Concomitant Activation of and Contributes to the Enhanced Accumulation of Iron and Zinc in Rice.

Nicotianamine (NA) is produced by NA synthase (NAS), which contains three genes in rice and is responsible for chelating metals such as iron (Fe) and zinc (Zn), as well as preserving metal homeostasis. In this study, we generated a transgenic plant () that shows simultaneous activation of and by crossing two previously identified activation-tagged mutants, () and (). Concomitant activation of both genes resulted in the highest Fe and Zn concentrations in shoots and roots of the plants grown under normal conditions and Fe and Zn limited growth conditions. Expression of genes for the biosynthesis of mugineic acid family phytosiderophores (MAs) and Fe and Zn uptake were enhanced in roots. Additionally, plants displayed superior growth to other plants at higher pH levels. Importantly, seeds had NA and 2'-deoxymugineic acid (DMA) concentrations that were 50.6- and 10.0-fold higher than those of the WT. As a result, the mature grain Fe and Zn concentrations of the plant were 4.0 and 3.5 times greater, respectively, than those of the WT. Furthermore, plants exhibited the greatest resistance to excess metals. Our research suggests that simultaneous activation of and can enhance Fe and Zn accumulation in rice grains while also increasing plant tolerance to growing situations with metal deficiency and excess metal availability.