Decoupling of plastid and endomembrane homeoviscous response to low temperature and darkness in Phaeodactylum tricornutum

Understanding how marine diatoms adapt to fluctuating environmental conditions is critical for deciphering their ecological success. Here, we investigated the lipidomic responses of the model diatom Phaeodactylum tricornutum to low temperatures (10°C), darkness, and combined stress. Using a detailed lipidomics approach, we revealed significant remodeling of plastidial and extraplastidial lipid species. Plastidial lipids showed increased unsaturation levels, particularly the 16:3-to-16:4 fatty acid switch, only under light conditions. This light-dependent adaptation suggests a tightly regulated mechanism that aligns lipid remodeling with photosynthetic activity. Phospholipids in the endomembrane system exhibited less dependency on light, with notable changes even under extended dark periods. These findings highlight distinct strategies employed by diatoms to maintain membrane fluidity and protect cellular processes during stress. Unlike plants, P. tricornutum lacks polygalactosyldiacylglycerols, underscoring a divergent adaptation pathway. Our results demonstrate that P. tricornutum adapts to cold and dark environments through lipid composition changes, supporting survival in variable marine habitats. This study provides critical insights into diatom resilience, paving the way for understanding their role in global biogeochemical cycles.