Characterization of FLOWERING LOCUS C 5 in Brassica rapa L.

Abstract

Brassica rapa L., which includes Chinese cabbage, turnip, and pak choi, has more complex flowering time regulation than does Arabidopsis thaliana due to the presence of multiple paralogous flowering time genes. FLOWERING LOCUS C (FLC) is one of the key genes regulating flowering time. Although there is a single gene in A. thaliana, there are four FLC paralogs in B. rapa. BrFLC1, BrFLC2, and BrFLC3 are involved in regulating flowering time, whereas BrFLC5 is deemed a pseudogene because of a mutation (from G to A) in the splice site of the third intron. However, some accessions do not have this mutation, and a flowering-time quantitative trait locus (QTL) covering BrFLC5 associated with late flowering has been identified, suggesting that some accessions in B. rapa have a functional BrFLC5 gene. However, it has not been shown whether BrFLC5 acts as a floral repressor. To examine the allelic variation of BrFLC5, we genotyped 310 B. rapa accessions and found 19 had homozygous and 81 had heterozygous putative functional BrFLC5 alleles. BrFLC5 acts as a floral repressor when overexpressed in A. thaliana. Variation in the BrFLC5 expression level in pre-vernalized plants was identified and this transcriptional variation was not associated with the G/A polymorphism in the third intron. However, higher BrFLC5 expression in pre-vernalized plants is associated with 584 bp insertion in the promoter region. The possibility that a high expression of a functional BrFLC5 could contribute to producing premature bolting-resistant lines in B. rapa vegetables is discussed.