Isolation of the 9-cis-epoxycarotenoid dioxygenase (NCED) gene from kiwifruit and its effects on postharvest softening and ripening

According to the general consensus, post-ripening effects of ABA on climacteric fruits accelerate the softening process, especially in kiwifruit. In order to further understand the mechanism of ABA action during postharvest ripening of kiwifruit, five ABA synthase genes related to 9-cis-epoxycarotenoid dioxygenase (NCED) were isolated from kiwifruit genome, namely, AcNCED1, AcNCED1.1, AcNCED2, AcNCED3, and AcNCED3.1. Gene expression analysis showed that the expression of AcNCED1 peaked early during postharvest ripening, a finding that was consistent with the trend observed for the changes in ABA content. AcNCED1 expression was induced by ABA and repressed by ABA synthesis inhibitor nordihydroguaiaretic acid. We found cis-elements related to fruit development and ripening in the AcNCED1 promoter sequence. Analysis of AcNCED1 promoter activity showed that ABA and ethylene significantly enhanced the expression of AcNCED1. Furthermore, AcNCED1 silencing inhibited ABA synthesis and delayed kiwifruit softening, whereas transient overexpression of AcNCED1 in tomato accelerated fruit color development relative to controls. These results indicated that AcNCED1 encodes a key enzyme involved in ABA synthesis in kiwifruit, and that it may play an important role in the softening process of fruits early in postharvest.