StWRKY40 and StMAPK3 positively regulate drought tolerance in potato (Solanum tuberosum L.) via mediating osmotic adjustment, photosynthetic capacity, and antioxidant defense.

Abstract

Potato (Solanum tuberosum L.) is a vital global food crop whose yield is severely constrained by drought stress. Both WRKY transcription factors (TFs) and the mitogen-activated protein kinase (MAPK) signaling pathway have been established as key components of plant stress response networks. However, the specific molecular regulatory mechanisms by which they coordinately mediate drought tolerance in potato remain largely elusive. This study identified and functionally characterized how StWRKY40 and StMAPK3 cooperatively confer drought resistance, confirming their core regulatory roles in drought tolerance in potato. Phylogenetic analysis classified StWRKY40 into the WRKY Group II-a subfamily. Both StWRKY40 and StMAPK3 were strongly induced by drought stress. Protein-protein interaction assays confirmed a direct physical interaction between nucleus-localized StWRKY40 and StMAPK3, primarily in the nucleus. Transgenic potato lines overexpressing either StWRKY40 or StMAPK3 exhibited significantly enhanced drought tolerance. This was evidenced by improved growth metrics, enhanced photosynthetic capacity, and strengthened osmotic adjustment, with lower osmotic potentials of proline, soluble sugars, and proteins. Overexpression lines also exhibited upregulated expression of stress-responsive genes (StCAT, StPOD, StSOD, and StP5CS), elevated antioxidant enzyme activities (SOD, CAT, POD), and reduced levels of H2O2 and malondialdehyde (MDA). In contrast, RNA interference (RNAi) lines displayed pronounced drought-sensitive phenotypes relative to non-transgenic (NT) controls, showing opposite trends across all assessed parameters. This study elucidates the coordinate role of StWRKY40 and StMAPK3 as key regulators of drought resistance in potato, providing a theoretical foundation and valuable genetic resources for molecular breeding.