Identification of the Nicotianamine Synthase (NAS) Gene Family in Wheat (Triticum aestivum.L) and the Role of Its Member TaNAS4-A in Zn and Fe Transport

Zinc (Zn) and Iron (Fe) are essential trace elements for human health, yet deficiencies in both are widespread worldwide. As a major staple crop, wheat is an important dietary source of Zn and Fe. However, the concentrations of Zn and Fe in common wheat grains are generally low, making it necessary to enhance the nutritional value of wheat. This study first elaborated that both elements are absorbed by wheat via "Strategy II" which relies on phytosiderophores (such as mugineic acids) and related transporter proteins (e.g., YSL and ZIP families). Nicotianamine (NA) plays a key chelating role in the long-distance transport of Zn and Fe. Therefore, we further analyzed the NAS gene family in wheat, which showed high genetic diversity, unique gene structures, distinct evolutionary features, and was subjected to purifying selection. Expression profiling revealed that NAS genes were tissue-specific and responsive to various stress conditions. The overexpression of TaNAS4-A in rice, as well as the silencing of TaNAS4-A in wheat using BSMV-VIGS confirmed the role of TaNAS4-A in enhancing NAS enzyme catalytic efficiency, promoting phytosiderophores secretion, and increasing the accumulation of Zn and Fe in grains. Additionally, this study suggested that NAS genes may confer other functions, such as stress resistance, which deserves further investigation. This research provides a theoretical basis for Zn and Fe biofortification in wheat.