Mapping and Validation of BrGOLDEN: A Dominant Gene Regulating Carotenoid Accumulation in Brassica rapa

In plants, the accumulation of carotenoids can maintain the balance of the photosystem and improve crop nutritional quality. Therefore, the molecular mechanisms underlying carotenoid synthesis and accumulation should be further explored. In this study, carotenoid accumulation differed significantly among parental Brassica rapa. Genetic analysis was carried out using the golden inner leaf ‘1900264′ line and the light−yellow inner leaf ‘1900262′ line, showing that the golden inner leaf phenotype was controlled by a single dominant gene. Using bulked−segregant analysis sequencing, BraA09g007080.3C encoding the ORANGE protein was selected as a candidate gene. Sequence alignment revealed that a 4.67 kb long terminal repeat insertion in the third exon of the BrGOLDEN resulted in three alternatively spliced transcripts. The spatiotemporal expression results indicated that BrGOLDEN might regulate the expression levels of carotenoid−synthesis−related genes. After transforming BrGOLDEN into Arabidopsis thaliana, the seed−derived callus showed that BrGOLDEN(Ins) and BrGOLDEN(Del) lines presented a yellow color and the BrGOLDEN(Ldel) line presented a transparent phenotype. In addition, using the yeast two−hybrid assay, BrGOLDEN(Ins), BrGOLDEN(Ldel), and Brgolden(wt) exhibited strong interactions with BrPSY1, but BrGOLDEN(Del) did not interact with BrPSY1 in the split−ubiquitin membrane system. In the secondary and 3D structure analysis, BrGOLDEN(Del) was shown to have lost the PNFPSFIPFLPPL sequences at the 125 amino acid position, which resulted in the α−helices of BrGOLDEN(Del) being disrupted, restricting the formation of the 3D structure and affecting the functions of the protein. These findings may provide new insights into the regulation of carotenoid synthesis in B. rapa.