Publications

• FATTY ACID DESATURASE4 of Arabidopsis encodes a protein distinct from characterized fatty acid desaturases.

  Gao J., Ajjawi I., Manoli A., Sawin A., Xu C., Froehlich J.E., Last R.L., Benning C.

  Polar membrane glycerolipids occur in a mixture of molecular species defined by a polar head group and characteristic acyl groups esterified to a glycerol backbone. A molecular species of phosphatidylglycerol specific to chloroplasts of plants carries a Delta(3-trans) hexadecenoic acid in the sn-2 ... >> More

  Polar membrane glycerolipids occur in a mixture of molecular species defined by a polar head group and characteristic acyl groups esterified to a glycerol backbone. A molecular species of phosphatidylglycerol specific to chloroplasts of plants carries a Delta(3-trans) hexadecenoic acid in the sn-2 position of its core glyceryl moiety. The fad4-1 mutant of Arabidopsis thaliana missing this particular phosphatidylglycerol molecular species lacks the necessary fatty acid desaturase, or a component thereof. The overwhelming majority of acyl groups associated with membrane lipids in plants contains double bonds with a cis configuration. However, FAD4 is unusual because it is involved in the formation of a trans double bond introduced close to the carboxyl group of palmitic acid, which is specifically esterified to the sn-2 glyceryl carbon of phosphatidylglycerol. As a first step towards the analysis of this unusual desaturase reaction, the FAD4 gene was identified by mapping of the FAD4 locus and coexpression analysis with known lipid genes. FAD4 encodes a predicted integral membrane protein that appears to be unrelated to classic membrane bound fatty acid desaturases based on overall sequence conservation. However, the FAD4 protein contains two histidine motifs resembling those of metalloproteins such as fatty acid desaturases. FAD4 is targeted to the plastid. Overexpression of the cDNA in transgenic Arabidopsis led to increased accumulation of the Delta(3-trans) hexadecanoyl group in phosphatidylglycerol relative to wild type. Taken together these results are consistent with the hypothesis that FAD4 is the founding member of a novel class of fatty acid desaturases. << Less

  Plant J. 60:832-839(2009) [PubMed] [EuropePMC]

• Channeling of eukaryotic diacylglycerol into the biosynthesis of plastidial phosphatidylglycerol.

  Fritz M., Lokstein H., Hackenberg D., Welti R., Roth M., Zahringer U., Fulda M., Hellmeyer W., Ott C., Wolter F.P., Heinz E.

  Plastidial glycolipids contain diacylglycerol (DAG) moieties, which are either synthesized in the plastids (prokaryotic lipids) or originate in the extraplastidial compartment (eukaryotic lipids) necessitating their transfer into plastids. In contrast, the only phospholipid in plastids, phosphatid ... >> More

  Plastidial glycolipids contain diacylglycerol (DAG) moieties, which are either synthesized in the plastids (prokaryotic lipids) or originate in the extraplastidial compartment (eukaryotic lipids) necessitating their transfer into plastids. In contrast, the only phospholipid in plastids, phosphatidylglycerol (PG), contains exclusively prokaryotic DAG backbones. PG contributes in several ways to the functions of chloroplasts, but it is not known to what extent its prokaryotic nature is required to fulfill these tasks. As a first step toward answering this question, we produced transgenic tobacco plants that contain eukaryotic PG in thylakoids. This was achieved by targeting a bacterial DAG kinase into chloroplasts in which the heterologous enzyme was also incorporated into the envelope fraction. From lipid analysis we conclude that the DAG kinase phosphorylated eukaryotic DAG forming phosphatidic acid, which was converted into PG. This resulted in PG with 2-3 times more eukaryotic than prokaryotic DAG backbones. In the newly formed PG the unique Delta3-trans-double bond, normally confined to 3-trans-hexadecenoic acid, was also found in sn-2-bound cis-unsaturated C18 fatty acids. In addition, a lipidomics technique allowed the characterization of phosphatidic acid, which is assumed to be derived from eukaryotic DAG precursors in the chloroplasts of the transgenic plants. The differences in lipid composition had only minor effects on measured functions of the photosynthetic apparatus, whereas the most obvious phenotype was a significant reduction in growth. << Less

  J Biol Chem 282:4613-4625(2007) [PubMed] [EuropePMC]