FLC genes control flowering time to varying degrees in a Brassica napus spring cultivar

Abstract

In the crop Brassica napus (oilseed rape), distinct growth types have been established that differ mainly in their vernalization requirement for flowering. The need for vernalization in Arabidopsis is controlled by the expression of the floral repressor FLOWERING LOCUS C (FLC), which also regulates cold-responsive flowering in B. napus. Notably, FLC homologs are also retained in spring oilseed rape despite its lack of vernalization requirement. To elucidate the functions of the nine BnFLC homologs in a spring type, we generated CRISPR/Cas9 knockout mutants of all homologs in the cultivar Westar. We show that the loss of BnFLC genes significantly accelerates flowering, demonstrating that BnFLC genes regulate flowering in spring types independently of vernalization. Transcriptomic analyses in leaves revealed distinct expression patterns among the BnFLC genes, with some remaining active during floral transition. Finally, no epigenetic regulation of the BnFLC homologs associated with flowering time was detected, while BnFLC.A03b carried persistent repressive marks and was constitutively silenced. Unexpectedly, additional flowering time regulators, including genes typically active in the shoot apical meristem, were expressed in leaves, with some showing altered expression and chromatin states in the mutant. These findings reveal that BnFLC genes are developmentally regulated and directly control flowering in spring oilseed rape, while also modulating the expression of other floral regulators in B. napus. CRISPR/Cas9 knockout of all nine BnFLC homologs reveals that these genes regulate flowering time developmentally in spring oilseed rape while influencing the expression and chromatin states of downstream flowering regulators.