Evolutionary Dynamics of <i>FLC</i>-like MADS-Box Genes in Brassicaceae

MADS-box genes encode transcription factors that play important roles in the development and evolution of plants. There are more than a dozen clades of MADS-box genes in angiosperms, of which those with functions in the specification of floral organ identity are especially well-known. From what has been elucidated in the model plant <i>Arabidopsis thaliana</i>, the clade of <i>FLC</i>-like MADS-box genes, comprising <i>FLC</i>-like genes <i>sensu strictu</i> and <i>MAF</i>-like genes, are somewhat special among the MADS-box genes of plants since <i>FLC</i>-like genes, especially <i>MAF</i>-like genes, show unusual evolutionary dynamics, in that they generate clusters of tandemly duplicated genes. Here, we make use of the latest genomic data of Brassicaceae to study this remarkable feature of the <i>FLC</i>-like genes in a phylogenetic context. We have identified all <i>FLC</i>-like genes in the genomes of 29 species of Brassicaceae and reconstructed the phylogeny of these genes employing a Maximum Likelihood method. In addition, we conducted selection analyses using PAML. Our results reveal that there are three major clades of <i>FLC</i>-like genes in Brassicaceae that all evolve under purifying selection but with remarkably different strengths. We confirm that the tandem arrangement of <i>MAF</i>-like genes in the genomes of Brassicaceae resulted in a high rate of duplications and losses. Interestingly, <i>MAF</i>-like genes also seem to be prone to transposition. Considering the role of <i>FLC</i>-like genes <i>sensu lato</i> (<i>s.l.</i>) in the timing of floral transition, we hypothesize that this rapid evolution of the <i>MAF</i>-like genes was a main contributor to the successful adaptation of Brassicaceae to different environments.