Objective This study aimed to reveal the physiological and molecular regulation mechanisms of PeCPK7 in plant salt stress tolerance.

Method According to the CDS of PeCPK7 in NCBI genome database, the PeCPK7 was cloned, DNAMAN was used for amino acid sequence alignment, and Mega 7 software was used for evolutionary tree construction. The mechanism of PeCPK7 in salt stress was studied from the level of physiology, biochemistry and molecular biology by Arabidopsis thaliana overexpressed lines (PeCPK7-OE1, PeCPK7-OE2 and PeCPK7-OE3), the wild-type (WT) and vector control (VC) as experimental materials.

Result (1) PeCPK7 was highly similar to CPK7 in other species, and was closely related to PtrCPK7 family of Populus trichocarpa. (2) In salt-treated Populus euphratica seedlings, the relative expression of PeCPK7 reached the maximum after 6 h of salt stress, and recovered to the initial state at 48 h. (3) PeCPK7 was localized in the cytoplasm. (4) After salt treatment, the survival rate and root length of overexpression lines were significantly higher than those of WT and VC. (5) Na⁺ and H₂O₂ accumulated in the root were significantly lower than those of WT and VC, and Ca²⁺ was significantly higher than WT and VC. The Na⁺ efflux and K⁺ influx were significantly higher than WT and VC. (6) Under salt stress, the activity of antioxidant enzymes (SOD, POD, CAT) of overexpression lines were significantly higher than WT and VC. (7) The decrease of chlorophyll content, PSII. maximum optical quantum efficiency, actual photosynthetic quantum yield, relative electron transfer rate and the photosynthetic rates of overexpression lines were higher than those of WT and VC, while the intercellular CO₂ concentration was lower than WT and VC.

Conclusion Overexpression of PeCPK7 gene can improve salt stress tolerance of Arabidopsis thaliana, which will provide a theoretical basis for improving plant salt tolerance through genetic engineering.