Mutations in BrRBM25 encoding an RNA binding motif protein cause premature bolting in Chinese cabbage

Bolting is an important agronomic character, and premature bolting leads to insufficient leafy head, which further affects the yield and quality of Chinese cabbage. In this study, two allelic early-bolting mutants ebm11-1 and ebm11-2 were isolated from a Chinese cabbage DH line 'FT' by EMS-mutagenesis. Genetic analysis showed that a single recessive nuclear gene controlled the mutant traits of these two mutants. MutMap combined with kompetitive allele specific PCR genotyping analyses indicated that BraA01g028120.3C was the candidate gene, which encoded RNA binding motif protein RBM25, named BrRBM25. Compared to wild-type 'FT', the mutations both existed on the eighth exon (G to A) of BrRBM25 gene in ebm11-1 and ebm11-2 mutants, resulting in the loss-of-function truncated protein. The function of BrRBM25 in regulating bolting time was verified by allelic variation. Subcellular localization revealed that BrRBM25 was a nuclear localization protein, and expression pattern analysis indicated that BrRBM25 gene was ubiquitously expressed in all organs. Compared with the wild-type 'FT', the endogenous ABA contents were significantly elevated and the expression levels of the flowering-related genes were also altered in ebm11-1 and ebm11-2 mutants. These results reveal for the first time that BrRBM25 is associated with regulating bolting time in Chinese cabbage.