title: Functional characterization in Xenopus oocytes of Na+ transport systems from durum wheat reveals diversity among two HKT1;4 transporters.
abstract: Plant tolerance to salinity constraint involves complex and integrated functions including control of Na(+) uptake, translocation, and compartmentalization. Several members of the high-affinity K(+) transporter (HKT) family, which comprises plasma-membrane transporters permeable to K(+) and Na(+) or to Na(+) only, have been shown to play major roles in plant Na(+) and K(+) homeostasis. Among them, HKT1;4 has been identified as corresponding to a quantitative trait locus (QTL) of salt tolerance in wheat but was not functionally characterized. Here, we isolated two HKT1;4-type cDNAs from a salt-tolerant durum wheat (Triticum turgidum L. subsp. durum) cultivar, Om Rabia3, and investigated the functional properties of the encoded transporters using a two-electrode voltage-clamp technique, after expression in Xenopus oocytes. Both transporters displayed high selectivity for Na(+), their permeability to other monovalent cations (K(+), Li(+), Cs(+), and Rb(+)) being ten times lower than that to Na(+). Both TdHKT1;4-1 and TdHKT1;4-2 transported Na(+) with low affinity, although the half-saturation of the conductance was observed at a Na(+) concentration four times lower in TdHKT1;4-1 than in TdHKT1;4-2. External K(+) did not inhibit Na(+) transport through these transporters. Quinine slightly inhibited TdHKT1;4-2 but not TdHKT1;4-1. Overall, these data identified TdHKT1;4 transporters as new Na(+)-selective transporters within the HKT family, displaying their own functional features. Furthermore, they showed that important differences in affinity exist among durum wheat HKT1;4 transporters. This suggests that the salt tolerance QTL involving HKT1;4 may be at least in part explained by functional variability among wheat HKT1;4-type transporters.
authors.affiliation: Plant Protection and Improvement Laboratory, Center of Biotechnology of Sfax (CBS)/University of Sfax, B.P. '1177' 3018, Sfax, Tunisia.
authors.forename: Siwar
authors.initials: S
authors.lastname: Ben Amar
authors.forename: Faiçal
authors.initials: F
authors.lastname: Brini
authors.forename: Hervé
authors.initials: H
authors.lastname: Sentenac
authors.forename: Khaled
authors.initials: K
authors.lastname: Masmoudi
authors.forename: Anne-Aliénor
authors.initials: AA
authors.lastname: Véry
mesh_terms: D000818:Animals; D001483:Base Sequence; D001692:Biological Transport; D027682:Cation Transport Proteins / Q000235:genetics / Q000378:metabolism*; D002412:Cations / Q000378:metabolism; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D018744:DNA, Plant / Q000737:chemistry / Q000235:genetics; D015870:Gene Expression; D008969:Molecular Sequence Data; D009865:Oocytes; D010802:Phylogeny; D018515:Plant Leaves / Q000235:genetics / Q000502:physiology; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D020033:Protein Isoforms; D054712:Salinity; D055049:Salt Tolerance; D017422:Sequence Analysis, DNA; D012964:Sodium / Q000378:metabolism*; D014908:Triticum / Q000235:genetics / Q000502:physiology*; D014981:Xenopus
chemical_list: D027682:Cation Transport Proteins; D002412:Cations; D018076:DNA, Complementary; D018744:DNA, Plant; D010940:Plant Proteins; D020033:Protein Isoforms; D012964:Sodium
keywords: Durum wheat; HKT1;4; Xenopus oocyte.; electrophysiology; salt tolerance; sodium transport