Differentiation of dicarboxylate transporters in mesophyll and bundle sheath chloroplasts of maize [Zea mays]

• Published in: Plant and cell physiology 2004-02, Vol.45 (2), p.187-200
• Main Authors: Taniguchi, Y. (Nagoya Univ. (Japan)), Nagasaki, J, Kawasaki, M, Miyake, H, Sugiyama, T, Taniguchi, M
• Format: Article
• Language: English
• Subjects: 2-oxoglutarate/malate transporter; 5-bisphosphate carboxylase/oxygenase; Amino Acid Sequence - genetics; Base Sequence - genetics; BSC; bundle sheath cell; Carrier Proteins - genetics; Carrier Proteins - isolation & purification; Carrier Proteins - metabolism; CHLOROPLASTS; Chloroplasts - genetics; Chloroplasts - metabolism; DCT; Dicarboxylic Acid Transporters - genetics; Dicarboxylic Acid Transporters - isolation & purification; Dicarboxylic Acid Transporters - metabolism; DNA, Complementary - analysis; DNA, Complementary - genetics; Energy Metabolism - genetics; EST; expression sequence tag; Gene Expression Regulation, Plant - genetics; general dicarboxylate transporter; GENETIC TRANSFORMATION; genome survey sequence; glutamate synthase; glutamine synthetase; GOGAT; GSS; Keywords: Chloroplast — C4 photosynthesis — Dicarboxylate transporter — Maize — Oxaloacetate transporter — 2-Oxoglutarate/malate transporter; Malates - metabolism; malic enzyme; Membrane Transport Proteins; mesophyll cell; Molecular Sequence Data; OAT; OMT; oxaloacetate transporter; Oxaloacetic Acid - metabolism; PEPC; phosphoenolpyruvate carboxylase; PHOTOSYSTEMS; Phylogeny; Plant Proteins - genetics; Plant Proteins - isolation & purification; Plant Proteins - metabolism; Recombinant Fusion Proteins - genetics; reverse transcription-polymerase chain reaction; ribulose-1; RT-PCR; Rubisco; Sequence Homology, Amino Acid; Sequence Homology, Nucleic Acid; ZEA MAYS; Zea mays - genetics; Zea mays - metabolism
• ISSN: 0032-0781; 1471-9053
• DOI: 10.1093/pcp/pch022

In NADP-malic enzyme-type C4 plants such as maize (Zea mays L.), efficient transport of oxaloacetate and malate across the inner envelope membranes of chloroplasts is indispensable. We isolated four maize cDNAs, ZmpOMT1 and ZmpDCT1 to 3, encoding orthologs of plastidic 2-oxoglutarate/malate and general dicarboxylate transporters, respectively. Their transcript levels were upregulated by light in a cell-specific manner; ZmpOMT1 and ZmpDCT1 were expressed in the mesophyll cell (MC) and ZmpDCT2 and 3 were expressed in the bundle sheath cell (BSC). The recombinant ZmpOMT1 protein expressed in yeast could transport malate and 2-oxoglutarate but not glutamate. By contrast, the recombinant ZmpDCT1 and 2 proteins transported 2-oxoglutarate and glutamate at similar affinities in exchange for malate. The recombinant proteins could also transport oxaloacetate at the same binding sites as those for the dicarboxylates. In particular, ZmpOMT1 transported oxaloacetate at a higher efficiency than malate or 2-oxoglutarate. We also compared the activities of oxaloacetate transport between MC and BSC chloroplasts from maize leaves. The Km value for oxaloacetate in MC chloroplasts was one order of magnitude lower than that in BSC chloroplasts, and was close to that determined with the recombinant ZmpOMT1 protein. Southern analysis revealed that maize has a single OMT gene. These findings suggest that ZmpOMT1 participates in the import of oxaloacetate into MC chloroplasts in exchange for stromal malate. In BSC chloroplasts, ZmpDCT2 and/or ZmpDCT3 were expected to import malate that is transported from MC.