Characterization of AgMaT2, a Plasma Membrane Mannitol Transporter from Celery, Expressed in Phloem Cells, including Phloem Parenchyma Cells

• Published in: Plant physiology (Bethesda) 2007-09, Vol.145 (1), p.62-74
• Main Authors: Juchaux-Cachau, Marjorie, Landouar-Arsivaud, Lucie, Pichaut, Jean-Philippe, Campion, Claire, Porcheron, Benoit, Jeauffre, Julien, Noiraud-Romy, Nathalie, Simoneau, Philippe, Maurousset, Laurence, Lemoine, Rémi
• Format: Article
• Language: English
• Subjects: Alternaria; Alternaria - physiology; Antibodies; Apium - cytology; Apium - genetics; Apium - metabolism; Apium graveolens; Biological and medical sciences; Celery; Cell Biology and Signal Transduction; Cell membranes; Cell physiology; Cloning, Molecular; Fundamental and applied biological sciences. Psychology; Gene Expression; Leaves; Life Sciences; Mannitol - metabolism; Membrane Transport Proteins - genetics; Membrane Transport Proteins - metabolism; Molecular Sequence Data; Nicotiana - genetics; Nicotiana - metabolism; Nicotiana - microbiology; Nicotiana tabacum; Parenchyma; Petioles; Phloem; Phloem - cytology; Phloem - metabolism; Plant Diseases; Plant physiology and development; Plant Proteins - genetics; Plant Proteins - metabolism; Plants; Plants, Genetically Modified - metabolism; Plants, Genetically Modified - microbiology; Plasma membrane and permeation; Saccharomyces cerevisiae; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae - metabolism; Sugars; Vegetables; Vegetal Biology; Yeasts
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.107.103143

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.