Poplar PdPTP1 Gene Negatively Regulates Salt Tolerance by Affecting Ion and ROS Homeostasis in Populus

High concentrations of Na⁺ in saline soil impair plant growth and agricultural production. Protein tyrosine phosphorylation is crucial in many cellular regulatory mechanisms. However, regulatory mechanisms of plant protein tyrosine phosphatases (PTPs) in controlling responses to abiotic stress remain limited. We report here the identification of a Tyrosine (Tyr)-specific phosphatase, PdPTP1, from NE19 (Populus nigra × (P. deltoides × P. nigra). Transcript levels of PdPTP1 were upregulated significantly by NaCl treatment and oxidative stress. PdPTP1 was found both in the nucleus and cytoplasm. Under NaCl treatment, transgenic plants overexpressing PdPTP1 (OxPdPTP1) accumulated more Na⁺ and less K⁺. In addition, OxPdPTP1 poplars accumulated more H₂O₂ and O₂·^-, which is consistent with the downregulation of enzymatic ROS-scavengers activity. Furthermore, PdPTP1 interacted with PdMAPK3/6 in vivo and in vitro. In conclusion, our findings demonstrate that PdPTP1 functions as a negative regulator of salt tolerance via a mechanism of affecting Na⁺/K⁺ and ROS homeostasis.