IbSIMT1, a novel salt-induced methyltransferase gene from Ipomoea batatas, is involved in salt tolerance

S-adenosyl-methionine (SAM)-dependent methyltransferase (MTase) genes are a multigene family; however, only a few have been characterized at the functional level. In the present study, a novel salt-induced SAM-dependent MTase gene, named IbSIMT1, was isolated from salt-tolerant sweetpotato (Ipomoea batatas (L.) Lam.) line ND98. IbSIMT1 contains a DUF248 domain of unknown function and an MTase domain. Expression of IbSIMT1 was up-regulated in sweetpotato under salt stress and abscisic acid treatment. The IbSIMT1-overexpressing sweetpotato (cv. Shangshu 19) plants exhibited significantly higher salt tolerance compared with the wild-type. Proline content was significantly increased, whereas malonaldehyde content was significantly decreased in the transgenic plants. The activities of superoxide dismutase (SOD) and photosynthesis were significantly enhanced in the transgenic plants. H₂O₂ was also found to be significantly less accumulated in the transgenic plants than in the wild-type. Overexpression of IbSIMT1 up-regulated the salt stress responsive genes, including pyrroline-5-carboxylate synthase, pyrroline-5-carboxylate reductase, SOD, psbA and phosphoribulokinase genes under salt stress. These findings suggest that the novel IbSIMT1 gene is involved in sweetpotato salt tolerance and enhances salt tolerance of the transgenic sweetpotato plants by regulating osmotic balance, protecting membrane integrity and photosynthesis and increasing reactive oxygen species scavenging capacity.