De novo activation of the beta-phaseolin promoter by phosphatase or protein synthesis inhibitors

Exogenously induced expression of ethylene biosynthesis, ethylene perception, phospholipase D, and Rboh-oxidase genes in broccoli seedlings

In higher plants, copper ions, hydrogen peroxide, and cycloheximide have been recognized as very effective inducers of the transcriptional activity of genes encoding the enzymes of the ethylene biosynthesis pathway. In this report, the transcriptional patterns of genes encoding the 1-aminocyclopropane-1-carboxylate synthases (ACSs), 1-aminocyclopropane-1-carboxylate oxidases (ACOs), ETR1, ETR2, and ERS1 ethylene receptors, phospholipase D (PLD)-alpha1, -alpha2, -gamma1, and -delta, and respiratory burst oxidase homologue (Rboh)-NADPH oxidase-D and -F in response to these inducers in Brassica oleracea etiolated seedlings are shown. ACS1, ACO1, ETR2, PLD-gamma1, and RbohD represent genes whose expression was considerably affected by all of the inducers used. The investigations were performed on the seedlings with (i) ethylene insensitivity and (ii) a reduced level of the PLD-derived phosphatidic acid (PA). The general conclusion is that the expression of ACS1, -3, -4, -5, -7, and -11, ACO1, ETR1, ERS1, and ETR2, PLD-gamma 1, and RbohD and F genes is undoubtedly under the reciprocal cross-talk of the ethylene and PA(PLD) signalling routes; both signals affect it in concerted or opposite ways depending on the gene or the type of stimuli. The results of these studies on broccoli seedlings are in agreement with the hypothesis that PA may directly affect the ethylene signal transduction pathway via an inhibitory effect on CTR1 (constitutive triple response 1) activity.

Phosphorylation of histone H3 in plants--a dynamic affair

Histones are the main protein components of chromatin: they undergo extensive post-translational modifications, particularly acetylation, methylation, phosphorylation, ubiquitination and ADP-ribosylation which modify the structural/functional properties of chromatin. Post-translational modifications of the N-terminal tails of the core histones within the nucleosome particle are thought to act as signals from the chromatin to the cell, for various processes. Thus, in many ways histone tails can be viewed as complex protein-protein interaction surfaces that are regulated by numerous post-translational modifications. Histone phosphorylation has been linked to chromosome condensation/segregation, activation of transcription, apoptosis and DNA damage repair. In plants, the cell cycle dependent phosphorylation of histone H3 has been described; it is hyperphosphorylated at serines 10/28 and at threonines 3/11 during both mitosis and meiosis in patterns that are specifically coordinated in both space and time. Although this post-translational modification is highly conserved, data show that the chromosomal distribution of individual modifications can differ between groups of eukaryotes. Initial results indicate that members of the plant Aurora kinase family have the capacity to control cell cycle regulated histone H3 phosphorylation, and in addition we describe other potential H3 kinases and discuss their functions.

Interaction of PvALF and VP1 B3 domains with the beta -phaseolin promoter

The phas promoter is potently transcribed during embryogenesis but in vegetative tissues it is completely silenced by a rotationally positioned nucleosome. Ectopic expression in leaves of PvALF, a seed-specific transcription factor belonging to the plant-exclusive B3 domain-containing VP1/ABI3 family, leads to chromatin remodeling of the phas promoter, permitting transcriptional activation by the growth regulator abscisic acid (ABA). Specific interaction with RY elements present in 40-42 bp oligonucleotide probes has been shown in vitro for Arabidopsis ABI3 and the isolated B3 domain of maize VP1. Here, both in vivo and in vitro approaches were used to show physical interaction of the B3 domain of VP1 or PvALF to RY elements in the native phas promoter. In electrophoretic mobility shift assays, small changes in B3 domain concentration differentiated between RY element-specific and sequence non-specific DNA binding. Increased affinity of the PvALF B3 domain to RY elements was observed in the presence of histones and other basic proteins, possibly reflecting the ability of this B3 factor to interact with the phas promoter in its nucleosomal configuration.

S phase progression is required for transcriptional activation of the beta-phaseolin promoter

Elucidating the mechanisms by which the transcription machinery accesses promoters in their chromatin environment is a fundamental aspect of understanding gene regulation. The phas promoter is normally constrained by a rotationally and translationally positioned nucleosome over its TATA region except during embryogenesis when it is potentiated by the presence of Phaseolus vulgaris ABI3-like factor (PvALF), a plant-specific transcription factor, and activated by an abscisic acid (ABA)-induced signal transduction cascade. Ectopic expression of PvALF and the supply of ABA in transgenic tobacco or Arabidopsis leaves can activate expression from phas. We confirmed by [3H]thymidine incorporation that active DNA replication occurred concomitant with the presence of PvALF and ABA. Arrest of DNA synthesis or S phase progression by infiltration of the leaves with replication inhibitors (hydroxyurea, roscovitine, mimosine) strongly inhibited transcriptional activation, especially the ABA-mediated activation step. Similarly, activation of endogenous Arabidopsis MAT and LEA genes in leaf tissue by the presence of ABA and ectopically expressed PvALF was inhibited by DNA replication arrest. No change in transcript levels on the arrest of replication was detected for abi1, abi2, and era1, negative regulators of the ABA signal transduction cascade or for cell cycle components ick1 and aip3. However, a reduction in transcript accumulation for the crucial ABA signaling effector, abi5, occurred upon DNA replication arrest (probably reflected in the decrease in MAT and LEA gene expression). Contrary to the conventional view that ABA inhibits DNA replication, our findings show that ABA acts in concert with S phase progression to activate gene expression.

Delayed-onset amnesia caused by protein synthesis inhibition in odor-taste associative memory of the terrestrial slug Limax valentianus

The terrestrial slug Limax avoids the odor of innately preferred food after it is presented with the aversive taste of quinidine. This type of associative memory persists for several weeks. We investigated effects of protein synthesis inhibitors on the retention of this odor-taste associative memory. Anisomycin or cycloheximide applied to the slug 30 min prior to conditioning impaired the memory retention as late as two or more days after the conditioning, while the retention of a short-term memory was normal for up to 24 h. In contrast, the inhibition of protein synthesis by these inhibitors decays within several hours. In Limax, the onset of amnesia is unusually delayed when protein synthesis is suppressed at the time of conditioning.

Identification of a novel nuclear factor-binding site in the Pisum sativum sad gene promoters

DNA fragments containing the 5' promoter regions of the Pisum sativum sadA and sadC genes were amplified from genomic DNA, cloned and sequenced. These sequences contain a number of conserved cis-acting elements, which are potentially involved in stress-induced transcription of the sad genes. To determine whether any of the identified elements are active in binding nuclear factors in vitro, 11 60-bp overlapping (by 30 bp) DNA probe fragments covering the proximal sadC promoter sequence (360 bp) were used in electrophoretic mobility shift assays with competition. Binding activities were compared in nuclear extracts from control, UV-B-stressed and wounded pea leaves. The pattern of DNA binding was almost identical with all three extracts, with one 30-bp region being the predominant site for factor binding. Using overlapping sub-fragments of this region, the majority of the specific binding could be attributed to the novel 11-bp GC-rich sequence GTGGCGCCCAC. An almost identical sequence is conserved in the sadA promoter. This motif has features in common with a number of recognised cis-elements, which suggests a possible binding site for factors which play a role in regulating sad gene transcription.

Chromatin remodelling

Epigenetic mechanisms are heritable traits that are mediated by changes in a genetic locus that do not involve a modification at the nucleotide level. As eukaryotic DNA is organised in chromatin units, epigenetic modifications can be mediated by chromatin remodelling. Although there are a number of well-characterised chromatin remodelling factors to which we can allocate a defined molecular function, we need to understand chromatin remodelling processes as the combined effects of such factors in higher order complexes.