Genome-Wide Identification, Expression Profiling, and Stress Responses of the Sugar Transporter Gene Family in Tomato (Solanum lycopersicum)

The Sugar Transporter Protein (STP) family mediates monosaccharide transport and plays essential roles in plant development and stress responses, yet systematic analysis in tomato remains limited. Here, we analyzed the 18 previously reported SlSTPs. Phylogeny classified them into four clades designated Clade I, Clade II, Clade III and Clade IV, with Clade I absent in tomato. Tandem duplications on chromosome 3 drove family expansion. Conserved motifs and gene structures showed clade-specific conservation. Promoters contained abundant light-responsive, hormone-responsive and stress-responsive cis-elements. Tissue expression revealed that SlSTP1 , SlSTP12 and SlSTP16 , which belong to Clade II, were predominantly expressed in roots, while SlSTP9 and SlSTP11 of Clade III were flower-specific; most genes were only detectable during early fruit development. Under nematode infection, SlSTP1 , SlSTP2 , SlSTP3 , SlSTP8 and SlSTP12 peaked at 21 days post inoculation, coinciding with the giant-cell stage. Under drought, salt and heat stresses, SlSTP7 and SlSTP12 showed broad responses; SlSTP6 and SlSTP12 were strongly induced in roots under drought stress, with log₂ fold changes exceeding 5. SlSTP2 was nematode-specific, whereas SlSTP5 , SlSTP 9 and SlSTP17 responded only to abiotic stresses. This study provides candidate genes for improving sugar metabolism and stress tolerance in tomato.