Research Projects

Lipids biosynthesis in plants: from basic science to application

Research focuses on plant lipids which serve as membrane components, cofac­tors and storage material and covers both basic and applied aspects.

Essential genes for plant lipid biosynthesis

Glycerolipids are by far the most abundant group of plant lipids. They include the phospho- and glycodiacyl­glycerols, the major membrane lipids, and triacylglycerols, which serve as storage lipids in most plant species. In plant cells glycerolipid synthesis occurs in plastids, mitochondria and endomem­brane systems, especially in the endoplas­mic reticu­lum (ER). ER and plastids are also the site of the formation of prenyl­lipids, such as sterols, carotenoids and prenyl­qui­nones.

After the elucidation of lipid biosynthetic pathways within different subcellular compartments, our current research projects are concerned with the functional characterisation of genes encoding enzymes involved in glycerolipid and prenyl­qui­none biosynthesis. Cloned genes are utilised to gain access to the encoded proteins which usually represent integral membrane proteins and to engineer the proteins in order to improve certain properties (supported by DFG and BMBF).

Purification of the microsomal phosphatidylglycerophosphate synthase from Arabidopsis as a recombinant protein of 25 kDa over-expressed in Escherichia coli. SDS-PAGE analysis of proteins at different purification steps are shown (Müller & Frentzen, 2001).

Biogenesis of plant cell compartments

The various membrane systems of plant cells possess typical membrane lipid compositions. Biogenesis and main­te­nance of these membrane systems re­quire a huge transfer of lipids between the different compartments. In this regard a close association of specific ER domains with other organelles appears to play an impor­tant role. Our recent data provided evidence that plant mitochondria, unlike plastids, can import phos­pha­tidylglycerol (PG) from the ER presumably via mitochondrial-associated ER membrane domains.

Membrane lipids are decisive not only for the structure but also for the function of cell compartments. The analysis of an Arabidopsis mutant de­ficient in the biosynthesis of plastidial PG, for in­stance, revealed that the anionic membrane lipid is essential for the bio­genesis of thylakoid membranes and, thus, for photoauto­trophic growth. Experi­ments are current­ly in pro­gress to investigate the functional role of membrane lipids in plant mito­chondria and to study the mecha­nisms of lipid fluxes in plant cells (supported by DFG).

Ultrastructure of plastids from Arabidopsis wild type and the pgp1 mutant deficient in plastidial PG biosynthesis (g, starch granules; s, grana thylacoids; m, mitchondria; p, plastoglobuli; Babiychuk et al., 2003)

Genetic engineering of oilseed crops

Lipids can be important determinants of certain plant traits such as oil quality and suitability for specific markets. The improvement of such traits in crop plants by genetic engineering has become technically feasible due to the progress in our understanding of lipid biosynthetic pathways, in cloning important genes and in developing efficient plant transformation methods.

In Europe rapeseed is one of the major oil seed crops, the seed oil of which is largely used for food purposes. Within the project ‘Napus 2000, healthy food from transgenic rapeseed’, we achieved a two to fourfold increase in the vitamin E content of seed oil by genetic engineering (supported by BMBF).

To develop high yielding sustainable oil crops that can produce the right oils for lubricants and other chemicals, the ICON project (industrial crops producing added value oils for novel chemistry) was initiated. It involves 23 partners from 11 countries and is sponsored by the EU. It aims to modify industrial oil seed plants like Crambe abyssinica in such a way that they accumulate wax esters which are much more resistant to high temperatures and pressures than normal plant oils. Within the ICON project we have cloned and functionally characterized genes required for the production of wax esters and developed gene constructs for the transformation of the new industrial oilseed crops.

Tocopherol (γa, δa) and tocotrienol (γb, δb) content in seed oil of transgenic and wild type plants (IS, internal standard)

Selected publications

Haselier, A., Akbari, H., Weth, A., Baumgartner, W. and Frentzen, M. (2010) Two closely related genes of Arabidopsis encode plastidial cytidinediphosphate diacylglycerol synthases essential for photoautotrophic growth. Plant Physiol. 153, 1372-1384

Sadre, R., Frentzen, M., Saeed, M. and Hawkes, T. (2010) Catalytic reactions of the homogentisate prenyl transferase involved in plastoquinone-9 biosynthesis. J. Biol. Chem. 285, 18191-18198

Sadre, R., and Frentzen, M. (2009) Lipids in plant mitochondria, in Lipids in Photosynthesis (Wada, H. and Murata, N., eds.), pp. 57-76, Springer, Dordrecht

Rijken, P.J., Houtkooper, R.H., Akbari, H., Brouwers, J.F., Koorengevel, M.C., de Kruijff, B., Frentzen, M., Vaz, F.M. and de Kroon, A.I. (2009) Cardiolipin molecular species with shorter acyl chains accumulate in Saccharomyces cerevisiae mutants lacking the acyl coenzyme A-binding protein Acb1p: new insights into acyl chain remodeling of cardiolipin. J. Biol. Chem. 284, 27609-27619

Sadre, R., Gruber, J. and Frentzen, M. (2006) Characterization of homogentisate prenyltransferases involved in plastoquinone and tocochromanol biosynthesis. FEBS Lett. 580, 5357-5362

Raclaru, M., Gruber, J., Kumar, R., Sadre, R., Lühs, W., Zarhloul, M.K., Friedt, W., Frentzen, M., and Weier, D. (2006) Increase of the tocochromanol content in transgenic Brassica napus seeds by overexpression of key enzymes involved in prenylquinone biosynthesis. Mol. Breeding 18, 93-107

Kumar, R., Raclaru, M., Schüßeler, T., Gruber, J., Sadre, R., Lühs, W., Zarhloul, K.M., Friedt, W., Enders, D., Frentzen, M. and Weier, D. (2005) Characterisation of plant tocopherol cyclases and their overexpression in transgenic Brassica napus seeds. FEBS Lett. 579, 1357-1364

Nowicki, M., Müller, F. and Frentzen, M. (2005) Cardiolipin synthase of Arabidopsis thaliana. FEBS Lett. 579, 2161-2165

Frentzen, M. (2004) Phosphatidylglycerol and sulfoquinovosyldiacylglycerol: anionic membrane lipids and phosphate regulation. Curr. Opin. Plant Biol. 7, 270-276

Babiychuk, E., Müller, F., Eubel, H., Braun, H.P., Frentzen, M. and Kushnir, S. (2003) Arabidopsis phosphatidylglycerophosphate synthase 1 is essential for chloroplast differentiation, but is dispensable for mitochondrial function. Plant J. 33, 899-909

Müller, F. and Frentzen, M. (2001) Phosphatidylglycerophosphate synthases from Arabidopsis thaliana. FEBS Lett. 509, 298-302

Han, J., Lühs, W., Sonntag, K., Zähringer, U., Borchardt, D.S., Wolter, F.P., Heinz, E. and Frentzen, M. (2001) Functional characterization of beta-ketoacyl-CoA synthase genes from Brassica napus L.. Plant Mol. Biol. 46, 229-239

Frentzen, M. (1998) Acyltransferases from basic science to modified seed oils. Fett/Lipid 100, 161-166