Chrysanthemum CmHSFA4 gene positively regulates salt stress tolerance in transgenic chrysanthemum

Salinity-induced Na⁺ toxicity and oxidative stress hamper plant growth. Here, we showed that expression of the chrysanthemum CmHSFA4, a homologue of the heat-shock factor AtHSFA4a, is inducible by salt and localizes to the nucleus. It is a transcription activator binding with HSE. Chrysanthemum overexpressing CmHSFA4 displayed enhanced salinity tolerance by limiting Na⁺ accumulation while maintaining K⁺ concentration, which is consistent with the up-regulation of ion transporters CmSOS1 and CmHKT2. Additionally, the transgenic plants reduced H₂ O₂ and O₂^∙- accumulation under salinity, which could be due to up-regulation of ROS scavenger activities such as SOD, APX and CAT as well as CmHSP70, CmHSP90. Together, these results suggest that CmHSFA4 conferred salinity tolerance in chrysanthemum as a consequence of Na⁺ /K⁺ ion and ROS homeostasis.