Reference "Folate metabolism in plants: an Arabidopsis homolog of the mammalian mitochondrial folate transporter mediates folate import into chloroplasts"

Reference ID

54969

Title

Folate metabolism in plants: an Arabidopsis homolog of the mammalian mitochondrial folate transporter mediates folate import into chloroplasts

Source

J Biol Chem, 2005, vol. 280, pp. 34823-34831

Authors (7)

Bedhomme-M	Hoffmann-M
McCarthy-E-A	Gambonnet-B
Moran-R-G	Rebeille-F
Ravanel-S

Abstract

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.