title: FAX1, a novel membrane protein mediating plastid fatty acid export.
abstract: Fatty acid synthesis in plants occurs in plastids, and thus, export for subsequent acyl editing and lipid assembly in the cytosol and endoplasmatic reticulum is required. Yet, the transport mechanism for plastid fatty acids still remains enigmatic. We isolated FAX1 (fatty acid export 1), a novel protein, which inserts into the chloroplast inner envelope by α-helical membrane-spanning domains. Detailed phenotypic and ultrastructural analyses of FAX1 mutants in Arabidopsis thaliana showed that FAX1 function is crucial for biomass production, male fertility and synthesis of fatty acid-derived compounds such as lipids, ketone waxes, or pollen cell wall material. Determination of lipid, fatty acid, and wax contents by mass spectrometry revealed that endoplasmatic reticulum (ER)-derived lipids decreased when FAX1 was missing, but levels of several plastid-produced species increased. FAX1 over-expressing lines showed the opposite behavior, including a pronounced increase of triacyglycerol oils in flowers and leaves. Furthermore, the cuticular layer of stems from fax1 knockout lines was specifically reduced in C29 ketone wax compounds. Differential gene expression in FAX1 mutants as determined by DNA microarray analysis confirmed phenotypes and metabolic imbalances. Since in yeast FAX1 could complement for fatty acid transport, we concluded that FAX1 mediates fatty acid export from plastids. In vertebrates, FAX1 relatives are structurally related, mitochondrial membrane proteins of so-far unknown function. Therefore, this protein family might represent a powerful tool not only to increase lipid/biofuel production in plants but also to explore novel transport systems involved in vertebrate fatty acid and lipid metabolism.
authors: Biochemie und Physiologie der Pflanzen, Department Biologie I - Botanik, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany; Research Center of Bioenergy and Bioremediation RCBB, College of Resources and Environment, Southwest University, Beibei Dist., Chongqing, P.R. China.
authors: Nannan
authors: N
authors: Li
authors: Biochemie und Physiologie der Pflanzen, Department Biologie I - Botanik, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany; Munich Centre for Integrated Protein Science CIPSM, Ludwig-Maximilians-Universität München, München, Germany.
authors: Irene Luise
authors: IL
authors: Gügel
authors: Max Planck Institut für Molekulare Pflanzenphysiologie MPIMP, Potsdam-Golm, Germany.
authors: Patrick
authors: P
authors: Giavalisco
authors: Institute of Cellular and Molecular Botany, Department of Ecophysiology, University of Bonn, Bonn, Germany.
authors: Viktoria
authors: V
authors: Zeisler
authors: Institute of Cellular and Molecular Botany, Department of Ecophysiology, University of Bonn, Bonn, Germany.
authors: Lukas
authors: L
authors: Schreiber
authors: Biochemie und Physiologie der Pflanzen, Department Biologie I - Botanik, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany; Munich Centre for Integrated Protein Science CIPSM, Ludwig-Maximilians-Universität München, München, Germany.
authors: Jürgen
authors: J
authors: Soll
authors: Biochemie und Physiologie der Pflanzen, Department Biologie I - Botanik, Ludwig-Maximilians-Universität München, Planegg-Martinsried, Germany; Munich Centre for Integrated Protein Science CIPSM, Ludwig-Maximilians-Universität München, München, Germany.
authors: Katrin
authors: K
authors: Philippar
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001692:Biological Transport; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005227:Fatty Acids / Q000378:metabolism*; D005298:Fertility / Q000235:genetics; D035264:Flowers / Q000235:genetics / Q000378:metabolism; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D055786:Gene Knockout Techniques; D005816:Genetic Complementation Test; D050356:Lipid Metabolism / Q000235:genetics; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D018087:Plastids / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment
chemical_list: D029681:Arabidopsis Proteins; C000604068:FAX1 protein, Arabidopsis; D005227:Fatty Acids; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins
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