title: GmN70 and LjN70. Anion transporters of the symbiosome membrane of nodules with a transport preference for nitrate.
abstract: A cDNA was isolated from soybean (Glycine max) nodules that encodes a putative transporter (GmN70) of the major facilitator superfamily. GmN70 is expressed predominantly in mature nitrogen-fixing root nodules. By western-blot and immunocytochemical analyses, GmN70 was localized to the symbiosome membrane of infected root nodule cells, suggesting a transport role in symbiosis. To investigate its transport function, cRNA encoding GmN70 was expressed in Xenopus laevis oocytes, and two-electrode voltage clamp analysis was performed. Ooctyes expressing GmN70 showed outward currents that are carried by anions with a selectivity of nitrate > nitrite > > chloride. These currents showed little sensitivity to pH or the nature of the counter cation in the oocyte bath solution. One-half maximal currents were induced by nitrate concentrations between 1 to 3 mm. No apparent transport of organic anions was observed. Voltage clamp records of an ortholog of GmN70 from Lotus japonicus (LjN70; K. Szczyglowski, P. Kapranov, D. Hamburger, F.J. de Bruijn [1998] Plant Mol Biol 37: 651-661) also showed anion currents with a similar selectivity profile. Overall, these findings suggest that GmN70 and LjN70 are inorganic anion transporters of the symbiosome membrane with enhanced preference for nitrate. These transport activities may aid in regulation of ion and membrane potential homeostasis, possibly in response to external nitrate concentrations that are known to regulate the symbiosis.
authors.affiliation: Department of Biochemistry and Cellular and Molecular Biology, The University of Tennessee, Knoxville, Tennessee 37996, USA.
authors.forename: Eric D
authors.initials: ED
authors.lastname: Vincill
authors.forename: Krzysztof
authors.initials: K
authors.lastname: Szczyglowski
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Roberts
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D027321:Anion Transport Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D018744:DNA, Plant / Q000235:genetics; D005260:Female; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D000070116:Lotus / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009566:Nitrates / Q000378:metabolism*; D009865:Oocytes / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013025:Glycine max / Q000235:genetics / Q000378:metabolism*; D013559:Symbiosis; D014982:Xenopus laevis
chemical_list: D027321:Anion Transport Proteins; D018744:DNA, Plant; D009566:Nitrates; D011994:Recombinant Proteins