Journal Article

Differentiation of Dicarboxylate Transporters in Mesophyll and Bundle Sheath Chloroplasts of Maize

Yojiro Taniguchi, Junko Nagasaki, Michio Kawasaki, Hiroshi Miyake, Tatsuo Sugiyama and Mitsutaka Taniguchi

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 45, issue 2, pages 187-200
Published in print February 2004 | ISSN: 0032-0781
Published online February 2004 | e-ISSN: 1471-9053 | DOI: http://dx.doi.org/10.1093/pcp/pch022
Differentiation of Dicarboxylate Transporters in Mesophyll and Bundle Sheath Chloroplasts of Maize

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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.

Keywords: Keywords: Chloroplast — C4 photosynthesis — Dicarboxylate transporter — Maize — Oxaloacetate transporter — 2-Oxoglutarate/malate transporter.; Abbreviations: BSC, bundle sheath cell; DCT, general dicarboxylate transporter; EST, expression sequence tag; GOGAT, glutamate synthase; GS, glutamine synthetase; GSS, genome survey sequence; MC, mesophyll cell; ME, malic enzyme; OAT, oxaloacetate transporter; OMT, 2-oxoglutarate/malate transporter; PEPC, phosphoenolpyruvate carboxylase; RT-PCR, reverse transcription-polymerase chain reaction; Rubisco, ribulose-1,5-bisphosphate carboxylase/oxygenase.

Journal Article.  9560 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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