Functional Characterization of DsRD22a and DsRD22b Genes in Dianthus spiculifolius and Their Roles in NaCl and Drought Stress Responses

Drought stress is one of the most prevalent abiotic stressors and severely impairs plant growth and productivity. Therefore, identifying functional genes associated with drought tolerance is essential for the molecular breeding of drought-resistant crops. The RD22 (Responsive to Desiccation 22) gene family encodes conserved BURP domain-containing proteins that participate in plant responses to drought stress. In this study, two RD22 homologs, DsRD22a and DsRD22b, were isolated and characterized from the drought-tolerant ornamental species Dianthus spiculifolius. Sequence analysis showed that both proteins contain a conserved BURP domain and are typical members of the RD22 family. Tissue-specific expression analysis revealed that both genes were predominantly expressed in leaves and stems. Abiotic stress assays demonstrated that the expression levels of DsRD22a and DsRD22b were significantly induced by abscisic acid (ABA), osmotic stress, and salt stress, whereas their transcriptional responses to relatively low-temperature and oxidative stress were relatively weak. Subcellular localization analysis indicated that DsRD22a and DsRD22b proteins are localized in the cytoplasm. Heterologous overexpression assays showed that transgenic Arabidopsis thaliana lines overexpressing DsRD22a or DsRD22b exhibited significantly enhanced tolerance to salt and osmotic stresses compared with wild-type (WT) plants. Soil drought assays further confirmed that the transgenic lines had higher soluble protein contents and improved drought tolerance than WT plants. These findings suggest that DsRD22a and DsRD22b positively regulate plant responses to drought stress, potentially by promoting soluble protein accumulation. Collectively, DsRD22a and DsRD22b represent valuable candidate genes for the genetic improvement of drought tolerance in plants.