SaTDT enhanced plant tolerance to NaCl stress by modulating the levels of malic acid and citric acid in cells.

The issue of soil salinization is a global concern that significantly impairs crop productivity, quality, and distribution. Tonoplast Dicarboxylate Transporter (TDT) is a pivotal malic acid transporter localized on the vacuolar membrane, involving in maintaining intracellular pH homeostasis in plants. However, the molecular mechanisms and regulatory pathways underlying plant salt tolerance through TDT remain elusive. In this study, we cloned a gene encoding vacuolar membrane dicarboxylic acid transporter designated as SaTDT from the halophyte Spartina alterniflora. Subsequently, its role in regulating salt stress was investigated. The heterologous expression of SaTDT in Arabidopsis thaliana was observed to enhance the transgenic plants' tolerance to salt stress and alleviate the growth damage caused by this stress. The overexpression of SaTDT can simultaneously enhance plant photosynthetic efficiency by regulating the cellular contents of malic acid and citric acid, or by increasing the activity of MDH and PEPC enzymes. It also regulates and balances energy utilization during carbon assimilation under salt-stressed conditions, thereby establishing an energetic foundation for enhancing plant tolerance to stress. SaTDT also has the capacity to enhance the plant cells' ability in regulating antioxidant enzyme activity or osmotic accumulation, thereby playing a crucial role in maintaining intracellular redox homeostasis. In conclusion, our findings establish a foundation basis for elucidating the regulatory role of the SaTDT gene in S.alterniflora's adaptation to high-salinity habitats.