IbMPK3/IbMPK6-mediated IbSPF1 phosphorylation promotes cold stress tolerance in sweet potato

Environmental stress caused by biotic and abiotic factors negatively affects crop quality and productivity. Plants employ multiple signaling mechanisms under stress, with the mitogen-activated protein kinase (MAPK) cascade-particularly MPK3 and MPK6-serving as a central regulator of stress adaptation through substrate phosphorylation. While these kinases are well-studied in model plants, their functional role in sweet potato [Ipomoea batatas (L.) Lam] remains poorly characterized. This study investigates how cold tolerance in sweet potato is modulated by IbMPK3/IbMPK6-mediated phosphorylation of the stress-responsive transcription factor IbSPF1 at Ser75 and Ser110. Wild-type and transgenic sweet potato plants were grown under normal and cold-stress conditions, followed by the assessment of IbSPF1 phosphorylation levels and plant physiological parameters. Notably, transgenic plants overexpressing IbSPF1 (IbSPF1^DD) exhibited significantly higher tolerance to cold stress than non-transgenic plants under cold stress condition, which was attributed to an increase in photosynthetic efficiency and a decrease in lipid peroxidation. Compared with non-transgenic plants, transgenic IbSPF1^DD plants showed significantly upregulated levels of cold-regulated genes. Conclusively, IbMPK3/IbMPK6-mediated phosphorylation of IbSPF1 plays an important role in cold stress signaling and tolerance in sweet potato.