Fig. 1

Plant carotenoid metabolic pathway and the expression profiling of thirteen genes by RT-qPCR. A The enzymes/genes in the pathway are as follows: GGPS, geranylgeranyl diphosphate synthase; PSY, phytoene synthase; PDS, phytoene desaturase; ZISO, ζ-carotene isomerase; ZDS, ζ-carotene desaturase; CRTISO, carotene isomerase; LCYB, lycopene β-cyclase; LCYE, lycopene Ɛ-cyclase; CHYB, β-carotene hydroxylase; CHYE, Ɛ-carotene hydroxylase; ZEP, zeaxanthin epoxidase; NSY, neoxanthin synthase; CCD, carotenoid cleavage dioxygenase; NCED, 9-cis-epoxycarotenoid dioxygenase. The metabolites are as follows: IPP, isopentenyl diphosphate; DMAPP, dimethylallyl diphosphate; GGPP, geranylgeranyl diphosphate; Phytoene; phytofluene; lycopene; α-carotene; β-carotene; δ-carotene; γ-carotene; lutein; β-cryptoxanthin; zeaxanthin; antheraxanthin; violaxanthin; neoxanthin; ABA (abscisic acid); apocarotenoids (figure is modified from the reports [22,23,24]). B Expression profiles of carotenoid metabolic genes (IbGGPS, IbPSY, IbPDS, IbZDS, IbCRTISO, IbLCYB, IbLCYE, IbCHYB, IbCHYE, IbZEP, IbCCD1, IbCCD4, and IbNCED3) in the three sweetpotato varieties with different flesh colors during six tuberous root developmental stages [60, 75, 90, 105, 120, and 135 days after planting (DAP)]. IbActin was used as an internal control. IbCCD1 expression level at 60 DAP in WFSP cv. XS18 was used for calibration. Actual relative expression levels are listed in Additional file 5: Table S4