Abstract
SummaryBread wheat (Triticum aestivum L.) is cultivated on more land than any other crop and produces a fifth of the calories consumed by humans. Wheat endosperm is rich in starch yet contains low concentrations of dietary iron (Fe) and zinc (Zn). Biofortification is a micronutrient intervention aimed at increasing the density and bioavailability of essential vitamins and minerals in staple crops; Fe biofortification of wheat has proved challenging. In this study we employed constitutive expression (CE) of the rice (Oryza sativa L.) nicotianamine synthase 2 (OsNAS2) gene in bread wheat to up‐regulate biosynthesis of two low molecular weight metal chelators – nicotianamine (NA) and 2′‐deoxymugineic acid (DMA) – that play key roles in metal transport and nutrition. The CE‐OsNAS2 plants accumulated higher concentrations of grain Fe, Zn, NA and DMA and synchrotron X‐ray fluorescence microscopy (XFM) revealed enhanced localization of Fe and Zn in endosperm and crease tissues, respectively. Iron bioavailability was increased in white flour milled from field‐grown CE‐OsNAS2 grain and positively correlated with NA and DMA concentrations.
Highlights
Micronutrient mineral deficiencies affect over two billion people worldwide with women and children most acutely at risk (Beal et al, 2017; Lopez et al, 2016)
In this study of glasshouse- and field-grown plants, we demonstrate that constitutive expression of the rice OsNAS2 gene (CE-OsNAS2) in bread wheat causes significant Fe and Zn enrichment of whole grain and flour fractions and increased concentrations of NA and deoxymugineic acid (DMA) that are positively correlated with Fe bioavailability in CE-OsNAS2 white flour
Bread wheat cultivar Bobwhite transformants with constitutive expression (CE) of the rice nicotianamine synthase 2 (OsNAS2) gene were generated through biolistic transformation of a cassette containing the OsNAS2 gene under regulatory control of the maize ubiquitin 1 promoter (UBI-1) (Figure 1a)
Summary
Micronutrient mineral deficiencies affect over two billion people worldwide with women and children most acutely at risk (Beal et al, 2017; Lopez et al, 2016). Iron (Fe) deficiency is the leading cause of anaemia, a condition that impairs cognitive development and work productivity and increases maternal and child mortality (Kassebaum et al, 2014; Lopez et al, 2016). Rising atmospheric CO2 concentrations will likely decrease Fe and Zn concentrations in C3 grains and could further exacerbate micronutrient deficiencies in SEA and MENA (Myers et al, 2014; Smith et al, 2017). The highest concentrations of Fe and Zn are found in the aleurone cells in conjunction with compounds such as phytic acid, polyphenols and fibre that inhibit bioavailability, while only low Fe and Zn concentrations are localized to endosperm tissues (Brouns et al, 2012; De Brier et al, 2016; Moore et al, 2012; Schlemmer et al, 2009; Singh et al, 2013; Stomph et al, 2011). Grain milling removes inhibitors of micronutrient bioavailability and a significant proportion of the grain Fe and Zn (Hourston et al, 2017; Zhang et al, 2010)
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