The differential expression of a heat shock promoter in floral and reproductive tissues

A detailed histochemical analysis of the expression of the soybean small heat shock protein gene promoter, GmHSP 17.5E, fused to the GUS reporter gene, has been made in all organs and tissues of the flower as a function of stage of development and heat stress. This promoter is not uniformly expressed after a heat shock in all floral tissues and organs. Expression is seen at all stages of development in the sepals but not in the petals. The expression pattern in the pistil and in anthers is complex. Heat stress-induced GUS staining is seen in the style and upper portion of the ovary, but not in the stigmatic papillae or in the lower part of the ovary or in ovules. In stamens the heat shock response is seen in the filament and in the extension of the vascular tissue from the filament into the anther. No induction is seen in other tissues of the anther or in microspores or pollen at any stage of development. Vegetative organs in contrast are more uniform in the beat shock inducibility of GUS activity. Based on evidence from transient assays after microprojectile particle bombardment of the GmHSP 17.5E/GUS construct into pollen, it is likely that the gene is transcriptionally in an inactive configuration in pollen nuclei in stably transformed transgenic plants. These results are discussed with reference to other information in the literature.