Overexpression of the barley nicotianamine synthase gene HvNAS1 increases iron and zinc concentrations in rice grains

In humans, iron (Fe) and zinc (Zn) deficiencies result in major worldwide health problems. Transgenic technologies to produce Fe- and Zn-biofortified rice varieties offer a promising potential solution. Nicotianamine, the precursor of phytosiderophores, chelates Fe ²⁺ and Zn ²⁺ and plays an important role in transporting these metals to both vegetative and reproductive organs within the plant. Our objective was to increase Fe and Zn contents in rice grains by overexpressing the barley nicotianamine synthase gene HvNAS1. HvNAS1-overexpressing transgenic rice showed increased HvNAS1 expression and subsequent increases in endogenous nicotianamine and phytosiderophore content in shoots, roots, and seeds. Fe and Zn concentrations in polished T ₁ seeds from transgenic plants increased more than three and twofold, respectively; Fe and Zn concentrations also increased in both polished and brown T ₂ seeds. These results suggest that the overproduction of nicotianamine enhances the translocation of Fe and Zn into rice grains.