Autophagy induced accumulation of lipids in pgrl1 and pgr5 of Chlamydomonas reinhardtii under high light

Abstract

Chlamydomonas (C) reinhardtii cells (wild-type CC125 and 137AH, and cyclic electron transport dependant mutants pgrl1 and pgr5) were grown in high light 500 {micro}mol photons m-2 s-1 where the growth was significantly enhanced after three days. The starch and lipid contents were also increased; however, starch content was decreased in pgr5. Further, the Nile Red fluorescence shows that a significant amount of lipid bodies were observed in pgr5 cells under high light. Similarly, the electron micrographs show that large vacuoles were formed in high light stress despite the change in stacks of grana structure. We also observed increased production of reactive oxygen species (ROS) that could lead to autophagy. Inline, a significant increase of ATG8 protein was noticed in pgr5, which is a hallmark characteristic for autophagy formation. Consequently, the triacylglycerol (TAG) content was increased due to DGAT and PDAT enzymes expression, especially in pgr5. Here, the TAG synthesis would have been obtained from degraded membrane lipids in pgr5. Additionally, mono, polyunsaturated, and saturated fatty acids were identified more in the high light condition. Our study shows that the high light induces ROS, leads to autophagy and TAGs accumulation, which is stored as an energy source to acclimatize the algae.