Sasaki Takayuki, Yamamoto Yoko, Ezaki Bunichi, Katsuhara Maki, Ahn Sung Ju, Ryan Peter R, Delhaize Emmanuel, Matsumoto Hideaki
Research Institute for Bioresources, Okayama University, Chuo 2-20-1, Kurashiki, Okayama 710-0046, Japan.
Plant J. 2004 Mar;37(5):645-53. doi: 10.1111/j.1365-313x.2003.01991.x.
The major constraint to plant growth in acid soils is the presence of toxic aluminum (Al) cations, which inhibit root elongation. The enhanced Al tolerance exhibited by some cultivars of wheat is associated with the Al-dependent efflux of malate from root apices. Malate forms a stable complex with Al that is harmless to plants and, therefore, this efflux of malate forms the basis of a hypothesis to explain Al tolerance in wheat. Here, we report on the cloning of a wheat gene, ALMT1 (aluminum-activated malate transporter), that co-segregates with Al tolerance in F2 and F3 populations derived from crosses between near-isogenic wheat lines that differ in Al tolerance. The ALMT1 gene encodes a membrane protein, which is constitutively expressed in the root apices of the Al-tolerant line at greater levels than in the near-isogenic but Al-sensitive line. Heterologous expression of ALMT1 in Xenopus oocytes, rice and cultured tobacco cells conferred an Al-activated malate efflux. Additionally, ALMT1 increased the tolerance of tobacco cells to Al treatment. These findings demonstrate that ALMT1 encodes an Al-activated malate transporter that is capable of conferring Al tolerance to plant cells.
酸性土壤中植物生长的主要限制因素是存在有毒的铝（Al）阳离子，它会抑制根的伸长。一些小麦品种表现出的增强的耐铝性与苹果酸从根尖的铝依赖性外流有关。苹果酸与铝形成一种对植物无害的稳定复合物，因此，这种苹果酸外流构成了解释小麦耐铝性的一个假说的基础。在此，我们报道了一个小麦基因ALMT1（铝激活苹果酸转运蛋白）的克隆，该基因在来自耐铝性不同的近等基因小麦品系杂交产生的F2和F3群体中与耐铝性共分离。ALMT1基因编码一种膜蛋白，在耐铝品系的根尖中组成型表达，其表达水平高于近等基因但铝敏感的品系。ALMT1在非洲爪蟾卵母细胞、水稻和培养的烟草细胞中的异源表达赋予了铝激活的苹果酸外流。此外，ALMT1提高了烟草细胞对铝处理的耐受性。这些发现表明，ALMT1编码一种铝激活的苹果酸转运蛋白，能够赋予植物细胞耐铝性。
