Multiple flowering time QTLs within several Brassica species could be the result of duplicated copies of one ancestral gene

Quantitative trait locus (QTL) analysis was used to study the evolution of genes controlling the timing of flowering in four Brassica genomes that are all extensively replicated. Comparative mapping showed that a chromosomal region from the top of Arabidopsis thaliana chromosome 5 corresponded to th ree homoeologous copies in each of the diploid species Brassica nigra, B. o leracea, and B. rapa and six copies in the amphidiploid B. juncea. QTLs wer e detected in two of the three replicated segments in each diploid genome a nd in three of the six replicated segments in B. juncea. These results indi cate that, for the studied trait, multiple QTLs resulting from genome dupli cation is the rule rather than the exception. Brassica homologues to two ca ndidate genes (CO and FLC) identified from the corresponding A. thaliana re gion were mapped. CO homologues mapped close to the QTL peaks in eight of n ine QTLs, while FLC homologues mapped farther away in those cases where the mapping resolution allowed a comparison. Thus, our data are consistent wit h the hypothesis that all the major QTLs we detected in the different speci es of Brassica could be the result of duplicated copies of the same ancestr al gene, possibly the ancestor of CO.