Flowering time is a major determinant of adaptation, fitness and yield
in the allopolyploid species rapeseed (Brassica napus). Despite being a
close relative to Arabidopsis thaliana, little is known about the timing
of floral transition and which genes govern this process. Winter,
semi-winter and spring type rapeseed have important life history
characteristics that differ in vernalization requirements for flowering
and are important for growing rapeseed in different regions of the
world. In this study, we investigated the timing of vernalization-driven
floral transition in winter rapeseed and the effect of photoperiod and
developmental age on flowering time and vernalization responsiveness.
Microscopy and whole transcriptome analysis at the shoot apical
meristems of plants grown under controlled conditions showed that floral
transition is initiated within few weeks of vernalization. Certain
Bna.SOC1 and Bna.SPL5 homeologs were among the induced genes, suggesting
that they are regulating the timing of cold-induced floral transition.
Moreover, the flowering response of plants with shorter
pre-vernalization period correlated with a delayed expression of
Bna.SOC1 and Bna.SPL5 genes. In essence, this study presents a detailed
analysis of vernalization-driven floral transition and the aspects of
juvenility and dormancy and their effect on flowering time in rapeseed.