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Many plant species have evolved to overwinter before flowering. In Arabidopsis thaliana a requirement for cold to flower is determined primarily by two genes FRIGIDA (FRI) and FLOWERING LOCUS C (FLC). FRI upregulates the expression of the floral repressor FLC, which in turn inhibits the expression of floral promoting genes like FLOWERING LOCUS T (FT). Prolonged cold temperatures overcome this inhibition through a process called vernalisation. Accessions of A. thaliana that do not need cold to flower often contain mutations at either FRI or FLC. Winter, spring and biennial cultivars of Brassica napus are grown for vegetable and seed production and variation for vernalisation requirement is investigated. Vernalisation treatment had a significant effect on flowering time and inflorescence architecture. Four orthologues of FRI and nine orthologues of FLC have previously been characterised in B. napus, but how these genes contribute to the vernalisation requirement is not fully understood. Molecular characterisation of FRI from a diverse panel of B. napus accessions revealed the presence of non-synonymous allelic variation at all four orthologues that was significantly associated with crop type. However, natural and induced mutations at FRI had a minimal effect on flowering time and FLC expression. Two genetic mapping approaches, Associative Transcriptomics and QTL-seq, were subsequently used to identify the genetic variation responsible for variation in vernalisation requirement in B. napus. Associations were detected in genomic regions that encompass orthologues of FLC and FT, but not FRI. Characterisation of the FLC and FT orthologues revealed the presence of DNA sequence and gene expression variation and I hypothesise this contributes to the flowering time differences measured. This work has enhanced our understanding of the vernalisation requirement of B. napus and could contribute to the improvement of cultivars with adapted flowering times and improved yields. |
