BrCER4 Plays a Critical Role in Cuticular Wax Biosynthesis in Purple Cai-Tai (Brassica campestris L. ssp. chinensis var. purpurea)

Purple cai-tai (Brassica campestris L. ssp. chinensis var. purpurea) is a distinctive vegetable in South China. Despite its popularity, the majority of purple cai-tai varieties exhibit a surface covered with pale white cuticular waxes. In contrast, the waxless mutant stands out with superior sensory quality, featuring a glossy stem and leaves that are more appealing to consumers. To investigate the genetic mechanisms governing the biosynthesis of cuticular wax and apply the waxless mutant in breeding, an F2 population resulting from a cross between H10-8 (glossy epidermis line) and 402-3 (normal epidermis line) was used to map the locus conferring cuticular wax biosynthesis in purple cai-tai. Genetic and BSA-seq analyses revealed that the glossy epidermis trait in H10-8 is governed by a singular recessive locus located within the 0-4 Mb region of chromosome A01. BrCER4, homologous to CER4 in Arabidopsis, was identified as the most likely candidate gene for glossy trait based on functional annotation analysis, comparative sequencing, and expression analysis. A 39-bp deletion, resulting in a premature stop codon due to a frameshift, may be the functional locus causing the glossy epidermis trait in H10-8. Furthermore, we developed and validated insertion/deletion polymorphism and single-nucleotide polymorphism markers associated with BrCER4. In summary, these discoveries offer valuable insights for marker-assisted selection in the breeding of purple cai-tai and enhance our understanding of the molecular mechanisms involved in cuticular wax biosynthesis in Brassicaceae.