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Harrington SA, Connorton JM, Nyangoma NIM, McNelly R, Morgan YML, Aslam MF, Sharp PA, Johnson AAT, Uauy C, Balk J. A two-gene strategy increases iron and zinc concentrations in wheat flour, improving mineral bioaccessibility. Plant Physiol 2023; 191:528-541. [PMID: 36308454 PMCID: PMC9806615 DOI: 10.1093/plphys/kiac499] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/23/2022] [Accepted: 10/13/2022] [Indexed: 05/09/2023]
Abstract
Dietary deficiencies of iron and zinc cause human malnutrition that can be mitigated by biofortified staple crops. Conventional breeding approaches to increase grain mineral concentrations in wheat (Triticum aestivum L.) have had only limited success, and our understanding of the genetic and physiological barriers to altering this trait is incomplete. Here we demonstrate that a transgenic approach combining endosperm-specific expression of the wheat VACUOLAR IRON TRANSPORTER gene TaVIT2-D with constitutive expression of the rice (Oryza sativa) NICOTIANAMINE SYNTHASE gene OsNAS2 significantly increases the total concentration of zinc and relocates iron to white-flour fractions. In two distinct bread wheat cultivars, we show that the so called VIT-NAS construct led to a two-fold increase in zinc in wholemeal flour, to ∼50 µg g-1. Total iron was not significantly increased, but redistribution within the grain resulted in a three-fold increase in iron in highly pure, roller-milled white flour, to ∼25 µg g-1. Interestingly, expression of OsNAS2 partially restored iron translocation to the aleurone, which is iron depleted in grain overexpressing TaVIT2 alone. A greater than three-fold increase in the level of the natural plant metal chelator nicotianamine in the grain of VIT-NAS lines corresponded with improved iron and zinc bioaccessibility in white flour. The growth of VIT-NAS plants in the greenhouse was indistinguishable from untransformed controls. Our results provide insights into mineral translocation and distribution in wheat grain and demonstrate that the individual and combined effects of the two transgenes can enhance the nutritional quality of wheat beyond what is possible by conventional breeding.
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Affiliation(s)
| | - James M Connorton
- John Innes Centre, Norwich Research Park, Norwich NR4 7UH, UK
- School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK
| | | | - Rose McNelly
- John Innes Centre, Norwich Research Park, Norwich NR4 7UH, UK
- School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK
| | - Yvie M L Morgan
- John Innes Centre, Norwich Research Park, Norwich NR4 7UH, UK
- School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, UK
| | - Mohamad F Aslam
- Department of Nutritional Sciences, King’s College London, London SE1 9NH, UK
| | - Paul A Sharp
- Department of Nutritional Sciences, King’s College London, London SE1 9NH, UK
| | | | - Cristobal Uauy
- John Innes Centre, Norwich Research Park, Norwich NR4 7UH, UK
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2
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Sheraz S, Wan Y, Venter E, Verma SK, Xiong Q, Waites J, Connorton JM, Shewry PR, Moore KL, Balk J. Subcellular dynamics studies of iron reveal how tissue-specific distribution patterns are established in developing wheat grains. New Phytol 2021; 231:1644-1657. [PMID: 33914919 DOI: 10.1111/nph.17440] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/03/2021] [Accepted: 04/14/2021] [Indexed: 06/12/2023]
Abstract
Understanding the mechanisms of iron trafficking in plants is key to enhancing the nutritional quality of crops. Because it is difficult to image iron in transit, we currently have an incomplete picture of the route(s) of iron translocation in developing seeds and how the tissue-specific distribution is established. We have used a novel approach, combining iron-57 (57 Fe) isotope labelling and nanoscale secondary ion mass spectrometry (NanoSIMS), to visualize iron translocation between tissues and within cells in immature wheat grain, Triticum aestivum. This enabled us to track the main route of iron transport from maternal tissues to the embryo through the different cell types. Further evidence for this route was provided by genetically diverting iron into storage vacuoles, with confirmation provided by histological staining and transmission electron microscopy energy dispersive X-ray spectroscopy (TEM-EDS). Almost all iron in both control and transgenic grains was found in intracellular bodies, indicating symplastic rather than apoplastic transport. Furthermore, a new type of iron body, highly enriched in 57 Fe, was observed in aleurone cells and may represent iron being delivered to phytate globoids. Correlation of the 57 Fe enrichment profiles obtained by NanoSIMS with tissue-specific gene expression provides an updated model of iron homeostasis in cereal grains with relevance for future biofortification strategies.
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Affiliation(s)
- Sadia Sheraz
- School of Materials and Photon Science Institute, University of Manchester, Manchester, M13 9PL, UK
| | - Yongfang Wan
- Department of Plant Sciences, Rothamsted Research, Harpenden, AL5 2JQ, UK
| | - Eudri Venter
- Bioimaging facility, Department of Computational and Analytical Sciences, Rothamsted Research, Harpenden, AL5 2JQ, UK
| | - Shailender K Verma
- Department of Biological Chemistry, John Innes Centre, Norwich, NR4 7UH, UK
| | - Qing Xiong
- Department of Biological Chemistry, John Innes Centre, Norwich, NR4 7UH, UK
| | - Joshua Waites
- Department of Biological Chemistry, John Innes Centre, Norwich, NR4 7UH, UK
- School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ, UK
| | - James M Connorton
- Department of Biological Chemistry, John Innes Centre, Norwich, NR4 7UH, UK
- School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ, UK
| | - Peter R Shewry
- Department of Plant Sciences, Rothamsted Research, Harpenden, AL5 2JQ, UK
| | - Katie L Moore
- School of Materials and Photon Science Institute, University of Manchester, Manchester, M13 9PL, UK
| | - Janneke Balk
- Department of Biological Chemistry, John Innes Centre, Norwich, NR4 7UH, UK
- School of Biological Sciences, University of East Anglia, Norwich, NR4 7TJ, UK
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Connorton JM, Balk J. Iron Biofortification of Staple Crops: Lessons and Challenges in Plant Genetics. Plant Cell Physiol 2019; 60:1447-1456. [PMID: 31058958 PMCID: PMC6619672 DOI: 10.1093/pcp/pcz079] [Citation(s) in RCA: 69] [Impact Index Per Article: 13.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/06/2019] [Accepted: 04/23/2019] [Indexed: 05/19/2023]
Abstract
Plants are the ultimate source of iron in our diet, either directly as staple crops and vegetables or indirectly via animal fodder. Increasing the iron concentration of edible parts of plants, known as biofortification, is seen as a sustainable approach to alleviate iron deficiency which is a major global health issue. Advances in sequencing and gene technology are accelerating both forward and reverse genetic approaches. In this review, we summarize recent progress in iron biofortification using conventional plant breeding or transgenics. Interestingly, some of the gene targets already used for transgenic approaches are also identified as genetic factors for high iron in genome-wide association studies. Several quantitative trait loci and transgenes increase both iron and zinc, due to overlap in transporters and chelators for these two mineral micronutrients. Research efforts are predominantly aimed at increasing the total concentration of iron but enhancing its bioavailability is also addressed. In particular, increased biosynthesis of the metal chelator nicotianamine increases iron and zinc levels and improves bioavailability. The achievements to date are very promising in being able to provide sufficient iron in diets with less reliance on meat to feed a growing world population.
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Affiliation(s)
- James M Connorton
- Department of Biological Chemistry, John Innes Centre, Norwich, UK
- School of Biological Sciences, University of East Anglia, Norwich, UK
| | - Janneke Balk
- Department of Biological Chemistry, John Innes Centre, Norwich, UK
- School of Biological Sciences, University of East Anglia, Norwich, UK
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Abstract
Wheat is the staple food crop in temperate countries and increasingly consumed in developing countries, displacing traditional foods. However, wheat products are typically low in bioavailable iron and zinc, contributing to deficiencies in these micronutrients in countries where wheat is consumed as a staple food. Two factors contribute to the low contents of bioavailable iron and zinc in wheat: the low concentrations of these minerals in white flour, which is most widely consumed, and the presence of phytates in mineral‐rich bran fractions. Although high zinc types of wheat have been developed by conventional plant breeding (biofortification), this approach has failed for iron. However, studies in wheat and other cereals have shown that transgenic (also known as genetically modified; GM) strategies can be used to increase the contents of iron and zinc in white flour, by converting the starchy endosperm tissue into a ‘sink’ for minerals. Although such strategies currently have low acceptability, greater understanding of the mechanisms which control the transport and deposition of iron and zinc in the developing grain should allow similar effects to be achieved by exploiting naturally induced genetic variation. When combined with conventional biofortification and innovative processing, this approach should provide increased mineral bioavailability in a range of wheat products, from white flour to wholemeal.
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Affiliation(s)
- J Balk
- John Innes Centre Norwich Research Park Norwich UK.,School of Biological Sciences University of East Anglia Norwich UK
| | - J M Connorton
- John Innes Centre Norwich Research Park Norwich UK.,School of Biological Sciences University of East Anglia Norwich UK
| | - Y Wan
- Department of Plant Science Rothamsted Research Harpenden UK
| | - A Lovegrove
- Department of Plant Science Rothamsted Research Harpenden UK
| | - K L Moore
- School of Materials University of Manchester Manchester UK.,Photon Science Institute University of Manchester Manchester UK
| | - C Uauy
- John Innes Centre Norwich Research Park Norwich UK
| | - P A Sharp
- Department of Nutritional Sciences Kings College London UK
| | - P R Shewry
- Department of Plant Science Rothamsted Research Harpenden UK
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Connorton JM, Jones ER, Rodríguez-Ramiro I, Fairweather-Tait S, Uauy C, Balk J. Wheat Vacuolar Iron Transporter TaVIT2 Transports Fe and Mn and Is Effective for Biofortification. Plant Physiol 2017; 174:2434-2444. [PMID: 28684433 PMCID: PMC5543970 DOI: 10.1104/pp.17.00672] [Citation(s) in RCA: 109] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/22/2017] [Accepted: 07/02/2017] [Indexed: 05/18/2023]
Abstract
Increasing the intrinsic nutritional quality of crops, known as biofortification, is viewed as a sustainable approach to alleviate micronutrient deficiencies. In particular, iron deficiency anemia is a major global health issue, but the iron content of staple crops such as wheat (Triticum aestivum) is difficult to change because of genetic complexity and homeostasis mechanisms. To identify target genes for the biofortification of wheat, we functionally characterized homologs of the VACUOLAR IRON TRANSPORTER (VIT). The wheat genome contains two VIT paralogs, TaVIT1 and TaVIT2, which have different expression patterns but are both low in the endosperm. TaVIT2, but not TaVIT1, was able to rescue the growth of a yeast (Saccharomyces cerevisiae) mutant defective in vacuolar iron transport. TaVIT2 also complemented a manganese transporter mutant but not a vacuolar zinc transporter mutant. By overexpressing TaVIT2 under the control of an endosperm-specific promoter, we achieved a greater than 2-fold increase in iron in white flour fractions, exceeding minimum legal fortification levels in countries such as the United Kingdom. The antinutrient phytate was not increased and the iron in the white flour fraction was bioavailable in vitro, suggesting that food products made from the biofortified flour could contribute to improved iron nutrition. The single-gene approach impacted minimally on plant growth and also was effective in barley (Hordeum vulgare). Our results show that by enhancing vacuolar iron transport in the endosperm, this essential micronutrient accumulated in this tissue, bypassing existing homeostatic mechanisms.
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Affiliation(s)
- James M Connorton
- Department of Biological Chemistry, John Innes Centre, Norwich NR4 7UH, United Kingdom
- School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom
| | - Eleanor R Jones
- Department of Biological Chemistry, John Innes Centre, Norwich NR4 7UH, United Kingdom
| | | | | | - Cristobal Uauy
- Department of Crop Genetics, John Innes Centre, Norwich NR4 7UH, United Kingdom
| | - Janneke Balk
- Department of Biological Chemistry, John Innes Centre, Norwich NR4 7UH, United Kingdom
- School of Biological Sciences, University of East Anglia, Norwich NR4 7TJ, United Kingdom
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Abstract
Iron plays a crucial role in biochemistry and is an essential micronutrient for plants and humans alike. Although plentiful in the Earth's crust it is not usually found in a form readily accessible for plants to use. They must therefore sense and interact with their environment, and have evolved two different molecular strategies to take up iron in the root. Once inside, iron is complexed with chelators and distributed to sink tissues where it is used predominantly in the production of enzyme cofactors or components of electron transport chains. The processes of iron uptake, distribution and metabolism are overseen by tight regulatory mechanisms, at the transcriptional and post-transcriptional level, to avoid iron concentrations building to toxic excess. Iron is also loaded into seeds, where it is stored in vacuoles or in ferritin. This is important for human nutrition as seeds form the edible parts of many crop species. As such, increasing iron in seeds and other tissues is a major goal for biofortification efforts by both traditional breeding and biotechnological approaches.
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Affiliation(s)
- James M Connorton
- John Innes Centre and University of East Anglia, Norwich Research Park, Norwich, NR4 7UH, UK.
| | - Janneke Balk
- John Innes Centre and University of East Anglia, Norwich Research Park, Norwich, NR4 7UH, UK.
| | - Jorge Rodríguez-Celma
- John Innes Centre and University of East Anglia, Norwich Research Park, Norwich, NR4 7UH, UK.
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Borrill P, Connorton JM, Balk J, Miller AJ, Sanders D, Uauy C. Biofortification of wheat grain with iron and zinc: integrating novel genomic resources and knowledge from model crops. Front Plant Sci 2014; 5:53. [PMID: 24600464 PMCID: PMC3930855 DOI: 10.3389/fpls.2014.00053] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2013] [Accepted: 02/04/2014] [Indexed: 05/18/2023]
Abstract
Wheat, like many other staple cereals, contains low levels of the essential micronutrients iron and zinc. Up to two billion people worldwide suffer from iron and zinc deficiencies, particularly in regions with predominantly cereal-based diets. Although wheat flour is commonly fortified during processing, an attractive and more sustainable solution is biofortification, which requires developing new varieties of wheat with inherently higher iron and zinc content in their grains. Until now most studies aimed at increasing iron and zinc content in wheat grains have focused on discovering natural variation in progenitor or related species. However, recent developments in genomics and transformation have led to a step change in targeted research on wheat at a molecular level. We discuss promising approaches to improve iron and zinc content in wheat using knowledge gained in model grasses. We explore how the latest resources developed in wheat, including sequenced genomes and mutant populations, can be exploited for biofortification. We also highlight the key research and practical challenges that remain in improving iron and zinc content in wheat.
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Affiliation(s)
| | | | - Janneke Balk
- John Innes CentreNorwich, UK
- School of Biological Sciences, University of East AngliaNorwich, UK
| | | | | | - Cristobal Uauy
- John Innes CentreNorwich, UK
- National Institute of Agricultural BotanyCambridge, UK
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Connorton JM, Webster RE, Cheng N, Pittman JK. Knockout of multiple Arabidopsis cation/H(+) exchangers suggests isoform-specific roles in metal stress response, germination and seed mineral nutrition. PLoS One 2012; 7:e47455. [PMID: 23071810 PMCID: PMC3470555 DOI: 10.1371/journal.pone.0047455] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2012] [Accepted: 09/17/2012] [Indexed: 11/18/2022] Open
Abstract
Cation/H+ exchangers encoded by CAX genes play an important role in the vacuolar accumulation of metals including Ca2+ and Mn2+. Arabidopsis thaliana CAX1 and CAX3 have been previously shown to differ phylogenetically from CAX2 but the physiological roles of these different transporters are still unclear. To examine the functions and the potential of redundancy between these three cation transporters, cax1/cax2 and cax2/cax3 double knockout mutants were generated and compared with wild type and cax single knockouts. These double mutants had equivalent metal stress responses to single cax mutants. Both cax1 and cax1/cax2 had increased tolerance to Mg stress, while cax2 and cax2/cax3 both had increased sensitivity to Mn stress. The cax1/cax2 and cax2/cax3 mutants did not exhibit the deleterious developmental phenotypes previously seen with the cax1/cax3 mutant. However, these new double mutants did show alterations in seed germination, specifically a delay in germination time. These alterations correlated with changes in nutrient content within the seeds of the mutants, particularly the cax1/cax2 mutant which had significantly higher seed content of Ca and Mn. This study indicates that the presence of these Arabidopsis CAX transporters is important for normal germination and infers a role for CAX proteins in metal homeostasis within the seed.
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Affiliation(s)
- James M. Connorton
- Faculty of Life Sciences, The University of Manchester, Manchester, United Kingdom
| | - Rachel E. Webster
- Faculty of Life Sciences, The University of Manchester, Manchester, United Kingdom
| | - Ninghui Cheng
- United States Department of Agriculture/Agricultural Research Service Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas, United States of America
| | - Jon K. Pittman
- Faculty of Life Sciences, The University of Manchester, Manchester, United Kingdom
- * E-mail:
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Zhao J, Connorton JM, Guo Y, Li X, Shigaki T, Hirschi KD, Pittman JK. Functional studies of split Arabidopsis Ca2+/H+ exchangers. J Biol Chem 2009; 284:34075-83. [PMID: 19819871 PMCID: PMC2797178 DOI: 10.1074/jbc.m109.070235] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2009] [Indexed: 11/06/2022] Open
Abstract
In plants, high capacity tonoplast cation/H(+) antiport is mediated in part by a family of cation exchanger (CAX) transporters. Functional association between CAX1 and CAX3 has previously been shown. In this study we further examine the interactions between CAX protein domains through the use of nonfunctional halves of CAX transporters. We demonstrate that a protein coding for an N-terminal half of an activated variant of CAX1 (sCAX1) can associate with the C-terminal half of either CAX1 or CAX3 to form a functional transporter that may exhibit unique transport properties. Using yeast split ubiquitin, in planta bimolecular fluorescence complementation, and gel shift experiments, we demonstrate a physical interaction among the half proteins. Moreover, the half-proteins both independently localized to the same yeast endomembrane. Co-expressing variants of N- and C-terminal halves of CAX1 and CAX3 in yeast suggested that the N-terminal region mediates Ca(2+) transport, whereas the C-terminal half defines salt tolerance phenotypes. Furthermore, in yeast assays, auto-inhibited CAX1 could be differentially activated by CAX split proteins. The N-terminal half of CAX1 when co-expressed with CAX1 activated Ca(2+) transport, whereas co-expressing C-terminal halves of CAX variants with CAX1 conferred salt tolerance but no apparent Ca(2+) transport. These findings demonstrate plasticity through hetero-CAX complex formation as well as a novel means to engineer CAX transport.
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Affiliation(s)
- Jian Zhao
- From the United States Department of Agriculture/Agricultural Research Service, Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas 77030-2600
| | - James M. Connorton
- the Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester M13 9PT, United Kingdom, and
| | - YingQing Guo
- From the United States Department of Agriculture/Agricultural Research Service, Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas 77030-2600
| | - Xiangkai Li
- From the United States Department of Agriculture/Agricultural Research Service, Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas 77030-2600
| | - Toshiro Shigaki
- From the United States Department of Agriculture/Agricultural Research Service, Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas 77030-2600
| | - Kendal D. Hirschi
- From the United States Department of Agriculture/Agricultural Research Service, Children's Nutrition Research Center, Baylor College of Medicine, Houston, Texas 77030-2600
- the Vegetable and Fruit Improvement Center, Texas A & M University, College Station, Texas 77845
| | - Jon K. Pittman
- the Faculty of Life Sciences, University of Manchester, Oxford Road, Manchester M13 9PT, United Kingdom, and
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