Mapping of the Waxy Gene in Brassica napus L. via Bulked Segregant Analysis (BSA) and Whole-Genome Resequencing

Plant cuticular wax is the covering of the outer layer of the plant. It forms a protective barrier on the epidermis of plants and plays a vital role like a safeguard from abiotic and biotic stresses. In the present study, Brassica napus L. materials with and without wax powder were observed. Genetic analysis showed that the separation ratio of waxy plants to waxless plants was 15:1 in the F2 population, which indicated that the wax powder formation was controlled by two pairs of genes. In order to identify the candidate genes associated with the wax powder trait of B. napus L., bulked segregant analysis (BSA) was performed. The homozygous waxy plants, the homozygous waxless plants, and plants from three parents were selected for establishing five DNA pools for genome-wide resequencing. The results of the resequencing showed that the site associated with wax powder trait was located in the region of 590,663-1,657,546 bp on chromosome A08. And 48 single nucleotide polymorphisms (SNPs) were found between the DNA sequences of waxy plants and waxless plants in this region. These SNPs were distributed across 16 gene loci. qRT-PCR analysis was conducted for the 16 candidate genes and three genes (BnaA08g01070D, BnaA08g02130D, and BnaA08g00890D) showed significantly differential expression between waxy and waxless parents. BnaA08g01070D and BnaA08g02130D were significantly down-regulated in the waxless parent, while BnaA08g00890D was significantly up-regulated in the waxless parent. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses revealed that the BnaA08g02130D gene was enriched in lipid biosynthetic or metabolic processes. All the results in our study would provide valuable clues for exploring the genes involved in wax powder development.