Abstract
Mitogen-Activated Protein Kinases (MAPKs) play crucial roles in plant stress signaling, but the mechanisms of MAPK genes in Portulaca oleracea remain functionally uncharacterized. In this study, transcriptomic screening of P. oleracea under salt stress identified PoMPK3 as a candidate gene, showing significant root-specific upregulation. Phylogenetic analysis classified it as a Group A MAPK protein, and subcellular localization confirmed its membrane association. Heterologous expression of PoMPK3 in Arabidopsis thaliana significantly enhanced salt tolerance, as evidenced by improved seed germination rates, longer primary roots, increased biomass, and reduced stress symptoms. Mechanistically, PoMPK3 expression activated ABA signaling, leading to increased ABA levels and upregulation of AtNCED3, AtPYR1, and AtABF3. Furthermore, it strengthened the antioxidant defense, as evidenced by elevated antioxidant enzyme activity, leading to a reduction in oxidative stress. The transgenic lines also demonstrated enhanced osmotic adjustment through osmolytes accumulation and ionic homeostasis, evidenced by tissue-specific Na(+)/K(+) ratios (low in shoots, high in roots) resulting from the concerted upregulation of AtSOS1, AtNHX1, and AtHKT1. In addition, gene co-expression network analysis and molecular docking predicted phosphorylation of WRKY transcription factors, suggesting a novel mechanism for transcriptome reprogramming. Collectively, our findings not only advance the understanding of salt tolerance mechanisms in purslane but also identify PoMPK3 as a key genetic determinant, thereby laying the foundation for its use in breeding programs aimed at enhancing salt stress resilience in crops.