Nicotianamine synthase (NAS) genes play a crucial role in transport and the distribution of metals within plants. Despite their importance, the role of NAS genes in the selective transport of essential and toxic metal elements remains inadequately understood. In this study, we identified an iron-excess-induced NAS gene, MsNAS7 , from alfalfa. Overexpression of MsNAS7 enhanced tolerance of tobacco to excessive Fe. The expression of MsNAS7 was significantly induced by cadmium (Cd), lead (Pb), and nickel (Ni) in alfalfa roots, while only significantly induced by Pb in alfalfa shoots. Heteroexpression of MsNAS7 in recombinant yeast resultied in a 1.87-fold increased in nicotianamine (NA) content and heightened sensitivity to Cd, Pb, and Ni stress. In tobacco, overexpression of MsNAS7 led to a 1.27-fold increase in NA content, improved tolerance to Cd, Pb, and Ni, and mitigated growth inhibition and oxidative damage. Furthermore, MsNAS7 enhanced the absorption of Cd, Pb, and Ni from the soil to plant by 1.90-, 2.57-, and 1.98-fold, respectively, while reduced the transport rates of these metals from root to shoot by 0.32, 0.49, and 0.32 times, respectively. Under both normal condition and Cd, Pb, and Ni stress, MsNAS7 facilitated increased iron (Fe) absorption (1.45–2.72 times) and zinc (Zn) absorption (1.15–4.56 times) in plants. Additionally, the MsNAS7 promoter demonstrated the ability to interact with the metal-responsive transcription factor MsMYB. This study elucidates the dual function of MsNAS7 in the uptake and transport of metals as well as toxic heavy metals detoxify, offering novel insights into the role of NAS genes. • Identified MsNAS7 , a nicotianamine synthase gene induced by Fe excess/Cd/Pb/Ni. • MsNAS7 confers tobacco tolerance to Fe excess/Cd/Pb/Ni, alleviating ROS damage. • MsNAS7 detoxifies Cd/Pb/Ni by root retention and enhanced Fe/Zn uptake. • The MsNAS7 and its promoter-binding protein gene MsMYB have promising applications.
Yang et al. (Sun,) studied this question.