethephon increased the expression levels of MdCER6 (a key gene in very long chain fatty acids synthesis), MdCER4 and MdWSD1 (two key genes in the alcohol-forming pathway of wax synthesis), while 1-MCP decreased their expression. In addition, neither ethephon nor 1-MCP regularly regulated the expression of MdMAH1, a key gene in the final step of the alkane-forming pathway of wax synthesis. Therefore, it was concluded that ethylene altered fruit cuticular wax composition and crystal morphology via MdCER6 and the subsequent alcohol-forming pathway, thus affecting the fruit quality to some extent during 'Starkrimson' apple fruit cold storage.