Mango MiEIL4 modulates starch degradation during fruit ripening by upregulating the expression of β-amylase and α-amylase genes

Abstract

Starch degradation contributes to the sweetening and softening of mango (Mangifera indica) fruit, but the molecular regulatory mechanism underlying this process remains unexplored. In this study, the levels of starch, amylose, and amylopectin exhibited a gradual decline, while soluble sugars increased progressively during the postharvest ripening of four mango cultivars: ‘Guifei’, ‘Hongxiangya’, ‘Jinhuang’, and ‘Tainong’. Moreover, the activities of the starch digesting enzymes amylase, α-amylase, and β-amylase, as well as the expression levels of genes encoding these enzymes were all up-regulated during the ripening in these four mango cultivars. Importantly, an important transcriptional regulator in the ethylene-responsive pathway, MiEIL4, was identified based on its upregulation during fruit ripening, and it was a nuclear-localized transcriptional activator. Transiently overexpressing MiEIL4 in mango fruit promoted starch degradation and thus fruit ripening by upregulating the expression of starch hydrolytic genes. MiEIL4 stimulated the transcription of MiAMY3, MiBAM4, MiBAM5, MiBAM6, MiBAMX1, and MiBAMX2, but it only directly bound to the MiBAMX2 promoter. Taken together, these observations suggest that MiEIL4 is an important activator of starch breakdown during mango fruit ripening by upregulating the expression of starch degrading genes, broadening our knowledge of starch-degradation in mango and other climacteric fruits.