Parallel Trajectories in the Evolution of C-class MADS-box Genes in Flowering Plants and Conifers

Gene duplication events frequently underpin phenotypic diversity due to the increase in genetic material that can be shaped by evolution. AGAMOUS (AG) genes are members of the MADS-box gene family that show conserved function in specifying reproductive organ identity in seed plants. While the function, expression, and evolution of these genes have been extensively studied in flowering plants, they remain understudied in gymnosperms. Consequently, little is known about how AG has contributed to reproductive diversity and evolution outside of the flowering plants. Here, we report that AG genes underwent two duplication events within conifers prior to the split between Cupressaceae and its sister family, Taxaceae. Further, we characterize the in situ expression pattern for each resulting paralog (AG1, AG2, and AG3) in seed cones of three Cupressaceae species, Metasequoia glyptostroboides, Taxodium distichum, and Juniperus virginiana. We discover gene expression patterns consistent with subfunctionalization: AG1 specialized in seed and sporangial development, AG2 in seed cone and seed coat development, and AG3 in ovuliferous scale development. This study provides an evolutionary mechanism for the development of unique seed cone reproductive traits in Cupressaceae. More broadly, our results uncover convergent patterns in the evolution of AG gene lineages across conifers and angiosperms.