Torres Romero, I.; Legeret, B.; Huleux, M.; Sorigue, D.; Damm, A.; Cuine, S.; Veillet, F.; Blot, C.; Brugiere, S.; Coute, Y.; Garneau, M. G.; Kotapati, H.; Xin, Y.; Xu, J.; Bates, P. D.; THIAM, A. R.; Beisson, F.; Li-Beisson, Y.

Lipid droplets (LDs) are the major sites of lipid and energy homeostasis. However, few LD biogenesis proteins have been identified. Here, using Chlamydomonas as a model, we show that ABHD1, a member of the /{beta} hydrolase domain-containing protein family, is a novel type of LD-associated protein which stimulates LD formation through two distinct actions on the LD surface, one enzymatic and the other structural. ABHD1 was localized to LD surface in Chlamydomonas cells. The knockout mutants contained similar amounts of triacylglycerols (TAG) but their LDs showed an increased content in lyso- derivatives of the betaine lipid diacylglyceryl-N,N,N-trimethylhomoserine (DGTS). Over-expression of ABHD1 in Chlamydomonas induced LD formation and boosted TAG content, suggesting a key role in LD biogenesis. The purified recombinant ABHD1 protein hydrolyzed lyso-DGTS, producing a free fatty acid and a glyceryltrimethylhomoserine moiety. In vitro experiments using droplet-embedded vesicles showed that ABHD1 promoted LD emergence. Taken together, these results identify ABHD1 as a new player in LD formation by its lipase activity on lyso-DGTS and by its distinct biophysical property. This study further suggests that lipases targeted to LDs and able to act on their polar lipid coat may be interesting tools to promote LD assembly in eukaryotic cells.