Flowering time variation in oilseed rape (Brassica napus L.) is associated with allelic variation in the FRIGIDA homologue BnaA.FRI.a

Abstract

Oilseed rape (Brassica napus L.) is a major oil crop which is grown worldwide. Adaptation to different environments and regional climatic conditions involves variation in the regulation of flowering time. Winter types have a strong vernalization requirement whereas semi-winter and spring types have a low vernalization requirement or flower without exposure to cold, respectively. In Arabidopsis thaliana, FRIGIDA (FRI) is a key regulator which inhibits floral transition through activation of FLOWERING LOCUS C (FLC), a central repressor of flowering which controls vernalization requirement and response. Here, four FRI homologues in B. napus were identified by BAC library screening and PCR-based cloning. While all homologues are expressed, two genes were found to be differentially expressed in aerial plant organs. One of these, BnaA.FRI.a, was mapped to a region on chromosome A03 which co-localizes with a major flowering time quantitative trait locus in multiple environments in a doubled-haploid mapping population. Association analysis of BnaA.FRI.a revealed that six SNPs, including at least one at a putative functional site, and one haplotype block, respectively, are associated with flowering time variation in 248 accessions, with flowering times differing by 13–19 d between extreme haplotypes. The results from both linkage analysis and association mapping indicate that BnaA.FRI.a is a major determinant of flowering time in oilseed rape, and suggest further that this gene also contributes to the differentiation between growth types. The putative functional polymorphisms identified here may facilitate adaptation of this crop to specific environments through marker-assisted breeding.

Functional alleles of the flowering time regulator FRIGIDA in the Brassica oleraceagenome

“…Variations in this domain in BoFRIb result in the loss of a predicted coiled-coil, emphasising a possible functional significance for the amino acid polymorphisms in this region. A similar degree of divergence from AtFRI is found in the N-terminal region of an orthologue of FRI isolated from the halophyte T. halophila and in four orthologues of FRI identified in B. napus [18,22]. By contrast, there is extensive amino acid conservation between BoFRIa, BoFRIb and AtFRI in the central and C-terminal regions (Figure 1c).…”

Size matters: Significant negative relationship between mature plant mass and residual neonicotinoid levels in seed-treated oilseed rape and maize crops

“…For example, late maize hybrids normally produce larger plants with more leaves than early varieties (Sangoi, 2001) and some oilseed rape varieties have an average flowering time some thirty days later than others (Wang et al, 2011), allowing more time for plant growth and, consequently, greater neonicotinoid dilution.…”

Vernalization – a cold-induced epigenetic switch

“…The rapid-cycling habit has evolved independently in many Arabidopsis accessions through mutations in FRI, the upregulator of FLC (Gazzani et al, 2003;Johanson et al, 2000;Shindo et al, 2005). Allelic variation at FRI also appears to contribute to differences in vernalization requirement in different Brassica species (Irwin et al, 2012;Wang et al, 2011). Variation in Arabidopsis FLC itself only rarely accounts for the rapid-cycling habit.…”