The primary function of cuticular wax is to prevent non-stomatal water loss, while the wax deficiency conferring a glossy appearance on plants is conductive to crop commodity qualities. We previously mapped a wax-deficient gene BrWax1 in a natural mutant ‘08A235-2’ by SSR marker, and predicted Bra013809 (BrWax1) as the candidate gene in Chinese cabbage (Brassica rapa L. ssp. pekinensis). In order to verifying the function of BrWax1, two allelic wax-crystal deficiency mutants wdm4 and wdm8 from an EMS mutagenesis population of Chinese cabbage were screened. wdm4 was applied to identify the mutant gene, with the finding that BraA01g015290.3C, the homologous of AT4G24510 (AtCER2), was the candidate gene. Bra013809 in Brara_Chiifu_V1.5 and BraA01g015290.3C in Brara_Chiifu_V3.0 were annotated as the same gene in Brassicaceae Database. A SNP (C to T) on BrWax1 in wdm4 resulted in a stopgain, and a SNP (G to A) on BrWax1 in wdm8 led to the deletion of 38 bases which caused a stopgain at the 190^th amino acid. These results finally verified the function of BrWax1 in the wax biosynthesis. Our findings emphasize the crucial role of the BrWax1 gene in cuticular wax biosynthesis in Chinese cabbage and suggest its potential as a valuable genetic resource for breeding for glossy appearance.

Leaf senescence is the final stage of leaf development, where the nutrients and energy of senescent leaves are redistributed to developing tissues or organs for plant growth, reproduction, and defense. Outer leaves are photosynthetic organs that usually senesce at the late heading stage in Chinese cabbage, and premature leaf senescence often reduces leafy head yield and quality. In this study, 11 premature leaf senescence mutants were screened from an ethyl methanesulfonate-mutagenized population of the double haploid line ‘FT’ in Chinese cabbage. At the early heading stage, the mutants exhibited edge yellowing within its outer leaves, and at the mature stage, its leafy head weight decreased significantly. Genetic analysis revealed that the mutated trait of all 11 mutants corresponds to single gene recessive inheritance. Semi-diallel cross tests showed that 5 of the 11 were allelic mutants. MutMap and Kompetitive Allele Specific PCR genotyping revealed that BraA01g001400.3C was the candidate gene, which is orthologous of Arabidopsis SUPPRESSOR OF rps4-RLD 1, encoding an immune regulator, so we named it as BrSRFR1. All the BrSRFR1 in the five allelic mutants exhibited single nucleotide polymorphisms at different positions on their exons and led to premature translation termination, which confirmed that defect in BrSRFR1 led to premature leaf senescence. These results verify the role of BrSRFR1 on leaf senescence and provide a new insight into the mechanisms of leaf senescence in Chinese cabbage, which reveals a novel function of SRFR1 in plant development.