Christoph Benning Research Interests
Research in my laboratory concerns the biochemistry and control of metabolism in plants, algae, and photosynthetic bacteria. Current areas of focus are: 1. Regulation of photosynthetic membrane lipid assembly; 2. Lipid trafficking between the endoplasmic reticulum (ER) and the plastid; and 3. Regulation of storage lipid biosynthesis.
Studying lipid metabolism is inherently challenging due to the complexity of lipid pathways in photosynthetic organisms. To meet this challenge we apply genetic and genomic approaches in suitable model organisms. The nature of the problems studied also demands the application of state-of-the-art techniques of enzyme biochemistry, analytical chemistry, and cell biology.
The discoveries made by students and postdoctoral researchers in my group encompass novel proteins and their biochemical function in plant lipid metabolism. Examples are proteins involved in sulfolipid [1, 2], phospholipid [3, 4], betaine lipid [5] and galactolipid [6] biosyntheses, transport proteins involved in ER-to-plastid lipid trafficking [7-10], and transcription factors [11] and enzymes [12, 13] critical for storage lipid biosynthesis. These findings have advanced our general understanding of lipid metabolism [14-16].
On occasion, students in my group make big discoveries “on the side”. For example, Karen Bohmert first described the founding member of the now famous Argonaute protein family, AGO1 [17]. Her work was acknowledged in the 2006 Nobel speeches by Mello and Fire [18, 19].
Aside from these advancements in basic science and the broad training of students and postdoctoral researchers, our research routinely leads to the development of patentable tools and methods that will be useful for the engineering of pharmaceutically relevant lipids, e.g. therapeutic liposomes, or the engineering of improved oil yield in crop plants and algae for the purpose of biofuel production. To enable the translation of basic research findings and to identify job opportunities for graduating students and postdoctoral researchers, extensive contacts and collaborations with biotech companies have been established.
1. Regulation of photosynthetic membrane lipid assembly
Chloroplasts are the defining plant organelles carrying out photosynthesis. Photosynthetic complexes are embedded into the thylakoid membrane which forms an intricate system of membrane lamellae and cisternae. This membrane contains a specific set of polar lipids: sulfolipid, galactolipids, and phosphatidylglycerol. In the past, we identified and characterized genes of Arabidopsis involved in the biosynthesis of all three lipid classes. Mutants have enabled us to study the function of these lipids. The lipid composition of the photosynthetic membrane is delicately regulated. We discovered that phosphate-deprived plants change their membrane lipid composition to replace phospholipids with non-phosphorous galactolipids. An alternative galactoglycerolipid pathway is induced under these conditions. This alternative pathway is also induced by reactive oxygen species (ROS). A project funded by the US Department of Energy is aimed at understanding the regulation of thylakoid lipid homeostasis and its breakdown under specific growth conditions.
2. Lipid trafficking between the ER and the chloroplast
Interorganelle lipid trafficking is essential in all eukaryotes, because different organelles cooperate in the biosynthesis of lipid precursors required for the assembly of specific subcellular membranes. A prominent example is the formation of the photosynthetic thylakoid membranes in plant chloroplasts. Galactolipids are the most abundant lipid components of these membranes and their biosynthesis serves as a paradigm for the study of lipid transfer from the endoplasmic reticulum (ER) to the chloroplast. A unique collection of Arabidopsis mutants affected in different aspects of ER-to-plastid lipid trafficking is available in my lab. Common to these mutants is a complex, but robust lipid phenotype, the accumulation of oligogalactoglycerolipids giving rise to the trigalactosyldiacylglycerol (tgd) mutant designation. Of the four TGD loci identified at this time, TGD1, TGD2, and TGD3 encode the permease, the substrate-binding protein, and the ATPase subunits of a putative ABC transporter complex in the inner chloroplast envelope membrane. Several lines of indirect evidence suggest that the TGD123 complex mediates the transfer of phosphatidic acid from the outer envelope to the inside of the inner envelope membrane, where it is processed into the diacylglycerol precursor for galactoglycerolipid biosynthes
is. The recently identified TGD4 locus encodes a novel cytosolic non-intrinsic membrane protein, which appears to be associated with the ER. It is hypothesized that the TGD4 protein is directly involved in the transfer of lipid precursors from the ER to the outer chloroplast envelope. A project funded by the US National Science Foundation is aimed at understanding the function of TGD proteins and the molecular mechanisms of ER-to-plastid lipid trafficking.
3. Regulation of storage lipid biosynthesis
The widely recognized need for the development of biomass-based domestic production systems for high energy liquid transportation fuels is addressed by exploring oil (triacylglycerol) biosynthesis in plants and microalgae. In designing new dedicated biofuel crops, it is desirable to maximize the energy content in the harvestable biomass. Already plants are available that can provide up to 50% of their biomass in starch, a versatile feedstock for biofuel production. Additional, more readily extractable energy derived from photosynthesis can be provided by redirecting metabolism into plant oils. Plant oils have twice the energy content per carbon atom compared with carbohydrates and can be extracted with low energy inputs and low costs. Plant triacylglycerols can be used directly as a fuel in many applications, including modified diesel engines. Research in my lab has identified transcription factors and other regulatory principles that control plant oil biosynthesis. Taking advantage of these new tools, plants are designed to produce triacylglycerols in vegetative tissues such as leaves or root storage organs. Efforts in my lab to design new biofuel crops are supported by the US Department of Energy funded Great Lakes Bioenergy Research Center (http://www.greatlakesbioenergy.org/). 
In addition, a project is directed at the rational engineering of algae-based production systems for high energy jet fuels. Initial efforts are focused on the unicellular model green alga Chlamydomonas reinhardtii with its abundance of genetic and genomic resources. The goal is to identify the genes and regulators required for microalgal oil biosynthesis. This project is funded by the US Air Force Office of Scientific Research.
[1] Essigmann B, Guler S, Narang RA, Linke D, Benning C. Phosphate availability affects the thylakoid lipid composition and the expression of SQD1, a gene required for sulfolipid biosynthesis in Arabidopsis thaliana. Proc Natl Acad Sci U S A 1998;95:1950-1955. Link to PubMed
[2] Yu B, Xu C, Benning C. Arabidopsis disrupted in SQD2 encoding sulfolipid synthase is impaired in phosphate-limited growth. Proc Natl Acad Sci U S A 2002;99:5732-5737. Link to PubMed
[3] Xu C, Hartel H, Wada H, Hagio M, Yu B, Eakin C, Benning C. The pgp1 locus of Arabidopsis encodes a phosphatidylglycerol synthase with impaired activity. Plant Physiol 2002;129:594-604. Link to PubMed
[4] Xu C, Cornish AJ, Froehlich JE, Benning C. Phosphatidylglycerol biosynthesis in chloroplasts of Arabidopsis mutants deficient in acyl-ACP glycerol-3-phosphate acyltransferase. Plant J 2006;47:296-309. Link to PubMed
[5] Riekhof WR, Sears BB, Benning C. Annotation of genes involved in glycerolipid biosynthesis in Chlamydomonas reinhardtii: discovery of the betaine lipid synthase BTA1Cr. Eukaryot Cell 2005;4:242-252. Link to PubMed
[6] Dormann P, Balbo I, Benning C. Arabidopsis galactolipid biosynthesis and lipid trafficking mediated by DGD1. Science 1999;284:2181-2184. Link to PubMed
[7] Awai K, Xu C, Tamot B, Benning C. A phosphatidic acid-binding protein of the chloroplast inner envelope membrane involved in lipid trafficking. Proc Natl Acad Sci USA 2006;103:10817-10822. Link to PubMed
[8] Lu B, Xu C, Awai K, Jones AD, Benning C. A small ATPase protein of Arabidopsis, TGD3, involved in chloroplast lipid import. J Biol Chem 2007;282:35945-35953. Link to PubMed
[9] Xu C, Fan J, Riekhof W, Froehlich JE, Benning C. A permease-like protein involved in ER to thylakoid lipid transfer in Arabidopsis. EMBO J 2003;22:2370-2379. Link to PubMed
[10] Xu C, Fan J, Froehlich J, Awai K, Benning C. Mutation of the TGD1 chloroplast envelope protein affects phosphatidate metabolism in Arabidopsis. Plant Cell 2005;17:3094-3110. Link to PubMed
[11] Cernac A, Benning C. WRINKLED1 encodes an AP2/EREB domain protein involved in the control of storage compound biosynthesis in Arabidopsis. Plant J 2004;40:575-585. Link to PubMed
[12] Andre C, Froehlich JE, Moll MR, Benning C. A heteromeric plastidic pyruvate kinase complex involved in seed oil biosynthesis in Arabidopsis. Plant Cell 2007;19:2006-2022. Link to PubMed
[13] Wakao S, Benning C. Genome-wide analysis of glucose-6-phosphate dehydrogenases in Arabidopsis. Plant J 2005;41:243-256. Link to PubMed
[14] Benning C, Ohta H. Three enzyme systems for galactoglycerolipid biosynthesis are coordinately regulated in plants. J Biol Chem 2005;280:2397-2400. Link to PubMed
[15] Benning C, Xu C, Awai K. Non-vesicular and vesicular lipid trafficking involving plastids. Curr Opin Plant Biol 2006;9:241-247. Link to PubMed
[16] Benning C. Questions remaining in sulfolipid biosynthesis: a historical perspective. Photosynth Res 2007;92:199-203. Link to PubMed
[17] Bohmert K, Camus I, Bellini C, Bouchez D, Caboche M, Benning C. AGO1 defines a novel locus of Arabidopsis controlling leaf development. EMBO J 1998;17:170-180. Link to PubMed
[18] Mello CC. Return to the RNAi world: rethinking gene expression and evolution (Nobel Lecture).
[19] Fire AZ. Gene silencing by double-stranded RNA (Nobel Lecture).