Comparative Genomic Insights into the Evolution of Aquatic and Terrestrial Adaptations in Plants

Terrestrial plants emerged from the water about 500 million years ago. Thereafter, they have diversified and now inhabit most of the Earth's surface. More recently, some species have re-adapted to an aquatic lifestyle, both in fresh and salt water, and fully or partially submerged. The mechanisms enabling these adaptations between terrestrial and aquatic life are extremely numerous, making it difficult to have a comprehensive overview of the phenomenon. Here, we performed a series of intraspecific measurements of the selection pressure affecting orthologous genes in eight aquatic and four terrestrial plants. Our analyses showed that aquatic plants have a relaxed selection pressure on nutrient assimilation mechanisms, probably linked to a greater bioavailability, as well as stronger adaptations to oxidative stress, while terrestrial plants evolution is linked to environment perception. Inter-species analyses have also highlighted a different evolution of chloroplast proteins between these two types of plants, suggesting adaptations to gas availability.