ENLIGHT · ExploriNg Light signals InteGration into diatom pHoToacclimation

Light is essential for photosynthetic organisms, providing them with both energy and environmental information. These organisms sense light intensity and spectral quality through direct photoreceptors and indirect signals from photosynthesis, enabling them to activate finely tuned responses called photoacclimation. Although well studied in terrestrial plants, photoacclimation in aquatic systems, particularly oceanic ones, remains poorly understood due to the complexity and variability of underwater light environments. Here, diatoms are one of the most ecologically successful group. This project aims to understand how marine diatoms sense and integrate different light signals to regulate photosynthetic responses, and to identify the molecular regulatory mechanisms involved. Diatoms are particularly well-suited for this research because of their set of specialized photoreceptors. Among them, the phytochrome DPH has been recently suggested to act as a depth sensor, putatively involved in adjusting photosynthetic capacity to deep-sea light conditions. This established a preliminary link between DPH-mediated photosensing and photosynthesis, although full characterization of the light signals activating DPH responses is still lacking. Through complementary approaches, this project will investigate the functional significance of light sensing for photoacclimation, using diatom DPH as case study. Specific light quality and quantity signals triggering DPH or plastid systems will be identified, together with consequent photosynthetic responses. Molecular pathways activated will be uncovered, to detect key genes targeted by DPH signalling cascade. Also, conserved or diversified photoacclimation strategies will be investigated across diatom lineages. Ultimately, this project will advance understanding of how marine microalgae face dynamic light conditions, providing the foundation for assessing their responses to complex environmental changes and implications for ecosystems.