Eelgrass (Zostera marina) is the dominant seagrass in the northern hemisphere and provides the foundation of highly productive ecosystems that rival tropical rain forests and coral reefs in ecosystem services.
A seagrass meadow in foggy northern California © SA Krueger-Hadfield
Zostera isn’t really a grass, but a monocot, like a tulip. It absorbs nutrients and pollutants and helps prevent erosion in near-shore marine ecosystems.
But it appears that seagrasses recolonized
the sea on at least three independent occasions to form the basis of one of the most productive and widespread coastal ecosystems on the planet (Olsen et al. 2016).
A team led by Jeanine Olsen, Thorsten Reusch and Yves Van de Peer, recently published the Zostera marina genome in Nature. This genome represents a huge advance for evolutionary ecologists working at the land-sea interface.
Olsen et al. (2016) found Zostera had lost and gained genes that enabled it to journey back to the sea from whence it came. For example, the entire repertoire of stomatal genes were lost. Stomata enable gas exchange and prevent water loss in land plants, but something that is less important to a seagrass living underwater. Similarly, seagrasses also lost genes involved in the response to UV damage as its dimly lit water home which is characterized by low penetration of UV-B.
However, with these gene losses, seagrasses have also have gained genes as they re-entered the sea, during what Olsen et al. (2016) contend is one of the most severe habitat shifts undertaken by any angiosperm. In order to cope with desiccation and osmotic stress, seagrasses have regained the cell wall compounds that were lost when marine algae transitioned to land.
The Zostera genome fills in a missing piece of angiosperm evolution and will improve our understanding of biochemical pathways. This may have ramifications to important crop plants and improve our understanding of salt tolerance in these species.
Seagrasses thrive over a huge latitudinal gradient in abiotic stressors from ice at high latitudes to the baking sun at lower latitudes. Understanding how seagrasses thrive across these environmental gradients will help us understanding how they will cope with environmental changes, such as ocean acidification or increasing seawater temperatures.
The genome will help researchers to delve into exactly which genetic elements facilitate such high biomass production and resilience (Williams 2016).
Finally, seagrasses are among the most impacted ecosystems worldwide, due in large part to anthropogenic disturbances from the construction of marinas to aquaculture. As Williams (2016) highlights,
[The Zostera] genome-sequencing feat may have come just in time [as an] understanding of the genes that adapt these fascinating species to marine life can only help [conservation] efforts.
References
Olsen et al. (2016) The genome of the seagrass Zostera marinareveals angiosperm adaptation to the sea. Nature 530, 331–335
Williams (2016) Genomics: From sea to sea. Nature 530, 290–291