Buried in PEAT—discovery of a new silencing complex with opposing activities

Posttranslational histone modifications serve critical roles in gene regulation by determining the functional status of chromatin. Histone‐modifying enzymes often work in large multiprotein complexes. A paper in this issue of The EMBO Journal describes a new chromatin‐modifying complex called PEAT that acts via histone deacetylation. The PEAT complex is involved in heterochromatin formation and gene repression but also appears to have a locus‐specific activating role, possibly through promoting histone acetylation.     

Dynamic Histone Acetylation of Late Embryonic Genes during Seed Germination

Histone acetylation is involved in the regulation of gene expression in plants and eukaryotes. Histone deacetylases (HDACs) are enzymes that catalyze the removal of acetyl groups from histones, which is associated with the repression of gene expression. To study the role of histone acetylation in the regulation of gene expression during seed germination, trichostatin A (TSA), a specific inhibitor of histone deacetylase, was used to treat imbibing Arabidopsis thaliana seeds. GeneChip arrays were used to show that TSA induces up-regulation of 45 genes and down-regulation of 27 genes during seed germination. Eight TSA-up-regulated genes were selected for further analysis – RAB18, RD29B, ATEM1, HSP70 and four late embryogenesis abundant protein genes (LEA). A gene expression time course shows that these eight genes are expressed at high levels in the dry seed and repressed upon seed imbibition at an exponential rate. In the presence of TSA, the onset of repression of the eight genes is not affected but the final level of repressed expression is elevated. Chromatin immunoprecipitation and HDAC assays show that there is a transient histone deacetylation event during seed germination at 1 day after imbibition, which serves as a key developmental signal that affects the repression of the eight genes. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

The developmental fate of angiosperm pollen is associated with a preferential decrease in the level of histone H1 in the vegetative nucleus

In angiosperm pollen, the vegetative cell is assumed to function as a gametophytic cell in pollen germination and growth of the pollen tube. The chromatin in the nucleus of the vegetative cell gradually disperses after microspore mitosis, whereas the chromatin in the nucleus of the other generative cell remains highly condensed during the formation of two sperm nuclei. In order to explain the difference in chromatin condensation between the vegetative and generative nuclei, we analyzed the histone composition of each nucleus in Lilium longiflorum Thunb. and Tulipa gesneriana immunocytochemically, using specific antisera raised against histones H1 and H2B of Lilium. We found that the level of histone H1 decreased gradually only in the vegetative nucleus during the development of pollen within anthers and that the vegetative nucleus in mature pollen after anther dehiscence contained little histone H1. By contrast, the vegetative nucleus contained the same amount or more of histone H2B than the generative nucleus. The preferential decrease in the level of histone H1 occurred in anomalous pollen with one nucleus (uninucleate pollen) or with two similar nuclei (equally divided pollen), which had been induced by treatment with colchicine. The nuclei in the anomalous pollen resembled vegetative nuclei in terms of structure and staining properties. The anomalous pollen was able to germinate and extend a pollen tube. From these results, it is suggested that the preferential decrease in level of histone H1 in pollen nuclei is essential for development of the male gametophytic cell through large-scale expression of genes that include pollen-specific genes, which results in pollen germination and growth of the pollen tube. Received: 9 May 1998 / Accepted: 4 June 1998     

Immunotherapy using algal‐produced Ara h 1 core domain suppresses peanut allergy in mice

Peanut allergy is an IgE‐mediated adverse reaction to a subset of proteins found in peanuts. Immunotherapy aims to desensitize allergic patients through repeated and escalating exposures for several months to years using extracts or flours. The complex mix of proteins and variability between preparations complicates immunotherapy studies. Moreover, peanut immunotherapy is associated with frequent negative side effects and patients are often at risk of allergic reactions once immunotherapy is discontinued. Allergen‐specific approaches using recombinant proteins are an attractive alternative because they allow more precise dosing and the opportunity to engineer proteins with improved safety profiles. We tested whether Ara h 1 and Ara h 2, two major peanut allergens, could be produced using chloroplast of the unicellular eukaryotic alga, Chlamydomonas reinhardtii. C. reinhardtii is novel host for producing allergens that is genetically tractable, inexpensive and easy to grow, and is able to produce more complex proteins than bacterial hosts. Compared to the native proteins, algal‐produced Ara h 1 core domain and Ara h 2 have a reduced affinity for IgE from peanut‐allergic patients. We further found that immunotherapy using algal‐produced Ara h 1 core domain confers protection from peanut‐induced anaphylaxis in a murine model of peanut allergy.     

Epigenetic chromatin modifiers in barley: III. Isolation and characterization of the barley GNAT-MYST family of histone acetyltransferases and responses to exogenous ABA

Histone acetylation is a vital mechanism for the activation of chromatin and the corresponding expression of genes competing the action of histone deacetylation and leading to chromatin inactivation. Histone acetyltransferases (HATs) comprise a superfamily including the GNAT/MYST, CBP and TF_II250 families. Histone acetyltransferases have been well studied in Arabidopsis but information from agronomically important crops is limited. In the present work three full-length sequences encoding members of the GNAT/MYST family, namely HvMYST, HvELP3 and HvGCN5, respectively, were isolated and characterized from barley (Hordeum vulgare L.), a crop of high economic value. Expression analysis of the barley GNAT/MYST genes revealed significant quantitative differences in different seed developmental stages and between cultivars with varying seed size and weight, suggesting an association of these genes with barley seed development. Furthermore, all three HvGNAT/MYST genes were inducible by the stress-related phytohormone abscisic acid (ABA) involved in seed maturation, dormancy and germination, implying a possible regulation of these genes by ABA, during barley seed development, germination and stress response.     

Seed-specific,developmentally regulated genes of peanut

Four cDNAs of seed-specific and developmentally regulated peanut (Arachis hypogaea L.) genes were identified by differential screening of a peanut-seed cDNA library using cDNA probes constructed from mRNAs isolated from immature and mature stages of the seed. Northern analysis, probed with the four cloned cDNAs, indicated that the genes represented by two cDNAs were expressed abundantly early in seed development, while another two were abundantly expressed later at the cell-expansion stages of seed development. These four genes did not show expression in roots, pegs or leaves. However, one of the early expressed genes was seed coat-specific. One of the clones, Psc11, had significant sequence similarity to subtilisin-like genes in Arabidopsis and soybean. Clones Psc32 and Psc33 had significant similarity to the peanut allergen genes Ara h II and Ara h 6, respectively. The sequence of clone Psc12 was unique and did not show significant similarity to any sequence in the databases. One of the four seed-specific clones showed restriction fragment length polymorphism (RFLP) among peanut lines representing the four peanut botanical varieties. These findings indicate that polymorphism exists in peanut seed-storage genes. This contrasts with other genes previously used for genetic mapping of cultivated peanut. Received: 1 September 2000 / Accepted: 4 May 2001     

Control of replication initiation by the Sum1/Rfm1/Hst1 histone deacetylase

Background  

Replication initiation at origins of replication in the yeast genome takes place on chromatin as a template, raising the question how histone modifications, for instance histone acetylation, influence origin firing. Initiation requires binding of the replication initiator, the Origin Recognition Complex (ORC), to a consensus sequence within origins. In addition, other proteins bind to recognition sites in the vicinity of ORC and support initiation. In previous work, we identified Sum1 as an origin-binding protein that contributes to efficient replication initiation. Sum1 is part of the Sum1/Rfm1/Hst1 complex that represses meiotic genes during vegetative growth via histone deacetylation by the histone deacetylase (HDAC) Hst1.     

2‐D DIGE analysis of the proteome of extracts from peanut variants reveals striking differences in major allergen contents

Over the last decade, an increasing prevalence of peanut allergies was observed worldwide. Peanuts are meanwhile categorized among the most dangerous food allergens. This is particularly relevant since peanut‐derived ingredients are widely used in industrial food production. To minimize the problem of hidden food allergens causing severe anaphylactic reactions, pre‐packaged food containing peanut components needs to be classified according to European ruling since 2005. Food companies search for strategies to reduce the allergenicity of peanut‐derived food additives either by genetically altering the allergen content or by identifying peanut varieties with low levels of major allergens. In our study, we focused on peanut extracts from Indonesia that apparently contain lower levels of the major Arachis hypogaea allergen 1 (Ara h 1). Basic extracts of Virginia‐type and Indonesian peanuts were compared by 1‐ and 2‐DE. We identified more than hundred individual components in these extracts by MS and provide a high‐resolution allergen map that also includes so far unknown fragments of major peanut allergens. The reduced level of Ara h 1 associated with a significantly lower abundance of the most potent peanut allergen Ara h 2 in various Indonesian peanuts was also confirmed by Western blotting with monoclonal antibodies and sera of allergic patients.