Fine mapping and characterization of the or gene in Chinese cabbage (Brassica rapa L. ssp pekinensis)

Orange inner leaves/heads is a qualitative trait in Chinese cabbage that is controlled by a single recessive gene. Orange head Chinese cabbage contain more carotenoids than its white head counterpart; hence, this trait is of interest to both researchers and consumers. In this study, we selected the orange head Chinese cabbage line 07A163 and the white head Chinese cabbage line Chiifu as test materials. We localized the target gene controlling the orange head trait to the A09 linkage group, with a physical distance of approximately 19.9 kb between the two markers, syau26 and syau28. This region contains six candidate genes, including Bra031539, which was predicted to encode CRTISO, a carotenoid isomerase specifically required for carotenoid biosynthesis. A comparison of the nucleic acid sequences of the two test materials revealed 88 and 7-bp deletions and 88 SNPs in the promoter region of Bra031539 in line 07A163, along with a 6-bp deletion in the first exon and early termination at the 3' end of this gene. BLAST analysis revealed that 22 amino acids were altered and 17 amino acids were lost in Bra031539 in the orange head line 07A163. We developed the BrPro1 molecular marker in the promoter region of Bra031539 that can be used for early identification of orange head materials, thereby accelerating the breeding process of orange head Chinese cabbage.