When bs are better than as: the relationship between B-Class MADS-Box gene duplications and the diversification of perianth morphology

Flowering plants (angiosperms) are the most species-rich and structurally diverse group of living plants. This evolutionary success is in great part due to morphological novelties characteristic to angiosperms such as the flower. The molecular mechanisms that allowed flowers to be formed and diversified are still unknown but certainly key roles are played by particular members of the MADS-box gene family. They encode transcriptional factors fundamental to several developmental processes, including the organization of floral structure in angiosperms. Studies concerning the evolution of the MADS-box gene family in flowering plants have uncovered several duplication events, followed by functional diversification of members of this gene family belonging to the so called ABC model. According to the literature, some of these duplication events involved B-class MADS-box genes and contributed to the diversification of angiosperm flower morphologies. In this review, we focus on examples of B-class gene duplications and their implications for flower structure and adaptation111