Multiple Genes, Tissue Specificity, and Expression-Dependent Modulation Contribute to the Functional Diversity of Potassium Channels in Arabidopsis fhaliana’

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 nove1 Arabidopsis fhaliana cDNA (AKTZ) that is highly homologous to the two previously identified K+ channel genes, KATl and AKT7. This cDNA mapped to the center of chromosome 4 by restriction fragment length polymorphism analysis and was highly expressed in leaves, whereas AKT7 was mainly expressed in roots. I n addition, we show that diversity in K+ channel function may be attributable to differences i n expression levels. lncreasing KAT7 expression i n Xenopus oocytes by polyadenylation of the KATl mRNA increased the current amplitude and led to higher levels of KATl protein, as assayed in western blots. The increase in KATl expression in oocytes produced shifts in the threshold potentia1 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.