S-adenosylmethionine synthetase 1 confers drought and salt tolerance in transgenic tomato

Environmental stresses, like drought and salt, seriously threaten the productivity of tomato (Solanum lycopersicum L.). S-adenosylmethionine synthetase (SAMS) is responsible for synthesis of SAM that plays important roles in regulating plant-environment interactions. In this study, we analyzed the function of tomato SAMS1 (SlSAMS1) gene under drought and salt stresses. Promoter analysis showed that the promoter region of SlSAMS1 had several stress-related cis-regulatory elements. Expression pattern analysis indicated that SlSAMS1 was induced by salt, drought, low temperature and abscisic acid (ABA) treatments. Overexpression of SlSAMS1 in tomato improved drought and salt stresses tolerance. Under drought and salt stresses, water-retention capacity and photosynthetic capacity were significantly enhanced in transgenic lines. In addition, overexpression of SlSAMS1 significantly reduced the accumulation of superoxide, hydrogen peroxide (H2O2) and malondialdehyde, and enhanced ABA content and reactive oxygen species scavenging enzymes (superoxide dismutase, catalase and ascorbate peroxidase) activities. Furthermore, drought and salt treatment enlarged the influences caused by overexpressing SlSAMS1 in polyamines (PAs) synthesis and ethylene emission. Interestingly, water loss assay indicated that SlSAMS1 modulated the generation of PAs and H2O2, not ethylene, to maintain a better water homeostasis in transgenic plants. Moreover, ABA induced the expression of PAs and ethylene synthesis related genes to change PAs contents and ethylene emission. Importantly, compared with wild type plants, transgenic plants reduced water loss under ABA treatment. Collectively, these results suggested that SlSAMS1 involved in tomato drought and salt tolerance mainly through mediated PAs, H2O2 and ABA signals.