Synthesis of fatty acid phytyl esters in chloroplasts of Arabidopsis thaliana (617.7)

Abstract

During senescence or stress, chloroplast membranes undergo severe changes. Galactolipids are broken down, releasing free fatty acids. At the same time, the plastoglobule size increases. Plastoglobules serve as lipid‐storage particles in chloropalsts, containing mostly neutral lipids such as triacylglycerol, tocopherol and fatty acid phytyl esters. Two genes (Phytyl Ester Sythase 1, PES1; Phytyl Ester Synthase 2, PES2) were identified that are primarily responsible for the synthesis of fatty acid phytyl esters in chloroplasts. In addition to phytyl ester synthesis, PES1 and PES2 harbor diacylglycerol acyltransferase activity and are presumably involved in the synthesis of triacylglycerol. An Arabidopsis double mutant (pes1 pes2) deficient in the two PES genes shows a reduction in the amounts of fatty acid phytyl esters and of triacylglycerol by more than 90 and by 30%, respectively. It is known that the bulk of triacylglycerol is produced by cytosolic acyltransferases at the ER. To investigate the role of PES1/PES2 in plastidial triacylglycerol production, we isolated chloroplasts from wild type and pes1 pes2 plants and analyzed the lipid composition of the individual chloroplast fractions. In addition to PES1 and PES2, the Arabidopsis genome contains 4 other genes encoding Esterase‐Lipase‐Thioesterase (ELT) proteins: ELT3, 4, 5 and 6, all of which are predicted to be chloroplast‐localized. We obtained insertion lines for ELT3, 4, 5 and 6 and analyzed the homozygous plants for triacylglycerol and fatty acid phytyl ester content.Grant Funding Source: Deutsche Forschungsgemeinschaft