Over-expression of Arabidopsis thaliana heat shock factor gene (AtHsfA1b) enhances chilling tolerance in transgenic tomato

Abstract

Heat shock pre-treatment or heat acclimation can enhance the subsequent chilling tolerance of many plant species. However, the exact mechanism is currently unknown. Transgenic tomato plants harboring an Arabidopsis thaliana HsfA1b (AtHsfA1b) and β-glucuronidase (gusA) fusion gene under the control of a constitutive CaMV35S promoter were generated to evaluate whether heat shock factor (Hsf), a major transcription regulator of heat shock response, is involved in heat shock-induced chilling tolerance. The transcripts or protein product of heat-shock induced genes in the transgenic plants highly expressing AtHsfA1b-gusA accumulated to higher levels than those of the wild-type or gusA transgenic plants under non-heat shock conditions. This suggests that AtHsfA1b-GUS can cross- talk with the heat shock responsive machinery in transgenic tomato plants. In addition, the specific activity of soluble isoforms of ascorbate peroxidase of the AtHsfA1b-gusA transgenic plants was about twofold higher than that of the wild-type or gusA transgenic plants under non-heat stress conditions. Without heat acclimation, seedlings of the AtHsfA1b-gusA transgenic tomato lines showed a significantly higher level of thermal and chilling tolerance than that of the wild-type or gusA transgenic plants. Based on these results, we suggest that Hsf may play a pivotal role in heat-shock-induced chilling tolerance, and constitutive expression of the transcription regulatory gene in chilling sensitive crops may be useful in improving tolerance against chilling stress.