Role of melatonin in regulation of lipid accumulation, autophagy and salinity-induced oxidative stress in microalga Monoraphidium sp. QLY-1

The aim of this study was to explore the effect of melatonin (MT) on lipid accumulation in Monoraphidium sp. QLY-1 under salinity stress. The interconnection between MT, oxidative stress and autophagy in the regulation of lipid synthesis was also clarified. MT application significantly promoted the lipid content, peaking at 51.74%, which was 1.16-and 1.44-fold higher than those induced by salinity stress alone (44.77%) and control group (35.96%), respectively. Exogenous MT also upregulated the transcription levels of lipogenesis-related genes and decreased salinity stress-induced oxidative stress. Interestingly, the application of MT upregulated autophagic activity, which led to the 1.47-fold upregulation of autophagy-related atg8 gene expression. Additional results demonstrated that autophagy promotion led to further increases in lipid accumulation by involving lipogenesis gene expression and ROS signalling in cells treated with MT under salinity stress conditions. The maximum lipid content (54.26%) was achieved by treatment with MT and rapamycin (RAPA), an activator of autophagy. Taken together, these findings indicate that combination of MT and salinity stress is a valuable strategy for enhancing lipid production in microalgae and provides novel insights into the regulatory mechanisms underlying the effects of MT and autophagy on the promotion of lipid synthesis and improvements to algal tolerance.

Automated summary

The study found that melatonin significantly promoted lipid accumulation in Monoraphidium sp. QLY-1 under salinity stress by upregulating lipogenesis-related genes, reducing oxidative stress, and promoting autophagic activity. Furthermore, the combination of melatonin and the autophagy activator rapamycin further increased lipid content, suggesting a valuable strategy for enhancing lipid production in microalgae.