LEA_2 proteins are intrinsically disordered proteins implicated in plant abiotic stress tolerance; however, their functional characterization under salt and osmotic stress, particularly regarding stress-inducible peripheral redistribution, remains limited. SiLEA_2-6, an LEA_2 protein from the extreme-cold-tolerant species Saussurea involucrata, was identified from a cold-stress cDNA library, but its role in salt and osmotic tolerance remains unknown. In the present study, transgenic Arabidopsis thaliana Col-0 lines constitutively overexpressing SiLEA_2-6–eGFP were generated. Overexpression significantly enhanced salt and osmotic tolerance across germination, vegetative, and reproductive stages, as evidenced by improved germination rates, root elongation, survival, and physiological performance. Physiological analyses revealed improved membrane integrity (REL and MDA accumulation), enhanced osmotic adjustment, and preserved chlorophyll content. Subcellularly, SiLEA_2-6–eGFP displayed diffuse cytoplasmic distribution with intracellular punctate structures under non-stress conditions; within 60 min of salt or osmotic stress, it showed pronounced peripheral association, notably at guard cells and stomatal-adjacent regions. These findings demonstrate that SiLEA_2-6 enhances salt and osmotic tolerance in Arabidopsis, with stress-inducible peripheral enrichment consistent with a potential membrane-associated protective function. This study adds to the growing evidence that LEA_2 proteins confer tolerance not only to cold/freezing but also to salt and osmotic stress.

Low temperature is a major constraint limiting the productivity and distribution of crops, and aquaporins have emerged as important determinants of plant stress tolerance. Saussurea involucrata, an alpine plant adapted to extreme low-temperature environments, provides a valuable source of cold-tolerance genes, yet the contribution of its PIP1-type plasma membrane aquaporins to freezing and chilling tolerance in heterologous systems has not been established. Here, we isolated SiPIP1;5b, a PIP1-type plasma membrane intrinsic protein from S. involucrata, and constitutively overexpressed it in Arabidopsis thaliana and tomato (Solanum lycopersicum). Under freezing treatment (−4 °C, 4 h), SiPIP1;5b-overexpressing Arabidopsis lines showed markedly higher survival rates (72.0–81.5%) than the wild type (36.2%), together with lower relative electrolyte leakage and malondialdehyde (MDA) content and higher chlorophyll content. Under chilling stress (0 °C, 4 h), transgenic tomato plants likewise exhibited reduced electrolyte leakage and MDA accumulation, elevated activities of superoxide dismutase, catalase, and peroxidase, and increased proline content relative to wild-type plants. These results indicate that SiPIP1;5b enhances freezing and chilling tolerance and is associated with improved membrane stability, reduced accumulation of excessive reactive oxygen species, and enhanced antioxidant and osmoprotective responses. Our findings establish SiPIP1;5b as a promising candidate gene for improving low-temperature tolerance in crops.