Nicotianamine Synthase Gene 1 from the hyperaccumulator Sedum alfredii Hance is associated with Cd/Zn tolerance and accumulation in plants

Abstract

Sedum alfredii Hance is a hyperaccumulator of cadmium (Cd) and zinc (Zn) that exhibits extraordinary accumulation of these metals in various tissues. The Nicotianamine synthase (NAS) genes play key roles in regulating the production of nicotianamine, a non-protein amino acid that facilitates metal homeostasis in plants, but the functions of these genes in S. alfredii remain unknown. The aims of this study were to identify and characterize the NAS gene from S. alfredii (SaNAS1) and explore NAS roles in Cd or Zn tolerance and accumulation. One Cd-induced NAS gene from S. alfredii (SaNAS1) was cloned. We determined the subcellular localization of the encoded protein and evaluated SaNAS1 expression. We also assessed SaNAS1 function by conducting a complementary assay with yeast mutants Δzrc1 exposed to Cd or Zn. Finally, transgenic Arabidopsis plants expressing SaNAS1 were produced, and SaNAS1 function was further examined in these plants. SaNAS1 was highly expressed in response to Cd or Zn exposure, and the encoded protein was distributed throughout the cytoplasm and nucleus. Furthermore, yeast expressing SaNAS1 exhibited increased tolerance to Cd or Zn. Finally, expression of SaNAS1 in Arabidopsis increased nicotianamine production and promoted Cd or Zn accumulation in roots and shoots. SaNAS1-expressing transgenic Arabidopsis lines showed improved seedling growth under Cd or Zn stress compared with wild type, indicating that SaNAS1 enhances tolerance to both Cd and Zn. SaNAS1 may play a critical role in Cd or Zn tolerance and hyperaccumulation by regulating nicotianamine level in S. alfredii.