Expression, evolution and genomic complexity of potassium ion channel genes of Arabidopsis thaliana

Potassium ion (K+) channels are of major importance in several functionally diverse processes in plant physiology, including K+ transport, membrane potential control, osmoregulation, and stomatal movement. In animals, K+ channels are encoded by multigene families and are differentially expressed during development. Little is known about the genomic organisation, expression or evolution of plant K+ channels. We report here, the partial sequence of a putative K+ channel cDNA from Arabidopsis (KAT2) showing sequence homology to previously identified voltage-gated K+ channel genes KAT1 and AKT1, and which hybridises to a single 2.1 kb mRNA in leaves. The existence of KAT2, together with numerous similar sequences identified by Southern blot analyses, suggest that K+ channels in Arabidopsis are encoded by multiple genes. Southern blot data also suggest that KAT and AKT homologs are present in many other plant species. Analysis of the expression pattern of KAT1, KAT2 and AKT1 demonstrate a tissue-specific regulation of K+ channel genes in plants.