Autophagy induced accumulation of lipids inpgrl1andpgr5ofChlamydomonas reinhardtiiunder 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 μmol 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.

Expression ofChlamydomonas reinhardtiichloroplast diacylglycerol acyltransferase-3 is activated by light in concert with triacylglycerol accumulation

“…All these results suggest that light activation and light stress operate via related, but not necessarily identical, pathways. We propose that, while limiting light might only activate DGAT3 expression and TAG accumulation in the chloroplast ( Figure 6A), high light might also activate the expression of other enzymes that participate either in the chloroplast or the ER, as shown in Figure 6B and as also proposed previously (Chouhan et al, 2020;Goold et al, 2016). In addition, while DGAT3 expression might be a target of the light signal transduction cascade, other enzymes involved in TAG synthesis might be targets of stress/ROS signaling cascades ( Figures 6A and 6B).…”

“…Even though not all enzymes that can synthesize TAGs have been evaluated in our high light experiments, one could hypothesize that a more general response to stress is activated in these conditions compared to moderate light. Recently, it was demonstrated that high light induces ROS, which leads to TAG accumulation, in agreement with an increase in DGAT2A and PDAT (Chouhan et al, 2020). All these results suggest that light activation and light stress operate via related, but not necessarily identical, pathways.…”

“…We cannot conclude from our results what the relative contribution of each enzyme under high light is or whether DGAT3 expression is activated at irradiances other than those evaluated in this work, but we propose that the responses shown in B) are activated gradually as more photons that are absorbed cannot be stored by the mechanisms in A). In addition, while light response to limiting light might only involve the chloroplast, the response to high light might occur in both the plastid and the ER/cytosol, as proposed previously (Chouhan et al, 2020;Goold et al, 2016). Dashed lines correspond to processes yet to be fully demonstrated.…”

“…B) When cells are transferred to high light, we hypothesize that DGAT3-mediated TAG accumulation is not enough to harness the electron excess furnished by light. Hence, the expression of stress/ROS-related enzymes, such as DGAT1 (this work), PDAT and DGAT2 (Chouhan et al, 2020) is activated. We cannot conclude from our results what the relative contribution of each enzyme under high light is or whether DGAT3 expression is activated at irradiances other than those evaluated in this work, but we propose that the responses shown in B) are activated gradually as more photons that are absorbed cannot be stored by the mechanisms in A).…”

Biochemical and phylogenetic characterization of the wastewater tolerant Chlamydomonas biconvexa Embrapa|LBA40 strain cultivated in palm oil mill effluent

“…grown in BBM [49] and in other wastewaters, such as in vinasse (32%) and raw chicken manure (35%) [40]. Palmitic acid was also shown to be the main fatty acid produced under sodium acetate stress [50], at nutrient limitation [48,51,52], at high temperatures [53], and at high light intensity [54]. Indeed, a limitation in the content of nitrogen and phosphorous in the AP-POME culture supernatants is observed after 5 days of cultivation (Table 2).…”