Angiosperms represent the most abundant and diverse lineage of land plants, and their evolutionary success is closely linked to major reproductive innovations, including the origin of flowers and the embryo-nourishing endosperm. Many of the genes underlying these innovations belong to the MADS-box transcription factor family. While the functions of MIKCC-type MADS-box genes in floral development are well established, this review focuses on the other two lineages, M-type and MIKC*-type genes, and synthesizes recent advances in the understanding of their functional roles and evolutionary histories. M-type genes are key regulators of female gametophyte and endosperm development, indicating that two hallmark features of angiosperms were promoted by distinct MADS-box gene classes. MIKC*-type genes govern pollen development and are phylogenetically more closely related to M-type genes; together, they form the plant-specific Type I clade, which primarily regulates gametophytic programs. This contrasts with the Type II clade, comprising MIKCC-type genes that diversified to control sporophytic development. Both Type I and Type II clades originated from plant-specific duplications of ancestral MEF2-like genes. Through extensive lineage-specific expansion and diversification, these MADS-box transcription factors have played a central role in plant terrestrialization by integrating stress responses with reproductive development and the patterning of progressively complex body plans.
Qiu et al. (Tue,) studied this question.