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Dual regulation of a heat shock promoter during embryogenesis: stage-dependent role of heat shock elements
- Almoguera, C., Prieto-Dapens, P., Jordano, J.
- plant journal 1998 v.13 no.4 pp. 437-446
- heat shock proteins, plant development, Helianthus annuus, seeds, transgenic plants, enzyme activity, mutation, gene expression, histochemistry, Nicotiana tabacum, reporter genes, binding sites, embryogenesis, promoter regions, beta-glucuronidase
- Transgenic tobacco expression was analysed of chimeric genes with point mutations in the heat shock element (HSE) arrays of small heat shock protein (sHSP) gene from sunflower hp17.7 G4. The promotor was developmentally regulated during zygotic and responded to heat stress in vegetative tissues. Mutations in the HSE affected nucleotides crucial for human heat shock transcription factor 1 (HSF1) binding. They abolished the heat shock response of Ha hsp17.7 G4 and produced expression changes that demonstrated dual regulation of this promotor during embryogenesis. Thus, whereas activation of the chimeric genes during early maturation stages did not require intact HSE, expression at later desiccation stages was reduced by mutations in both the proximal (-57 to -89) and distal (-99 to -121) HSE. In contrast, two point mutations in the proximal HSE that did not severely affect gene expression during zygotic embryogenesis, eliminated the heat shock response of the same chimeric gene in vegetative organs. Therefore, by site-directed mutagenesis, it was possible to separate the heat shock response of Ha hsp17.7 G4 from its developmental regulation. The results indicate the co-existence, in a single promoter, of HSF-dependent and -independent regulation mechanisms that would control sHSP gene expression at different stages during plant embryogenesis.