The project aims to study the plastidial lipid metabolism of two microalgae using the CRISPR-Cas9 system. This project is in the context of increasing atmospheric CO2 and climate change. Photosynthetic microalgae can capture CO2 and convert it into lipids, which is useful for various industrial applications. However, stramenopile microalgae have a unique cellular structure, making it challenging to apply knowledge from simpler models. Therefore, we need a better understanding of lipid synthesis in these microalgae to enhance their ability to sequester CO2 and produce lipids for biotechnological applications. Our research focuses on the biosynthesis pathway of plastidial galactoglycerolipids, the dominant lipids in photosynthetic organisms, in two model microalgae, Phaeodactylum tricornutum and Microchloropsis gaditana. These lipids consist of a glycerol backbone, fatty acids (FAs), and galactose residues. FAs are produced in the plastids, then modified in other parts of the cell to form long-chain polyunsaturated FAs, such as eicosapentaenoic acid (EPA). The transport pathway of EPA to the plastid is still poorly understood. Then, EPA is esterified onto glycerol-3-phosphate (G3P) through enzymes called acyltransferases (AT). This study is one of the key research areas of our team. The synthesis of galactoglycerolipids in stramenopiles involves several steps, including esterifying an FA onto G3P, forming phosphatidic acid, converting it to diacylglycerol, and adding galactose residues to form the final lipids. In summary, our research aims to understand how these microalgae produce important lipids for CO2 capture and industrial applications. This research is relevant for combating climate change and reducing our dependence on fossil fuels.