Study on the Mechanism of Carotenoid Production and Accumulation in Orange Red Carrot (Daucus carota L.)

Abstract

In this experiment, orange‒red carrot at different development stages was used as material to observe the dynamic morphological structure of roots, and the displaying color stage of carrot was identified as 50 days after sowing (DAS). Metabolome and RNA sequencing (RNA-Seq) were jointly performed on carrot epidermis at the pale stage (30 DAS), starting accumulating carotenoids stage (50 DAS) and highest accumulation of carotenoids stage (115 DAS). A total of 37 kinds of carotene were detected, including 6 kinds of carotene, 10 kinds of lutein and 21 kinds of carotene ester. The main carotene of orange carrot was α-carotene, whose content reached 545.09 μg/g at 115 DAS. The content of α-carotene was 2.95, 2.45 and 2.27 times that of β-carotene at the three developmental stages, respectively. In addition, previously unreported echinenone, canthaxathin and apocarotenal and a large amount of carotenoid esters were detected in carrot epidermis. A total of 14466 differentially expressed genes (DEGs) were identified by RNA-Seq, and 62 DEGs related to carotenoid biosynthesis were screened. The transcription levels of GGPS4, PSY2, PDS, ZDS, Z-ISO, CRTISO2, LCYE, LCYB1 and BCH1 were positively correlated with carotenoid content in carrot epidermis, and the high expression of PSY2, LCYE and LCYB1 was the main reason for the synthesis of α-carotene and β-carotene, which resulted in the root color change in carrot. The expression of NCED1/2/3 was upregulated at first and then downregulated to almost no expression, which played an important role in carotenoid accumulation during root development. In addition, the expression level of LCYE was higher than that of LCYB1, which was speculated to be the main reason for the higher content of α-carotene than β-carotene in orange‒red carrot.