Piñeros Miguel A, Cançado Geraldo M A, Maron Lyza G, Lyi Sangbom M, Menossi Marcelo, Kochian Leon V
United States Plant, Soil, and Nutrition Laboratory, United States Department of Agriculture-Agricultural Research Service, Cornell University, Ithaca, NY 14853-2901, USA.
Plant J. 2008 Jan;53(2):352-67. doi: 10.1111/j.1365-313X.2007.03344.x. Epub 2007 Dec 6.
The phytotoxic effects of aluminum (Al) on root systems of crop plants constitute a major agricultural problem in many areas of the world. Root exudation of Al-chelating molecules such as low-molecular-weight organic acids has been shown to be an important mechanism of plant Al tolerance/resistance. Differences observed in the physiology and electrophysiology of root function for two maize genotypes with contrasting Al tolerance revealed an association between rates of Al-activated root organic acid release and Al tolerance. Using these genotypes, we cloned ZmALMT1, a maize gene homologous to the wheat ALMT1 and Arabidopsis AtALMT1 genes that have recently been described as encoding functional, Al-activated transporters that play a role in tolerance by mediating Al-activated organic acid exudation in roots. The ZmALMT1 cDNA encodes a 451 amino acid protein containing six transmembrane helices. Transient expression of a ZmALMT1::GFP chimera confirmed that the protein is targeted to the plant cell plasma membrane. We addressed whether ZmALMT1 might underlie the Al-resistance response (i.e. Al-activated citrate exudation) observed in the roots of the Al-tolerant genotype. The physiological, gene expression and functional data from this study confirm that ZmALMT1 is a plasma membrane transporter that is capable of mediating elective anion efflux and influx. However, gene expression data as well as biophysical transport characteristics obtained from Xenopus oocytes expressing ZmALMT1 indicate that this transporter is implicated in the selective transport of anions involved in mineral nutrition and ion homeostasis processes, rather than mediating a specific Al-activated citrate exudation response at the rhizosphere of maize roots.
铝（Al）对农作物根系的植物毒性效应是世界许多地区的一个主要农业问题。根系分泌铝螯合分子，如低分子量有机酸，已被证明是植物耐铝/抗铝的重要机制。对两种耐铝性不同的玉米基因型根系功能的生理和电生理差异进行观察，发现铝激活的根系有机酸释放速率与耐铝性之间存在关联。利用这些基因型，我们克隆了ZmALMT1，这是一个与小麦ALMT1和拟南芥AtALMT1基因同源的玉米基因，最近已被描述为编码功能性铝激活转运蛋白，通过介导根系中铝激活的有机酸分泌在耐铝性中发挥作用。ZmALMT1 cDNA编码一个含有六个跨膜螺旋的451个氨基酸的蛋白质。ZmALMT1::GFP嵌合体的瞬时表达证实该蛋白质定位于植物细胞质膜。我们研究了ZmALMT1是否可能是耐铝基因型根系中观察到的抗铝反应（即铝激活的柠檬酸分泌）的基础。本研究的生理、基因表达和功能数据证实，ZmALMT1是一种能够介导选择性阴离子外流和内流的质膜转运蛋白。然而，从表达ZmALMT1的非洲爪蟾卵母细胞获得的基因表达数据以及生物物理转运特性表明，该转运蛋白参与了与矿质营养和离子稳态过程相关的阴离子的选择性转运，而不是介导玉米根际特定的铝激活柠檬酸分泌反应。
