Diatom phytochromes integrate the entire visible light spectra for photosensing in marine environments

Aquatic life is strongly structured by light gradients, with gradual decrease in light intensity and differential attenuation of sunlight wavelengths with depth. How phytoplankton perceive these variations is unknown. By providing the first in vivo quantitative assessment of the action of marine diatom phytochrome photoreceptors (DPH), we show that they efficiently trigger photoreversible responses across the entire light spectrum, unlike current models of phytochrome photosensing. The distribution and activity of DPHs in the environment indicate that they are extremely sensitive detectors of spectral light variations related to depth and optical properties of the water column in temperate and polar oceans, revealing a completely novel view of how light is perceived in the marine environment.