To maintain optimal cytosolic Ca2+ concentrations, cells employ three distinct strategies: 1) tightly regulated influx of Ca2+; 2) efficient efflux of Ca2+ from the cell; and 3) sequestration of Ca2+ in organelles. Ca2+efflux and influx are mediated by diverse transporter systems, such as pumps, channels and antiporters. Yeast (Saccharomyces cerevisiae) are unicellular fungi that have a relatively small genome but complex internal cell structures, which are similar to those of plant cells. The availability of mutant yeast strains lacking endogenous transport systems provides an efficient tool to study Ca2+ transporters from higher eukaryotes upon their expression in yeast cells. The discovery, biochemical characterization, and protein designing of plant transporters have been aided by yeast systems. Of special note, yeast played an indispensable role in the study of CAX-type cation/H+ exchangers. Therefore, yeast is a tractable model for studying the biochemical properties and physiological functions of Ca2+ transporters from plants.
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