Mills Rebecca F, Krijger Gerard C, Baccarini Paul J, Hall J L, Williams Lorraine E
School of Biological Sciences, University of Southampton, Biomedical Sciences Building, Bassett Crescent East, Southampton SO16 7PX, UK.
Plant J. 2003 Jul;35(2):164-76. doi: 10.1046/j.1365-313x.2003.01790.x.
Mechanisms are required by all organisms to maintain the concentration of essential heavy metals (e.g. Zn and Cu) within physiological limits and to minimise the detrimental effects of non-essential heavy metals (e.g. Cd). Heavy-metal P-type ATPases (HMAs) are a subgroup of the P-type ATPase superfamily that may contribute to metal homeostasis in plants. We cloned and characterised a member of this family, AtHMA4, from Arabidopsis thaliana that clusters with the Zn/Co/Cd/Pb subclass of HMAs on phylogenetic analysis. Sequencing of the AtHMA4 cDNA showed that it contained the conserved motifs found in all P-type ATPases and also motifs that are characteristic of heavy-metal ATPases. Escherichia coli mutants defective in the HMAs, CopA and ZntA, were used in functional complementation studies. AtHMA4 was able to restore growth at high [Zn] in the zntA mutant but not at high [Cu] in the copA mutant, suggesting a role in zinc transport. Heterologous expression of AtHMA4 in Saccharomyces cerevisiae made the yeast more resistant to Cd but did not affect sensitivity to other metals compared with vector-transformed controls. The organ specificity of AtHMA4 was analysed in Arabidopsis and showed that AtHMA4 was expressed in a range of tissues with highest expression in roots. AtHMA4 was upregulated in roots exposed to elevated levels of Zn and Mn but downregulated by Cd. Possible physiological roles of this transporter in Arabidopsis are discussed.
所有生物体都需要有机制来将必需重金属（如锌和铜）的浓度维持在生理限度内，并将非必需重金属（如镉）的有害影响降至最低。重金属P型ATP酶（HMA）是P型ATP酶超家族的一个亚组，可能有助于植物中的金属稳态。我们从拟南芥中克隆并鉴定了该家族的一个成员AtHMA4，在系统发育分析中，它与HMA的锌/钴/镉/铅亚类聚类。AtHMA4 cDNA的测序表明，它包含在所有P型ATP酶中发现的保守基序，以及重金属ATP酶特有的基序。在功能互补研究中使用了在HMA、CopA和ZntA中存在缺陷的大肠杆菌突变体。AtHMA4能够恢复zntA突变体在高锌浓度下的生长，但不能恢复copA突变体在高铜浓度下的生长，这表明它在锌转运中发挥作用。与载体转化对照相比，AtHMA4在酿酒酵母中的异源表达使酵母对镉更具抗性，但不影响对其他金属的敏感性。在拟南芥中分析了AtHMA4的器官特异性，结果表明AtHMA4在一系列组织中表达，在根中表达量最高。AtHMA4在暴露于高浓度锌和锰的根中上调，但被镉下调。本文讨论了该转运蛋白在拟南芥中的可能生理作用。
