Ectopic expression of the Sesuvium portulacastrum genes SpHDZ39 and SpHDZ41 enhances cadmium tolerance in Arabidopsis

The homeodomain-leucine zippers ( HDZs ) function as key regulators to regulating plant growth, development, and environmental responses. Its functions have been extensively investigated in many plant species, while the HDZs family in Sesuvium portulacastrum has not been thoroughly explored. We carried out a genome wide analysis of S. portulacastrum to identify and characterize the SpHDZs . The functional of SpHDZ39 and SpHDZ41 were investigated through subcellular localization, transient expression, and yeast one hybrid assays. Their roles in the response to cadmium stress were further analyzed using quantitative real time polymerase chain reaction and transgenic approaches. We identified 46 SpHDZs in the S. portulacastrum genome and classified into four subgroups. The SpHDZs were unevenly distributed across 21 chromosomes. Their physicochemical features were examined, including isoelectric points, hydrophobicity, stability, and predicted secondary and tertiary structures. Gene duplication analysis revealed that all identified duplications resulted from whole-genome or segmental events, and most gene pairs exhibited signs of purifying selection. Promoter analysis indicated the presence of numerous cis -elements associated with stress signaling and development. Expression profiling of heavy metal and salt treatment identified a subset of SpHDZs that respond to these treatments, of which, SpHDZ39 and SpHDZ41 showed significant induction under cadmium treatment. Both SpHDZ39 and SpHDZ41 functioned as transcription factors, and transgenic experiments demonstrated that they enhanced cadmium tolerance by promoting root growth and increasing biomass. These results contribute to a deeper understanding of SpHDZs function in halophytic species and provide candidate genes for future applications in low cadmium crop breeding.