Molecular Mechanism, Evolution, Expression, and Functional Analyses of MAF/FLC Clade Members in Pak-Choi (Brassica rapa ssp. chinensis)

The MAF (MADS AFFECTING FLOWERING)/FLC (FLOWERING LOCUS C) subfamily is one of the key families that control flowering. This family has been well studied and characterized in Arabidopsis thaliana and other model plants. However, information regarding the evolution and functions of MAF/FLC genes in Brassica rapa (B. rapa) is limited. To further study the evolutionary history of MAF/FLC family during flowering of Pak-choi (B. rapa ssp. chinensis), the evolutionary patterns, footprints, and conservation of the MAF/FLC family in selected plants were investigated. The results showed that splitting of Brassica-Arabidopsis resulted in a preferential retention of the MAF/FLC family in Brassicas. Sequence similarity and the intracellular expression pattern of BrMAF2 suggested that the function of the MAF/FLC family might be conserved in B. rapa. However, protein interactions revealed that given the high sequence similarity between BrMAFs and AtMAFs, functional divisions of the BrMAF gene family still occurred. Additionally, the temporal and spatial expression of MAF/FLC genes in B. rapa further confirmed that a functional division occurred during gene duplication. Meanwhile, our finding partially confirmed the triplication event in B. rapa at the gene expression level. Furthermore, we found that high gene sequence homology does not indicate high function conservation. Thus, we suggest that when we name a gene in other plants, both gene sequence homology and function verification are needed. In addition, our studies also suggest that a new candidate BrMAF3 gene may be more important than other BrMAFs in the response to brief cold spells. Finally, the results of this study can help to better understand the evolution and function of MAF/FLC in plants.