title: Cloning and functional characterization of LjPLT4, a plasma membrane xylitol H(+)- symporter from Lotus japonicus.
abstract: Polyols are compounds that play various physiological roles in plants. Here we present the identification of four cDNA clones of the model legume Lotus japonicus, encoding proteins of the monosaccharide transporter-like (MST) superfamily that share significant homology with previously characterized polyol transporters (PLTs). One of the transporters, named LjPLT4, was characterized functionally after expression in yeast. Transport assays revealed that LjPLT4 is a xylitol-specific H(+)-symporter (K (m), 0.34 mM). In contrast to the previously characterized homologues, LjPLT4 was unable to transport other polyols, including mannitol, sorbitol, myo-inositol and galactitol, or any of the monosaccharides tested. Interestingly, some monosaccharides, including fructose and xylose, inhibited xylitol uptake, although no significant uptake of these compounds was detected in the LjPLT4 transformed yeast cells, suggesting interactions with the xylitol binding site. Subcellular localization of LjPLT4-eYFP fusions expressed in Arabidopsis leaf epidermal cells indicated that LjPLT4 is localized in the plasma membrane. Real-time RT-PCR revealed that LjPLT4 is expressed in all major plant organs, with maximum transcript accumulation in leaves correlating with maximum xylitol levels there, as determined by GC-MS. Thus, LjPLT4 is the first plasma membrane xylitol-specific H(+)-symporter to be characterized in plants.
authors.affiliation: Laboratory of Molecular Biology, Department of Agricultural Biotechnology, Agricultural University of Athens, Athens, Greece.
authors.forename: Katerina I
authors.initials: KI
authors.lastname: Kalliampakou
authors.forename: Evangelia D
authors.initials: ED
authors.lastname: Kouri
authors.forename: Haralabia
authors.initials: H
authors.lastname: Boleti
authors.forename: Ourania
authors.initials: O
authors.lastname: Pavli
authors.forename: Laurence
authors.initials: L
authors.lastname: Maurousset
authors.forename: Michael K
authors.initials: MK
authors.lastname: Udvardi
authors.forename: Panagiotis
authors.initials: P
authors.lastname: Katinakis
authors.forename: Rémi
authors.initials: R
authors.lastname: Lemoine
authors.forename: Emmanouil
authors.initials: E
authors.lastname: Flemetakis
mesh_terms: D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D000070116:Lotus / Q000235:genetics* / Q000378:metabolism; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D027981:Symporters / Q000235:genetics* / Q000378:metabolism; D014993:Xylitol / Q000378:metabolism*
chemical_list: D018076:DNA, Complementary; D027981:Symporters; D014993:Xylitol