A single SNP in Brcer1 results in wax deficiency in Chinese cabbage (Brassica campestris L. ssp. pekinensis)

Cuticle wax covering the surface of plants is mainly composed of derivatives of long-chain saturated fatty acids. Chinese cabbage leaves with wax deficiency has a bright green phenotype, which makes it attractive and improves its commercial value. In this study, a wax deficiency mutant, cer1, was obtained from an ethyl methanesulfonate (EMS) mutagenesis population in Chinese cabbage. Scanning electron microscopy (SEM) revealed that cuticular wax in the leaves and stems of mutants was significantly less than that in the wild type (WT). The mutants decreased the total wax, alkanes, ketones and alcohols contents in leaves, but aldehydes content increased compared to WT. Genetic analysis showed that the mutant cer1 phenotype was controlled by a single recessive nuclear gene. MutMap and Kompetitive Allele-Specific PCR (KASP) analyses indicated that BraA09g066480.3C, which encoded aldehyde decarboxylase, might be the causal gene. A single nucleotide substitution (SNP) from C to T in the fourth exon of BraA09g066480.3C resulted in an amino acid substitution from serine to phenylalanine, which led to changes in the three-dimensional structure of proteins. SNP 45,148,866 occurred in the highly conserved fatty acid hydroxylase domain. This study revealed that SNP is effective for marker-assisted selection of wax deficient Chinese cabbage and provides convenience for breeding new varieties exhibiting a wax deficient phenotype.