Association of molecular markers derived from the BrCRTISO1 gene with prolycopene-enriched orange-colored leaves in Brassica rapa [corrected]..

KEY MESSAGE: Sequence polymorphism in BrCRTISO1, encoding carotenoid isomerase, is identified in orange-colored B. rapa , and three resulting gene-based markers will be useful for marker-assisted breeding of OC cultivars. Carotenoids are color pigments that are important for protection against excess light in plants and essential sources of retinols and vitamin A for animals. We identified a single recessive gene that might cause orange-colored (OC) inner leaves in Brassica rapa. The inner leaves of the OC cultivar were enriched in lycopene-like compounds, specifically prolycopene and its isomers, which can be a useful functional trait for Kimchi cabbage. We used a candidate gene approach based on the 21 genes in the carotenoid pathway to identify a candidate gene responsible for the orange color. Among them, we focused on two carotenoid isomerase (CRTISO) genes, BrCRTISO1 and BrCRTISO2. The expression of BrCRTISO1 was higher than that of BrCRTISO2 in a normal yellow-colored (YE) cultivar, but full-length BrCRTISO1 transcripts were not detected in the OC cultivar. Genomic sequence analysis revealed that BrCRTISO1 of the OC cultivar had many sequence variations, including single nucleotide polymorphisms (SNPs) and insertions and deletions (InDels), compared to that of the YE cultivar. We developed molecular makers for the identification of OC phenotype based on the polymorphic regions within BrCRTISO1 in B. rapa breeding. The BrCRTISO1 gene and its markers identified in this study are novel genetic resources and will be useful for studying the carotenoid biosynthesis pathway as well as developing new cultivars with unique carotenoid contents in Brassica species.