Heat-inducible expression system for a foreign gene in cultured tobacco cells using the HSP18.2 promoter of Arabidopsis thaliana

A system for the controlled expression of a foreign gene in cultured tobacco cells (Nicotiana tabacum, BY2) by temperature shift was constructed. A 925-base-pair (bp) DNA fragment containing the 5′-flanking region of a low-molecular-mass heat-shock protein gene (HSP18.2) of Arabidopsis thaliana was inserted upstream of the β-glucuronidase reporter gene (GUS). The resulting HSP18.2-GUS construct was introduced into BY2 cells by electroporation or Agrobacterium-mediated transformation. Transient expression of the HSP18.2 promoter in protoplasts was very low regardless of the heat shock. Although expression of the HSP18.2-GUS chimeric gene in the stable transformants of BY2 was hardly detected in culture at 25°C, the expression increased rapidly on the transcriptional level when the incubation temperature was shifted to 35-37°C. The optimal temperature for heat-shock induction was 37°C. After a 2-h incubation at 37°C, GUS activity was about 1000-fold greater than that before heat shock. The amount of GUS mRNA was maximum 2 h after heat shock, and then decreased gradually.