Phytoremediation by Reduction of Toxic Metal Ions

9513347 Meagher重金属污染在世界许多地方已经达到了有毒的水平，已经成为一个紧迫的问题。我们的长期目标是识别和利用单基因性状，以实现基于植物修复的生态合理的解决方案，以金属离子污染。 细菌merA基因的项目，汞离子还原酶（MerA），催化离子汞，Hg++的解毒，将其还原为毒性较小的金属形式，Hg 0。 最近，它已被证明，一个高度诱变的merA基因，merApe 9，赋予显着水平的抗性转基因拟南芥中的Hg++。 转基因种子发芽，幼苗生长，植物开花，并设置在培养基中含有高达100 μ M Hg++（20 ppm）的种子，而对照幼苗死亡期间或萌发后不久在25 μ M。 这些植物在这个过程中进化出了显著水平的Hgo。 抗性最强的植物株系在Hg++上生长良好，与未受挑战的对照植物一样，实际上需要汞才能达到最佳生长。 转基因植株还表现出对培养基中毒性水平的Au++的抗性。 本项目的近期目标是探索金属离子还原作为植物修复多种重金属污染物的方法。 初步证据表明，除了Hg ~（++），merA pe 9还能还原大肠杆菌中的Au ~（+）和Cu ~（++）。杆菌 MerA属于序列相关还原酶的多样性家族，其识别除Hg++之外的多种有机和硫醇底物。 除了Hg++之外，MerA还结合Ag+、Cu++、Cd++和Au+。 因此，假设：merA基因可以被突变以指导多种金属离子的有效还原用于修复或提取。 该提议的具体目的是产生具有新底物特异性的merA突变体（例如，Hg++的增强还原和Cu++、Pb++和Cd++的新还原）。 在未来的转基因构建体将在模式植物中检查其潜在的用于金属离子污染的植物修复。

9513347 Meagher Heavy metal contamination has reached toxic levels in many parts of the world and has become an urgent problem. Our long term goal is to identify and utilize single gene traits to effect ecologically sound solutions to metal ion contamination based on phytoremediation. The project of the bacterial merA gene, mercuric ion reductase (MerA), catalzes the detoxification of ionic mercury, Hg++, reducing it to its less toxic metallic form, Hg0. Recently it has been shown that a highly mutagenized merA gene, merApe9, confers remarkable levels of resistance to Hg++ in transgenic Arabidopsis plants. Transgenic seeds germinate, seedlings grow, and plants flower and set seed on media containing up to 100 uM Hg++ (20 ppm), while control seedlings die during or shortly after germination at 25 uM. These plants evolved significant levels of Hgo in the process. The most resistant plant lines grow as well on Hg++ as unchallenged control plants and acturally require mercury for optimum growth. The transgenic plants also show resistance to toxic levels of Au+++ in media. The immediate goal of this project is to explore metal ion reduction as a method of phytoremediation for a variety of heavy metal pollutants. Preliminary evidence is presented to suggest that besides Hg++ merA pe9 also can reduce Au+++ and Cu++ in E. coli. MerA belongs to a diverse family of sequence-related reductases, which recognize a wide variety of organic and thiol substrates in addition to Hg++. Besides Hg++ MerA already binds Ag+, Cu++, Cd++, and Au+++. Therefore, it is hypothesized that: the merA gene can be mutated to direct the efficient reduction of a wide variety of metal ions for remediation or extraction. The specific aim of the proposal is to generate merA mutants with novel substrate specificities (e.g., enhanced reduction of Hg++ and novel reduction of Cu++, Pb++, and Cd++). In the future transgenic constructs will be examined in model plants for their potential use in the phytoremediation of metal ion pollution.