First published online December 23, 2004; 10.1104/pp.104.055079
Plant Physiology 137:117-126 (2005)
© 2005 American Society of Plant Biologists
CELL BIOLOGY AND SIGNAL TRANSDUCTION
The AtProT Family. Compatible Solute Transporters with Similar Substrate Specificity But Differential Expression Patterns1
Silke Grallath2,
Thilo Weimar3,
Andreas Meyer,
Christophe Gumy,
Marianne Suter-Grotemeyer,
Jean-Marc Neuhaus and
Doris Rentsch*
Institute of Plant Sciences, University of Bern, 3013 Bern, Switzerland (S.G., A.M., C.G, M.S., D.R); Zentrum für Molekularbiologie der Pflanzen, Plant Physiology, 72076 Tübingen, Germany (T.W.); and Université de Neuchâtel, Laboratoire de Biochimie, 2007 Neuchâtel, Switzerland (J.-M.N.)
Proline transporters (ProTs) mediate transport of the compatible solutes Pro, glycine betaine, and the stress-induced compound -aminobutyric acid. A new member of this gene family, AtProT3, was isolated from Arabidopsis (Arabidopsis thaliana), and its properties were compared to AtProT1 and AtProT2. Transient expression of fusions of AtProT and the green fluorescent protein in tobacco (Nicotiana tabacum) protoplasts revealed that all three AtProTs were localized at the plasma membrane. Expression in a yeast (Saccharomyces cerevisiae) mutant demonstrated that the affinity of all three AtProTs was highest for glycine betaine (Km = 0.10.3 mM), lower for Pro (Km = 0.41 mM), and lowest for -aminobutyric acid (Km = 45 mM). Relative quantification of the mRNA level using real-time PCR and analyses of transgenic plants expressing the -glucuronidase (uidA) gene under control of individual AtProT promoters showed that the expression pattern of AtProTs are complementary. AtProT1 expression was found in the phloem or phloem parenchyma cells throughout the whole plant, indicative of a role in long-distance transport of compatible solutes. -Glucuronidase activity under the control of the AtProT2 promoter was restricted to the epidermis and the cortex cells in roots, whereas in leaves, staining could be demonstrated only after wounding. In contrast, AtProT3 expression was restricted to the above-ground parts of the plant and could be localized to the epidermal cells in leaves. These results showed that, although intracellular localization, substrate specificity, and affinity are very similar, the transporters fulfill different roles in planta.
1 This work was supported by the Swiss National Foundation SNF (grant no. 3164918.01) and by the Deutsche Forschungsgemeinschaft (grant no. SFB466). T.W. was a recipient of a scholarship of the Studienstiftung des Deutschen Volkes.
2 Present address: Max-Planck-Institut für Biochemie, Zelluläre Biochemie, Am Klopferspitz 18a, 82152 Martinsried, Germany.
3 Present address: University of Cambridge, Department of Biochemistry, Building O, Downing Site, Cambridge CB2 1QW, UK.
Article, publication date, and citation information can be found at www.plantphysiol.org/cgi/doi/10.1104/pp.104.055079.
* Corresponding author; e-mail doris.rentsch{at}ips.unibe.ch; fax 41316314942.
Received October 15, 2004;
returned for revision November 5, 2004;
accepted November 22, 2004.
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