Regulation of lipid metabolism by epigenetic mechanisms. Application to microalgae

Microalgae are emerging as valuable model systems for studying epigenetic regulation in unicellular eukaryotes and as promising platforms for biotechnological lipid production. In these organisms, DNA and RNA methylation, histone modifications, and non-coding RNAs form interconnected regulatory layers that shape chromatin structure, genome stability, transcriptional responses, and metabolic plasticity. This review synthesizes current knowledge on epigenetic mechanisms in microalgae, with particular emphasis on environmental responsiveness, and links to lipid metabolism. The major epigenetic pathways will be described in model species, including cytosine and adenine DNA methylation, RNA methylation, histone post-translational modifications, and RNA-guided silencing mediated by small and long non-coding RNAs. Then it will be reported how environmental drivers such as salinity, nutrient limitation, light, temperature, and carbon availability remodel the microalgal epigenome. Finally, the evidence connecting epigenetic regulation to lipid accumulation will be presented, including methylation-dependent carbon reallocation, histone-modification dynamics under nutrient stress, and RNA-based regulation of lipid-related genes. Chemical perturbation and emerging epigenome-editing approaches further support the functional relevance of these pathways, although interpretation remains complicated by stress-associated secondary effects and strong lineage dependence. Overall, available studies indicate that epigenetic regulation contributes to both environmental acclimation and metabolic rewiring in microalgae, but direct causal links to lipid productivity remain limited to a small number of systems. A better mechanistic understanding of these processes will be essential for exploiting epigenetic regulation as a lever for strain improvement and sustainable lipid biotechnology.