Genome Triplication Leads to Transcriptional Divergence of FLOWERING LOCUS C Genes During Vernalization in the Genus Brassica

Abstract

The genusBrassicaincludes oil crops, vegetables, condiments, fodder crops, and ornamental plants.Brassicaspecies underwent a whole genome triplication event after speciation between ancestral species ofBrassicaand closely related genera includingArabidopsis thaliana. Diploid species such asBrassica rapaandBrassica oleraceahave three copies of genes orthologous to eachA. thalianagene, although deletion in one or two of the three homologs has occurred in some genes. The floral transition is one of the crucial events in a plant’s life history, and time of flowering is an important agricultural trait. There is a variation in flowering time within species of the genusBrassica, and this variation is largely dependent on a difference in vernalization requirements. InBrassica, like inA. thaliana, the key gene of vernalization isFLOWERING LOCUS C(FLC). InBrassicaspecies, the vernalization response including the repression ofFLCexpression by cold treatment and the enrichment of the repressive histone modification tri-methylated histone H3 lysine 27 (H3K27me3) at theFLClocus is similar toA. thaliana.B. rapaandB. oleraceaeach have four paralogs ofFLC, and the allotetraploid species,Brassica napus, has nine paralogs. The increased number of paralogs makes the role ofFLCin vernalization more complicated; in a single plant, paralogs vary in the expression level ofFLCbefore and after vernalization. There is also variation inFLCexpression levels between accessions. In this review, we focus on the regulatory circuits of the vernalization response ofFLCexpression in the genusBrassica.