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	View Edit Domain: GreenBio Title: * Body: Rice plants have been developed that contain six times more iron in polished rice kernels. <br /> <br /> To accomplish this, two plant genes were transferred into an existing rice variety. In the future, high-iron rice could help to reduce iron deficiency in human nutrition, especially in developing countries in Africa and Asia. Moreover, engineered plants will be useful to study the regulation of iron homeostasis <em>in planta</em>.<br /> <br /> <strong>Iron Malnutrition Is a Serious Problem</strong><br /> <br /> Iron deficiency is the most common and widespread nutritional disorder in the world. According to the World Health Organization, approximately two billion people suffer from iron deficiency—they tire easily, experience problems metabolizing harmful substances, and eventually suffer from anemia. Based on the recorded incidence of anemia, most preschool children and pregnant women in developing countries and at least 30 – 40% in industrialized countries are iron deficient.  In developing countries where rice is the major staple food, children are particularly affected, as well as women during their fertile life period. Peeled rice, also called polished rice, does not have enough iron to satisfy the daily requirement,<br /> even if consumed in large quantities. Rice actually has a lot of iron, but only in the seed coat. Because unpeeled rice quickly becomes rancid in tropical and subtropical climates, the seed coat—along with precious iron—must be removed for storage. For many people, a balanced diet or iron supplements are often unaffordable. Moreover, iron is the most difficult mineral for food fortification, since the most soluble and absorbable iron compounds (e.g., FeSO4) are unpalatable, and less soluble iron compounds are poorly absorbed.3<br /> <br /> Conventional breeding and genetic engineering are promising alternative approaches for increasing the iron content of food crops. Until now, however, conventional breeding has only produced a very limited increase of iron in rice endosperm, most likely because seed iron content is a complex trait. Similarly, genetic engineering using single transgenes for iron transport or accumulation has not produced the expected increase, and whether gene transfer of transcription factors leads to the desired higher iron content without detrimental side effects is an open question.4<br /> <br /> <strong>Two Plant Genes Help to Mobilize and Store Iron</strong><br /> <br /> We have recently succeeded in increasing the iron content in polished rice by transferring two plant genes into an existing japonica rice variety.5 One gene encodes nicotianamine synthase, the enzyme that produces nicotianamine. Nicotianamine chelates iron temporarily and facilitates its transport in the plant. Nicotianamine synthase is expressed under a constitutive promoter. The second gene encodes the protein ferritin, which functions as a storage depot for up to four thousand iron atoms per protein molecule in both plants and humans. Since the ferritin gene is under the control of an endosperm-specific promoter, ferritin comprises a sink for iron in the center of the endosperm. The synergistic action of these two genes allows the rice plant to absorb more iron from the soil, transport it in the plant, and store it in the rice kernel. A third gene encoding phytase was also engineered into this rice line. Phytase degrades phytate, a compound that stores phosphate and binds divalent cations like iron and thus inhibits their absorption in the intestine.<br /> <br /> <strong>Iron Content of Biofortified Line is Relevant</strong><br /> <br /> The genetically engineered lines expressing nicotianamine synthase, ferritin, and phytase (NFP-line) contain up to a 6.3-fold increase of iron in the endosperm of polished kernels as compared to wild type, and significantly more than the lines that contain only single genes, i.e., nicotianamine synthase (NAS) or ferritin (FER). This increase is independent of the iron concentration in the medium.5 In contrast, iron content in leaves does not differ significantly, but increases concomitantly with iron content in the medium. Laser ablation inductive coupled plasma mass spectroscopy (LA-ICP-MS)6 confirmed the accumulation of additional iron in the endosperm of NFP lines.5 <br /> by imaging micro-X-ray fluorescence spectroscopy.5<br /> <br /> There are no reports of bred or engineered rice varieties with a comparably high iron increase in endosperm. Field experiments and feeding studies are planned to test the agronomic performance and efficacy of high-iron rice lines. Previous nutritional studies, using a conventionally-bred rice variety with less than half the iron content of our NFP lines, demonstrate that the iron status of women can be improved by rice varieties containing about 3 μg Fe/g dry-weight (DW).7 Our engineered rice line contains up to 7 μg Fe/g DW. Further increasing the iron content of our NFP rice lines from 7 μg to about 15-18 μg Fe/g DW would satisfy the iron requirement with one meal of rice a day. In order to achieve this, it might be sufficient to use high iron genotypes for genetic engineering, containing up to 4 μg Fe/g DW already in the starting material.8<br /> <br /> <strong>Maintenance of Iron Homeostasis</strong><br /> <br /> One obstacle to iron biofortification of plants is the toxicity of iron when it accumulates to higher concentrations in cytoplasm. Plants therefore regulate the uptake and concentration of iron in their cells by altering nicotianamine concentration through expression or activity of nicotianamine synthase or a degrading enzyme, nicotianamine amino transferase (NAAT), in response to an iron-dependant signal. Constitutive expression of nicotianamine synthase in combination with ferritin in the endosperm increases iron in sink tissue, but does not change iron homeostasis in leaves, despite higher levels of nicotianamine.5 Expression of the gene for nicotianamine-degrading NAAT is stimulated,9 probably by higher levels of nicotianamine in leaves of NFP-plants.<br /> <br /> Studies are underway to monitor the expression of other endogenous rice genes involved in iron homeostasis. Understanding the regulation of these genes in our NFP lines will allow us to make further targeted improvements in iron content, e.g., by uncoupling regulated genes from product feedback, using appropriate promoters.<br /> <br /> <strong>Distribution of High Iron Rice to Farmers Still Many Years Away</strong><br /> <br /> The NFP high-iron rice lines were phenotypically and physiologically normal under greenhouse conditions.<br /> 5 It is unlikely that the high-iron rice will negatively affect soil, because iron is the most prevalent<br /> metallic element on earth and very abundant in soil. Nevertheless, before these improved rice lines can be released, they must be extensively tested in the field for their agronomic performance, trait stability, and biosafety. The genes also need to be transferred to other widely-used japonica and indica varieties before they can be made available to farmers. The experience with high-vitamin A “Golden Rice,” which was also developed at ETH Zurich in collaboration with researchers at the University of Freiburg (Germany), has shown that it takes many years before genetically engineered rice can actually be planted by farmers.10 The regulatory hurdles and costs involved in making genetically modified plants available to agriculture and consumers are very high. In addition, appropriate seed distribution channels and agricultural production systems must be established before high-iron rice plants can be available to small-scale and self-sufficient farmers free of charge.<br /> <br /> <strong>References</strong><br /> <br /> 1. Lucca P, Poletti S, Sautter C (2006) Genetic engineering approaches to enrich rice with iron and vitamin A. Physiologia Plantarum 126, 291-303<br /> 2. Poletti S, Gruissem W, Sautter C (2004) The nutritional fortification of cereals. Curr. Opin. Biotechnol. 15, 162–165<br /> 3. Hurrell R, et al. (2002) The usefulness of elemental iron for cereal flour fortification: a SUSTAIN Task Force report. Sharing United States Technology to Aid in the Improvement of Nutrition. Nutr. Rev. 60(12), 391-406<br /> 4. Kobayashi T, et al (2009) The rice transcription factor IDEF1 is essential for the early response to iron deficiency and induces vegetative expression of late embryogenesis abundant genes. The Plant Journal 60, 948-96<br /> 5. Wirth J, Poletti S, Aeschlimann B, Yakandawala N, Drosse B, Osorio S, Tohge T, Fernie A, Günther D, Gruissem W, Sautter C (2009) Rice endosperm iron biofortification by targeted and synergistic action of nicotianamine synthase and ferritin. Plant Biotechnol. J. 7(7), 631-644<br /> 6. Günther D, Frischknecht R, Heinrich CA, Kahlert HJ (1997) Capabilities of a 193 nm ArF excimer laser for LA-ICPMS micro analysis of geological materials. J. Anal. At. Spectrom. 12, 939–944<br /> 7. Haas JD, et al. (2005) Iron-Biofortified Rice improves iron stores of nonanemic Filipino women. J Nutrition 135(12), 2823-30<br /> 8. Lee S, et al. (2009) Iron fortification of rice seeds through activation of the nicotianamine synthase gene. PNAS (USA) 106 (51), 22014-22019<br /> 9. Zambrana Pessano AI (2009) Expression of transgenes and endogenous genes involved in iron metabolism in two transgenic rice lines (Master Thesis) Universidad de la Repiublica Uruguay, Facultad de Ciencias, Licenciatura en Bioquimica.<br /> 10. Golden Rice: www.goldenrice.org<br /> Captcha: Please Enter Code : * Time Zone: * Select the time zone Vocabularies Newsletter: Domain: Show summary in full view Input format Filtered HTML Web page addresses and e-mail addresses turn into links automatically. Lines and paragraphs break automatically. Full HTML Web page addresses and e-mail addresses turn into links automatically. 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