Effects of gene multiplication on flowering time regulation in spring and winter varieties of Brassica napus

Brassica napus (oilseed rape) is an economically important crop species that exhibits considerable varietal differences in flowering behaviour. Efforts to translate knowledge of flowering time control from model species are complicated by the evolutionary history of the crop. Whole genome duplication events have resulted in multiple copies of genes being present in the B. napus genome. A better understanding of the roles additional gene copies play during the floral transition would aid predictive models in directing future breeding efforts. As a first step towards unravelling the regulatory network underlying the floral transition in the crop, a transcriptomic time series was conducted and used to investigate gene expression during the floral transition. Expression differences between homologous flowering time genes indicated that duplicated genes occupy separate locations in the gene regulatory network. This suggests the complexity of the regulatory network is vastly increased in B. napus relative to model species, and that the duplicated genes are likely to have different roles during the floral transition. Duplicated genes were observed to diverge in different ways. Loss of regulatory elements surrounding certain B. napus TFL1 homologues correlated with expression changes, highlighting the importance of cis-regulatory elements in the evolution of gene function. Sequence differences between B. napus FD homologues were found to alter the predicted dimerization affinities of the proteins. Expression variation between B. napus FLC homologues suggests only some confer a vernalization response, revealing these genes have diverged to have altered sensitivity to cold. The finding that multiple homologues of the same flowering time gene in B. napus are expressed but show different expression dynamics reveals that the floral regulatory network from model species cannot be directly translated, but will require modification. This added complexity likely contributes to the developmental and genetic plasticity that has been exploited in this important crop