Heterologous expression of the AtDREB1A gene in tomato confers tolerance to chilling stress

Tomato is highly sensitive to chilling stress (0 - 12 degrees C) which severely affects plant growth and development. Transgenic tomato plants expressing the AtDREB1A gene under the control of the rd29A promoter were evaluated for its tolerance to chilling stress by exposing them to 4 degrees C for 5 d. The cold stress caused an increase in production of reactive oxygen species, however, transgenic plants had an effective antioxidant system due to an enhanced synthesis of catalase (CAT), superoxide dismutase (SOD), and ascorbate and so the reduced content of hydrogen peroxide and superoxide anions. Transgenic plants showed a slightly less reduction of chlorophyll and carotenoid content compared to wild-type plants. Similarly, a higher relative water content and a less electrolyte leakage were observed in transgenic plants. Accumulation of osmoprotectants, like proline and soluble sugars, helped transgenic plants to maintain a proper osmotic balance under the cold stress. Stress-responsive genes pyrroline-5-carboxylate synthase, CAT, SOD, and lipid peroxidase showed enhanced expressions under the cold stress in transgenic plants compared to wild-type plants. A recurrent exposure to the cold stress at the reproductive stage showed even higher expressions of these genes as compared to plants exposed to the cold stress for the first time. Thus, transgenic plants showed a better adaptation to the cold stress than non-transgenic plants by acquiring the stress memory of the stress experienced at the seedling stage.