Evolutionary plasticity of MADS-box genes in ornamental plants: from floral development to horticultural improvement

The MADS-box gene family, particularly the ABCE-class genes, plays a pivotal role in regulating floral development and reproductive processes in angiosperms. Expansion of the MADS-box gene family through ancient whole-genome duplications and lineage-specific duplication events has generated extensive regulatory flexibility across flowering plants. This review summarizes current findings on the evolutionary expansion and functional diversification of MADS-box genes, with a focus on the evolution of the ABCE-class in ornamental plants. We highlight how differential gene retention, expression divergence, and functional specialization have shaped the remarkable morphological diversity of floral organs across flowering plants. Comparative analyses across angiosperms reveal a lineage-dependent distinction between phylogenetic A-class genes and the developmental A-function: while AP1 represents the canonical A-class gene in core eudicots, AGL6 -like genes fulfill ancestral A-function roles in early-diverging angiosperms, magnoliids, and monocots. Lineage-specific expansion and rewiring of ABCE gene networks, as observed in Orchidaceae, Asteraceae, and Rosaceae, have enabled reassembly of MADS-box protein complexes and rebalancing of expression domains, driving innovative floral forms. Beyond floral development, numerous MADS-box genes have diversified to function in flowering-time regulation and environmental stress responses, highlighting their broader adaptive significance beyond reproduction. This review provides an integrated evolutionary and functional perspective on MADS-box genes plasticity, and offers valuable insights for ornamental plant breeding and horticultural improvement.