Ectopic Expression of GhSAMDC3 Enhanced Salt Tolerance Due to Accumulated Spd Content and Activation of Salt Tolerance-Related Genes in Arabidopsis thaliana

Polyamines (PAs), especially spermidine and spermine (which are involved in various types of abiotic stress tolerance), have been reported in many plant species. In this study, we identified 14 putative S-adenosylmethionine decarboxylase genes (GhSAMDC1-14) in upland cotton. Based on phylogenetic and expression analyses conducted under different abiotic stresses, we selected and transferred GhSAMDC3 into Arabidopsis thaliana. Compared to the wild type, transgenic plants displayed rapid growth and increases in average leaf area and leaf number of 52% and 36%, respectively. In transgenic plants, the germination vigor and rate were markedly enhanced under NaCl treatment, and the plant survival rate increased by 50% under 300 mM NaCl treatment. The spermidine content was significantly increased, possibly due to the synthesis of a series of PAs and oxidant and antioxidant genes, resulting in improved salinity tolerance in Arabidopsis. Various salinity resistance-related genes were upregulated in transgenic plants. Together, these results indicate that ectopic expression of GhSAMDC3 raised salinity tolerance by the accumulation of spermidine and activation of salinity tolerance-related genes in A. thaliana.