Regulation of TG accumulation and lipid droplet morphology by the novel TLDP1 in Aurantiochytrium limacinum F26-b

Abstract

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 <i>Aurantiochytrium limacinum</i> 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 <i>tldp1</i> gene decreased the content of TG and number of LDs per cell; however, irregular and unusually large LDs were generated in <i>tldp1</i>-deficient mutants. Although the level of TG synthesis was unchanged by the disruption of <i>tldp1</i>, the level of TG degradation was higher in <i>tldp1</i>-deficient mutants than in the WT. These phenotypic abnormalities in <i>tldp1</i>-deficient mutants were restored by the expression of <i>tldp1</i> These results indicate that TLDP1 is a thraustochytrid-specific LD protein and regulates the TG accumulation and LD morphology in <i>A. limacinum</i> F26-b.