PoMPK3, an MAPK Gene from Purslane (Portulaca oleracea), Conferred Salt Tolerance in Transgenic Arabidopsis thaliana

Mitogen-Activated Protein Kinases (MAPKs) play crucial roles in plant stress signaling, but the mechanisms of MAPK genes in <i>Portulaca oleracea</i> remain functionally uncharacterized. In this study, transcriptomic screening of <i>P. oleracea</i> under salt stress identified <i>PoMPK3</i> 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 <i>PoMPK3</i> in <i>Arabidopsis thaliana</i> significantly enhanced salt tolerance, as evidenced by improved seed germination rates, longer primary roots, increased biomass, and reduced stress symptoms. Mechanistically, <i>PoMPK3</i> expression activated ABA signaling, leading to increased ABA levels and upregulation of <i>AtNCED3</i>, <i>AtPYR1</i>, and <i>AtABF3</i>. 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 <i>AtSOS1</i>, <i>AtNHX1</i>, and <i>AtHKT1</i>. 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 <i>PoMPK3</i> as a key genetic determinant, thereby laying the foundation for its use in breeding programs aimed at enhancing salt stress resilience in crops.