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Multiple genes, tissue specificity, and expression-dependent modulation contribute to the functional diversity of potassium channels in Arabidopsis thaliana

Cao, Y., Ward, J.M., Kelly, W.B., Ichida, A.M., Gaber, R.F., Anderson, J.A., Uozumi, N., Schroeder, J.I., Crawford, N.M.
Plant physiology 1995 v.109 no.3 pp. 1093-1106
Arabidopsis thaliana, potassium, cations, ion transport, membrane potential, complementary DNA, polymerase chain reaction, gene transfer, Xenopus laevis, oocytes, Saccharomyces cerevisiae, chromosome mapping, gene expression, leaves, spatial distribution, enzymes, enzyme activity, amino acid sequences, nucleotide sequences, multigene family, structure-activity relationships, membrane proteins
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 gene 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 polyedenylation 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.