Asparagus bean VunMED2 gene enhances Arabidopsis multi-stress resistance and activates VunSRC2 transcription

The Mediator (MED) complex plays a crucial role in eukaryotic transcriptional regulation and responds to various abiotic stresses. However, the role and regulatory mechanism of asparagus bean (Vigna unguiculata subsp. sesquipedalis) VunMED2 in plant defense responses remain unclear. Here, VunMED2 was overexpressed (OE-VunMED2) in Arabidopsis thaliana, and its role in abiotic stress responses were investigated. Under 4 °C + 300 μmol m^-2 s^-1, OE-VunMED2 plants exhibited enhanced anthocyanin accumulation, freezing tolerance and VunMED2 expression compared to the WT. Under H₂O₂ stress, OE-VunMED2 plants displayed reduced oxidative damage, significantly higher antioxidant enzymes (SOD/POD/CAT) activity, and improved membrane stability compared to WT, confirming that VunMED2 enhances oxidative stress tolerance by activating antioxidant defense systems. Similarly, VunMED2 overexpression significantly reduced Nacl stress-induced reactive oxygen species accumulation, elevated antioxidant enzyme activity, and mitigated membrane damage, further demonstrating its role in Nacl stress alleviation via enhanced antioxidant mechanisms. Yeast one-hybrid and dual-luciferase reporter assays confirmed that VunMED2 activates the promoter of the downstream target gene VunSRC2. Under various stresses, the expression of VunSRC2 orthologous gene AtSRC2 was significantly up-regulated in VunMED2 overexpressing Arabidopsis, indicating that AtSRC2 is a key effector that mediates multi-stress tolerance. Therefore, VunMED2 enhances multi-stress tolerance by activating VunSRC2 and anti-oxidation, which provides a new target for stress-resistant breeding of asparagus bean.