The Arabidopsis HSP18.2 promoter/GUS gene fusion in transgenic Arabidopsis plants: a powerful tool for the isolation of regulatory mutants of the heat‐shock response

A detailed study of the expression of the promoter of the HSP18.2 gene from Arabidopsis fused to the bacterial gene for β‐glucuronidase (GUS) in transgenic Arabidopsis plants is described. High levels of GUS activity were induced in all organs of transformants except for seeds during heat shock. The optimum temperature for expression of GUS in Arabidopsis was 35°C regardless of the plant growth temperature. Heat shock of 40°C did not induce any detectable levels of GUS activity. Pre‐incubation at 35°C was found to have a protective effect on the induction of GUS activity at 40°C. GUS activity was also increased in response to a gradual increase in temperature. Histochemical analysis revealed that basal levels of GUS activity were induced in the vascular tissue of leaves and sepals, as well as at the tips of carpels, at the normal growth temperature. Heat treatment of a limited part of the plant tissue did not appear to cause systemic induction of GUS activity. To extend the analysis of the plant heat‐shock response, we attempted to screen mutations in genes involved in the regulation of the induction of heat‐shock protein (HSP) genes, using the GUS gene as a selection marker in transgenic Arabidopsis plants, and the results of this analysis are described. 1992 BIOS Scientific Publishers Ltd