In marine and freshwater environments, algae are primary producers that are at the base of the food web and essential for all aquatic life. However, they are outnumbered ten to one by lytic viruses, which thereby shape the compositions of algal populations. Prasinoviruses are the most abundant large DNA viruses infecting eukaryotic marine microalgae. They thus have an important impact on global primary production.</p><p>We inoculated clonal lines of Ostreococcus tauri with the large DNA virus, OtV5 and subsequently obtained 38 independent clonal cells, all of which were resistant to this virus. Twenty-three lines were sequenced (RNA-Seq), 19 resistants and 4 susceptibles. We aimed to find genes with changed expression in resistant lines.