Functional analysis of StMAPK19 gene in response to salt stress in potato (Solanum tuberosum L.)

Soil salinization critically impacts potato cultivation by restricting growth, yield, and tuber quality. The MAPK pathway, evolutionarily conserved in plants, modulates hormonal balance, development, and abiotic stress responses. This study investigates the functional role of StMAPK19, a TDY-type mitogen-activated protein kinase gene, in potato salt tolerance. Phylogenetic analysis classified StMAPK19 into a TDY-motif subgroup, and subcellular localization revealed its presence in the plasma membrane, cytoplasm, and nucleus. Under NaCl stress (50, 100, and 150 mM), StMAPK19 expression was significantly upregulated in roots, stems, and leaves. Phenotypic analyses demonstrated that StMAPK19-overexpressing (OE) plants exhibited enhanced salt tolerance, marked by improved plant height, tuber yield, and biomass (fresh/dry weights), whereas RNA interference (RNAi) knockdown lines showed reduced growth. OE plants displayed elevated antioxidant enzyme activities, such as catalase (CAT), peroxidase (POD), superoxide dismutase (SOD), higher proline accumulation, and reduced oxidative stress markers, including hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), while RNAi lines exhibited compromised antioxidant capacity and exacerbated oxidative damage. Expression profiling revealed upregulation of stress-responsive genes (StCAT, StSOD, StPOD, StP5CS) in OE plants and downregulation in RNAi lines. Gas exchange measurements further indicated that OE plants maintained higher photosynthetic rates, transpiration, and stomatal conductance under salt stress compared to non-transgenic (NT) controls, whereas RNAi plants experienced significant declines. These findings demonstrate that StMAPK19 enhances salt tolerance by modulating ROS scavenging, osmoregulatory substance biosynthesis, photosynthetic efficiency, and stress-related gene expression. This study provides critical insights into the molecular mechanisms of salt tolerance in potatoes, offering potential targets for breeding resilient varieties to mitigate salinity-induced agricultural losses.