Tissue-specific expression and environmental regulation of the barley Hvhsp17 gene promoter in transgenic tobacco plants

The 5′ upstream region (-1700 to +1) of the barley Hvhsp17 gene, inducible by heat shock in young barley seedlings, was transcriptionally fused with the β-glucuronidase (GUS) reporter gene. A 2 kb fragment, carrying the CaMV35S promoter, intron 1 from ADH gene of maize, and the BAR gene, was excised from plasmid pBARGUS (Fromm et al., 1990) and the dual expression vector pBARHSGUS was created. Plasmid pBARHSGUS was used to transform tobacco protoplasts via PEG-mediated direct DNA uptake. Four chosen transgenic tobacco plants containing from 1 to 5 integrated copies of the chimeric GUS gene (confirmed by PCR and Southern analyses) were further analysed. Histochemical and fluorimetrical analyses were performed in various plant tissues after thermal induction and other environmental treatments. The results obtained show that the chimeric pHS/GUS fusion was not only induced by heat treatment, but also regulated by some metal ions, and abscisic acid. Furthermore, β-glucuronidase expression in transgenic tobacco was strictly tissue-specific, being restricted to the vascular boundles of the xylematic component in the stem and petioles, and absent in any other tissue, with the exception (in one case), of a faint signal in the inner tissue of the style. It was therefore demonstrated that the 1700 bp upstream region of the monocot heat shock gene Hvhsp17 was capable of driving a heat-inducible tissue-specific expression of the marker GUS gene in a heterologous dicot plant.