BrWAX3, encoding a β-ketoacyl-CoA synthase, participates in cuticular wax biosynthesis in Chinese cabbage

Abstract In this study, we identified a novel glossy mutant from Chinese cabbage, named SD369, all wax monomers longer than 26 carbons were significantly decreased. Inheritance analysis revealed that the glossy trait of SD369 was controlled by a single recessive locus, BrWAX3. We fine-mapped the BrWAX3 locus to an interval of 161.82 kb on chromosome A09. According to the annotated genome of Brassica rapa, Bra024749 (BrCER60.A09), which encodes a β-ketoacyl-CoA synthase, was identified as the candidate gene. Expression analysis showed that BrCER60.A09 was significantly downregulated in all aerial organs of glossy plants. Subcellular localization indicated that the BrCER60.A09 protein functions in the endoplasmic reticulum. A 5,567-bp insertion was identified in exon 1 of BrCER60.A09 in SD369, which lead to a premature stop codon and thus causing a loss of function of the BrCER60.A09 enzyme. Moreover, comparative transcriptome analysis revealed that the 'cutin, suberine and wax biosynthesis' pathway was significantly enriched, and genes involved in this pathway were almost upregulated in glossy plants. Further, two functional markers, BrWAX3-InDel and BrWAX3-KASP1, were developed and validated. Overall, these results provide new information for the cuticular wax biosynthesis and provide applicable markers for marker-assisted selection (MAS)-based breeding of Brassica rapa.