Robert W. Holley Center for Agriculture and Health, USDA-ARS, Cornell University, Ithaca, New York 14853, USA.
Plant Cell Environ. 2012 Jul;35(7):1185-200. doi: 10.1111/j.1365-3040.2011.02479.x. Epub 2012 Jan 17.
Root efflux of organic acid anions underlies a major mechanism of plant aluminium (Al) tolerance on acid soils. This efflux is mediated by transporters of the Al-activated malate transporter (ALMT) or the multi-drug and toxin extrusion (MATE) families. ZmALMT2 was previously suggested to be involved in Al tolerance based on joint association-linkage mapping for maize Al tolerance. In the current study, we functionally characterized ZmALMT2 by heterologously expressing it in Xenopus laevis oocytes and transgenic Arabidopsis. In oocytes, ZmALMT2 mediated an Al-independent electrogenic transport product of organic and inorganic anion efflux. Ectopic overexpression of ZmALMT2 in an Al-hypersensitive Arabidopsis KO/KD line lacking the Al tolerance genes, AtALMT1 and AtMATE, resulted in Al-independent constitutive root malate efflux which partially restored the Al tolerance phenotype. The lack of correlation between ZmALMT2 expression and Al tolerance (e.g., expression not localized to the root tip, not up-regulated by Al, and higher in sensitive versus tolerance maize lines) also led us to question ZmALMT2's role in Al tolerance. The functional properties of the ZmALMT2 transporter presented here, along with the gene expression data, suggest that ZmALMT2 is not involved in maize Al tolerance but, rather, may play a role in mineral nutrient acquisition and transport.
有机酸阴离子的根系外排是植物在酸性土壤中耐铝的主要机制。这种外排是由铝激活的苹果酸转运蛋白（ALMT）或多药和毒素外排（MATE）家族的转运蛋白介导的。基于玉米耐铝的联合关联连锁作图，先前认为 ZmALMT2 参与了耐铝性。在本研究中，我们通过在非洲爪蟾卵母细胞和转基因拟南芥中异源表达来对 ZmALMT2 进行功能表征。在卵母细胞中，ZmALMT2 介导了有机和无机阴离子外排的铝不依赖的电致产物。在缺乏耐铝基因 AtALMT1 和 AtMATE 的拟南芥 KO/KD 线系中异位过表达 ZmALMT2 导致铝不依赖的组成型根苹果酸外排，部分恢复了耐铝表型。ZmALMT2 的表达与耐铝性之间缺乏相关性（例如，表达不局限于根尖，不受 Al 上调，在敏感玉米品系中高于耐受玉米品系）也使我们对 ZmALMT2 在耐铝性中的作用产生了怀疑。这里提出的 ZmALMT2 转运蛋白的功能特性以及基因表达数据表明，ZmALMT2 不参与玉米耐铝性，而是可能在矿质养分的获取和运输中发挥作用。
