Seagrass genome provides insights into the way marine ecosystems might adapt to climate change
Coastal ecosystems are highly productive and diverse, and seagrasses form the bedrock of these habitats. Seagrasses are marine angiosperms (flowering plants) that underwent a severe habitat shift: They colonized the seas from a terrestrial environment, a move that required extreme structural and physiological adaptations. An international research team led by Yves Van de Peer (VIB/UGent, BIG N2N) and Jeanine Olsen (GELIFES, University of Groningen) has now analyzed the genome of Zostera marina, the first marine angiosperm to be fully sequenced, and revealed the genetic changes that accompanied the radical environmental transition.
Vast seagrass meadows are an essential part of coastal ecosystems, harboring a wealth of biodiversity. These habitats are present along the shorelines of all continents, save for Antarctica, and their environmental and ecological impact is comparable to that of rainforests and coral reefs. However, seagrass beds are increasingly threatened by factors such as pollution and a growing coastal population.
High effort, high gain
Terrestrial in origin, seagrasses evolved and eventually colonized the sedimentary shorelines of the world’s oceans. While such an extreme change in habitat is rare for any organism, seagrasses had a lot to gain from the transition: They found a vast new habitat free of terrestrial competitors or pests. However, life beneath the waves also presented challenges that required drastic changes to the plant’s structure and function.
In a collaborative effort, researchers from VIB and the Groningen Institute of Evolutionary Life Sciences (GELIFES) analyzed the genome of Zostera marina, the most common seagrass in the Northern Hemisphere. Their study, which was published in the top-notch journal Nature, offers a unique insight into the genomic gains and losses that accompanied Zostera marina’s environmental shift.
Several critical structural and functional features of angiosperms disappeared during Zostera marina’s dive into the blue. All genes involved in the development of stomata were lost, as were those responsible for the synthesis and sensing of volatile molecules such as ethylene and terpenoids. Defense mechanisms against terrestrial pathogens were also thrown in the genetic trash bin, recalling the evolutionary motto: “If you don’t use it, you lose it.” A significant change in light intensity and composition required additional adaptation: The low penetration of UV-B, red and far-red wavelengths resulted in a corresponding loss of UV-light resistance genes and receptors for red and far-red light.
Genetic adaptations to marine conditions such as high salinity and osmotic stress were also found, mainly regarding ion transportation and homeostasis. Although the Zostera marina cell walls show signs of adaptation to the underwater environment, such as improved water retention, they also display features common to land plants, revealing the terrestrial origin of this seagrass.
The Zostera marina genome could be an important source of information on how plants adapt to changing environments. VIB/UGent professor Yves Van de Peer comments: “Today, more and more people are inhabiting our planet’s coastal areas. Consequently, many ecosystems are under pressure, including seagrass beds. As a result, other ecosystems may be at risk, too. Seagrasses not only sustain harvestable fish and invertebrates like lobsters, shrimp and crabs; they also play a part in controlling erosion effects and capturing carbon dioxide. Having unraveled the genomic basis of Zostera marina’s complex adaptations to life in ocean waters, this study can advance ecological studies on how marine ecosystems might adapt to climate change.”