Metal Homeostasis Genes As Targets to Enhance Bread Wheat Growth and Nutrition

Iron (Fe) and zinc (Zn) are essential plant micronutrients and their deficiencies and toxicities are important limiting factors affecting both crop yield and nutritional quality. Maintaining appropriate intracellular concentrations of these metals through tightly regulated uptake, transport and storage – a process broadly referred to as metal homeostasis – is essential for proper plant growth and development. Nicotianamine synthase (NAS) genes are involved in the production of nicotianamine, a non-protein amino acid that functions as an important chelator of ferrous Fe (Fe²⁺), Zn²⁺ and other divalent metal cations in plant tissues. Nicotianamine is also the biosynthetic precursor to mugineic acid family phytosiderophores (MAs) that graminaceous plant species secrete into the rhizosphere to chelate and absorb ferric Fe (Fe³⁺). Our group is working to identify and characterize novel NAS and MAs biosynthetic genes in bread wheat (Triticum aestivum L.) as a first step towards improving Fe and Zn efficiency of this major staple food. Using orthologous barley (Hordeum vulgare L.) genes as references and the IWGSC database, we have identified a large family of 21 NAS genes¹ as well as 6 nicotianamine aminotransferase (NAAT) and 3 deoxymugineic acid synthase (DMAS) genes that are required for MAs biosynthesis. Altered expression of these genes could yield major agricultural and health benefits such as improved wheat growth under micronutrient limiting or excess conditions as well as the production of Fe and Zn biofortified grain.

¹Bonneau et al. (2016) Identification and molecular characterization of the nicotianamine synthase gene family in bread wheat. Plant Biotech J. in press.