Metal Uptake in Arabidopsis thaliana

拟南芥的金属吸收

• 批准号: 9974837
• 负责人: Mary Lou Guerinot
• 金额: $ 37.5万
• 依托单位: Dartmouth College
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1999
• 资助国家: 美国
• 起止时间: 1999-09-01 至 2003-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9974837&HistoricalAwards=false
• 关键词: Metal; Uptake; Arabidopsis; thaliana

Iron is an essential nutrient for higher plants, with iron-containing compounds figuring prominently in the electron transport systems of photosynthesis and respiration. Although iron is abundant in the soil, the acquisition of iron is problematic due to its low solubility at neutral pH. In response to iron deficiency, all plants except the grasses induce Fe(III) chelate reductase activity, Fe(II) transport activity and proton release into the rhizosphere. Of the three responses, Fe(III) reduction is thought to be the primary factor in making iron available to plants. During the current funding period, Arabidopsis mutants that have defects in Fe(III) chelate reduction were identified. frd1 cannot induce Fe(III) chelate reductase activity in response to iron deficiency and frd3 has high levels of Fe(III) reductase activity relative to wild type when plants are grown under iron sufficient conditions. The gene identified by the frd1 mutation, FRO2, has been cloned and shown to complement the frd1 mutant. FRO2 encodes a metal chelate reductase belonging to a superfamily of flavocytochromes whose members pass electrons across membranes. During the course of this work, another gene family, the ZIP gene family, was also identified that encodes metal transporters capable of transporting Fe(II), Mn(II) and Zn(II). One of the family members, IRT1, is only expressed in the roots of iron deficient plants and is suggested to be responsible for uptake of Fe(II) from the rhizosphere. This project will build on the discoveries made during the current funding period, specifically focusing on strategies to make Fe available to the plant (i.e., metal reduction and proton release). The specific objectives of this proposal are to: 1) determine the role of the FRO2 metalloreductase in Arabidopsis metal ion uptake and metabolism using functional expression studies in yeast and genetic, cytological and biochemical analyses in Arabidopsis. As time permits, analyze the role of other members of the FRO gene family.2) further characterize the frd3 mutant and clone the FRD3 gene.As part of the characterization of the FRO2 gene, organ and tissue specificity as well as subcellular localization will be determined. A knockout mutant that carries an insertion in FRO2 gene will also be identified in order to determine the contribution of the FRO2 gene product to metal ion homeostasis. Null alleles of FRO2, IRT1 and AHA2 will also be used to test the hypothesis that Fe(III) reduction is indeed limiting iron acquisition by plants, as has been suggested from physiological studies. The gene identified by the frd3 mutation may be involved in metal transport, metal sensing or metal regulation, based on the physiological characterization carried out to date. Fine mapping of the frd3 mutation will be done by analyzing inter-ecotype recombinants to facilitate the cloning of the FRD3 gene. Understanding iron uptake in plants is extremely important as one-third of the world's soils are iron deficient. Furthermore, iron deficiency in humans is the most prevalent nutritional problem in the world today, affecting an estimated 2.7 billion people in developed and developing countries. For most of the world, plant material is the major source of iron so ensuring that plants have higher stores of bio-available iron will go a long way towards solving an important problem in human nutrition.

铁是较高植物的必不可少的营养素，含铁化合物在光合作用和呼吸的电子传输系统中显着。 尽管铁在土壤中很丰富，但由于中性pH值低的溶解度，铁的采集是有问题的。 为了响应铁缺乏症，除草以外的所有植物都诱导了Fe（III）螯合酶还原酶活性，Fe（II）转运活性和质子释放到根际。 在这三个反应中，Fe（III）的减少被认为是使植物可用的铁的主要因素。 在当前的资金期间，发现了拟南芥减少缺陷的拟南芥突变体。 FRD1不能响应铁缺乏症而诱导Fe（III）螯合还原酶活性，而在铁足够的条件下植物生长时，相对于野生型，FRD3具有高水平的Fe（III）还原酶活性。 通过FRD1突变FRO2鉴定的基因已被克隆并证明可以补充FRD1突变体。 FRO2编码属于黄叶染色体的超家族的金属螯合还原酶，其成员通过跨膜的电子经过。 在这项工作的过程中，还确定了另一个基因家族，即ZIP基因家族，它编码能够运输Fe（II），MN（II）和Zn（II）的金属转运蛋白。 其中一位家庭成员IRT1仅在铁不足的植物的根部表达，并被认为是从根际摄入的Fe（II）。 该项目将建立在当前资金期间发现的发现，特别关注使工厂可用的策略（即金属还原和质子释放）。 该提案的具体目标是：1）确定FRO2金属核苷酸在拟南芥金属离子摄取和代谢中的作用，并在拟南芥中使用酵母，遗传学，细胞学和生化分析中的功能表达研究。 随着时间的允许，分析FRO基因家族的其他成员的作用。2）进一步表征FRD3突变体并克隆FRD3基因。作为FRO2基因，器官和组织特异性以及亚细胞定位的表征的一部分，将确定。 还将鉴定出在FRO2基因中插入的敲除突变体，以确定FRO2基因产物对金属离子稳态的贡献。 FRO2，IRT1和AHA2的无效等位基因也将用于检验以下假设：Fe（iii）的减少确实在限制植物的铁采集，正如生理研究所建议的那样。 通过FRD3突变鉴定的基因可能与迄今为止进行的生理表征有关，可能与金属传输，金属传感或金属调节有关。 FRD3突变的精细映射将通过分析指型重组因子来促进FRD3基因的克隆来完成。 了解植物中的铁的吸收非常重要，因为世界上三分之一的土壤是铁不足的。 此外，人类的铁缺乏症是当今世界上最普遍的营养问题，影响了发达国家和发展中国家的27亿人。 对于世界上的大多数地区，植物材料是铁的主要来源，因此确保植物拥有较高的生物可用铁储存量将大大解决人类营养中的重要问题。