Overexpression of S-Adenosyl-l-Methionine Synthetase 2 from Sugar Beet M14 Increased Arabidopsis Tolerance to Salt and Oxidative Stress.

The sugar beet monosomic addition line M14 is a unique germplasm that contains genetic materials from L. and Zoss, and shows tolerance to salt stress. Our study focuses on exploring the molecular mechanism of the salt tolerance of the sugar beet M14. In order to identify differentially expressed genes in M14 under salt stress, a subtractive cDNA library was generated by suppression subtractive hybridization (SSH). A total of 36 unique sequences were identified in the library and their putative functions were analyzed. One of the genes, -adenosylmethionine synthetase (), is the key enzyme involved in the biosynthesis of -adenosylmethionine (SAM), a precursor of polyamines. To determine the potential role of in salt tolerance, we isolated from the salt-tolerant sugar beet M14. The expression of in leaves and roots was greatly induced by salt stress. Overexpression of in resulted in enhanced salt and H₂O₂ tolerance. Furthermore, we obtained a knock-down T-DNA insertion mutant of , which shares the highest homology with . Interestingly, the mutant showed sensitivity to salt and H₂O₂ stress. We also found that the antioxidant system and polyamine metabolism play an important role in salt and H₂O₂ tolerance in the -overexpressed plants. To our knowledge, the function of the sugar beet SAMS has not been reported before. Our results have provided new insights into SAMS functions in sugar beet.