FAX1, a Novel Membrane Protein Mediating Plastid Fatty Acid Export

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 pro...

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Published in:PLoS biology Vol. 13; no. 2; p. e1002053
Main Authors: Li, Nannan, Gügel, Irene Luise, Giavalisco, Patrick, Zeisler, Viktoria, Schreiber, Lukas, Soll, Jürgen, Philippar, Katrin
Format: Journal Article
Language:English
Published: United States Public Library of Science 01.02.2015
Public Library of Science (PLoS)
Subjects:
Amino Acid Sequence
Arabidopsis - genetics
Arabidopsis - metabolism
Arabidopsis Proteins - chemistry
Arabidopsis Proteins - genetics
Arabidopsis Proteins - metabolism
Biodiesel fuels
Biological Transport
Chloroplasts
Colleges & universities
Deoxyribonucleic acid
DNA
Endoplasmic Reticulum - metabolism
Fatty acids
Fatty Acids - metabolism
Fertility - genetics
Flowers & plants
Flowers - genetics
Flowers - metabolism
Gene expression
Gene Expression Profiling
Gene Expression Regulation, Plant
Gene Knockout Techniques
Genetic Complementation Test
Genomes
Glycerol
Lipid Metabolism - genetics
Lipids
Membrane proteins
Membrane Proteins - chemistry
Membrane Proteins - genetics
Membrane Proteins - metabolism
Membranes
Metabolism
Models, Molecular
Molecular Sequence Data
NMR
Nuclear magnetic resonance
Physiological aspects
Plant Leaves - genetics
Plant Leaves - metabolism
Plastids
Plastids - metabolism
Protein Structure, Secondary
Protein Structure, Tertiary
Proteins
Recombinant Fusion Proteins - chemistry
Recombinant Fusion Proteins - genetics
Recombinant Fusion Proteins - metabolism
Sequence Alignment
Vertebrates
Yeast
ISSN:1545-7885, 1544-9173, 1545-7885
Online Access:Get full text
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Summary: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.
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Conceived and designed the experiments: NL JS KP. Performed the experiments: NL ILG PG VZ LS. Analyzed the data: NL PG LS KP. Wrote the paper: NL PG LS KP. Performed structural modeling: KP.
The authors have declared that no competing interests exist.
ISSN:1545-7885
1544-9173
1545-7885
DOI:10.1371/journal.pbio.1002053