Characterization of CAX-like genes in plants: implications for functional diversity

Transporter-mediated Ca2+ efflux from the cytoplasm is an important compone nt of plant signal transduction. To elucidate the diversity and role of Ca2 +/H+ in controlling plant cytosolic Ca2+ concentrations, homologs of CAX (f or calcium exchanger) genes were cloned from Zea mays and Arabidopsis thali ana cDNA libraries. The A. thaliana homolog of CAX (AtHCX1) is 77% identica l to CAX1 while the Z. mays homolog of CAX (ZmHCX1) is 64% identical to CAX 1 in amino acid sequence. AtHCX1 transcripts appeared to be expressed in al l tissues, and levels of AtHCX1 RNA increased after Ca2+ or Na+ treatment. When expressed in yeast mutants defective in vacuolar Ca2+ uptake, ZmHCX1 a nd AtHCX1 failed to suppress the Ca2+ sensitivity of these strains. These r esults imply that CAX-like genes may have functions in plant ion homeostasi s that differ from those of previously characterized CAX genes. (C) 2000 El sevier Science B.V. All rights reserved.