Compréhension/acceptation de la radiothérapie : un dilemme éthique résolu par une éthique de la considération et de la sollicitude

PURPOSE

Ethical questions are poorly investigated specifically in radiation oncology. The objective of the study was to identify and understand the main ethical issue in radiation oncology.

MATERIALS AND METHODS

A quantitative analysis was based on the answers to a questionnaire of 200 professionals from 22 radiation oncology departments. The questionnaire mainly aimed to characterize the main ethical issue. A monocentric qualitative analysis was based on semi-structured interviews focused on the main identified ethical issue, carried out with eight technologists, and 20 patients undergoing radiotherapy.

RESULTS

The main ethical issue was the understanding and/or acceptance of the treatment by the patients (71 %), which frequently arises (more than once a month) (52 %), and corresponds to an ethical tension between the principles of respect for autonomy and beneficence (the good as viewed by the patient) as defined by Beauchamp and Childress. The technologists, wish the patient to be fully involved in his treatment, with the even possibility of refusing it. However, excluding paternalism and autonomic relentlessness, the technologists have the feeling of acting for the good of the patients by treating them with radiation, even if the patients are not always aware of it, because they are within a situation of vulnerability. If the hierarchy of principles is a compromise alternative, this problem is finally well resolved by the effective implementation of an ethic of consideration and solicitude, restoring the patient capabilities, i.e. the maximum development of his potentialities in his situation of vulnerability. Beyond the legal dimension, patient information is crucial and must consider the specific temporality of the patient.

CONCLUSION

The main ethical issue in radiation oncology is the understanding and/or acceptance of the treatment involving the development of an ethic of consideration and solicitude.

Distinct triterpene synthases in the laticifers of Euphorbia lathyris

Euphorbia lathyris was proposed about fifty years ago as a potential agroenergetic crop. The tremendous amounts of triterpenes present in its latex has driven investigations for transforming this particular biological fluid into an industrial hydrocarbon source. The huge accumulation of terpenes in the latex of many plant species represent a challenging question regarding cellular homeostasis. In fact, the enzymes, the mechanisms and the controllers that tune the amount of products accumulated in specialized compartments (to fulfill ecological roles) or deposited at important sites (as essential factors) are not known. Here, we have isolated oxidosqualene cyclases highly expressed in the latex of Euphorbia lathyris. This triterpene biosynthetic machinery is made of distinct paralogous enzymes responsible for the massive accumulation of steroidal and non-steroidal tetracyclic triterpenes. More than eighty years after the isolation of butyrospermol from shea butter (Heilbronn IM, Moffet GL, and Spring FS J. Chem. Soc. 1934, 1583), a butyrospermol synthase is characterized in this work using yeast and in folia heterologous expression assays.

Walking Responses of Tribolium castaneum (Coleoptera: Tenebrionidae) to Its Aggregation Pheromone and Odors of Wheat Infestations

The red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), is a worldwide pest of stored grains. Using "Y"-tube olfactometry we studied the response of T. castaneum to odors from simulated wheat infestations containing conspecifics, and infestations containing the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), and the granary weevil Sitophilus granarius (L.) (Coleoptera: Curculionidae). Tribolium castaneum larvae were significantly attracted to odors from all three test species. Tribolium castaneum adults were attracted to grains infested by R. dominica and flour infested by T. castaneum but repelled from grains infested by S. granarius. Further behavioral analysis with pheromones showed that T. castaneum were significantly attracted to their aggregation pheromone, dimethyldecanal (DMD), but not to the R. dominica aggregation pheromone, a mixture of dominicalure 1 and 2. Female T. castaneum adults were attracted to ∼50-fold less DMD than larvae and 100-fold less than male adults, suggesting they are more sensitive to DMD. This study improves our understanding of T. castaneum behaviors to infested grain volatile compounds and pheromones, and may help develop new control methods for grain pest species.

Formal thought disorder in schizophrenia and bipolar disorder: A systematic review and meta-analysis

Historically, formal thought disorder has been considered as one of the distinctive symptoms of schizophrenia. However, research in last few decades suggested that there is a considerable clinical and neurobiological overlap between schizophrenia and bipolar disorder (BP). We conducted a meta-analysis of studies comparing positive (PTD) and negative formal thought disorder (NTD) in schizophrenia and BP. We included 19 studies comparing 715 schizophrenia and 474 BP patients. In the acute inpatient samples, there was no significant difference in the severity of PTD (d = –0.07, CI = –0.22–0.09) between schizophrenia and BP. In stable patients, schizophrenia was associated with increased PTD compared to BP (d = 1.02, CI = 0.35–1.70). NTD was significantly more severe (d = 0.80, CI = 0.52–0.1.08) in schizophrenia compared to BP. Our findings suggest that PTD is a shared feature of both schizophrenia and BP but persistent PTD or NTD can distinguish subgroups of schizophrenia from BP and schizophrenia patients with better clinical outcomes.

Disclosure of interest

The authors have not supplied their declaration of competing interest.

Wine Aroma Concentration by Using a General Purpose simulator (ProSim)

In this work is proposed the application of the ProSim process simulator for the analysis of wine aroma concentration by performing a two-level simulation: First, ProSim is used to attain a preliminary design of a distillation tower, and afterward the simulator is employed to analyze the behavior of the tower in a more precise way. The UNIFAC model was used for nonideal behavior description of the mixtures. In this application, the concentration of a 13-compound mixture was simulated. In fact, the numerical methods implemented in ProSim made it possible to attain the convergence quickly even with minor compounds. The results obtained showed that the use of ProSim results to be very advantageous because it is timesaving and improvements are attained with respect to the specific programs developed by researchers.

Plant Sterol Diversity in Pollen from Angiosperms

Here we have examined the composition of free sterols and steryl esters of pollen from selected angiosperm species, as a first step towards a comprehensive analysis of sterol biogenesis in the male gametophyte. We detected four major sterol structural groups: cycloartenol derivatives bearing a 9β,19-cyclopropyl group, sterols with a double bond at C-7(8), sterols with a double bond at C-5(6), and stanols. All these groups were unequally distributed among species. However, the distribution of sterols as free sterols or as steryl esters in pollen grains indicated that free sterols were mostly Δ(5)-sterols and that steryl esters were predominantly 9β,19-cyclopropyl sterols. In order to link the sterol composition of a pollen grain at anthesis with the requirement for membrane lipid constituents of the pollen tube, we germinated pollen grains from Nicotiana tabacum, a model plant in reproductive biology. In the presence of radiolabelled mevalonic acid and in a time course series of measurements, we showed that cycloeucalenol was identified as the major neosynthesized sterol. Furthermore, the inhibition of cycloeucalenol neosynthesis by squalestatin was in full agreement with a de novo biogenesis and an apparent truncated pathway in the pollen tube.

Plant oxidosqualene metabolism: cycloartenol synthase-dependent sterol biosynthesis in Nicotiana benthamiana

The plant sterol pathway exhibits a major biosynthetic difference as compared with that of metazoans. The committed sterol precursor is the pentacyclic cycloartenol (9β,19-cyclolanost-24-en-3β-ol) and not lanosterol (lanosta-8,24-dien-3β-ol), as it was shown in the late sixties. However, plant genome mining over the last years revealed the general presence of lanosterol synthases encoding sequences (LAS1) in the oxidosqualene cyclase repertoire, in addition to cycloartenol synthases (CAS1) and to non-steroidal triterpene synthases that contribute to the metabolic diversity of C30H50O compounds on earth. Furthermore, plant LAS1 proteins have been unambiguously identified by peptidic signatures and by their capacity to complement the yeast lanosterol synthase deficiency. A dual pathway for the synthesis of sterols through lanosterol and cycloartenol was reported in the model Arabidopsis thaliana, though the contribution of a lanosterol pathway to the production of 24-alkyl-Δ(5)-sterols was quite marginal (Ohyama et al. (2009) PNAS 106, 725). To investigate further the physiological relevance of CAS1 and LAS1 genes in plants, we have silenced their expression in Nicotiana benthamiana. We used virus induced gene silencing (VIGS) based on gene specific sequences from a Nicotiana tabacum CAS1 or derived from the solgenomics initiative (http://solgenomics.net/) to challenge the respective roles of CAS1 and LAS1. In this report, we show a CAS1-specific functional sterol pathway in engineered yeast, and a strict dependence on CAS1 of tobacco sterol biosynthesis.

Supercritical fluid extraction of resveratrol from grape skin of Vitis vinifera and determination by HPLC

Supercritical fluid extraction of resveratrol from grape skin of Vitis vinifera was studied. Extraction variables such pressure, modifier concentration (ethanol), and extraction time were optimised. Final extraction conditions were: 40 degrees C, 150 bar, 7.5% ethanol and extraction time 15 min. Extraction recovery and precision (variation coefficient between 0.2 and 1.0%) were calculated. The resveratrol content in the ethanolic extract was determined by HPLC with UV detection at 306 nm. Acetic acid-methanol-water was used as the mobile phase, and C-18 and C-8 columns were tested, instrumental parameters were optimised, and analytical parameters were calculated (lineal interval 0-75 mg l(-1), detection limit 0.1 mg l(-1), sensitivity 125530 mg(-1) mg l(-1), coefficient variation 0.8-1.6%). Six different varieties of grape skin, from the same geographical area and representative of the wine elaboration, were analysed.

Phosphoproteome exploration reveals a reformatting of cellular processes in response to low sterol biosynthetic capacity in Arabidopsis

Sterols are membrane-bound isoprenoid lipids that are required for cell viability and growth. In plants, it is generally assumed that 3-hydroxy-3-methylglutaryl-CoA-reductase (HMGR) is a key element of their biosynthesis, but the molecular regulation of that pathway is largely unknown. In an attempt to identify regulators of the biosynthetic flux from acyl-CoA toward phytosterols, we compared the membrane phosphoproteome of wild-type Arabidopsis thaliana and of a mutant being deficient in HMGR1. We performed a N-terminal labeling of microsomal peptides with a trimethoxyphenyl phosphonium (TMPP) derivative, followed by a quantitative assessment of phosphopeptides with a spectral counting method. TMPP derivatization of peptides resulted in an improved LC-MS/MS detection due to increased hydrophobicity in chromatography and ionization efficiency in electrospray. The phosphoproteome coverage was 40% higher with this methodology. We further found that 31 proteins were in a different phosphorylation state in the hmgr1-1 mutant as compared with the wild-type. One-third of these proteins were identified based on novel phosphopeptides. This approach revealed that phosphorylation changes in the Arabidopsis membrane proteome targets major cellular processes such as transports, calcium homeostasis, photomorphogenesis, and carbohydrate synthesis. A reformatting of these processes appears to be a response of a genetically reduced sterol biosynthesis.

Modeling of the process of moisture loss during the storage of dried apricots

Moisture content is a reference parameter for dried food because the growth of most microorganisms is inhibited below certain water activity levels. In addition, it has a determining influence on the evolution of important parameters, such as color and flavor, and on other properties and deterioration reactions, such as texture, oxidation processes and nutritional value. During the storage of some dried fruits, moisture is produced due to Maillard reactions and exchanged with the surrounding environment through the packaging. The evolution of dried foods during their shelf life depends on the storage conditions. The aim of this study is to analyze the evolution of the moisture content in dried apricots packaged in different types of containers, namely glass and thermosealed polypropylene trays. The samples were stored at constant temperatures: 5, 15, 25 and 35 °C and were analyzed periodically over a period of 12 months. The sorption isotherms of apricots used in this study were also determined. In order to model how the moisture evolved, an empirical kinetic model was tested. This model considers both water transfer from the fruit and also water production as a result of the Maillard processes. The explained variance was higher than 95% in the samples stored in trays, which were thermosealed with film.

Involvement of the phospholipid sterol acyltransferase1 in plant sterol homeostasis and leaf senescence

Genes encoding sterol ester-forming enzymes were recently identified in the Arabidopsis (Arabidopsis thaliana) genome. One belongs to a family of six members presenting homologies with the mammalian Lecithin Cholesterol Acyltransferases. The other one belongs to the superfamily of Membrane-Bound O-Acyltransferases. The physiological functions of these genes, Phospholipid Sterol Acyltransferase1 (PSAT1) and Acyl-CoA Sterol Acyltransferase1 (ASAT1), respectively, were investigated using Arabidopsis mutants. Sterol ester content decreased in leaves of all mutants and was strongly reduced in seeds from plants carrying a PSAT1-deficient mutation. The amount of sterol esters in flowers was very close to that of the wild type for all lines studied. This indicated further functional redundancy of sterol acylation in Arabidopsis. We performed feeding experiments in which we supplied sterol precursors to psat1-1, psat1-2, and asat1-1 mutants. This triggered the accumulation of sterol esters (stored in cytosolic lipid droplets) in the wild type and the asat1-1 lines but not in the psat1-1 and psat1-2 lines, indicating a major contribution of the PSAT1 in maintaining free sterol homeostasis in plant cell membranes. A clear biological effect associated with the lack of sterol ester formation in the psat1-1 and psat1-2 mutants was an early leaf senescence phenotype. Double mutants lacking PSAT1 and ASAT1 had identical phenotypes to psat1 mutants. The results presented here suggest that PSAT1 plays a role in lipid catabolism as part of the intracellular processes at play in the maintenance of leaf viability during developmental aging.

The DING family of proteins: ubiquitous in eukaryotes, but where are the genes?

PstS and DING proteins are members of a superfamily of secreted, high-affinity phosphate-binding proteins. Whereas microbial PstS have a well-defined role in phosphate ABC transporters, the physiological function of DING proteins, named after their DINGGG N termini, still needs to be determined. PstS and DING proteins co-exist in some Pseudomonas strains, to which they confer a highly adhesive and virulent phenotype. More than 30 DING proteins have now been purified, mostly from eukaryotes. They are often associated with infections or with dysregulation of cell proliferation. Consequently, eukaryotic DING proteins could also be involved in cell-cell communication or adherence. The ubiquitous presence in eukaryotes of proteins structurally and functionally related to bacterial virulence factors is intriguing, as is the absence of eukaryotic genes encoding DING proteins in databases. DING proteins in eukaryotes could originate from unidentified commensal or symbiotic bacteria and could contribute to essential functions. Alternatively, DING proteins could be encoded by eukaryotic genes sharing special features that prevent their cloning. Both hypotheses are discussed.

For whom the bell tolls? DING proteins in health and disease

DING proteins, identified mainly by their eponymous N-terminal sequences, are ubiquitous in living organisms. Amongst bacteria, they are common in pseudomonads, and have been characterised with respect to genetics and structure. They form part of a wider family of phosphate-binding proteins, with emerging roles in phosphate acquisition and pathogenicity. Many DING proteins have been isolated in eukaryotes, in which they have been associated with very diverse biological activities, often in the context of possible signalling roles. Disease states in which DING proteins have been implicated include rheumatoid arthritis, lithiasis, atherosclerosis, some tumours and tumour-associated cachexia, and bacterial and viral adherence. Complete genetic and structural characterisation of eukaryotic DING genes and proteins is still lacking, though the phosphate-binding site seems to be conserved. Whether as bacterial proteins related to bacterial pathogenicity, or as eukaryotic components of biochemical signalling systems, DING proteins require further study.

Proteins related to St. John's Wort p27SJ, a suppressor of HIV-1 expression, are ubiquitous in plants

Proteins belonging to the family of DING proteins are ubiquitous in animals and several of them are associated with various diseases. Their presence in a few plant species has previously been reported and the St John's Wort DING protein was recently described as an inhibitor of HIV replication and transcription. However, data about DING protein occurrence in plants and their biochemical properties remain almost nonexistent. We describe methods for the purification of DING proteins from plants that may have general applicability since they are not dependent upon specific affinity ligands, contrary to previously described protocols. Cibacron Blue chromatography, sometimes preceded by an ion-exchange chromatographic step, is suitable for most plant extracts. DING proteins were purified from various species and cell types and their identity was confirmed immunologically and, in some cases, by N-terminal sequence analysis, indicating that they are ubiquitous in the plant kingdom. They are associated with the cell wall and sometimes secreted in the medium for in vitro grown cells. High-molecular-weight DING precursors were often observed. Internal peptides were also sequenced, as a prelude to gene cloning experiments.

Characterization of wheat germin (oxalate oxidase) expressed by Pichia pastoris

High-level secretory expression of wheat (Triticum aestivum) germin/oxalate oxidase was achieved in Pichia pastoris fermentation cultures as an alpha-mating factor signal peptide fusion, based on the native wheat cDNA coding sequence. The oxalate oxidase activity of the recombinant enzyme is substantially increased (7-fold) by treatment with sodium periodate, followed by ascorbate reduction. Using these methods, approximately 1 g (4x10(4) U) of purified, activated enzyme was obtained following eight days of induction of a high density Pichia fermentation culture, demonstrating suitability for large-scale production of oxalate oxidase for biotechnological applications. Characterization of the recombinant protein shows that it is glycosylated, with N-linked glycan attached at Asn47. For potential biomedical applications, a nonglycosylated (S49A) variant was also prepared which retains essentially full enzyme activity, but exhibits altered protein-protein interactions.

Découverte et structure cristallographique d’une apolipoprotéine humaine

We report the serendipitous discovery of a human plasma phosphate binding protein (HPBP). This 38 kDa protein is co-purified with paraoxonase (PON1). The association between HPON1 and HPBP is modulated by phosphate and calcium concentrations. The HPBP X-ray structure solved at 1.9 A resolution is similar to the prokaryotic phosphate solute-binding proteins (SBPs) associated with ATP binding cassette transmembrane transporters, though phosphate-SBPs have never been characterized or predicted from nucleic acid databases in eukaryotes. However, HPBP belongs to the family of ubiquitous eukaryotic proteins named DING, meaning that phosphate-SBPs are also widespread in eukaryotes. The absence of complete genes for eukaryotic phosphate-SBP from databases is intriguing, but the astonishing 90% sequence conservation of genes between evolutionary distant species suggests that the corresponding proteins play an important function. HPBP is the first identified transporter capable of binding phosphate ions in human plasma. Thus it is thought to become a new predictor and a potential therapeutic agent for phosphate-related diseases such as atherosclerosis.

DING proteins; novel members of a prokaryotic phosphate-binding protein superfamily which extends into the eukaryotic kingdom

PstS proteins are the cell-bound phosphate-binding elements of the ubiquitous bacterial ABC phosphate uptake mechanisms. Primary and tertiary structures, characteristic of pstS proteins, are conserved in proteins, which are expressed in secretory operons and induced by phosphate deprivation, in Pseudomonas species. There are two subsets of these proteins; AP proteins, which are alkaline phosphatases, and DING proteins, named for their N-terminal sequence, which are phosphate-binding proteins. Both form elements of a proposed phosphate-scavenging system in pseudomonads. DING proteins have also been isolated from many eukaryotic sources, and are associated with both normal and pathological functions in mammals. Their phosphate-binding function suggests a role in biomineralization, but the ability to bind other ligands may be related to signal transduction in eukaryotes. Though it has been claimed that all such proteins may originate from pseudomonads, many eukaryotic DING proteins have unique features which are incompatible with a bacterial origin.

Serendipitous discovery and X-ray structure of a human phosphate binding apolipoprotein

We report the serendipitous discovery of a human plasma phosphate binding protein (HPBP). This 38 kDa protein is copurified with the enzyme paraoxonase. Its X-ray structure is similar to the prokaryotic phosphate solute binding proteins (SBPs) associated with ATP binding cassette transmembrane transporters, though phosphate-SBPs have never been characterized or predicted from nucleic acid databases in eukaryotes. However, HPBP belongs to the family of ubiquitous eukaryotic proteins named DING, meaning that phosphate-SBPs are also widespread in eukaryotes. The systematic absence of complete genes for eukaryotic phosphate-SBP from databases is intriguing, but the astonishing 90% sequence conservation between genes belonging to evolutionary distant species suggests that the corresponding proteins play an important function. HPBP is the only known transporter capable of binding phosphate ions in human plasma and may become a new predictor of or a potential therapeutic agent for phosphate-related diseases such as atherosclerosis.

Proteome analysis differentiates between two highly homologues germin-like proteins in Arabidopsis thaliana ecotypes Col-0 and Ws-2

A proteome approach based on 2-D gel electrophoresis (2-DE) was used to compare the protein patterns of the Arabidopsis ecotypes Col-0 and Ws-2. In leaf extracts a pair of protein spots were found to be diagnostic for each of the lines. Both pairs of spots were identified as closely related germin-like proteins differing in only one amino acid by using peptide mass finger printing of tryptic digests and by gaining additional data from post-source decay spectra in the MALDI-TOF analysis. Western blot analysis after separation of protein extracts by 2-DE confirmed results from Coomassie blue-stained gels and revealed additional immunoreactive spots for both ecotypes most likely representing dimers of the spots first identified. Western blot analysis and mass spectrometrical identification of the corresponding weakly stained protein in Coomassie blue-stained gels of the ecotype Col-0 also demonstrated for the first time the occurrence of AtGER3 protein in root extracts. Our results demonstrate the capacity of proteome analysis to analyse and distinguish closely related members of large protein families.

Allergologic exploration of germins and germin-like proteins, a new class of plant allergens

BACKGROUND

Germins and the related germin-like proteins (GLPs) are glycoproteins expressed in many plants in response to biotic and abiotic stress. To test the potential impact of germins and GLPs, recombinant germin from Triticum aestivum (tGermin) and GLPs from Arabidopsis thaliana (tGLP), both produced in transformed tobacco plants, were used.

METHODS

Sera from 82 patients with type I allergy to birch, grass or mugwort pollen and/or wheat were tested in immunoblot for IgE binding to tGermin and tGLP, and the IgE reactivity after chemical and enzymatic deglycosylation was analysed. The biological activity of tGermin and tGLP was determined in a histamine release assay and in skin prick testing (SPT).

RESULTS

In an immunoblotting assay, 24 out of 82 tested sera (29.26%) from allergic patients showed IgE-binding to tGermin, and 18 of these sera (21.95%) displayed also IgE-binding to tGLP. The deglycosylation experiments indicated that glycan moieties contribute significantly to the IgE-binding of tGermin and tGLP. Both tGermins and tGLP induced specifically histamine release in an in vitro assay as well as in SPT.

CONCLUSION

Our in vitro and in vivo findings demonstrate that germin and GLPs are capable to bind IgE most likely via carbohydrate determinants, and represent allergenic molecules.

Ring up the curtain on DING proteins

DING proteins have a characteristic DINGGG- or closely related N-terminal sequence. One is found in human synovial fluid, and may be associated with rheumatoid arthritis. Other examples have receptor or signalling roles in various human and animal cells, or are involved in biomineralisation, and several of them bind to phytochemicals. As plant DING proteins have recently been discovered, we hypothesise that the DING protein-phytochemical association may represent one aspect of a ubiquitous receptor-linked signalling system. Several microbial proteins related to DING proteins have phosphatase activity, which may relate to biomineralisation in eukaryotic systems. Plant DING proteins and their microbial relatives may elicit allergic responses leading to arthritic disease.

Functional consequences of integrin gene mutations in mice

Integrins are cell-surface receptors responsible for cell attachment to extracellular matrices and to other cells. The application of mouse genetics has significantly increased our understanding of integrin function in vivo. In this review, we summarize the phenotypes of mice carrying mutant integrin genes and compare them with phenotypes of mice lacking the integrin ligands.

Arabidopsis thaliana germin-like proteins: common and specific features point to a variety of functions

Germin-like proteins (GLPs) are ubiquitous plant proteins encoded by diverse multigene families. It is not known whether they share germin's unusual biochemical properties and oxalate oxidase activity. Using specific antibodies, we have studied three GLPs (AtGER1. AtGER2 and AtGER3) in Arabidopsis thaliana (L.) Heynh. as well as in transgenic tobacco (Nicotiana tabacum L.) plants overexpressing these proteins. Like wheat ( Triticum aestivum L.) germin, these Arabidopsis GLPs are associated with the extracellular matrix (ECM) and they also seem to exist as two glycosylated isoforms. However, none of them is an oxalate oxidase. Although GLPs display several conserved features, each has its specific characteristics. Both AtGER2 and AtGER3 are oligomeric proteins that share germin's resistance to pepsin and to dissociation by heat and SDS. In contrast, AtGER1 seems to exist as a monomer. The GLPs may interact with the ECM in a variety of ways, since each is efficiently extracted by different conditions. In addition, germins and GLPs all bind Cibacron Blue, a dye often but not exclusively used for the purification of enzymes having nucleotide cofactors. In the case of AtGER2, binding to the dye is so tight that it almost allows a one-step purification of this protein. The variety of sequences, expression patterns and biochemical features indicates that GLPs could be a class of receptors localized in the ECM and involved in physiological and developmental processes as well as stress response.

Regulation by biotic and abiotic stress of a wheat germin gene encoding oxalate oxidase, a H2O2-producing enzyme

Germins and germin-like proteins (GLPs) constitute a ubiquitous family of plant proteins that seem to be involved in many developmental and stress-related processes. Wheat germin has been extensively studied at the biochemical level: it is found in the apoplast and the cytoplasm of germinating embryo cells and it has oxalate oxidase activity (EC 1.2.3.4). Germin synthesis can also be induced in adult wheat leaves by auxins and by a fungal pathogen but it remains to be determined whether the same gene is involved in developmental, hormonal and stress response. In this work, we have studied the expression of one of the wheat germin genes, named gf-2.8, in wheat as well as in transgenic tobacco plants transformed with either this intact gene or constructs with GUS driven by its promoter. This has allowed us to demonstrate that expression of this single gene is both developmentally and pathogen-regulated. In addition, we show that expression of the wheat gf-2.8 germin gene is also stimulated by some abiotic stresses, especially the heavy metal ions Cd2+, Cu2+ and Co2+. Several chemicals involved in stress signal transduction pathways were also tested: only polyamines were shown to stimulate expression of this gene. Because regulation of the wheat gf-2.8 germin gene is complex and because its product results in developmental and stress-related release of hydrogen peroxide in the apoplast, it is likely that it plays an important role in several aspects of plant growth and defence mechanisms.

cDNA sequence, genomic organization and differential expression of three Arabidopsis genes for germin/oxalate oxidase-like proteins

Wheat germin is a protein expressed during germination which possesses an oxalate oxidase activity. Germin-type oxalate oxidases have been extensively studied in monocotyledons (wheat and barley) where they are thought to have important functions for development, stress response and defence against pathogens. In contrast, almost nothing is known about the germin-like proteins found in dicotyledons, gymnosperms and myxomycetes. In this work, cDNA clones for three genes (ATGER1, ATGER2 and ATGER3) encoding germin-like proteins, initially characterized as expressed sequence tags (ESTs), from Arabidopsis thaliana cDNA libraries were further characterized. In addition, we isolated and sequenced a Brassica napus cDNA which was strongly homologous to the cDNA for ATGER1. Sequence analysis and secondary structure predictions of the proteins encoded by these cDNAs showed that they possess all the characteristic features of members of the germin family and of the germin/seed globulins/sucrose binding protein superfamily. Sequence comparisons and mapping demonstrated the existence of at least two different gene families in the A. thaliana genome encoding a minimum of three genes for germins. These three genes have been mapped in three different location on the Arabidopsis genome. By northern blot hybridizations we found that these genes are differentially regulated. ATGER1 was expressed during germination, like wheat germin, but also in leaves whereas ATGER2 transcripts were exclusively found in developing embryos, like wheat pseudo-germin. ATGER3 mRNAs were found in leaves and flowers and their abundance was shown to vary during the circadian cycle.

Regulated expression of a wheat germin gene in tobacco: oxalate oxidase activity and apoplastic localization of the heterologous protein

Wheat (Triticum aestivum) germin is a homopentameric glycoprotein whose synthesis is allied with seed germination. Germin pentamers show an unusual resistance to dissociation and possess an oxalate oxidase (OxO) activity. In order to increase our knowledge of germin gene expression, the function(s) of germin during development and possible uses in plant genetic engineering, an in vivo expression system is required. To this end, a gene for germin, named gf-2.8, was studied by expressing either promoter-GUS fusions or the intact gene in transgenic tobacco (Nicotiana tabacum) plants. Heterologous gene transcription was monitored in vitro and in vivo by GUS or OxO activity and was found to occur in developing seeds and in seedlings. This transcription was stimulated by auxins, as would be expected because of the presence of putative auxin-responsive elements in the promoter of the gf-2.8 gene. Auxin stimulation also extended to young leaves since OxO activity could be detected in treated but not in untreated leaves. The biochemical characteristics of wheat germin were also conserved in a transgenic host: the OxO activity was present under the form of a doublet co-migrating with germin G and G' isoforms. Also, germin distributed between a soluble and an apoplastic fractions despite the fact that wheat cell wall substantially differs from tobacco cell wall. Therefore, tobacco constitutes a suitable host for in vivo studies of this monocotyledon gene.

Mapping of the RNA-binding domain of the alfalfa mosaic virus movement protein

In-frame contiguous deletions were created in the movement protein gene of alfalfa mosaic virus by site-directed mutagenesis. The mutated movement proteins were expressed in Escherichia coli, extracted and then purified by denaturing gel electrophoresis and then renatured. Their binding ability with RNA was assayed by electrophoretic retardation and u.v.-crosslinking. Results indicated that a domain included within amino acids 36 to 81 was necessary for RNA binding.

Effect of the alfalfa mosaic virus movement protein expressed in transgenic plants on the permeability of plasmodesmata

Symplastic transport of different sized fluorescent probes has been assessed in leaf epidermal cells of transgenic Nicotiana plants expressing the movement protein (MP) of alfalfa mosaic virus (AMV). In both N. tabacum and N. benthamiana, the size exclusion limit (SEL) of plasmodesmata increased from M(r) 1000, which represents the commonly accepted limit, to over 4.4K. However, in control plants, movement of a 3K probe was seen in 11 to 22% of the injections, indicating that plasmodesmata may on occasion allow the passage of molecules larger than was previously thought. The increase of SEL due to the presence of the AMV MP, although significant, remains insufficient to permit the passage of viral particles and the possibility of other mechanisms involved in viral cell-to-cell spread is discussed.

An N-proximal sequence of the alfalfa mosaic virus movement protein is necessary for association with cell walls in transgenic plants

We have made transgenic tobacco plants (Nicotiana tabacum, cv. Xanthi nc) expressing the movement protein (P3, 300 amino acids) of alfalfa mosaic virus (A1MV) and two N-terminally deleted proteins lacking respectively 12 and 77 amino acids of the P3 sequence (P3 delta[1-12] and P3 delta[1-77]). The same proteins were expressed in recombinant yeast. By subcellular fractionation, the full-length P3 protein expressed by transgenic plants was found to be associated with cell walls as well as with cytoplasmic particulate material, as was the wild type movement protein expressed by A1MV-infected tobacco plants. P3 delta[1-12] behaved similarly but P3 delta[1-77] was found only in the cytoplasm. It thus appears that a polypeptide domain located between amino acids 13 and 77 of the P3 sequence is necessary for association of the protein with cell walls.

Nucleic acid-binding properties of the alfalfa mosaic virus movement protein produced in yeast

The movement protein of alfalfa mosaic virus (P3) was purified from yeasts transformed with an expression vector containing the P3 gene. Its nucleic acid-binding properties were tested by electrophoretic retardation, nitrocellulose retention, and RNA-protein cross-linking. The recombinant protein had a higher affinity for single-stranded RNA and DNA than for double-stranded nucleic acids. Each nucleic acid molecule bound several protein molecules without sequence specificity. The binding was 80% inhibited by 0.2 M NaCl. These properties are qualitatively similar, but not strictly identical, to those of two other viral movement proteins, the 30-kDa protein of tobacco mosaic virus and the gene I product of cauliflower mosaic virus.

Effects of terminal deletion mutations on function of the movement protein of tobacco mosaic virus

A series of carboxy- and amino-terminal deletion mutations in the movement protein (MP) gene of tobacco mosaic virus (TMV) were ligated into a cloned TMV cDNA deleted for the endogenous MP gene. RNA transcripts were produced in vitro from clones carrying the various mutated MP genes. The effect of the deletion mutations on local and systemic movements of the infection was evaluated. Deletion of 9 or 33 amino acids from the carboxy terminus of the movement protein did not effect cell-to-cell movement as reflected by local lesion formation on Nicotiana tabacum cv. Xanthi NN plants. Deletion of 55 amino acids resulted in impaired MP that supported the formation of local lesions of 1 mm in diameter compared to lesions of 3-5 mm caused by the wild-type MP. Deletion of 74 amino acids (or more) from the carboxy terminus resulted in a protein that could not support virus movement. Modified viruses that contained repeated sequences in the 3' region of the MP gene lost the repeated sequences during replication and reverted to the wild type. This was evidenced by the size of the MP produced and by sequence analysis of reverse-transcribed PCR-amplified products, following infection by the modified virus. MP deleted for as few as 3 amino acids at the amino terminus could not support virus movement thus indicating that the amino-terminal domain is critical for MP activity.

The TMV movement protein: role of the C-terminal 73 amino acids in subcellular localization and function

The role of the C-terminal one-third of the tobacco mosaic virus (TMV) 30-kDa movement protein (MP) on its subcellular localization and on virus spread was investigated. We have constructed eight cDNAs encoding MPs with variable size deletions from the C-terminal end. Expression of the truncated proteins was verified in recombinant yeast using an antiserum directed to a synthetic peptide corresponding to 21 amino acids near the N-terminal end of the MP. In transgenic tobacco plants, MP from which more than 55 amino acids were deleted no longer accumulated in the cell wall fraction of a cellular extract, where the complete MP accumulates. Dye diffusion studies showed that both unmodified and modified MPs that accumulate in the cell wall fraction are able to alter plasmodesmatal size exclusion limits. Biological function of the modified MPs was tested in the transgenic plants with the TMV thermosensitive mutant Ls1 and a TMV genomic RNA transcript lacking a functional MP. There was a correlation between the cell wall localization of the modified MPs and its ability to potentiate virus spread. The results presented here demonstrate the dispensability of the C-terminal 55 amino acids of the MP in its subcellular localization in tobacco plants and its role in virus movement. Moreover, our results show that a stretch of 19 amino acids (195 to 213) is essential for localization of the MP to the cell wall fraction of plant cells.