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The heat shock response (HSR) is a highly conserved mechanism that enables organisms to survive environmental and pathophysiological stress. In Drosophila, the HSR is regulated by a single transcription factor, heat shock factor (HSF). During stress, HSF trimerizes and binds to over 200 loci on Drosophila polytene chromosomes with only nine mapping to major heat shock (HS) inducible gene loci. The function of HSF binding to the other sites in the genome is currently unknown. Some of these sites may contain yet unidentified “minor” HS genes. Interestingly, the binding of HSF also coincides with puff regression at some sites. Two such sites contain the major developmentally regulated genes Eip74 and Eip75: key regulators in the response to 20-hydroxyecdysone (20E), the main hormone responsible for the temporal co-ordination of post-embryonic development in Drosophila. Previous work in our and other labs indicates that the regression of non-HS puffs during the HSR is dependent on the presence of functional HSF. Using chromatin immunoprecipitation (ChIP) followed by hybridization to genome tiling arrays (Chip), I have identified 434 regions in the Drosophila Kc cell genome that are bound by HSF during HS, and have determined that 57% of these sites are located within the transcribed regions of genes. By examining the transcriptional response to HS in Kc cells and third instar larvae using expression microarrays, I found that only about 10% of all genes within 1250 bp of an HSF binding site are transcriptionally regulated by HS and many genes whose transcript levels change during HS do not appear to be near an HSF binding site. Furthermore, genes with an HSF binding site within their introns are significantly enriched (modified Fisher Exact p-value between 2.0x10-3 and 1.5x10-6) in gene ontology terms related to developmental processes and reproduction. Using expression microarray technology, I characterized the transcriptional response to 20E and its structural analog ponasterone A. I have identified multiple HSF binding sites within Eip74 and Eip75, and show that induction of the HSR correlates with repression of these genes and all other 20E-inducible genes. Taken together, this work provides a basis for further investigation into the role of HSF binding to sites not associated with HS genes and its possible function as a repressor of gene transcription during conditions of stress and as a regulator of developmental genes under stress and non-stress conditions.

Brassinosteroids and ecdysteroid are naturally occuring chemical compounds in plants. The aim of this study was to show whether the application of exogenous steroids such as brassinosteroids (24-epibrassinolide, 28-homobrassinolide, 24-epicastasterone) and ecdysteroid (20-hydroxyecdysone) can affect the morphological parameters and primary photosyntetic processes of selected monocotyledons that was barley, wheat, maize and sorghum. Non-destructive method for measuring of fast kinetics of chlorophyll fluorescence in investigated plants was used. Analysis of primary photosynthetic processes was realized in five time periods from the application of exogenous steroids on the two different old leaves. The response to the treatment by exogenous steroid was different species by plant species. One week after the application of exogenous steroids plants showed differences in their morphological parameters but most of them were not signifficant. The most steroid-sensitive plant was wheat morphological parameters of were significantly different from untreated control plants. No change in maximum quantum yield of photosystem II to the application of exogenous steroid in plants of Sorghum bicolor L. was detected. In the other examined plant species changes in photosynthesis parameters were detected which...

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