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.

铁是高等植物必需的营养元素，含铁化合物在光合作用和呼吸作用的电子传递系统中占有重要地位。 虽然铁是丰富的土壤中，铁的收购是有问题的，由于其在中性pH值的低溶解度。在响应缺铁，除草所有植物诱导Fe（III）螯合还原酶活性，Fe（II）运输活性和质子释放到根际。 在这三种反应中，Fe（III）还原被认为是使植物获得铁的主要因素。 在目前的资助期间，拟南芥突变体，有缺陷的铁（III）螯合还原被确定。 frd1不能诱导Fe（III）螯合还原酶活性以响应铁缺乏，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frd 1突变识别的基因FRO2已被克隆，并显示出与frd 1突变互补。 FRO2编码属于黄细胞色素超家族的金属螯合还原酶，其成员通过电子穿过膜。 在这项工作的过程中，另一个基因家族，ZIP基因家族，也被确定为编码能够运输Fe（II），Mn（II）和Zn（II）的金属转运蛋白。 该家族成员之一，IRT1，仅在缺铁植物的根中表达，并被认为是负责从根际吸收Fe（II）。 该项目将建立在当前资助期间的发现基础上，特别关注使工厂获得铁的策略（即，金属还原和质子释放）。 本发明的具体目的是：1）使用酵母中的功能表达研究和拟南芥中的遗传学、细胞学和生物化学分析来确定FRO 2金属还原酶在拟南芥金属离子吸收和代谢中的作用。 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FRO 2基因插入的敲除突变体，以确定FRO 2基因产物对金属离子稳态的贡献。 FRO2，IRT 1和AHA2的等位基因也将被用来测试的假设，铁（III）的还原确实是限制铁的收购植物，从生理学研究表明。 根据迄今为止进行的生理学表征，frd3突变所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进行frd3突变的精细作图，以促进FRD3基因的克隆。 了解植物对铁的吸收是非常重要的，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，影响到发达国家和发展中国家约27亿人。 对于世界上大多数地区来说，植物材料是铁的主要来源，因此确保植物具有更高的生物可利用铁储备将对解决人类营养中的一个重要问题大有帮助。