title: OsHKT2;2/1-mediated Na(+) influx over K(+) uptake in roots potentially increases toxic Na(+) accumulation in a salt-tolerant landrace of rice Nona Bokra upon salinity stress.
abstract: HKT transporters are Na(+)-permeable membrane proteins, which mediate Na(+) and K(+) homeostasis in K(+)-depleted and saline environments in plants. Class II HKT transporters, a distinct subgroup found predominantly in monocots, are known to mediate Na(+)-K(+) co-transport in principle. Here we report features of ion transport functions of No-OsHKT2;2/1, a class II transporter identified in a salt tolerant landrace of indica rice, Nona Bokra. We profiled No-OsHKT2;2/1 expression in organs of Nona Bokra plants with or without salinity stress. Dominant accumulation of the No-OsHKT2;2/1 transcript in K(+)-starved roots of Nona Bokra plants largely disappeared in response to 50 mM NaCl. We found that No-OsHKT2;2/1 expressed in the high-affinity K(+) uptake deficient mutant of Saccharomyces cerevisiae and Xenopus laevis oocytes shows robust K(+) selectivity even in the presence of a large amount of NaCl as reported previously. However, No-OsHKT2;2/1-expressing yeast cells exhibited Na(+) hypersensitive growth under various concentrations of K(+) and Na(+) as the cells expressing Po-OsHKT2;2, a similar class II transporter from another salt tolerant indica rice Pokkali, when compared with the growth of cells harboring empty vector or cells expressing OsHKT2;4. The OsHKT2;4 protein expressed in Xenopus oocytes showed strong K(+) selectivity in the presence of 50 mM NaCl in comparison with No-OsHKT2;2/1 and Po-OsHKT2;2. Together with apparent plasma membrane-localization of No-OsHKT2;2/1, these results point to possibilities that No-OsHKT2;2/1 could mediate destructive Na(+) influx over K(+) uptake in Nona Bokra plants upon salinity stress, and that a predominant physiological function of No-OsHKT2;2/1 might be the acquisition of Na(+) and K(+) in K(+)-limited environments.
authors.affiliation: Division of Applied Biology, Faculty of Textile Science and Technology, Shinshu University, 3-15-1, Tokida, Ueda, Nagano, 386-8567, Japan.
authors.forename: Kei
authors.initials: K
authors.lastname: Suzuki
authors.affiliation: Department of Biosciences, University of Milan, Via G. Celoria 26, 20133, Milan, Italy.|Institute of Biophysics, Consiglio Nazionale delle Ricerche, Via G. Celoria 26, 20133, Milan, Italy.
authors.forename: Alex
authors.initials: A
authors.lastname: Costa
authors.affiliation: Institute of Environmental Studies, Graduate School of Fisheries Science and Environmental Studies, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki, 852-8521, Japan.
authors.forename: Hideki
authors.initials: H
authors.lastname: Nakayama
authors.affiliation: Institute of Plant Science and Resources, Okayama University, Chuo 2-20-1, Kurashiki, 710-0046, Japan.
authors.forename: Maki
authors.initials: M
authors.lastname: Katsuhara
authors.affiliation: Nara Institute of Science and Technology, 8916-5 Takayama-cho, Ikoma, Nara, 630-0192, Japan.
authors.forename: Atsuhiko
authors.initials: A
authors.lastname: Shinmyo
authors.affiliation: Division of Applied Biology, Faculty of Textile Science and Technology, Shinshu University, 3-15-1, Tokida, Ueda, Nagano, 386-8567, Japan. horie@shinshu-u.ac.jp.
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Horie
mesh_terms: D027682:Cation Transport Proteins / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D012275:Oryza / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D018517:Plant Roots / Q000378:metabolism; D011188:Potassium / Q000378:metabolism*; D055049:Salt Tolerance; D017422:Sequence Analysis, DNA; D012964:Sodium / Q000378:metabolism*
chemical_list: D027682:Cation Transport Proteins; C434985:HKT2 protein, Oryza sativa; D010940:Plant Proteins; D012964:Sodium; D011188:Potassium
keywords: HKT; K+ uptake; Na+ transport; Rice; Salt stress