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.

铁是高等植物的必需营养素，含铁化合物在光合作用和呼吸的电子传输系统中发挥着重要作用。 尽管土壤中铁含量丰富，但由于其在中性pH下溶解度低，铁的获取存在问题。 为了应对缺铁，除草以外的所有植物都会诱导 Fe(III) 螯合还原酶活性、Fe(II) 转运活性和质子释放到根际。 在这三种反应中，Fe(III) 还原被认为是使铁可供植物利用的主要因素。 在当前资助期间，鉴定出具有 Fe(III) 螯合物还原缺陷的拟南芥突变体。 frd1 不能响应缺铁而诱导 Fe(III) 螯合还原酶活性，并且当植物在铁充足的条件下生长时，frd3 相对于野生型具有高水平的 Fe(III) 还原酶活性。 由 frd1 突变识别的基因 FRO2 已被克隆并显示与 frd1 突变体互补。 FRO2 编码一种金属螯合还原酶，属于黄细胞色素超家族，其成员可跨膜传递电子。 在这项工作过程中，还鉴定了另一个基因家族，即 ZIP 基因家族，它编码能够转运 Fe(II)、Mn(II) 和 Zn(II) 的金属转运蛋白。 该家族成员之一 IRT1 仅在缺铁植物的根部表达，并被认为负责从根际吸收 Fe(II)。 该项目将建立在当前资助期间所取得的发现的基础上，特别关注为工厂提供铁的策略（即金属还原和质子释放）。 该提案的具体目标是：1）利用酵母中的功能表达研究和拟南芥中的遗传、细胞学和生化分析，确定FRO2金属还原酶在拟南芥金属离子摄取和代谢中的作用。 如果时间允许，分析FRO基因家族其他成员的作用。2)进一步表征frd3突变体并克隆FRD3基因。作为FRO2基因表征的一部分，将确定器官和组织特异性以及亚细胞定位。 还将鉴定携带 FRO2 基因插入的敲除突变体，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这样的假设：Fe(III) 还原确实限制了植物对铁的获取，正如生理学研究所表明的那样。 根据迄今为止进行的生理表征，frd3突变鉴定的基因可能涉及金属转运、金属传感或金属调节。 将通过分析生态型间重组体来完成 frd3 突变的精细定位，以促进 FRD3 基因的克隆。 了解植物对铁的吸收极为重要，因为世界上三分之一的土壤缺铁。 此外，人类缺铁是当今世界最普遍的营养问题，影响着发达国家和发展中国家约 27 亿人。 对于世界上大多数国家来说，植物材料是铁的主要来源，因此确保植物储存更多的生物可利用铁将大大有助于解决人类营养中的重要问题。