Identifying and characterizing plastidic 2-oxoglutarate/malate and dicarboxylate transporters in Arabidopsis thaliana.
We characterized three Arabidopsis genes, AtpOMT1, AtpDCT1 and AtpDCT2, localized on chromosome 5 and homologous to spinach chloroplastic 2-oxoglutarate/malate transporter (OMT) gene. The yeast-expressed recombinant AtpOMT1 protein transported malate and 2-oxoglutarate but not glutamate. By contrast, the recombinant AtpDCT1 protein transported 2-oxoglutarate and glutamate at similar affinities in exchange for malate. These findings suggested that AtpOMT1 is OMT and AtpDCT1 is a general dicarboxylate transporter (DCT). The recombinant proteins could also transport oxaloacetate at the same binding sites for dicarboxylates. In particular, the AtpOMT1 had a K(m) value for oxaloacetate one order of magnitude lower than those for malate and 2-oxoglutarate. Although the transcripts for the three genes were accumulated in all tissues examined, the expression of the genes in leaf tissues was light inducible. The expression of the three genes was also induced by nitrate supplement but the induction was most prominent and transient in AtpOMT1 similar to nitrate reductase gene. These findings lead to a proposition that AtpOMT1 functions as an oxaloacetate transporter in the malate-oxaloacetate shuttle across chloroplast membranes. We identified T-DNA insertional mutants of AtpOMT1 and AtpDCT1. Although the AtpOMT1 mutants could grow normally in normal air, the AtpDCT1 mutants were non-viable under the same conditions. The AtpDCT1 mutants were able to grow under the high CO2 condition to suppress photorespiration. These findings suggested that at least AtpDCT1 is a necessary component for photorespiratory nitrogen recycling.
Taniguchi
Mitsutaka
M
Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Aichi, 464-8601 Japan. taniguti@agr.nagoya-u.ac.jp
Taniguchi
Yojiro
Y
Kawasaki
Michio
M
Takeda
Satomi
S
Kato
Tomohiko
T
Sato
Shusei
S
Tabata
Satoshi
S
Miyake
Hiroshi
H
Sugiyama
Tatsuo
T
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D016208:Databases, Factual; D029382:Dicarboxylic Acid Transporters / Q000235:genetics* / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D018745:Genome, Plant; D007700:Kinetics; D008293:Malates / Q000378:metabolism; D008780:Methyltransferases; D024101:Mitochondrial Proteins; D008969:Molecular Sequence Data; D009154:Mutation; D010641:Phenotype; D018087:Plastids / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D015003:Yeasts / Q000235:genetics
D029681:Arabidopsis Proteins; C466939:AtpOMT1 protein, Arabidopsis; D002352:Carrier Proteins; C466938:DCT1 protein, Arabidopsis; C466940:DCT2 protein, Arabidopsis; D029382:Dicarboxylic Acid Transporters; D008293:Malates; D024101:Mitochondrial Proteins; C066909:2-oxoglutarate-malate carrier protein; C030298:malic acid; D008780:Methyltransferases; C019608:caffeate O-methyltransferase