Expression Analysis and Protein Modeling of Small Heat Shock Protein 20 VIS1 Gene in Six Solanum lycopersicum Determinate Varieties

High temperatures impact plants, affecting their growth and significantly reducing production. Climate change is making it more challenging for those countries with intense summers. Nature copes with it by expressing the small heat shock protein 20 (sHSP20) gene in plants during heat stress. This study investigates the response of six Solanum lycopersicum Pakistani varieties, i.e., Roma, Riogrande, Nadir, Pakit, Advanta, and T-1359, to high temperature stress through sHSP20 gene expression analysis, accompanying protein modeling of the Roma variety, and phylogenetic characterization of the sHSP20 gene. Varieties were selected from Punjab, Pakistan, and seeds were grown in the glasshouse at the National Agricultural Research Center (NARC). Split-plot design was used for within-variety comparison, with heat stress treatment applied to 3-month-old plants up to 50 °C for 10 days. Phylogenetic analysis revealed a diverse evolutionary pattern of the sHSP20 protein, suggesting that evolution is not species-dependent. The expression analysis of the sHSP20 gene depicted that the Roma tomato variety has higher expression, followed by T-1359, Pakit, Nadir, Riogrande, and Advanta. Structural prediction of NCBI_VIS1 and Roma_VIS1 depicted conserved α-crystalline domain core but extended N and C terminals in Roma_VIS1 protein, suggesting enhanced binding efficiency, flexibility, and improved aggregation prevention of proteins. The results indicate that all varieties responded well to heat stress, with significant expression by Roma and T-1359, making them the best candidates to be grown in the high-temperature regions of Pakistan.