Marine Angiosperm Genome Initiative (MAGI)

Seagrasses comprise the only submerged marine angiosperms. This feat of adaptation occurred in at least three independent freshwater lineages within the monocot order of Alismatales, offering the unique opportunity to study convergent versus lineage-specific adaptation to a fully marine lifestyle. The Marine Angiosperm Genome Initiative (MAGI) sequenced and presented chromosome-level genome assemblies from a representative species in each of the seagrass lineages - Posidonia oceanica (Posidoniaceae), Cymodocea nodosa (Cymodoceaceae), and Thalassia testudinum (Hydrocharitaceae). Genome analysis reveals that all seagrasses share an ancient whole genome triplication (WGT) event, dating to the early evolution of the Alismatales. Additional whole genome duplication (WGD) events were uncovered for C. nodosa and for Z. marina. Comparative analysis of selected gene families suggests that the transition from the submerged-freshwater to submerged-marine environment did not require revolutionary changes. Major gene losses related to, e.g., stomata, volatiles, defense, and lignification, are likely a consequence of the submerged lifestyle rather than the cause ('use it or lose it'). Likewise, genes, often retained from the WGD and WGT, were co-opted for functions requiring the alignment of many small adaptations ('tweaking'), e.g., osmoregulation, salinity, light capture, carbon acquisition, and temperature.