Identification of a putative patatin-like phospholipase domain-containing protein 3 (PNPLA3) ortholog involved in lipid metabolism in microalga Phaeodactylum tricornutum

Patatin-like phospholipase domain-containing protein 3 (PNPLA3) has been associated with nonalcoholic fatty liver disease which promoted hepatic lipid synthesis. With high lipid content, microalgae are found to be a potential source of biofuel. Phaeodactylum tricornutum, a fast-growing and oleaginous microalga, is a promising target for enhancing the biofuel by means of metabolic engineering. Here a putative PtPNPLA3 gene from P. tricornutum was cloned and characterized in transgenic P. tricornutum for the first time. Amino acid sequence analysis showed a high homology between PNPLA3 from P. tricornutum and other organisms. Overexpression of PtPNPLA3 increased the transcript level of PtPNPLA3 by 70% in transgenic microalgae compared to wild type. The neutral lipid content in transgenic microalgae was significantly increased by 70%, representing a notable enhancement of the lipid productivity in the transgenic microalgae. The fatty acid profile was also altered as determined by GC-MS analysis, with a significant increase of C20:4 in the transgenic microalgae compared to wild type. This work identified a microalgal PNPLA3 and proved it to be an important node in regulating lipid accumulation in microalgae, also demonstrating an efficient way to improve lipid productivity in microalgae by metabolic engineering.