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J. Biol. Chem., Vol. 283, Issue 20, 13520-13527, May 16, 2008

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Arabidopsis ANTR1 Is a Thylakoid Na⁺-dependent Phosphate Transporter

FUNCTIONAL CHARACTERIZATION IN ESCHERICHIA COLI^*

Lorena Ruiz Pavón¹, Fredrik Lundh², Björn Lundin³, Arti Mishra⁴, Bengt L. Persson, and Cornelia Spetea⁵

From the Division of Molecular Genetics, Department of Physics, Chemistry, and Biology, Linköping University, SE-581 83 Linköping, Sweden and School of Pure and Applied Natural Sciences, Kalmar University, SE-391 82 Kalmar, Sweden

In this study, the putative anion transporter 1 (ANTR1) from Arabidopsis thaliana was shown to be localized to the chloroplast thylakoid membrane by Western blotting with two different peptide-specific antibodies. ANTR1 is homologous to the type I of mammalian Na⁺-dependent inorganic phosphate (P_i) transporters. The function of ANTR1 as a Na⁺-dependent P_i transporter was demonstrated by heterologous expression and uptake of radioactive P_i into Escherichia coli cells. The expression of ANTR1 conferred increased growth rates to the transformed cells and stimulated P_i uptake in a pH- and Na⁺-dependent manner as compared with the control cells. Among various tested effectors, P_i was the preferred substrate. Although it competed with the uptake of P_i, glutamate was not transported by ANTR1 into E. coli. In relation to its function as a P_i transporter, several physiological roles for ANTR1 in the thylakoid membrane are proposed, such as export of P_i produced during nucleotide metabolism in the thylakoid lumen back to the chloroplast stroma and balance of the trans-thylakoid H⁺ electrochemical gradient storage.

Received for publication, November 15, 2007 , and in revised form, February 25, 2008.

^* This work was supported in part by the Swedish Research Council (to C. S. and B. L. P.), the Swedish Research Council for Environment, Agriculture, and Space Planning (Formas) and the Hagberg Foundation (to C. S.), and Kalmar University (to B. L. P.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

¹ Recipient of a postdoctoral fellowship from Linköping University.

² Supported by a Ph.D. program within the Graduate Research School in Pharmaceutical Sciences, Kalmar University.

³ Supported by a Ph.D. program within the Graduate Research School in Genomics and Bioinformatics, Linköping University.

⁴ Present address: Dept. of General and Molecular Botany, Ruhr-University Bochum, D-44780 Bochum, Germany.

⁵ To whom correspondence should be addressed. Tel.: 46-13-282681; Fax: 46-13-281399; E-mail: corsp{at}ifm.liu.se.

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