Role of the PoKASII gene in Paeonia ostii ‘Fengdan’ in resistance to abiotic stress

• Under low-temperature, salt, and drought stress, transgenic tobacco plants enhanced antioxidant and osmotic protection abilities. • Expression levels of three classic resistance genes were significantly up-regulated in transgenic tobacco under stress. • The PoKASII gene enhanced the abiotic stress resistance of ‘Fengdan’ peony by up-regulating antioxidant defenses and osmoprotectant synthesis. The Paeonia ostii ‘Fengdan’ is an important ornamental plant with strong inherent resistance to abiotic stress. The β-ketoacyl carrier protein synthase II (KASII) in ‘Fengdan’ peony is a key enzyme in the fatty acid synthesis pathway. In this study, we focused on PoKASII and obtained transgene tobacco plants through heterologous transformation. These transgene plants were treated with 4 °C, 200 mM NaCl, and 20 % PEG-6000 to simulate low-temperature, salt, and drought stress, respectively. Overexpression of PoKASII in tobacco led to the upregulation of classic stress-responsive transcription factors, including NtCBF1 and NtNAC , indicating PoKASII acts as a positive regulator in stress-response pathways. Phenotypically, the transgene tobacco plants exhibited enhanced root elongation, and increased trichome length and density. Physiologically, the gene promoted the accumulation of osmoprotectants including proline and soluble proteins to maintain cellular osmotic balance. Concurrently, it upregulated the expression of the proline synthesis gene P5CS and downregulated the expression of the degradation-related gene ProDH , thereby promoting proline accumulation. It also enhanced the activities of antioxidant enzymes (SOD, POD, CAT) to scavenge reactive oxygen species. Furthermore, under abiotic stress, its expression led to a complex physiological state characterized by increased MDA content. These coordinated mechanisms collectively improved the plant’s resistance to abiotic stress. In conclusion, the PoKASII enhances the abiotic stress resistance of ‘Fengdan’ peony by upregulating antioxidant defenses and osmoprotectant synthesis, with its association with the fatty acid pathway providing a unique regulatory axis. This study revealed PoKASII -mediated resistance and provided a target for peony stress breeding.