EMPHY

Phytoplankton is one of the most ecologically important groups on Earth. Phytoplankton is the base of the marine food web, is involved in several biogeochemical cycles and produces half of the dioxygen. However, phytoplankton is subject to global change and is in decline, raising questions on its capacity to adapt and regenerate diversity. To assess this, it is necessary to understand the evolution of spontaneous mutation rates. The spontaneous mutation rate defines the amount of new diversity that provides the raw material for adaptation. The mutation rate varies by several orders of magnitude, and recent researches on classical models (e.g. yeast) showed that this variation may be linked to the environment. If this is also the case for phytoplankton, its adaptive capacity varies between populations and species in different environments. Global change would also influence the mutation rate and thus the capacity to adapt, including to the global change itself. Therefore, EMPHY aims to make the first step to find out whether the environment is the main determinant of mutation rate for all types of mutations (nucleotide, short insertion-deletions and structural mutations) in phytoplankton. By combining mutation accumulation experiments in different salinities and temperatures with high-throughput genomic sequencing in short and long reads, two questions are addressed: Is the environment the main determinant of the mutation rate of phytoplankton? Does the mutation spectrum, i.e. the proportion of each type of mutation, change with the environment? EMPHY will use Ostreococcus tauri, a phytoplanktonic model from the green lineage. Ostreococcus tauri is ubiquitous in coastal areas, easy to grow, has a small haploid genome and a high-quality annotation that facilitates the identification of de novo mutations.