BrABA2 mutation conferred glossy leaf via epicuticular wax crystal disruption in Chinese cabbage

Leaf glossiness is an important quality trait affecting the commercial value of Chinese cabbage. Identifying the genes controlling the glossy leaf trait in Chinese cabbage is crucial for cultivar improvement. In this study, we characterized a glossy leaf mutant wdm19 isolated from an EMS-mutagenized population of the doubled haploid line 'FT'. Scanning electron microscopy revealed the absence of epicuticular wax crystal on the mutant leaf surface, accompanied by significantly increased water loss and chlorophyll leaching rates. GC-MS analysis confirmed a marked reduction in total cuticular wax load in wdm19 compared with 'FT'. Genetic analysis indicated that the glossy leaf phenotype was controlled by a single recessive nuclear gene. By combining MutMap analysis with KASP genotyping, BraA08g002170.3.5C was identified as the candidate gene named BrABA2, which is orthologous to AtABA2 and is involved in abscisic acid biosynthesis. A single nucleotide substitution (G to A) was detected at position 304 bp downstream of the TAG stop codon within the 3' UTR of BrABA2, which significantly reduced its expression at both transcript and protein levels. Heterologous complementation in Arabidopsis confirmed that the aba2 mutant phenotype could be restored by overexpressing BrABA2. Our findings demonstrated that mutation of BrABA2 led to the glossy leaf phenotype in Chinese cabbage.