The Regulation and Function of Histone Methylation

Histones are wrapped around by genomic DNA to form nucleosomes which are the basic units of chromatin. In eukaryotes histones undergo various covalent modifications such as methylation, phosphorylation, acetylation, ubiquitination and ribosylation. Histone modifications play a fundamental role in the epigenetic regulation of gene expression in multicellular eukaryotes. Histone methylation is one of the most important modifications occurring on Lysine (K) and Arginine (R) residues of histones, dynamically regulated by histone methyltransferases and demethylases. Identifications of such histone modification enzymes and to study how they work are the most fundamental questions needs to be answered. Uncovering the regulation and functions of the various histone methylation enzymes will help us to better understand the epigenetic code. This review summarizes the regulation of histone methyltransferases activity, the recruitment of methyltransferases and the distribution patterns and function of histone methylations.     

Independence of stem and leaf hydraulic traits in six Euphorbiaceae tree species with contrasting leaf phenology

Hydraulic traits and hydraulic-related structural properties were examined in three deciduous (Hevea brasiliensis, Macaranga denticulate, and Bischofia javanica) and three evergreen (Drypetes indica, Aleurites moluccana, and Codiaeum variegatum) Euphorbiaceae tree species from a seasonally tropical forest in south-western China. Xylem water potential at 50% loss of stem hydraulic conductivity (P50_stem) was more negative in the evergreen tree, but leaf water potential at 50% loss of leaf hydraulic conductivity (P50_leaf) did not function as P50_stem did. Furthermore, P50_stem was more negative than P50_leaf in the evergreen tree; contrarily, this pattern was not observed in the deciduous tree. Leaf hydraulic conductivity overlapped considerably, but stem hydraulic conductivity diverged between the evergreen and deciduous tree. Correspondingly, structural properties of leaves overlapped substantially; however, structural properties of stem diverged markedly. Consequently, leaf and stem hydraulic traits were closely correlated with leaf and stem structural properties, respectively. Additionally, stem hydraulic efficiency was significantly correlated with stem hydraulic resistance to embolism; nevertheless, such a hydraulic pattern was not found in leaf hydraulics. Thus, these results suggest: (1) that the evergreen and deciduous tree mainly diverge in stem hydraulics, but not in leaf hydraulics, (2) that regardless of leaf or stem, their hydraulic traits result primarily from structural properties, and not from leaf phenology, (3) that leaves are more vulnerable to drought-induced embolism than stem in the evergreen tree, but not always in the deciduous tree and (4) that there exists a trade-off between hydraulic efficiency and safety for stem hydraulics, but not for leaf hydraulics.     

Subcellular localization of EGFR in esophageal carcinoma cell lines

Background: The EGF receptor is a therapeutic target in cancer cells, whereby mutations of EGFR and/or signalling members act as predictive markers. EGFR however also exhibits dynamic changes of subcellular localization, leading to STAT5 complex formation, nuclear translocation and induction of Aurora-A expression in squamous cancer cells. We previously described high EGFR and Aurora-A expression in esophageal cancer cells. Here, we investigated subcellular localization of EGFR and STAT5 in esophageal cancer cells. Results: Quantitative immunofluorescence analyses of four esophageal cancer cell lines reflecting esophageal squamous cell carcinomas (ESCC) and esophageal adenocarcinomas (EAC) revealed that the subcellular localization of EGFR was shifted from a membranous to cytoplasmic localization upon EGF-stimulation in OE21 (ESCC) cells. Thereby, EGFR in part co-localized with E-Cadherin. In parallel, phosphorylated STAT5-Tyr694 appeared to increase in the nucleus and to decrease at the cell membrane. In three additional cell lines, EGFR was only marginally (Kyse-410/ESCC; OE19/EAC) and weakly (OE33, EAC) detectable at the cell membrane. Partial co-localization of EGFR and E-Cadherin occurred in OE33 cells. Post EGF-stimulation, EGFR was detected in the cytoplasm, resembling endosomal compartments. Furthermore, OE19 and OE33 exhibited nuclear STAT5-Tyr694 phosphorylation upon EGF-stimulation. None of the four cell lines showed nuclear EGFR expression and localization. Conclusion: In contrast to other (squamous) cancer cells, activation of EGFR in esophageal squamous cancer cells does not result in nuclear translocation of EGFR. Still, the subcellular localization of EGFR may influence STAT5-associated signaling pathways in esophageal cancer cells and hence possibly also the responses to ErbB, respective EGFR-targeted therapies.     

Generation of <Emphasis Type="Italic">Vibrio anguillarum</Emphasis> Ghost by Coexpression of PhiX 174 Lysis <Emphasis Type="Italic">E</Emphasis> gene and Staphylococcal Nuclease <Emphasis Type="Italic">A</Emphasis> Gene

Vibrio anguillarum ghosts (VAG) were generated, for the first time, using a conjugation vector containing a ghost bacteria inducing cassette, pRK-λP_R-cI-Elysis, in which the expression of PhiX174 lysis gene E was controlled by the P _R /cI regulatory system of lambda phage. By scanning electron microscopy, holes ranging 80–200 nm in diameter were observed in the VAG. To avoid the presence of bacterial genomic DNA and an antibiotic resistance gene in the final VAG product, we constructed a new dual vector, pRK-λP_R-cI-E-SNA, containing the E-mediated lysis cassette and the staphylococcal nuclease A (SNA)-mediated DNA degradation cassette, and generated safety-enhanced VAG for use as a fish vaccine.     

Non-synonymous single nucleotide polymorphisms in the watermelon eIF4E gene are closely associated with resistance to <Emphasis Type="Italic">Zucchini yellow mosaic virus</Emphasis>

Zucchini yellow mosaic virus (ZYMV) is one of the most economically important potyviruses infecting cucurbit crops worldwide. Using a candidate gene approach, we cloned and sequenced eIF4E and eIF(iso)4E gene segments in watermelon. Analysis of the nucleotide sequences between the ZYMV-resistant watermelon plant introduction PI 595203 (Citrullus lanatus var. lanatus) and the ZYMV-susceptible watermelon cultivar ‘New Hampshire Midget’ (‘NHM’) showed the presence of single nucleotide polymorphisms (SNPs). Initial analysis of the identified SNPs in association studies indicated that SNPs in the eIF4E, but not eIF(iso)4E, were closely associated to the phenotype of ZYMV-resistance in 70 F₂ and 114 BC_1R progenies. Subsequently, we focused our efforts in obtaining the entire genomic sequence of watermelon eIF4E. Three SNPs were identified between PI 595203 and NHM. One of the SNPs (A241C) was in exon 1 and the other two SNPs (C309A and T554G) were in the first intron of the gene. SNP241 which resulted in an amino acid substitution (proline to threonine) was shown to be located in the critical cap recognition and binding area, similar to that of several plant species resistance to potyviruses. Analysis of a cleaved amplified polymorphism sequence (CAPS) marker derived from this SNP in F₂ and BC_1R populations demonstrated a cosegregation between the CAPS-2 marker and their ZYMV resistance or susceptibility phenotype. When we investigated whether such SNP mutation in the eIF4E was also conserved in several other PIs of C. lanatus var. citroides, we identified a different SNP (A171G) resulting in another amino acid substitution (D71G) from four ZYMV-resistant C. lanatus var. citroides (PI 244018, PI 482261, PI 482299, and PI 482322). Additional CAPS markers were also identified. Availability of all these CAPS markers will enable marker-aided breeding of watermelon for ZYMV resistance.     

Manipulation of <Emphasis Type="SmallCaps">l</Emphasis>-ascorbic acid biosynthesis pathways in <Emphasis Type="Italic">Solanum lycopersicum</Emphasis>: elevated GDP-mannose pyrophosphorylase activity enhances <Emphasis Type="SmallCaps">l</Emphasis>-ascorbate levels in red fruit

Ascorbate (AsA) plays a fundamental role in redox homeostasis in plants and animals, primarily by scavenging reactive oxygen species. Three genes, representing diverse steps putatively involved in plant AsA biosynthesis pathways, were cloned and independently expressed in Solanum lycopersicum (tomato) under the control of the CaMV 35S promoter. Yeast-derived GDP-mannose pyrophosphorylase (GMPase) and arabinono-1,4-lactone oxidase (ALO), as well as myo-inositol oxygenase 2 (MIOX2) from Arabidopsis thaliana, were targeted. Increases in GMPase activity were concomitant with increased AsA levels of up to 70% in leaves, 50% in green fruit, and 35% in red fruit. Expression of ALO significantly pulled biosynthetic flux towards AsA in leaves and green fruit by up to 54 and 25%, respectively. Changes in AsA content in plants transcribing the MIOX2 gene were inconsistent in different tissue. On the other hand, MIOX activity was strongly correlated with cell wall uronic acid levels, suggesting that MIOX may be a useful tool for the manipulation of cell wall composition. In conclusion, the Smirnoff–Wheeler pathway showed great promise as a target for biotechnological manipulation of ascorbate levels in tomato.     

Enzymatic Dehalogenation of Pentachlorophenol by <Emphasis Type="Italic">Pseudomonas fluorescens</Emphasis> of the Microbial Community from Tannery Effluent

Four different bacterial isolates obtained from a stable bacterial consortium were capable of utilizing pentachlorophenol (PCP) as sole carbon and energy source. The consortium was developed by continuous enrichment in the chemostat. The degradation of PCP by bacterial strain was preceded through an oxidative route as indicated by accumulation of tetrachloro-ρ-hydroquinone and dichlorohydroquinone as determined by high performance liquid chromatography (HPLC). Among the four isolates, Pseudomonas fluorescens exhibited maximum degradation capability and enzyme production. PCP-monooxygenase enzyme was extracted from culture extract and fractionated by DEAE-cellulose ion exchange chromatography. The molecular weight of the enzyme, purified from Pseudomonas fluorescens, determined by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and gel filtration chromatography was found to be 24,000 Da. Received: 22 July 2002 / Accepted: 23 September 2002     

Differential distribution and association of repeat DNA sequences in the lateral element of the synaptonemal complex in rat spermatocytes

The synaptonemal complex (SC) is an evolutionarily conserved structure that mediates synapsis of homologous chromosomes during meiotic prophase I. Previous studies have established that the chromatin of homologous chromosomes is organized in loops that are attached to the lateral elements (LEs) of the SC. The characterization of the genomic sequences associated with LEs of the SC represents an important step toward understanding meiotic chromosome organization and function. To isolate these genomic sequences, we performed chromatin immunoprecipitation assays in rat spermatocytes using an antibody against SYCP3, a major structural component of the LEs of the SC. Our results demonstrated the reproducible and exclusive isolation of repeat deoxyribonucleic acid (DNA) sequences, in particular long interspersed elements, short interspersed elements, long terminal direct repeats, satellite, and simple repeats. The association of these repeat sequences to the LEs of the SC was confirmed by in situ hybridization of meiotic nuclei shown by both light and electron microscopy. Signals were also detected over the chromatin surrounding SCs and in small loops protruding from the lateral elements into the SC central region. We propose that genomic repeat DNA sequences play a key role in anchoring the chromosome to the protein scaffold of the SC. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The promoter of the pepper pathogen-induced membrane protein gene <Emphasis Type="Italic">CaPIMP1</Emphasis> mediates environmental stress responses in plants

The promoter of the pepper pathogen-induced membrane protein gene CaPIMP1 was analyzed by an Agrobacterium-mediated transient expression assay in tobacco leaves. Several stress-related cis-acting elements (GT-1, W-box and ABRE) are located within the CaPIMP1 promoter. In tobacco leaf tissues transiently transformed with a CaPIMP1 promoter-β-glucuronidase (GUS) gene fusion, serially 5′-deleted CaPIMP1 promoters were differentially activated by Pseudomonas syringae pv. tabaci, ethylene, methyl jasmonate, abscisic acid, and nitric oxide. The −1,193 bp region of the CaPIMP1 gene promoter sequence exhibited full promoter activity. The −417- and −593 bp promoter regions were sufficient for GUS gene activation by ethylene and methyl jasmonate treatments, respectively. However, CaPIMP1 promoter sequences longer than −793 bp were required for promoter activation by abscisic acid and sodium nitroprusside treatments. CaPIMP1 expression was activated in pepper leaves by treatment with ethylene, methyl jasmonate, abscisic acid, β-amino-n-butyric acid, NaCl, mechanical wounding, and low temperature, but not with salicylic acid. Overexpression of CaPIMP1 in Arabidopsis conferred hypersensitivity to mannitol, NaCl, and ABA during seed germination but not during seedling development. In contrast, transgenic plants overexpressing CaPIMP1 exhibited enhanced tolerance to oxidative stress induced by methyl viologen during germination and early seedling stages. These results suggest that CaPIMP1 expression may alter responsiveness to environmental stress, as well as to pathogen infection. The nucleotide sequence data reported here has been deposited in the GenBank database under the accession number DQ356279.     

Nitric Oxide Signalling In Plants

Nitric oxide (NO) is an important molecule that acts in many tissues to regulate a diverse range of physiological processes. It is becoming apparent that NO is a ubiquitous signal in plants. Since the discovery of NO emission by plants in the 1970s, this gaseous compound has emerged as a major signalling molecule involved in multiple physiological functions. Research on NO in plants has gained significant awareness in recent years and there is increasing indication on the role of this molecule as a key-signalling molecule in plants. The investigations about NO in plants have been concentrated on three main fields: The search of NO or any source of NO generation, effects of exogenous NO treatments, NO transduction pathways. However we have limited information about signal transduction procedures by which NO interaction with cells results in altered cellular activities. This article reviews recent advances in NO synthesis and its signalling functions in plants. First, different sources and biosynthesis of NO in plants, then biological processes involving NO signalling are reviewed. NO signalling relation with cGMP, protein kinases and programmed cell death are also discussed. Besides, NO signalling in plant defense response is also examined. Especially NO signalling between animal and plant systems is compared.