An Endoplasmic Reticulum-Bound Ca2+/Mn2+Pump, ECA1, Supports Plant Growth and Confers Tolerance to Mn2+ Stress1
An Endoplasmic Reticulum-Bound Ca2+/Mn2+Pump, ECA1, Supports Plant Growth and Confers Tolerance to Mn2+ Stress1
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DOI：
10.1104/pp.004440
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发表时间：
2002-09
期刊：
影响因子：
7.4
通讯作者：
Zhong-Yi Wu;F. Liang;B. Hong;J. Young;M. Sussman;J. Harper;H. Sze
中科院分区：
文献类型：
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作者：
Zhong-Yi Wu;F. Liang;B. Hong;J. Young;M. Sussman;J. Harper;H. Sze
植物可以在含有大量矿物质营养的土壤中生长，如钙和锰，尽管适应机制尚不清楚。在这里，我们报道了第一个确定植物体内钙泵功能的遗传学研究。在ECA1中含有T-DNA中断的纯合子突变体显示内质网型钙泵活性降低4倍。令人惊讶的是，当突变植株生长在含有1.5mMCa~(2+)和50μm~(2+)的标准营养培养基上时，突变植株的表型与野生植株几乎没有区别。但突变株在低钙(0.2 mM)或高锰(0.5 mM)条件下生长不良。在高Mn2+条件下，突变体不能伸长根毛，这表明突变体在顶端生长过程中受到了损害。野生型基因(CAMV35S：：ECA1)的表达逆转了这些条件表型。ECA1的活性通过在酵母突变株K616中表达来检测，该突变株含有内源性钙泵的缺失。体外实验表明，Ca~(2+)、Mn~(2+)和Zn~(2+)促进了磷酸酶中间体的形成，这与泵对这些离子的转运是一致的。ECA1提高了酵母突变株对Mn2+(1 MM)和Zn2+(3 MM)毒性水平的耐受性，这与从细胞质中去除这些离子是一致的。这些结果表明，尽管在拟南芥中存在多个钙泵和钙/氢逆向转运蛋白的潜在冗余，但在钙缺乏或锰毒害的条件下，ECA1将钙和锰泵入内质网是支持植物生长所必需的。
Plants can grow in soils containing highly variable amounts of mineral nutrients, like Ca2+ and Mn2+, though the mechanisms of adaptation are poorly understood. Here, we report the first genetic study to determine in vivo functions of a Ca2+ 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 mmCa2+ and 50 μm Mn2+. However, mutants grew poorly on medium with low Ca2+ (0.2 mm) or high Mn2+ (0.5 mm). On high Mn2+, 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 Ca2+, Mn2+, and Zn2+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 Mn2+ (1 mm) and Zn2+(3 mm), consistent with removal of these ions from the cytoplasm. These results show that despite the potential redundancy of multiple Ca2+ pumps and Ca2+/H+ antiporters in Arabidopsis, pumping of Ca2+ and Mn2+ by ECA1 into the endoplasmic reticulum is required to support plant growth under conditions of Ca2+ deficiency or Mn2+ toxicity.