The repressor and co-activator HsfB1 regulates the major heat stress transcription factors in tomato

Plants code for a multitude of heat stress transcription factors (Hsfs). Three of them act as central regulators of heat stress (HS) response in tomato (Solanum lycopersicum). HsfA1a regulates the initial response, and HsfA2 controls acquired thermotolerance. HsfB1 is a transcriptional repressor but can also act as co-activator of HsfA1a. Currently, the mode of action and the relevance of the dual function of HsfB1 remain elusive. We examined this in HsfB1 overexpression or suppression transgenic tomato lines. Proteome analysis revealed that HsfB1 overexpression stimulates the co-activator function of HsfB1 and consequently the accumulation of HS-related proteins under non-stress conditions. Plants with enhanced levels of HsfB1 show aberrant growth and development but enhanced thermotolerance. HsfB1 suppression has no significant effect prior to stress. Upon HS, HsfB1 suppression strongly enhances the induction of heat shock proteins due to the higher activity of other HS-induced Hsfs, resulting in increased thermotolerance compared with wild-type. Thereby, HsfB1 acts as co-activator of HsfA1a for several Hsps, but as a transcriptional repressor on other Hsfs, including HsfA1b and HsfA2. The dual function explains the activation of chaperones to enhance protection and regulate the balance between growth and stress response upon deviations from the homeostatic levels of HsfB1.

HsfA2 Controls the Activity of Developmentally and Stress-Regulated Heat Stress Protection Mechanisms in Tomato Male Reproductive Tissues

Male reproductive tissues are more sensitive to heat stress (HS) compared to vegetative tissues, but the basis of this phenomenon is poorly understood. Heat stress transcription factors (Hsfs) regulate the transcriptional changes required for protection from HS In tomato (Solanum lycopersicum), HsfA2 acts as coactivator of HsfA1a and is one of the major Hsfs accumulating in response to elevated temperatures. The contribution of HsfA2 in heat stress response (HSR) and thermotolerance was investigated in different tissues of transgenic tomato plants with suppressed HsfA2 levels (A2AS). Global transcriptome analysis and immunodetection of two major Hsps in vegetative and reproductive tissues showed that HsfA2 regulates subsets of HS-induced genes in a tissue-specific manner. Accumulation of HsfA2 by a moderate HS treatment enhances the capacity of seedlings to cope with a subsequent severe HS, suggesting an important role for HsfA2 in regulating acquired thermotolerance. In pollen, HsfA2 is an important coactivator of HsfA1a during HSR HsfA2 suppression reduces the viability and germination rate of pollen that received the stress during the stages of meiosis and microspore formation but had no effect on more advanced stages. In general, pollen meiocytes and microspores are characterized by increased susceptibility to HS due to their lower capacity to induce a strong HSR This sensitivity is partially mitigated by the developmentally regulated expression of HsfA2 and several HS-responsive genes mediated by HsfA1a under nonstress conditions. Thereby, HsfA2 is an important factor for the priming process that sustains pollen thermotolerance during microsporogenesis.

In the complex family of heat stress transcription factors, HsfA1 has a unique role as master regulator of thermotolerance in tomato

We generated transgenic tomato plants with altered expression of heat stress transcription factor HsfA1. Plants with 10-fold overexpression of HsfA1 (OE plants) were characterized by a single HsfA1 transgene cassette, whereas plants harboring a tandem inverted repeat of the cassette showed cosuppression (CS plants) by posttranscriptional silencing of the HsfA1 gene connected with formation of small interfering RNAs. Under normal growth conditions, major developmental parameters were similar for wild-type (WT), OE, and CS plants. However, CS plants and fruits were extremely sensitive to elevated temperatures, because heat stress-induced synthesis of chaperones and Hsfs was strongly reduced or lacking. Despite the complexity of the plant Hsf family with at least 17 members in tomato, HsfA1 has a unique function as master regulator for induced thermotolerance. Using transient reporter assays with mesophyll protoplasts from WT tomato, we demonstrated that plasmid-encoded HsfA1 and HsfA2 were well expressed. However, in CS protoplasts the cosuppression phenomenon was faithfully reproduced. Only transformation with HsfA2 expression plasmid led to normal expression of the transcription factor and reporter gene activation, whereas even high amounts of HsfA1 expression plasmids were silenced. Thermotolerance in CS protoplasts was restored by plasmid-borne HsfA2, resulting in expression of chaperones, thermoprotection of firefly luciferase, and assembly of heat stress granules.

The protein encoded by the Drosophila position-effect variegation suppressor gene Su(var)3-9 combines domains of antagonistic regulators of homeotic gene complexes

Modifier mutations of position-effect variegation (PEV) represent a useful tool for a genetic and molecular dissection of genes connected with chromatin regulation in Drosophila. The Su(var)3-9 gene belongs to the group of haplo suppressor loci which manifest a triplo enhancer effect. Mutations show a strong suppressor effect even in the presence of PEV enhancer mutations, indicating a central role of this gene in the regulation of PEV. By molecular analysis, Su(var)3-9 could be correlated with a 2.4 kb transcript which encodes a putative protein of 635 amino acids containing a chromo domain and a region of homology to Enhancer of zeste and trithorax, two antagonistic regulators of the Antennapedia and Bithorax gene complexes, as well as to the human protein ALL-1/Hrx which is implicated in acute leukemias. This region of homology is found in all four proteins at the C-terminus. The homology of Su(var)3-9 to both negative (Polycomb and Enhancer of zeste) and positive (trithorax) regulators of the Antennapedia and Bithorax complexes also suggests similarities in the molecular processes connected with stable transmission of a determined state and the clonal propagation of heterochromatinization.

P transposon-induced dominant enhancer mutations of position-effect variegation in Drosophila melanogaster

P transposon induced modifier mutations of position-effect variegation (PEV) were isolated with the help of hybrid dysgenic crosses (pi 2 strain) and after transposition of the mutator elements pUChsneory+ and P[lArB]. Enhancer mutations were found with a ten times higher frequency than suppressors. The 19 pUChsneory(+)- and 15 P[lArB]-induced enhancer mutations can be used for cloning of genomic sequences at the insertion sites of the mutator elements via plasmid rescue. Together with a large sample of X-ray-induced (48) and spontaneous (93) enhancer mutations a basic genetic analysis of this group of modifier genes was performed. On the basis of complementation and mapping data we estimate the number of enhancer genes at about 30 in the third chromosome and between 50 and 60 for the whole autosome complement. Therefore, enhancer of PEV loci are found in the Drosophila genome as frequently as suppressor genes. Many of the enhancer mutations display paternal effects consistent with the hypothesis that some of these mutations can induce genomic imprinting. First studies on the developmentally regulated gene expression of PEV enhancer genes were performed by beta-galactosidase staining in P[lArB] induced mutations.

Non-selective action of 4-hydroxyanisole on melanoma cells in vivo

In order to clarify the role of tyrosinase (E.C. 1.14.18.1) in the cytotoxicity of 4-hydroxyanisole (4HA) in vivo, we have compared the therapeutic effects of 4HA on the B16 melanoma and Harding-Passey melanoma, which differ significantly in their tyrosinase content. The observed therapeutic effects are moderate and similar in both tumors. Therefore, there is no evidence for an increase of the cytotoxic effect of 4HA by tyrosinase in vivo. Application of 4HA to mice carrying B16 melanoma and Harding-Passey melanoma results in an inhibition of [3H]-TdR incorporation into melanoma DNA as well as into DNA of liver, intestine, kidney, and spleen. There is no selective activity on melanoma cells by 4HA in vivo. Therefore, in the therapy of human melanoma by 4HA, side effects on normal tissues cannot be excluded.

[Synthesis of 5-bromosalicyl-4'-chloroanilide-O-beta-D-xylopyranoside and other transport forms enzymatically activated by microbes]

The synthesis of 5-bromosalicyl-4'-chloroanilide-O-beta-D-xylopyranoside and other glycosides of 5-bromosalicyl-4'-chloroanilide, salicylanilide, 3,5-dichlorophenol and tetrachlorohydrochinone is described. Glycosidations follow the procedures described by Latham et al. Sabalitschka and Helferich et al. These glycosides represent relatively untoxic transport-forms of drugs, which are activated to the free drug by specific enzymes of the organisms to be destroyed. This new mechanisms can help to destroy fungi and parasites in dermatology, agriculture, horticulture and cultivation of decorative plants without side effects on the host.

[Synthesis and properties of digitoxigenin-3 beta-O-alpha-L-arabinofuranoside]

The synthesis of a cardenolide glycoside with a furanoide sugar component, digitoxigenin-3 beta-O-alpha-L-arabinofuranoside (4), is described for the first time. 4 was prepared by the reaction of digitoxigenin with 2,3,5-tri-O-benzoyl-alpha-L-arabinofuranosylchloride and Fétizon-reagent in benzene/dioxan followed by debenzoylation with ammonia in dry methanol. Compound 4 is cleaved by alpha-L-arabinofuranosidase (Aspergillus niger K1) into digitoxigenin and L-arabinose. Hydrolytic stability against methanolic HCl (0.1 mol/l) is relatively high. 4 X 10(-8) mol/l 4 gives a 50% inhibition of the Na,K-ATPase (pig heart muscle) and is 2.5 times more active at this receptor than the aglycon digitoxigenin.

Selective tumor DNA synthesis inhibition: in vivo prodrug activation by an exogenous enzyme

Using the combination of alpha-L-arabinofuranosidase from Aspergillus niger with beta-peltatin A-alpha-L-arabinofuranoside, the selective effect of a new cancer of chemotherapy method based on a pH-dependent activation of cancerostatic prodrugs by exogenous enzymes was studied. In comparative experiments the selectivity of prodrug activation was measured by 3H-thymidine incorporation in tumor and normal tissues of CBA mice inoculated im with the transplantable mammary carcinoma, MA-21224. The results show that this special type of carrier principle may lead to a higher degree of selectivity than the usual direct application of cancerostatic drugs.