Chrysanthemum CmDOF2 Positively Regulates Salt Tolerance in Transgenic Arabidopsis thaliana

Chrysanthemum (Chrysanthemum morifolium) is a globally significant ornamental plant, whose growth, development, and ornamental quality are frequently impaired by salt stress. DOF (DNA-binding with one finger) family transcription factors extensively act as crucial regulators in medicating reactions to environmental pressures on plants. But their specific functions in regulating salt stress tolerance in chrysanthemum still remain largely elusive and require further investigation. Here, we isolated CmDOF2, a DOF family transcription factor from chrysanthemum, whose expression was up-regulated in chrysanthemums under salt stress. Functional analysis demonstrated that CmDOF2 functions as a nuclear-localized transcriptional activator. Comprehensive phenotypic and physiological characterization showed that heterologous expression of CmDOF2 in Arabidopsis thaliana conferred markedly increased salt stress tolerance, as reflected by higher chlorophyll, leaf relative water, and proline content; lower leaf relative electric conductivity and malondialdehyde content; and increased activities of superoxide dismutase, peroxidase, and catalase. Furthermore, qRT-PCR analyses confirmed that stable expression of CmDOF2 in Arabidopsis led to increased transcript levels of key salt-responsive genes, including stress marker genes (AtRD29A, AtRD29B), components of the SOS signaling pathway (AtSOS1, AtSOS2, AtSOS3), genes involved in osmotic adjustment (AtP5CS1, AtP5CS2), and genes encoding antioxidant enzymes (AtSOD1, AtPOD34, AtCAT3). Collectively, our data demonstrate that CmDOF2 serves as a nuclear-localized transcriptional regulator with activation activity and positively regulates salt stress tolerance by mediating the transcript levels of stress-related genes in multiple signaling pathways.