Chapter 7 - Nicotianamine enhances zinc transport to seeds for biofortification

Abstract

Zinc (Zn) is an essential nutrient for most living organisms. Zn deficiency poses a serious health risk worldwide, especially in developing countries. Biofortification, i.e., the production of nutritionally enhanced food crops, has great potential to combat hidden hunger including Zn deficiency. Rice is a highly suitable target crop for biofortification because it is a staple food widely consumed worldwide. Zn uptake and transport to seeds has been well characterized in rice. Nicotianamine (NA) is a metal chelator that plays a crucial role in Zn and iron (Fe) uptake, translocation, and storage in seeds. Deoxymugineic acid, which is synthesized from NA, also functions in root-to-shoot Zn mobilization and long-distance Zn transport in rice; thus, it contributes to increased Zn levels in rice seeds. Overexpression of NA synthase (NAS) genes increases Zn and Fe concentrations in seeds. The combination approaches with the overexpression of NAS, and other genes involved in Zn homeostasis are more effective than a single-gene approach for achieving sufficient rice Zn biofortification. Importantly, high Zn-NA in rice grains was shown to increase Zn bioavailability in Zn-deficient mice. A more thorough understanding of Zn uptake and transport based on NA expression could lead to Zn biofortification in rice via breeding and transgenic approaches. In this chapter, we discuss the crucial role of NA in plant metal homeostasis and the development of Zn biofortification strategies based on NAS expression.