Alternative splicing of BrTFL2 resulted in early bolting in Chinese cabbage

Mapping of an early bolting mutant and functional verification of its causal gene revealed that BrTFL2 was associated with bolting in Chinese cabbage. Early bolting is a breeding target trait of Chinese cabbage for stalk-type cultivars. In this study, we characterized an early bolting mutant in Chinese cabbage, ebm13, which bolted earlier than its WT under both LD and SD conditions. Genetic analysis indicated that the mutant phenotype was controlled by a monogenic recessive nuclear gene. Using MutMap combined with KASP genotyping, we identified a candidate SNP (SNP15757783) in BrTFL2, a key gene regulating the meristem's response to light signals. BrTFL2 was functionally validated through VIGS and ectopic overexpression in Arabidopsis thaliana. In ebm13, SNP15757783 was located at the junction of the 6th intron and the 7th exon, disrupting the 3' splice site from AG to AA and thereby leading to an obstacle to proper RNA splicing, while CDS sequence analysis displayed that the 7th exon had a loss of twenty-one bases (CTGATTGAATTCTACGAGCAG). BrTFL2 was localized in the nucleus. Compared with the WT, the ebm13 mutant exhibited reduced H3K27me3 enrichment in the promoter regions (P1 and P2) of BrFTa/b and elevated expression levels of BrFTa/b.