Genome-wide identification of 9-cis-epoxy-carotenoid dioxygenases (NCEDs) and potential function of OfNCED4 in carotenoid biosynthesis of Osmanthus fragrans

Key message: We identified seven OfNCEDs and analyzed the potential function of OfNCED4, which is involved in the biosynthesis of carotenoids and abscisic acid in Osmanthus fragrans. Abstract: In plants, 9-cis-epoxycarotenoid dioxygenases (NCEDs) can cleave carotenoids and are rate-limiting enzymes for the biosynthesis of abscisic acid (ABA). Sweet osmanthus (Osmanthus fragrans Lour.), an important ornamental and fragrant tree, contains abundant carotenoids in its flowers. To examine the function of the 9-cis-epoxycarotenoid dioxygenases (NCEDs) involved in ABA biosynthesis and floral coloration in O. fragrans, the sequences of seven OfNCEDs were isolated from the genomic DNA and cDNA of O. fragrans. A bioinformatics analysis showed that these OfNCEDs encode 422 ~ 591 amino acids, and they all contain the RPE65 domain. These OfNCEDs showed different patterns of expression, and that of OfNCED4 was most consistent to the patterns of ABA accumulation during the flowering process. Moreover, the levels of expression of seven OfNCEDs in the O. fragrans flowers were significantly induced by exogenous ABA. ABA-responsive elements were found in the promoters of OfNCEDs. The overexpression of OfNCED4 resulted in increased contents of chlorophylls, carotenoids and ABA, and up-regulation of NtCRTISO, NtLCYE, NtLCYB, and NtNXS, and down-regulation of NtCCD1 and NtCCD4 in tobacco leaves. It suggests that OfNCED4 probably mediates the biosynthesis of ABA. Taken together, this study systematically identified the bioinformatics, pattern of expression of OfNCED genes and the potential function of OfNCED4, which could provide molecular evidence for further research on the regulation of carotenoid biosynthesis and floral color of O. fragrans.