Transcriptome Analysis of Orange Head Chinese Cabbage (Brassica rapa L. ssp. pekinensis) and Molecular Marker Development

Due to the visual appearance and high carotenoid content, orange inner leaves are a desirable trait for the Chinese cabbage. To understand the molecular mechanism underlying the formation of orange inner leaves, the BrCRTISO (Bra031539) gene, as the Br-or candidate gene, was analyzed among the white and orange varieties, and 7 single nucleotide polymorphisms (SNPs) were identified. However, only one SNP (C952 to T952) altered the amino acid sequence, resulting in a mutation from Leu318 to Phe318 in the orange varieties. Additionally, we analyzed differentially expressed genes (DEGs) between the orange and white F2 individuals (14-401 × 14-490) and found four downregulated genes were involved in the carotenoid biosynthesis pathway, which may lead to the accumulation of prolycopene and other carotenoid pigments in the orange inner leaves. In addition, we developed a novel InDel marker in the first intron, which cosegregates with the phenotypes of orange color inner leaves. In conclusion, these findings enhance our understanding of the underlying mechanism of pigment accumulation in the inner leaves of the Chinese cabbage. Additionally, the SNP (C952 to T952) and the InDel marker will facilitate the marker-assisted selection during Chinese cabbage breeding.