Identification of BoFLC2 As a Major Gene Controlling Flowering Time in Cabbage (brassica Oleracea Var. Capitata)

Cabbage (Brassica oleracea var. capitata), a world-widely cultivated leafy vegetable, is characterized by its dense-leaved head formation. Premature bolting, where flowering occurs before head formation significantly reduces cabbage quality and yield. In this study, we employed bulked segregant analysis (BSA) and linkage analysis to identify the quantitative trait loci (QTL) associated with flowering time variation in cabbage. Our analysis revealed a major QTL-designed as qFT2.1, located on chromosome C02. The QTL spans a 12.8 kb region that encompasses five genes. Further analysis identified BoFLC2 (an ortholog of AtFLC) as the candidate gene for qFT2.1. Comparative sequence analysis revealed a 215 bp-insertion in the first intron of BoFLC2 in the early-flowering parental line, along with a 3 bp-insertion and three missense mutations in the second exon. RNA-sequencing revealed that BoFLC2 expression in non-flowering individuals (extremely late flowering) was significantly higher than that in the early-flowering individuals. Analysis of the BoFLC2 sequence across 37 published B. oleracea genomes revealed six haplotypes that are likely associated with flowering time domestication in B. oleracea. Our results suggest that BoFLC2 as a major regulator in flowering time control, has been under selection during the domestication of B. oleracea.