Centre for Membrane Pumps in Cells and Disease (PUMPKIN), Danish National Research Foundation, Frederiksberg, Denmark.
PLoS One. 2012;7(11):e49027. doi: 10.1371/journal.pone.0049027. Epub 2012 Nov 14.
Heavy metal transporters belonging to the P(1B)-ATPase subfamily of P-type ATPases are key players in cellular heavy metal homeostasis. Heavy metal transporters belonging to the P(1B)-ATPase subfamily of P-type ATPases are key players in cellular heavy metal homeostasis. In this study we investigated the properties of HvHMA1, which is a barley orthologue of Arabidopsis thaliana AtHMA1 localized to the chloroplast envelope. HvHMA1 was localized to the periphery of chloroplast of leaves and in intracellular compartments of grain aleurone cells. HvHMA1 expression was significantly higher in grains compared to leaves. In leaves, HvHMA1 expression was moderately induced by Zn deficiency, but reduced by toxic levels of Zn, Cu and Cd. Isolated barley chloroplasts exported Zn and Cu when supplied with Mg-ATP and this transport was inhibited by the AtHMA1 inhibitor thapsigargin. Down-regulation of HvHMA1 by RNA interference did not have an effect on foliar Zn and Cu contents but resulted in a significant increase in grain Zn and Cu content. Heterologous expression of HvHMA1 in heavy metal-sensitive yeast strains increased their sensitivity to Zn, but also to Cu, Co, Cd, Ca, Mn, and Fe. Based on these results, we suggest that HvHMA1 is a broad-specificity exporter of metals from chloroplasts and serve as a scavenging mechanism for mobilizing plastid Zn and Cu when cells become deficient in these elements. In grains, HvHMA1 might be involved in mobilizing Zn and Cu from the aleurone cells during grain filling and germination.
属于 P 型 ATP 酶 P(1B)-ATP 酶亚家族的重金属转运蛋白是细胞内重金属稳态的关键因子。属于 P 型 ATP 酶 P(1B)-ATP 酶亚家族的重金属转运蛋白是细胞内重金属稳态的关键因子。在这项研究中，我们研究了大麦拟南芥 AtHMA1 同源物 HvHMA1 的特性，HvHMA1 定位于叶绿体被膜。HvHMA1 定位于叶片叶绿体的周围和谷物糊粉层细胞的细胞内隔室。与叶片相比，HvHMA1 在谷物中的表达显著更高。在叶片中，HvHMA1 的表达在 Zn 缺乏时适度诱导，但在有毒水平的 Zn、Cu 和 Cd 时降低。当提供 Mg-ATP 时，分离的大麦叶绿体可将 Zn 和 Cu 输出，而 AtHMA1 抑制剂 thapsigargin 抑制这种转运。通过 RNA 干扰下调 HvHMA1 对叶片 Zn 和 Cu 含量没有影响，但导致谷物 Zn 和 Cu 含量显著增加。HvHMA1 在重金属敏感酵母菌株中的异源表达增加了它们对 Zn 的敏感性，但也增加了对 Cu、Co、Cd、Ca、Mn 和 Fe 的敏感性。基于这些结果，我们认为 HvHMA1 是一种从叶绿体中输出金属的广谱特异性转运蛋白，当细胞缺乏这些元素时，它作为一种动员质体 Zn 和 Cu 的清除机制。在谷物中，HvHMA1 可能参与在谷物灌浆和萌发期间从糊粉层细胞中动员 Zn 和 Cu。
