ClbHLH3 enhances salt tolerance by suppressing the expression of ClHB52 and ClHB16 in Chrysanthemum

Salt stress is a major environmental constraint that severely limits the normal growth and development of plants. The soil salinization in the cultivation environment of cut-flower chrysanthemums has been progressively increasing over recent years. Therefore, the rational utilization of saline-affected land and the breeding of novel salt-tolerant varieties are critically important for sustainable crop production. HD-Zip transcription factors are widely involved in plant responses to salt stress. However, the molecular mechanisms underlying HD-Zip regulation of salt tolerance remain poorly understood. This study revealed that salt stress significantly induced ClHB52 expression, and ClHB52 overexpressing chrysanthemums exhibited increased sensitivity to salt stress; Protein interaction assays confirmed that ClHB52 directly interacts with ClHB16. Further investigation demonstrated that overexpression of ClHB16 upregulates the expression of the downstream ClPP2C gene while simultaneously suppressing ClSnRK2 and ClRD29A , thereby exacerbating salt sensitivity in chrysanthemum. Furthermore, the transcription factor ClbHLH3 specifically binds to the ClHB52 promoter and suppresses the expression of both ClHB52 and ClHB16, thereby enhancing salt tolerance in chrysanthemum. These findings provide important insights into how ClbHLH3 regulates salt tolerance in chrysanthemums.