Decoding flowering regulation in neotropical orchids: insights from epiphytic and terrestrial species

Orchids exhibit dramatic differences in flowering transitions across their evolutionarily diverse life forms and habitats. Some bloom year-round, while others flower biannually, annually, or biennially. Flowering adaptations have been crucial for orchid diversification, reaching 29 000 species. We analyzed morpho-anatomical changes and differentially expressed genes (DEGs) during the transition from vegetative to reproductive meristems in three Andean orchid species: the epiphytic Cattleya trianae (Lindl. & Rchb.f.), and the terrestrials Elleanthus aurantiacus (Lindl.) Rchb.f. and Epidendrum fimbriatum Kunth. Our analyses identified shared key flowering promoters, including FT2A, FUL1A, FUL1B, LFY, and SOC1L1a, and common flowering repressors, such as AP2L, COL4A, COL4B, GHD7, SVP2A, and TFL1 in all three species. Terrestrial species lacking storage organs have a higher proportion of DEGs that are transcription factors, while the epiphytic C. trianae, with pseudobulbs, shows additional enriched categories like carbohydrate and lipid metabolism, and transport proteins. Most flowering integrators are duplicated in Orchidaceae, but only some copies are transcriptionally active and retain expected protein interactions. We identified major flowering hubs shared among the species, as well as pathways exclusive to epiphytic species with storage organs. Our results set the stage for future functional analyses of key flowering regulators in one of the most speciose angiosperm families.