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Plant calcium (Ca2+) gradients, millimolar levels in the vacuole and micromolar levels in the cytoplasm, are regulated in part by high-capacity vacuolar cation/H+ exchangers (CAXs). Several CAX transporters, including CAX1, appear to contain an approximately 40-amino acid N-terminal regulatory region (NRR) that modulates transport through N-terminal autoinhibition. Deletion of the NRR from several CAXs (sCAX) enhances function in plant and yeast expression assays; however, to date, there are no functional assays for CAX3 (or sCAX3), which is 77% identical and 91% similar in sequence to CAX1. In this report, we create a series of truncations in the CAX3 NRR and demonstrate activation of CAX3 in both yeast and plants by truncating a large portion (up to 90 amino acids) of the NRR. Experiments with endomembrane-enriched vesicles isolated from yeast expressing activated CAX3 demonstrate that the gene encodes Ca2+/H+ exchange with properties distinct from those of CAX1. The phenotypes produced by activated CAX3-expressing in transgenic tobacco lines are also distinct from those produced by sCAX1-expressing plants. These studies demonstrate shared and unique aspects of CAX1 and CAX3 transport and regulation. [ABSTRACT FROM AUTHOR]

Describes the preliminary localization of Cation Exchanger1 (cax1) to the tonoplast and the molecular characterization of cax1 mutants of Arabidopsis. Properties exhibited by cax1 mutants; Perturbation of ion homeostasis in cax1 mutants; Morphological phenotypes of cax1 alleles.