Phytoplankton are aquatic microscopic photosynthetic organisms responsible for about half of the photosynthetic activity on Earth. Over the past two decades, breakthroughs in genomics and ecosystem biology have significantly expanded our understanding of the crucial role these microbes play in global ecosystems.
The life of phytoplankton is profoundly influenced by the underwater light distribution, which diminishes in intensity and changes in spectrum with depth. Phytoplankton have evolved effective systems for optimizing light harvesting and energy generation through photosynthesis. However, the role of light sensing in acclimation mechanisms, which control growth and distribution of these phototrophs across different environments, remains poorly understood. To address these gaps, we are conducting integrated analyses of light-driven processes in diatoms, a prominent and highly diverse group of phytoplankton that stand at the crossroads of several evolutionary lineages. Recent functional studies in diatom model species and environmental investigations have identified new regulators of photosynthesis, photoreceptor variants, and a long-sought circadian clock controlling diatom responses to periodic light/dark cycles. Notably, sensors typically responsive to red and far-red light, such as the Diatom Phytochrome (DPH) have been described despite their presence seems counterintuitive in the red-absorbing water column. Our recent research reveals that DPH indeed mediates photoreversible responses across the entire underwater light spectrum, acting as a sensitive detector of optical depth. The observed regulation of photosynthesis acclimation by DPH links the optical depth detection with a relevant physiological response.
These findings provide new insights into how light-driven processes have evolved, diversified, and function in the marine environment. They also highlight the central role of photoregulation in the functional biodiversity of phytoplankton and the importance of integrated laboratory and environmental studies for understanding life in marine ecosystems.