Florigen and antiflorigen gene expression correlates with reproductive state in a marine angiosperm, .

• Florigen and antiflorigen genes within the phosphatidylethanolamine-binding protein (PEBP) family regulate flowering in angiosperms. In eelgrass (), a marine foundation species threatened by climate change, flowering and seed production are crucial for population resilience. Yet, the molecular mechanism underpinning flowering remains unknown. • Using phylogenetic analysis and functional assays in , we identified thirteen genes in () and showed that four genes altered flowering phenotypes when overexpressed. We used quantitative RT-PCR on shoots from perennial and annual populations in Willapa Bay, USA to assess expression of these four genes in different tissue and expression changes throughout the growth season. • We demonstrated that and promote flowering, and and repress flowering in . Across five natural sites exhibiting different degrees of population genetic structure, and were expressed in leaves of vegetative and reproductive shoots and in stems and rhizomes of reproductive shoots. was distinctively expressed in leaves of vegetative and juvenile shoots, while levels increased after flowering shoots emerged. • Our results suggest that and may promote flowering, while may inhibit a floral transition in eelgrass. We speculate that may be involved in flowering shoot architecture.