RAPID ANALYSIS OF AN OSMOTIC-STRESS RESPONSIVE PROMOTER BY TRANSIENT EXPRESSION IN INTACT WHEAT EMBRYOS

Expression of the wheat 'Em' genes in embryos is strongly induced both by abscisic acid and by subjection to osmotic stress. We have examine d the basis of this induction in an homologous system by constructing fusions between the promoter sequences of a cloned 'Em' gene and the G US reporter gene. The ABA-and stress-mediated expression of these cons tructs has been assayed following delivery to intact wheat embryos by particle bombardment. Staining of bombarded embryos with the chromogen ic substrate X-gluc enabled a simple and rapid visual identification o f promoter activity by scoring the numbers of stained spots. Although not rigorously quantitative, a general correspondence between number o f expression events (spots) and promoter activity could be inferred wh en the results obtained with bombarded embryos were compared with thos e obtained by the fluorimetric measurement of GUS activity in cereal a leurone protoplasts transfected with the same constructs. Analysis of a series of 5'-deletions of the 'Em' promoters indicated that the stre ss-responsive cis-acting regulatory elements comprise the same sequenc es as those responsible for ABA-mediated gene expression.