| Summary: | Dehydrin (DHN), a member of the late embryogenesis abundant protein (LEA) family, was recently found to play a role in physiological responses to salt and drought stress. In this study, we identified and cloned the <i>PtrDHN-3</i> gene from <i>Populus trichocarpa</i>. The PtrDHN-3 protein encoded 226 amino acids, having a molecular weight of 25.78 KDa and an isoelectric point of 5.18. It was identified as a SKn-type DHN and was clustered with other resistance-related DHN proteins. Real-time fluorescent quantitative PCR showed that transcription levels of <i>PtrDHN-3</i> were induced by mannitol stress, and more significantly by salt stress. Meanwhile, in a yeast transgenic assay, salt tolerance increased in the <i>PtrDHN-3</i> transgenic yeast, while the germination rate, fresh weight and chlorophyll content increased in <i>PtrDHN-3</i>-overexpressing transgenic <i>Arabidopsis</i> plants (OE) under salt stress. Significant increases in expression levels of six antioxidant enzymes genes, and SOD and POD enzyme activity was also observed in the OE lines, resulting in a decrease in O<sub>2</sub><sup>-</sup> and H<sub>2</sub>O<sub>2</sub> accumulation. The proline content also increased significantly compared with the wild-type, along with expression of proline synthesis-related genes <i>P5CS1</i> and <i>P5CS2</i>. These findings suggest that <i>PtrDHN-3</i> plays an important role in salt resistance in plants.
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