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Allelic variation at the FRIGIDA (FRI) locus is a major contributor to natural variation of flowering time and vernalization requirement in Arabidopsis thaliana. Dominant FRI inhibits flowering by activating the expression of the MADS box transcriptional repressor FLOWERING LOCUS C (FLC), which represses flowering and responses to vernalization. Four FRI orthologues had been identified in the domesticated amphidiploid Brassica napus. Linkage and association studies had revealed that one of the FRI orthologues, BnaA3.FRI, contributes to flowering time variation and growth type differentiation. Haplotype analysis of the four BnaFRI copies indicated that only BnaA3.FRI was highly conserved in winter type oilseed rape. Polymorphism analysis of BnaA3.FRI using PCR markers in a panel of 174 B. napus accessions identified four haplotypes, all of which showed significantly non-random distribution (P < 0.01) among different growth types and geographical regions. In addition, a large number of nonsynonymous mutations within the coding region of BnaA3.FRI were revealed. Both association analysis and transgenic functional complementation demonstrated that mutations in the coding sequence of BnaA3.FRI lead to weak alleles, and subsequently to flowering time variation. This study for the first time provides a molecular basis for flowering time control by BnaA3.FRI in B. napus, and will facilitate predictive oilseed rape breeding to select varieties with favorable flowering time and better adaption to latitude and seasonal shifts due to changing climate. |
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Keywords:Brassica napus; FRIGIDA; haplotype; flowering time; growth type |
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