title: Multiple genes, tissue specificity, and expression-dependent modulationcontribute to the functional diversity of potassium channels in Arabidopsis thaliana.
abstract: K+ channels play diverse roles in mediating K+ transport and in modulating the membrane potential in higher plant cells during growth and development. Some of the diversity in K+ channel functions may arise from the regulated expression of multiple genes encoding different K+ channel polypeptides. Here we report the isolation of a novel Arabidopsis thaliana cDNA (AKT2) that is highly homologous to the two previously identified K+ channel genes, KAT1 and AKT1. This cDNA mapped to the center of chromosome 4 by restriction fragment length polymorphism analysis and was highly expressed in leaves, whereas AKT1 was mainly expressed in roots. In addition, we show that diversity in K+ channel function may be attributable to differences in expression levels. Increasing KAT1 expression in Xenopus oocytes by polyadenylation of the KAT1 mRNA increased the current amplitude and led to higher levels of KAT1 protein, as assayed in western blots. The increase in KAT1 expression in oocytes produced shifts in the threshold potential for activation to more positive membrane potentials and decreased half-activation times. These results suggest that different levels of expression and tissue-specific expression of different K+ channel isoforms can contribute to the functional diversity of plant K+ channels. The identification of a highly expressed, leaf-specific K+ channel homolog in plants should allow further molecular characterization of K+ channel functions for physiological K+ transport processes in leaves.
authors.affiliation: Department of Biology, University of California, San Diego, La Jolla 92093-0116, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Cao
authors.forename: J M
authors.initials: JM
authors.lastname: Ward
authors.forename: W B
authors.initials: WB
authors.lastname: Kelly
authors.forename: A M
authors.initials: AM
authors.lastname: Ichida
authors.forename: R F
authors.initials: RF
authors.lastname: Gaber
authors.forename: J A
authors.initials: JA
authors.lastname: Anderson
authors.forename: N
authors.initials: N
authors.lastname: Uozumi
authors.forename: J I
authors.initials: JI
authors.lastname: Schroeder
authors.forename: N M
authors.initials: NM
authors.lastname: Crawford
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017360:Arabidopsis / Q000235:genetics*; D029681:Arabidopsis Proteins; D001483:Base Sequence; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D014644:Genetic Variation; D008564:Membrane Potentials; D008969:Molecular Sequence Data; D009865:Oocytes; D018515:Plant Leaves; D010940:Plant Proteins / Q000235:genetics*; D015221:Potassium Channels / Q000235:genetics*; D024661:Potassium Channels, Inwardly Rectifying; D017433:Protein Structure, Secondary; D012333:RNA, Messenger; D011994:Recombinant Proteins; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution; D014981:Xenopus
chemical_list: C097485:AKT2 protein, Arabidopsis; D029681:Arabidopsis Proteins; D018076:DNA, Complementary; C501210:KAT1 protein, Arabidopsis; D010940:Plant Proteins; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D012333:RNA, Messenger; D011994:Recombinant Proteins