Genetic mapping reveals a candidate gene (BraBAN) contributing to the purple leaves in non-heading Chinese cabbage

Anthocyanins are water-soluble pigments widely found in plants and play an important role in plant stress resistance and the prevention of chronic diseases in humans. Purple non-heading Chinese cabbage, known for its rich anthocyanin content and significant nutritional and health benefits, is a focal point for enhancing the appearance quality of non-heading Chinese cabbage through breeding. In this study, an F2 population resulted from the hybridization of the purple-leaved parental line S46P with the green-leaved line S46G. Genetic analysis revealed a 3:1 ratio consistent with Mendelian inheritance, indicating that the purple-leaved trait is governed by a single nuclear gene with dominant inheritance. Using BSA-seq technology, the gene was initially mapped to a 3.41 Mb interval on chromosome A03. Subsequent positional cloning pinpointed the target gene between markers I-63 and I-64, spanning 189.4 kb. Within this interval, 16 candidate genes were predicted. Variant annotation identified three genes with coding region mutations with amino acid changes. Notably, the candidate gene BraA03g064730.3C, encoding NAD-dependent epimerase/dehydratase involved in anthocyanin metabolism, exhibited differential expression in plants with varied leaf colors. Map-based cloning and sangersequencing revealed a single-base substitution (G -> T) in exon 1, resulting in the amino acid change from valine to phenylalanine. This SNP mutation is speculated to alter the function or expression of the BraA03g064730.3C gene, confirming its candidacy for controlling the purple-leaved trait in non-heading Chinese cabbage. Furthermore, the low-light treatment showed that changes in the expression of BraA03g064730.3C is correlated with anthocyanin content. This discovery establishes a foundation for delving into the molecular mechanisms of anthocyanin synthesis and offers theoretical support and gene source for breeding varieties with diverse leaf colors of non-heading Chinese cabbage.