Molecular evolution of floral development genes in spiral gingers with divergent pollination syndromes

The evolution of floral traits is a major contributor to plant diversification and pollination specialization. In the Neotropical genus Costus , closely related species exhibit distinct pollination syndromes, offering an opportunity to investigate the molecular basis of floral adaptation. We present the first comparative analysis of key floral developmental genes in two closely related spiral gingers with contrasting pollination syndromes: Costus bracteatus (bee-pollinated) and Costus zingiberoides (hummingbird-pollinated). Using newly generated genome assemblies, phylogenetic inference, positive selection analyses, and in silico protein modeling, we identified signatures of episodic positive selection in four genes, with AGL6 and CUC -like showing lineage-specific divergence in C. zingiberoides . Structural comparisons indicated notable conformational differences, particularly in conserved domains such as the MADS-box and NAC domains, with alanine scanning highlighting both stabilizing and destabilizing mutations that may affect protein functionality. Overall, evolutionarily significant divergence among floral developmental genes in these Costus lineages is concentrated at a limited number of sites rather than widespread across genes, suggesting that a small set of substitutions may contribute to differences in floral morphology, providing insights into the genetic architecture of floral diversification in monocots.