Ectopic expression of Limonium bicolor (Bag.) Kuntze DREB (LbDREB) results in enhanced salt stress tolerance of transgenic Populus ussuriensis Kom

High salinity is one of the most common abiotic stresses that plants have to confront, and selecting salt-tolerant plants is becoming a very important task in breeding. In this study, non-transgenic (NT) and three LbDREB-transgenic Populus ussuriensis Kom. (Dr22, Dr8, and Dr2) lines were treated with 150 mM NaCl. The salt tolerance of NT, Dr2, Dr8, and Dr22 were evaluated and compared. Phenotypic observation, chlorophyll content detection and leaf salt injury index calculation suggested NT exhibited more severe salt injury symptoms and weaker photosynthetic capacity than Dr2, Dr8, and Dr22. LbDREB gene exhibited opposite temporal expression patterns with no apical meristem (NAM), trihelix transcription factor (GT-1) and WRKY transcription factor 70 (WRKY70), and consistent expression patterns with Cu-Zn superoxide dismutase and peroxidase-PO1 genes, in Dr2, Dr8, and Dr22 under salt stress. The superoxide dismutase and peroxidase activities of transgenic lines were higher than NT plants during the salt stress treatment. Malonaldehyde accumulation in NT leaves was more significant than in transgenic leaves, while proline accumulation in NT leaves was much less than that in transgenic leaves under salt stress. The root to shoot ratios were significantly increased in Dr2, Dr8, and Dr22 plants, but were slightly decreased in NT plants, 12 days after salt stress treatment. The relative water content of NT leaves decreased more than transgenic leaves, meanwhile, the relative electrolytic leakage of NT leaves increased more significantly than transgenic leaves after salt stress. In summary, Dr2, Dr8, and Dr22 exhibited stronger salt stress tolerance than NT. The transgenic lines Dr2, Dr8, and Dr22 can serve as alternative salt-tolerant germplasm resources in P. ussuriensis breeding.