Characterization of the MADS-Box Gene Family in Akebia trifoliata and Their Evolutionary Events in Angiosperms

As the largest clade of modern plants, flower plants have evolved a wide variety of flowers and fruits. MADS-box genes play key roles in regulating plant morphogenesis, while basal eudicots have an evolutionarily important position of acting as an evolutionary bridge between basal angiosperms and core eudicots. Akebia trifoliata is an important member of the basal eudicot group. To study the early evolution of angiosperms, we identified and characterized the MADS-Box gene family on the whole-genome level of A. trifoliata. There were 47 MADS-box genes (13 type I and 34 type II genes) in the A. trifoliata genome; type I genes had a greater gene length and coefficient of variation and a smaller exon number than type II genes. A total of 27 (57.4%) experienced whole or segmental genome duplication and purifying selection. A transcriptome analysis suggested that three and eight genes were involved in whole fruit and seed development, respectively. The diversification and phylogenetic analysis of 1479 type II MADS-box genes of 22 angiosperm species provided some clues indicating that a γ whole genome triplication event of eudicots possibility experienced a two-step process. These results are valuable for improving A. trifoliata fruit traits and theoretically elucidating evolutionary processes of angiosperms, especially eudicots.