A Novel Wheat Nicotianamine Synthase Gene, TaNAS-D, Confers High Salt Tolerance in Transgenic Arabidopsis

Nicotianamine synthase (NAS) plays a pivotal role in balancing the concentrations of heavy metals in plants, but its characteristics and functions in salt stress responses are not completely understood, particularly in wheat. In this study, the salt-induced gene TaNAS-D was cloned from wheat and characterized. TaNAS-D, localized throughout the cell, is mainly expressed in developed vascular bundle tissues and is responsive to NaCl, ABA, and H2O2 stresses. Overexpression of TaNAS-D in Arabidopsis led to elevated NA levels and enhanced salt stress tolerance, which was demonstrated by higher germination rates and improved growth of TaNAS-D transgenic Arabidopsis plants compared with WT when exposed to salt stress. Further investigation revealed that TaNAS-D transgenic Arabidopsis plants displayed higher K+/Na+ ratios, lower malondialdehyde (MDA) levels, and less ion leakage (IL) consistently accompanied by increased peroxidase (POD), superoxide dismutase (SOD), and catalase (CAT) activities, thereby reducing membrane injury. Moreover, TaNAS-D overexpression under salt stress increased AtSOS1, AtSOS2, AtSOS3, AtFAD5, and AtSAD1 transcript levels. These findings indicate that TaNAS-D plays a positive role in salt tolerance by improving the antioxidant defense system and upregulating salt overly sensitive (SOS) pathway genes.