Fine mapping of Brebm6, a gene conferring the early-bolting phenotype in Chinese cabbage (Brassica rapa ssp. pekinensis)

Abstract

In flowering plants, bolting signals the transition from vegetative to reproductive growth, and it is consequently an important agronomic trait for the stalk-use Chinese cabbage Baicaitai. There is an urgent need to create germplasm resources for Chinese cabbage that have easy bolting characteristics. In this investigation, early bolting mutant 6 (ebm6) was created by treating Chinese cabbage double haploid (DH) 'FT' seeds with an ethyl methanesulfonate (EMS) solution. Phenotypic analysis showed that the mutant ebm6 flowered remarkably earlier than the wild-type 'FT'. Genetic analysis indicated that this early bolting trait was controlled by a recessive nuclear gene. In mutant ebm6, the causal gene BraA02g003340.3C (BrFLC2) was predicted using MutMap and Kompetitive Allele Specific PCR genotyping (KASP), as the gene encodes a MADS-box transcription factor. The 3259-bp BrFLC2 gene possessed seven exons and six introns, and in the first exon, a single nucleotide C-to-T substitution in the highly conserved MADS-box domain resulted in the premature termination of translation of the BrFLC2 protein sequence. This research supported a critical role of BrFLC2 in controlling flowering time in B. rapa. The early flowering ebm6 mutant could also be a useful material in Baicaitai breeding.