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JXB Advance Access originally published online on October 25, 2009
Journal of Experimental Botany 2009 60(15):4263-4274; doi:10.1093/jxb/erp257
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© 2009 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.5/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited. This paper is available online free of all access charges (see http://jxb.oxfordjournals.org/open_access.html for further details)

RESEARCH PAPER

Wheat (Triticum aestivum) NAM proteins regulate the translocation of iron, zinc, and nitrogen compounds from vegetative tissues to grain

Brian M. Waters1,*, Cristobal Uauy2 {dagger}, Jorge Dubcovsky2 and Michael A. Grusak1

1USDA/ARS Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, 1100 Bates Street, Houston, Texas 77030, USA
2Department of Plant Sciences, University of California, One Shields Avenue, Davis, California 95616, USA

* Present address and to whom correspondence should be sent: Department of Agronomy and Horticulture, University of Nebraska, 279 Plant Sciences Hall, Lincoln, Nebraska 68583, USA. E-mail: bwaters2{at}unl.edu

The NAM-B1 gene is a NAC transcription factor that affects grain nutrient concentrations in wheat (Triticum aestivum). An RNAi line with reduced expression of NAM genes has lower grain protein, iron (Fe), and zinc (Zn) concentrations. To determine whether decreased remobilization, lower plant uptake, or decreased partitioning to grain are responsible for this phenotype, mineral dynamics were quantified in wheat tissues throughout grain development. Control and RNAi wheat were grown in potting mix and hydroponics. Mineral (Ca, Cu, Fe, K, Mg, Mn, P, S, and Zn) and nitrogen (N) contents of organs were determined at regular intervals to quantify the net remobilization from vegetative tissues and the accumulation of nutrients in grain. Total nutrient accumulation was similar between lines, but grain Fe, Zn, and N were at lower concentrations in the NAM knockdown line. In potting mix, net remobilization of N, Fe, and Zn from vegetative tissues was impaired in the RNAi line. In hydroponics with ample nutrients, net remobilization was not observed, but grain Fe and Zn contents and concentrations remained lower in the RNAi line. When Fe or Zn was withheld post-anthesis, both lines demonstrated remobilization. These results suggest that a major effect of the NAM genes is an increased efflux of nutrients from the vegetative tissues and a higher partitioning of nutrients to grain.

Key words: Biofortification, grain protein content, iron, remobilization, senescence, zinc

{dagger} Present address: Department of Crop Genetics, John Innes Centre, Colney Lane, Norwich NR4 7UH, UK.

Received 26 June 2009; Revised 5 August 2009 Accepted 6 August 2009


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