The overexpression of DgPR1 enhances chrysanthemum cold tolerance through the ROS-mediated pathway

Cold stress affects the quality and yield of chrysanthemums and hinders the development of the chrysanthemum industry. PR-1, the first pathogenesis-related (PR) protein identified, is crucial in bolstering plant defenses by modulating responses to biotic and abiotic environmental pressures. Nevertheless, the precise contribution of PR-1 to chrysanthemum's resistance to cold stress is still not well defined. In the present study, a PR-1-like protein, DgPR1, was isolated from chrysanthemums. According to RT-qPCR analysis, DgPR1 expression was significantly elevated in the stems compared to the roots and leaves, with a notable upregulation observed under cold stress. Both CRISPR/Cas9-facilitated gene editing and overexpression of DgPR1 have demonstrated its beneficial effect on regulating cold-stress resistance in chrysanthemums. Overexpression of DgPR1 in transgenic chrysanthemums enhanced cold tolerance, as evidenced by increased survival rates, reduced symptoms of low-temperature injury, and levels of hydrogen peroxide (H₂O₂), malondialdehyde (MDA), superoxide anion (O₂^-) and relative electrolyte conductivity (REC). The ROS-scavenger enzyme-activity assay showed that DgPR1 enhanced peroxidase (POD) enzyme activity in chrysanthemums under cold stress. Additionally, the expression of DgPOD was higher in the overexpressing lines under cold stress compared to both the wild-type (WT) and the mutant dgpr1. Collectively, these findings indicate that DgPR1 contributes positively to improving cold stress tolerance in chrysanthemums.