Kim Donggiun, Gustin Jeffery L, Lahner Brett, Persans Michael W, Baek Dongwon, Yun Dae-Jin, Salt David E
Center for Plant Environmental Stress Physiology, Purdue University, 625 Agricultural Mall Drive, West Lafayette, IN 47907, USA.
Plant J. 2004 Jul;39(2):237-51. doi: 10.1111/j.1365-313X.2004.02126.x.
To avoid metal toxicity, organisms have evolved mechanisms including efflux of metal ions from cells and sequestration into internal cellular compartments. Members of the ubiquitous cation diffusion facilitator (CDF) family are known to play an important role in these processes. Overexpression of the plant CDF family member metal tolerance protein 1 (MTP1) from the Ni/Zn hyperaccumulator Thlaspi goesingense (TgMTP1), in the Saccharomyces cerevisiaeDelta zinc resistance conferring (zrc)1Delta cobalt transporter (cot)1 double mutant, suppressed the Zn sensitivity of this strain. T. goesingense was found to contain several allelic variants of TgMTP1, all of which confer similar resistance to Zn in Deltazrc1Deltacot1. Similarly, MTP1 from various hyperaccumulator and non-accumulator species also confer similar resistance to Zn. Deltazrc1Deltacot1 lacks the ability to accumulate Zn in the vacuole and has lower accumulation of Zn after either long- or short-term Zn exposure. Expression of TgMTP1 in Deltazrc1Deltacot1 leads to further lowering of Zn accumulation and an increase in Zn efflux from the cells. Expression of TgMTP1 in a V-type ATPase-deficient S. cerevisiae strain also confers increased Zn resistance. In vivo and in vitro immunological staining of hemagglutinin (HA)-tagged TgMTP1::HA reveals the protein to be localized in both the S. cerevisiae vacuolar and plasma membranes. Taken together, these data are consistent with MTP1 functioning to enhance plasma membrane Zn efflux, acting to confer Zn resistance independent of the vacuole in S. cerevisiae. Transient expression in Arabidopsis thaliana protoplasts also reveals that TgMTP1::green fluorescent protein (GFP) is localized at the plasma membrane, suggesting that TgMTP1 may also enhance Zn efflux in plants.
为避免金属毒性，生物体已进化出多种机制，包括将金属离子从细胞中排出并隔离到细胞内区室中。普遍存在的阳离子扩散促进因子（CDF）家族成员在这些过程中发挥重要作用。来自镍/锌超富集植物高山遏蓝菜（TgMTP1）的植物CDF家族成员金属耐受蛋白1（MTP1）在酿酒酵母锌抗性赋予（zrc）1钴转运蛋白（cot）1双突变体中的过表达，抑制了该菌株对锌的敏感性。发现高山遏蓝菜含有几种TgMTP1等位变体，所有这些变体在zrc1cot1中对锌具有相似的抗性。同样，来自各种超富集植物和非富集植物物种的MTP1对锌也具有相似的抗性。zrc1cot1缺乏在液泡中积累锌的能力，并且在长期或短期锌暴露后锌的积累较低。TgMTP1在zrc1cot1中的表达导致锌积累进一步降低以及细胞中锌流出增加。TgMTP1在V型ATP酶缺陷型酿酒酵母菌株中的表达也赋予了更高的锌抗性。对血凝素（HA）标记的TgMTP1::HA进行体内和体外免疫染色，结果显示该蛋白定位于酿酒酵母的液泡膜和质膜中。综上所述，这些数据与MTP1的功能一致，即增强质膜锌流出，从而在酿酒酵母中独立于液泡赋予锌抗性。在拟南芥原生质体中的瞬时表达还表明，TgMTP1::绿色荧光蛋白（GFP）定位于质膜，这表明TgMTP1也可能增强植物中的锌流出。
