Novel properties of the wheat aluminum tolerance organic acid transporter (TaALMT1) revealed by electrophysiological characterization in Xenopus oocytes:: Functional and structural implications
Novel properties of the wheat aluminum tolerance organic acid transporter (TaALMT1) revealed by electrophysiological characterization in Xenopus oocytes:: Functional and structural implications
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DOI：
10.1104/pp.108.119636
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发表时间：
2008-08-01
期刊：
影响因子：
7.4
通讯作者：
Kochian, Leon V.
中科院分区：
文献类型：
--
作者：
Pineros, Miguel A.;Cancado, Geraldo M. A.;Kochian, Leon V.
许多植物通过分泌二羧酸和三羧酸来避免铝（Al）的植物毒性作用，这些二羧酸和三羧酸可以螯合和固定根表面的Al 31，从而阻止其进入根细胞。最近，研究人员克隆了几个编码ALMT和MATE家族膜转运蛋白的新基因，并发现这些基因介导了铝耐受反应背后的有机酸转运。鉴于我们对almt的功能特性了解有限，本研究详细表征了在非洲爪蟾卵母细胞中表达的小麦（Triticum aestivum）中的TaALMT1（以前称为ALMT1）的运输特性。电生理结果如下：尽管TaALMT1的活性高度依赖于细胞外Al 31的存在（km1 / 2约为5 mM Al 31活性），但TaALMT1在功能上是活跃的，并且可以在细胞外Al 31缺失的情况下介导离子转运。暴露于Al 31后，逆转电位（E rev）没有变化，这表明Al对TaALMT1苹果酸盐转运的“增强”不是由于转运体选择性的改变，而仅仅是由于其阴离子渗透性的增加。随着细胞内苹果酸盐活性的增加，E rev方向的一致移动表明，TaALMT1对苹果酸盐的转运比其他阴离子有选择性。苹果酸盐和氯化物的渗透率比值估计在1到30之间。然而，随着细胞外Cl 2活性的变化，E rev的复杂行为表明，这一估计只能作为理解TaALMT1对苹果酸盐相对亲和力的一般指导，仅代表在生理相关离子条件下预期的近似。TaALMT1也能介导大量阴离子内流（即向外电流）。TaALMT1不仅可以渗透苹果酸盐，还可以渗透其他生理上相关的阴离子，如Cl 2、no32和so422（程度较轻）。
Many plant species avoid the phytotoxic effects of aluminum (Al) by exuding dicarboxylic and tricarboxylic acids that chelate and immobilize Al 31 at the root surface, thus preventing it from entering root cells. Several novel genes that encode membrane transporters from the ALMT and MATE families recently were cloned and implicated in mediating the organic acid transport underlying this Al tolerance response. Given our limited understanding of the functional properties of ALMTs, in this study a detailed characterization of the transport properties of TaALMT1 ( formerly named ALMT1) from wheat ( Triticum aestivum) expressed in Xenopus laevis oocytes was conducted. The electrophysiological findings are as follows. Although the activity of TaALMT1 is highly dependent on the presence of extracellular Al 31 ( K m1/ 2 of approximately 5 mM Al 31 activity), TaALMT1 is functionally active and can mediate ion transport in the absence of extracellular Al 31. The lack of change in the reversal potential ( E rev) upon exposure to Al 31 suggests that the `` enhancement'' of TaALMT1 malate transport by Al is not due to alteration in the transporter's selectivity properties but is solely due to increases in its anion permeability. The consistent shift in the direction of the E rev as the intracellular malate activity increases indicates that TaALMT1 is selective for the transport of malate over other anions. The estimated permeability ratio between malate and chloride varied between 1 and 30. However, the complex behavior of the E rev as the extracellular Cl 2 activity was varied indicates that this estimate can only be used as a general guide to understanding the relative affinity of TaALMT1 for malate, representing only an approximation of those expected under physiologically relevant ionic conditions. TaALMT1 can also mediate a large anion influx ( i. e. outward currents). TaALMT1 is permeable not only to malate but also to other physiologically relevant anions such as Cl 2, NO 3 2, and SO 4 22 ( to a lesser degree).