Folate metabolism in plants: an Arabidopsis homolog of the mammalian mitochondrial folate transporter mediates folate import into chloroplasts.
The distribution of folates in plant cells suggests a complex traffic of the vitamin between the organelles and the cytosol. The Arabidopsis thaliana protein AtFOLT1 encoded by the At5g66380 gene is the closest homolog of the mitochondrial folate transporters (MFTs) characterized in mammalian cells. AtFOLT1 belongs to the mitochondrial carrier family, but GFP-tagging experiments and Western blot analyses indicated that it is targeted to the envelope of chloroplasts. By using the glycine auxotroph Chinese hamster ovary glyB cell line, which lacks a functional MFT and is deficient in folates transport into mitochondria, we showed by complementation that AtFOLT1 functions as a folate transporter in a hamster background. Indeed, stable transfectants bearing the AtFOLT1 cDNA have enhanced levels of folates in mitochondria and can support growth in glycine-free medium. Also, the expression of AtFOLT1 in Escherichia coli allows bacterial cells to uptake exogenous folate. Disruption of the AtFOLT1 gene in Arabidopsis does not lead to phenotypic alterations in folate-sufficient or folate-deficient plants. Also, the atfolt1 null mutant contains wild-type levels of folates in chloroplasts and preserves the enzymatic capacity to catalyze folate-dependent reactions in this subcellular compartment. These findings suggest strongly that, despite many common features shared by chloroplasts and mitochondria from mammals regarding folate metabolism, the folate import mechanisms in these organelles are not equivalent: folate uptake by mammalian mitochondria is mediated by a unique transporter, whereas there are alternative routes for folate import into chloroplasts.
Bedhomme
Mariette
M
Laboratoire de Physiologie Cellulaire Végétale, UMR5168 CNRS-CEA-INRA-Université Joseph Fourier Grenoble I, Département Réponse et Dynamique Cellulaires, CEA-Grenoble, 17 rue des Martyrs, F-38054 Grenoble Cedex 9, France.
Hoffmann
Michaela
M
McCarthy
Erin A
EA
Gambonnet
Bernadette
B
Moran
Richard G
RG
Rébeillé
Fabrice
F
Ravanel
Stéphane
S
D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000502:physiology; D015153:Blotting, Western; D016466:CHO Cells; D002384:Catalysis; D002734:Chlorophyll / Q000737:chemistry; D002736:Chloroplasts / Q000737:chemistry / Q000378:metabolism*; D003001:Cloning, Molecular; D006224:Cricetinae; D018076:DNA, Complementary / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004926:Escherichia coli / Q000378:metabolism; D005492:Folic Acid / Q000378:metabolism; D005816:Genetic Complementation Test; D005998:Glycine / Q000737:chemistry; D049452:Green Fluorescent Proteins / Q000378:metabolism; D015151:Immunoblotting; D026901:Membrane Transport Proteins / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology; D008928:Mitochondria / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D009154:Mutation; D009696:Nucleic Acids / Q000737:chemistry; D010802:Phylogeny; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D013997:Time Factors; D014162:Transfection
D029681:Arabidopsis Proteins; D018076:DNA, Complementary; C506089:FOLT1 protein, Arabidopsis; D026901:Membrane Transport Proteins; D009696:Nucleic Acids; D002734:Chlorophyll; D049452:Green Fluorescent Proteins; D005492:Folic Acid; D005998:Glycine