Thraustochytrids are marine single-cell protists that produce large amounts of PUFAs, such as DHA. They accumulate PUFAs in lipid droplets (LDs), mainly as constituent(s) of triacylglycerol (TG). We identified a novel protein in the LD fraction of F26-b using 2D-difference gel electrophoresis. The protein clustered with orthologs of thraustochytrids; however, the cluster was evolutionally different from known PAT family proteins or plant LD protein; thus, we named it thraustochytrid-specific LD protein 1 (TLDP1). TLDP1 surrounded LDs when expressed as a GFP-tagged form. Disruption of the gene decreased the content of TG and number of LDs per cell; however, irregular and unusually large LDs were generated in -deficient mutants. Although the level of TG synthesis was unchanged by the disruption of, the level of TG degradation was higher in -deficient mutants than in the WT. These phenotypic abnormalities in-deficient mutants were restored by the expression of These results indicate that TLDP1 is a thraustochytrid-specific LD protein and regulates the TG accumulation and LD morphology in F26-b.

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