Sensing the rainbow: genetic and physiological responses to light quality in Ostreococcus, an ecologically important photosynthetic picoeukaryote

Phytoplankton is exposed to dramatic variations in light quality as it moves up and down the water column or encounters the presence of sediments in the water. We investigated the potential impact on Ostreococcus, a key marine photosynthetic picoeukaryote, by analysing changes in its transcriptome, pigment content and photophysiology after acclimation to monochromatic red, green or blue light. The clade B species RCC809, isolated from the deep Atlantic Ocean, responded to blue light by accelerating cell division at the expense of storage reserves, and by increasing the relative level of blue-light absorbing pigments. In contrast, it responded to red and green light by increasing its potential for photoprotection. In contrast, the clade A species OTTH0595, which originates from a shallow water environment, showed no difference in photosynthetic properties and minor differences in carotenoid contents between light qualities. These results demonstrate that light quality can have a major influence on the physiology of eukaryotic phytoplankton, and suggest that different light quality environments can drive selection for diverse patterns of responsiveness and environmental niche partitioning. HighlightWe characterise the effects of light quality on the transcriptome and photophysiology of Ostreococcus, a photosynthetic picoeukaryote, and show that responses are distinct between two ecotypes originating from different environments.