[Identification of the regulation elements in heat-inducible Lehsp23.8 promoter]

The promoter of mitochondria-localized small heat shock protein gene in Lycopersicon esculentum (Lehsp23.8) is characterized as strongly heat-inducible. In this study, to determine how the expression of Lehsp23.8 is regulated, we conducted five expression vectors carrying the gus gene driven by the 5' deletion products of the Lehsp23.8 promoter. The corresponding transgenic tobacco plants were generated via Agrobacterium tumefaciens-mediated transformation. Transgenic plants were identified by PCR and Southern blotting analysis. GUS activities under heat-shock conditions were characterized in transgenic tobacco plants. After heat shock, obvious GUS staining was detected in the leaves, shoots, roots, flowers and fruits of the transgenic tobacco plants. The result of fluorometric GUS assays in leaves showed that the heat-induced GUS activity of the 565 bp promoter was the strongest, while that of the 255 bp promoter was the lowest. Deletion analysis shows that the smallest promoter fragment (-255 bp to -23 bp) is sufficient for heat induction. It also indicates that the sequences between -255 bp and -565 bp serve as enhancers, while the sequences between -565 bp and -871 bp can repress the heat-induced activity of the Lehsp23.8 promoter.