An endoplasmic reticulum-bound Ca(2+)/Mn(2+) pump, ECA1, supports plant growth and confers tolerance to Mn(2+) stress.
Plants can grow in soils containing highly variable amounts of mineral nutrients, like Ca(2+) and Mn(2+), though the mechanisms of adaptation are poorly understood. Here, we report the first genetic study to determine in vivo functions of a Ca(2+) pump in plants. Homozygous mutants of Arabidopsis harboring a T-DNA disruption in ECA1 showed a 4-fold reduction in endoplasmic reticulum-type calcium pump activity. Surprisingly, the phenotype of mutant plants was indistinguishable from wild type when grown on standard nutrient medium containing 1.5 mM Ca(2+) and 50 microM Mn(2+). However, mutants grew poorly on medium with low Ca(2+) (0.2 mM) or high Mn(2+) (0.5 mM). On high Mn(2+), the mutants failed to elongate their root hairs, suggesting impairment in tip growth processes. Expression of the wild-type gene (CAMV35S::ECA1) reversed these conditional phenotypes. The activity of ECA1 was examined by expression in a yeast (Saccharomyces cerevisiae) mutant, K616, which harbors a deletion of its endogenous calcium pumps. In vitro assays demonstrated that Ca(2+), Mn(2+), and Zn(2+) stimulated formation of a phosphoenzyme intermediate, consistent with the translocation of these ions by the pump. ECA1 provided increased tolerance of yeast mutant to toxic levels of Mn(2+) (1 mM) and Zn(2+)(3 mM), consistent with removal of these ions from the cytoplasm. These results show that despite the potential redundancy of multiple Ca(2+) pumps and Ca(2+)/H(+) antiporters in Arabidopsis, pumping of Ca(2+) and Mn(2+) by ECA1 into the endoplasmic reticulum is required to support plant growth under conditions of Ca(2+) deficiency or Mn(2+) toxicity.
Wu
Zhongyi
Z
Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, Maryland 20742, USA.
Liang
Feng
F
Hong
Bimei
B
Young
Jeff C
JC
Sussman
Michael R
MR
Harper
Jeffrey F
JF
Sze
Heven
H
D000222:Adaptation, Physiological / Q000187:drug effects*; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000187:drug effects / Q000235:genetics / Q000254:growth & development*; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D000252:Calcium-Transporting ATPases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D008345:Manganese / Q000378:metabolism* / Q000494:pharmacology; D008969:Molecular Sequence Data; D009154:Mutation; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development; D030821:Plants, Genetically Modified; D012441:Saccharomyces cerevisiae / Q000235:genetics; D015032:Zinc / Q000494:pharmacology
D002352:Carrier Proteins; D010940:Plant Proteins; D008345:Manganese; D000252:Calcium-Transporting ATPases; D015032:Zinc; D002118:Calcium