Computational analysis and expression profiling of the Sulfate Transporter gene family in tomato under selenium and abiotic stress treatment

Selenium (Se) is an essential micronutrient for human health, primarily due to its antioxidant properties and role in disease resistance. Biofortification of crops with Se is an effective strategy to improve human Se intake. Due to the chemical similarity between Se and sulfur (S), plants utilize sulfate transporters (SULTRs) for the uptake and translocation of selenate. However, the molecular characterization and stress responsiveness of SULTR family members in tomato (Solanum lycopersicum) remain poorly understood. In this study, we performed a genome-wide identification of 12 SlSULTR genes. Bioinformatics analysis showed that most SlSULTR proteins possess conserved motifs, as well as a core sulfate permease (sulP) domain. Promoter analysis revealed an abundance of cis-regulatory elements related to phytohormone signaling, such as abscisic acid (ABA) and methyl jasmonate (MeJA). Expression profiling demonstrated that application of sodium selenate differentially enhanced SlSULTR1;1 and SlSULTR3;1 expression in roots, SlSULTR3;1 and SlSULTR3;2 in leaves, and SlSULTR3;2 and SlSULTR4;2 in stems. Notably, SlSULTR4;2 showed fruit-preferential induction and was localized to the plasma membrane, whose expression significantly and positively correlated with fruit Se content. Under various abiotic stresses, Se treatment upregulated the expression of specific members, including SULTR1;2 under cold and osmotic stress, and SlSULTR2;2 and SlSULTR4;1 under heat and salt stress. Furthermore, exogenous application of 1 mg/L sodium selenate effectively increased Se accumulation in fruits and promoted the accumulation of phosphorus (P), potassium (K), and manganese (Mn). This study provides the first comprehensive characterization of the tomato SlSULTR family under Se treatment and multiple abiotic stresses. Our findings highlight the potential of SlSULTR4;2 as a candidate gene for Se biofortification, offering a theoretical basis for developing tomato varieties with enhanced stress tolerance and nutritional quality.