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CELL BIOLOGY AND SIGNAL TRANSDUCTION

Characterization of AgMaT2, a Plasma Membrane Mannitol Transporter from Celery, Expressed in Phloem Cells, Including Phloem Parenchyma Cells^[OA]

Unité Mixte de Recherche Centre National de la Recherche Scientifique 6161 Transport des Assimilats, Université de Poitiers, Bâtiment Botanique, 86022 Poitiers cedex, France

A second mannitol transporter, AgMaT2, was identified in celery (Apium graveolens L. var. dulce), a species that synthesizes and transports mannitol. This transporter was successfully expressed in two different heterologous expression systems: baker's yeast (Saccharomyces cerevisiae) cells and tobacco (Nicotiana tabacum) plants (a non-mannitol-producing species). Data indicated that AgMaT2 works as an H⁺/mannitol cotransporter with a weak selectivity toward other polyol molecules. When expressed in tobacco, AgMaT2 decreased the sensitivity to the mannitol-secreting pathogenic fungi Alternaria longipes, suggesting a role for polyol transporters in defense mechanisms. In celery, in situ hybridization showed that AgMaT2 was expressed in the phloem of leaflets, petioles from young and mature leaves, floral stems, and roots. In the phloem of petioles and leaflets, AgMaT2, as localized with specific antibodies, was present in the plasma membrane of three ontologically related cell types: sieve elements, companion cells, and phloem parenchyma cells. These new data are discussed in relation to the physiological role of AgMaT2 in regulating mannitol fluxes in celery petioles.

² Present address: UMR INRA-UCBN 950, Ecophysiologie Végétale, Agronomie and Nutritions NCS, Université de CAEN, Esplanade de la Paix, 14032 Caen cedex, France.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Rémi Lemoine (remi.lemoine{at}univ-poitiers.fr).

^[OA] Open Access articles can be viewed online without a subscription.

www.plantphysiol.org/cgi/doi/10.1104/pp.107.103143

^* Corresponding author; e-mail remi.lemoine{at}univ-poitiers.fr.

Received May 31, 2007; accepted July 3, 2007; published July 13, 2007.