Comparative Functional Analysis of COLD1 and GPA1 in Processing Tomatoes: Overexpression of COLD1 Significantly Enhances Seedling Cold Tolerance and Physiological Responses

Low temperature severely limits tomato (Solanum lycopersicum) production, yet the molecular mechanisms governing cold tolerance—particularly those involving COLD1 and GPA1—remain incompletely defined. To address this, processing tomato lines overexpressing COLD1 or GPA1 were generated and evaluated for seedling-stage cold tolerance, with a focus on the expression of key genes such as SlICE1, SlCBF1, and SlCOR518 to elucidate the molecular pathways conferring enhanced cold tolerance. Under cold stress conditions (4 °C for 5 days), physiological and biochemical responses were compared between wild-type and transgenic lines. The results demonstrated that COLD1-overexpressing lines exhibited markedly greater cold tolerance than both wild-type and GPA1-overexpressing lines, notably displaying reduced wilting and membrane injury. At 4 °C, the activities of superoxide dismutase, peroxidase, and catalase in COLD1-overexpressing lines were 122%, 67.4%, and 97.4% higher than those in the wild type, and 44.7%, 21.0%, and 20.6% higher than in GPA1-overexpressing lines, respectively. Furthermore, hydrogen peroxide and superoxide levels were 33.4% and 40.6% lower in COLD1-overexpressing lines compared to the wild type, and 17.8% and 24.0% lower compared to GPA1-overexpressing lines, respectively. Osmolyte accumulation was more pronounced in COLD1 lines, with soluble sugar and proline levels 95.4% and 66.2% higher than in the wild type, and 30.9% and 23.6% higher than in GPA1 lines, respectively. Importantly, changes in key gene expression indicated that both transgenic lines enhance cold tolerance by modulating the ICE1-CBF-COR pathway. Collectively, these findings highlight the superior contribution of COLD1 to cold tolerance in tomato seedlings and provide insights into the molecular mechanisms underlying cold adaptation.