A nodule-specific dicarboxylate transporter from alder is a member of the peptide transporter family.
Alder (Alnus glutinosa) and more than 200 angiosperms that encompass 24 genera are collectively called actinorhizal plants. These plants form a symbiotic relationship with the nitrogen-fixing actinomycete Frankia strain HFPArI3. The plants provide the bacteria with carbon sources in exchange for fixed nitrogen, but this metabolite exchange in actinorhizal nodules has not been well defined. We isolated an alder cDNA from a nodule cDNA library by differential screening with nodule versus root cDNA and found that it encoded a transporter of the PTR (peptide transporter) family, AgDCAT1. AgDCAT1 mRNA was detected only in the nodules and not in other plant organs. Immunolocalization analysis showed that AgDCAT1 protein is localized at the symbiotic interface. The AgDCAT1 substrate was determined by its heterologous expression in two systems. Xenopus laevis oocytes injected with AgDCAT1 cRNA showed an outward current when perfused with malate or succinate, and AgDCAT1 was able to complement a dicarboxylate uptake-deficient Escherichia coli mutant. Using the E. coli system, AgDCAT1 was shown to be a dicarboxylate transporter with a K(m) of 70 microm for malate. It also transported succinate, fumarate, and oxaloacetate. To our knowledge, AgDCAT1 is the first dicarboxylate transporter to be isolated from the nodules of symbiotic plants, and we suggest that it may supply the intracellular bacteria with dicarboxylates as carbon sources.
Department of Life Science, Pohang University of Science and Technology, Hyoja-dong, san 31, Pohang 790-784, Korea.
Jeeyon
J
Jeong
SuJeong
S
Suh
Changhui
C
Guan
Yi-Fang
YF
Tsay
Nava
N
Moran
Chang Jae
CJ
Oh
Chung Sun
CS
An
Kirill N
KN
Demchenko
Katharina
K
Pawlowski
Youngsook
Y
Lee
D029661:Alnus / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D018076:DNA, Complementary / Q000235:genetics / Q000302:isolation & purification; D018744:DNA, Plant / Q000235:genetics / Q000302:isolation & purification; D029382:Dicarboxylic Acid Transporters / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D005260:Female; D005816:Genetic Complementation Test; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D007700:Kinetics; D008293:Malates / Q000378:metabolism; D008564:Membrane Potentials; D008969:Molecular Sequence Data; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014982:Xenopus laevis
D018076:DNA, Complementary; D018744:DNA, Plant; D029382:Dicarboxylic Acid Transporters; D008293:Malates; D010940:Plant Proteins; D011994:Recombinant Proteins; C030298:malic acid