Expression analysis of the DkNCED1, DkNCED2 and DkCYP707A1 genes that regulate homeostasis of abscisic acid during the maturation of persimmon fruit

To reveal details of the role(s) of abscisic acid (ABA) during fruit ripening and the regulation of ABA levels, two 9-cis-epoxycarotenoid dioxygenase genes (DkNCED1 and DkNCED2) and the DkCYP707A1 gene for ABA 8'-hydroxylase were isolated from unripened persimmon fruit. Expression of DkNCED1 increased at the start of fruit maturation and peaked 20 d before harvest, which was consistent with the accumulation of ABA during ripening in persimmon. Expression of the DkNCED2 gene was high in fruit at the immature stage, then declined continuously throughout ripening. Compared to the DkNCED genes, expression of DkCYP707A1 peaked 145 d after full-bloom (DAFB), then declined. Ethylene release decreased gradually from 65 DAFB to 115 DAFB, then peaked at 10 d after harvest. Water-deficit stress enhanced the expression of DkNCED1, but down-regulated transcript levels of DkCYP707A1 in the calyx. These results suggest that endogenous ABA content is modulated by a dynamic balance between ABA biosynthesis and catabolism, which is regulated by expression of the DkNCED1 and DkCYP707A1 genes, respectively, during persimmon fruit development and under drought stress.