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The phosphatidylethanolamine-binding protein DTH1 mediates degradation of lipid droplets in Chlamydomonas reinhardtii
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Edité par CCSD ; National Academy of Sciences -
International audience. Lipid droplets (LDs) are intracellular organelles found in a wide range of organisms and play important roles in stress tolerance. During nitrogen (N) starvation, Chlamydomonas reinhardtii stores large amounts of triacylglycerols (TAGs) inside LDs. When N is resupplied, the LDs disappear and the TAGs are degraded, presumably providing carbon and energy for regrowth. The mechanism by which cells degrade LDs is poorly understood. Here, we isolated a mutant ( dth1-1 , Delayed in TAG Hydrolysis 1) in which TAG degradation during recovery from N starvation was compromised. Consequently, the dth1-1 mutant grew poorly compared to its parental line during N recovery. Two additional independent loss-of-function mutants ( dth1-2 and dth1-3 ) also exhibited delayed TAG remobilization. DTH1 transcript levels increased sevenfold upon N resupply, and DTH1 protein was localized to LDs. DTH1 contains a putative lipid-binding domain (DTH1$^{LBD}$) with alpha helices predicted to be structurally similar to those in apolipoproteins E and A–I. Recombinant DTH1$^{LBD}$ bound specifically to phosphatidylethanolamine (PE), a major phospholipid coating the LD surface. Overexpression of DTH1$^{LBD}$ in Chlamydomonas phenocopied the dth1 mutant’s defective TAG degradation, suggesting that the function of DTH1 depends on its ability to bind PE. Together, our results demonstrate that the lipid-binding DTH1 plays an essential role in LD degradation and provide insight into the molecular mechanism of protein anchorage to LDs at the LD surface in photosynthetic cells.
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