Fine mapping of BrWax1, a gene controlling cuticular wax biosynthesis in Chinese cabbage (Brassica rapa L. ssp. pekinensis)

The surface of plants is covered with a cuticular wax, which contains a mixture of very-long-chain fatty acid derivatives. This wax layer provides a hydrophobic barrier which reduces non-stomatal water loss and prevents pathogen attack. The biosynthesis pathway of cuticular wax in Arabidopsis is well studied; however, little is known about the synthesis of cuticular wax in Brassica rapa. Genetic analyses indicated that the waxy characteristic is controlled by a single dominant gene. In the present study, preliminary mapping results from an F2 population consisting of 308 recessive individuals showed that the BrWax1 (Brassica Wax) gene is located on linkage group A01. We developed a set of new markers closely linked to the target gene, and used another population of 1,020 recessive F2 individuals to fine-map the BrWax1 gene to a genomic DNA fragment of approximately 86.4 kb. Fifteen genes were identified in this target region. Based on gene annotation, the Bra013809 gene was the candidate for the BrWax1 gene. Quantitative real-time PCR analysis and expression pattern of the two parents showed that the expression level of Bra013809 was much higher in the waxy phenotype than in the glossy phenotype. This result should provide not only important information for functional studies of the BrWax1 gene, but also the starting point for studying the pathway of cuticular wax biosynthesis in Brassica rapa.