ORGANIZATION AND EXPRESSION OF THE GENE CODING FOR THE POTASSIUM-TRANSPORT SYSTEM AKT1 OF ARABIDOPSIS-THALIANA

We have isolated and sequenced the genomic clone coding for the potass ium transport system AKT1 of Arabidopsis thaliana. Southern blot analy sis indicated that the gene is present in one copy in the Arabidopsis genome. The coding sequence is interrupted by ten introns. Sequence co mparisons of AKT1 polypeptide with the voltage-gated inward rectifying Arabidopsis K+ channel KAT1, and with voltage-or cyclic nucleotide-ga ted channels from insects and mammals, revealed a highly conserved dom ain found specifically in both plant polypeptides, and correponding to about the last 50 amino acids of their C-terminal region. Northern bl ot analysis of AKT1 expression in Arabidopsis seedlings indicated that AKT1 is preferentially expressed in roots. No transcript was detected in extracts from heterotrophic suspension culture cells. Depleting K in the Arabidopsis seedling culture medium for 4 days led to a strong decrease in K+ tissue content (ca. 50%), but did not affect AKT1 tran script level.