Preformed expression of defense is a hallmark of partial resistance to rice blast fungal pathogen Magnaporthe oryzae

Background: Partial resistance to plant pathogens is extensively used in breeding programs since it could contribute to resistance durability. Partial resistance often builds up during plant development and confers quantitative and usually broad-spectrum resistance. However, very little is known on the mechanisms underlying partial resistance. Partial resistance is often explained by poorly effective induction of plant defense systems. By exploring rice natural diversity, we asked whether expression of defense systems before infection could explain partial resistance towards the major fungal pathogen Magnaporthe oryzae. The constitutive expression of 21 defense-related genes belonging to the defense system was monitored in 23 randomly sampled rice cultivars for which partial resistance was measured. Results: We identified a strong correlation between the expression of defense-related genes before infection and partial resistance. Only a weak correlation was found between the induction of defense genes and partial resistance. Increasing constitutive expression of defense-related genes also correlated with the establishment of partial resistance during plant development. Some rice genetic sub-groups displayed a particular pattern of constitutive expression, suggesting a strong natural polymorphism for constitutive expression of defense. Constitutive levels of hormones like salicylic acid and ethylene cannot explain constitutive expression of defense. We could identify an area of the genome that contributes to explain both preformed defense and partial resistance. Conclusion: These results indicate that constitutive expression of defense-related genes is likely responsible for a large part of partial resistance in rice. The finding of this preformed defense system should help guide future breeding programs and open the possibility to identify the molecular mechanisms behind partial resistance. ( Résumé d'auteur

Crosstalks between Myo-Inositol Metabolism, Programmed Cell Death and Basal Immunity in Arabidopsis

BACKGROUND: Although it is a crucial cellular process required for both normal development and to face stress conditions, the control of programmed cell death in plants is not fully understood. We previously reported the isolation of ATXR5 and ATXR6, two PCNA-binding proteins that could be involved in the regulation of cell cycle or cell death. A yeast two-hybrid screen using ATXR5 as bait captured AtIPS1, an enzyme which catalyses the committed step of myo-inositol (MI) biosynthesis. atips1 mutants form spontaneous lesions on leaves, raising the possibility that MI metabolism may play a role in the control of PCD in plants. In this work, we have characterised atips1 mutants to gain insight regarding the role of MI in PCD regulation. METHODOLOGY/PRINCIPAL FINDINGS: - lesion formation in atips1 mutants depends of light intensity, is due to PCD as evidenced by TUNEL labelling of nuclei, and is regulated by phytohormones such as salicylic acid - MI and galactinol are the only metabolites whose accumulation is significantly reduced in the mutant, and supplementation of the mutant with these compounds is sufficient to prevent PCD - the transcriptome profile of the mutant is extremely similar to that of lesion mimic mutants such as cpr5, or wild-type plants infected with pathogens. CONCLUSION/SIGNIFICANCE: Taken together, our results provide strong evidence for the role of MI or MI derivatives in the regulation of PCD. Interestingly, there are three isoforms of IPS in Arabidopsis, but AtIPS1 is the only one harbouring a nuclear localisation sequence, suggesting that nuclear pools of MI may play a specific role in PCD regulation and opening new research prospects regarding the role of MI in the prevention of tumorigenesis. Nevertheless, the significance of the interaction between AtIPS1 and ATXR5 remains to be established

Comportement des fongicides au niveau des relations hote parasite : invited paper

Jusqu'à présent, les fongicides ont été considérés comme des agents létaux pour les champignons in vitro et in vivo. Depuis quelques années une solution alternative a été envisagée, par l'emploi de nouveaux pesticides qui agissent sur la maladie elle-même. De tels composés interfèrent avec les processus de la pathogenèse, les modalités de l'agression par les parasites et les mécanismes de défense de la plante. Une perturbation provoquée à ces différents niveaux pourrait être gérée utilement pour la protection des cultures. L'exploitation de ces nouvelles possibilités dans un futur proche est analysée. (Résumé d'auteur

Effect of oxide fluxes on activation mechanisms of tungsten inert gas process

Activated tungsten inert gas (TIG) welding, which involves the deposition of an inorganic powder on the metal surface prior welding, improves TIG welding performances in terms of weld bead penetration. Most common commercial fluxes contain halides and oxides. The present paper focuses on fluxes made of oxides. It appears that oxides have two different effects: one on the fusion zone chemistry and the other on the electric arc behaviour. First, oxygen reverses the Marangoni convection movements that become centripetal, contributing thus to increase ‘D'penetration. On the other hand, oxides may cause an increase in the energy flux density transferred by the arc to the metal. The characterisation of the arc plasma by optical emission spectroscopy suggests that oxides do not increase the arc temperature. It is established that the oxide effects by Marangoni convection appear for a critical value of the welding energy, whereas the oxide effects on the electrical arc exist irrespective of the welding energy value

FRACTURE BEHAVIOUR OF QUENCHED NICKEL DURING SULFUR SEGREGATION ANNEALINGS

La ségrégation intergranulaire du soufre provoque la fragilité intergranulaire du nickel. Cette fragilité résultant d'une ségrégation d'équilibre a été corrélée à la concentration du soufre dans le joint de grain du nickel. Nous présentons ici des résultats de fragilité intergranulaire du nickel, conséquence d'une ségrégation dynamique : ségrégation induite par un flux de lacunes de trempe. En raison de l'absence de trempe à coeur, la fragilité n'apparaît qu'au voisinage de la surface. Sur des matériaux plus minces, la fragilité apparaît dans toute la masse du nickel, avec une cinétique environ 1000 fois supérieure à celle observée à l'issue d'un mécanisme d'équilibre. Cette fragilité se restaure également avec une cinétique 1000 fois plus grande.The intergranular segregation of sulfur is responsible for the intergranular brittleness of nickel. These results, established as a consequence of equilibrium segregation, show a perfect correlation between intergranular brittleness and intergranular sulfur segregation. We present here, similar results concerning interganular segregations resulting from a non-equilibrium mechanism (segregation due to quenched-in vacancies). Through the usual criterion (strain to failure), the nickel is not brittle if it is too thick : in the absence of quenched-in vacancies in the core of the specimen, the brittleness appears only in the vicinity of the surface. With thinner samples, we observe a total embrittlement with a kinetic 1000 times faster than those resulting from an equilibrium mechanism. This embrittlement vanishes with the same kinetic recovering the ductility

Experimental validation of an electro-thermo-metallurgical predictive model in resistance spot welding

In order to address spot welding numerical simulation of high strength steel, the validation of the model developed by the author in collaboration with PSA inc. using thermal kinetics measured within electrodes and sheets is described. The instrumentation techniques experimented here on either zinc coated or bare sheet assemblies aim at hindering interferences inevitably generated by the installation of intrusive sensors. Numerical and experimental results are compared for shape and size of welding spots, thermal kinetics and microstructures. All hypotheses and data sets considered to define interfacial conditions are then discussed

Ségrégation du soufre à la surface d'un matériau multicouche. Rôle du platine dans l'écaillage des couches d'oxyde protectrices

Le rôle du soufre sur l'adhérence des couches d'oxyde formées à la surface de matériaux métalliques a clairement été mis en évidence : le soufre ségrège à l'interface entre le métal et la couche d'oxyde et provoque l'écaillage de cette dernière. La mesure du taux de ségrégation dans une interface nécessite l'utilisation de techniques lourdes. Nous avons donc choisi d'étudier la ségrégation sur des surfaces libres. Notre travail porte sur trois matériaux : un superalliage monocristallin base-nickel, que l'on appellera 'A', un revêtement d'aluminiure simple β-NiAl, déposé sur 'A', un revêtement d'aluminiure modifié β-NiAl, déposé sur 'A'. Les cinétiques de ségrégation sont mesurées par spectrométrie des électrons Auger à chaud. L'interprétation des données a nécessité le développement d'un programme informatique permettant de traiter la ségrégation dans le cas d'un profil de concentration initial quelconque. L'utilisation de ce modèle numérique permet d'ajuster les paramètres thermodynamiques (enthalpies de ségrégation) et cinétiques (coefficients de diffusion) intervenant dans les cinétiques de ségrégation. Les résultats montrent que la ségrégation du soufie sur le superalliage 'A' se rapproche de celle du soufre sur le nickel. L'ajout de platine aux revêtements d'aluminiure β-NiAl retarde fortement l'arrivée du soufre sur la surface. Ce résultat permet de comprendre l'effet bénéfique de l'ajout de platine sur la tenue à l'oxydation des revêtements d'aluminiures

Preformed expression of defense is a hallmark of partial resistance to rice blast fungal pathogen <it>Magnaporthe oryzae</it>

Abstract Background Partial resistance to plant pathogens is extensively used in breeding programs since it could contribute to resistance durability. Partial resistance often builds up during plant development and confers quantitative and usually broad-spectrum resistance. However, very little is known on the mechanisms underlying partial resistance. Partial resistance is often explained by poorly effective induction of plant defense systems. By exploring rice natural diversity, we asked whether expression of defense systems before infection could explain partial resistance towards the major fungal pathogen Magnaporthe oryzae. The constitutive expression of 21 defense-related genes belonging to the defense system was monitored in 23 randomly sampled rice cultivars for which partial resistance was measured. Results We identified a strong correlation between the expression of defense-related genes before infection and partial resistance. Only a weak correlation was found between the induction of defense genes and partial resistance. Increasing constitutive expression of defense-related genes also correlated with the establishment of partial resistance during plant development. Some rice genetic sub-groups displayed a particular pattern of constitutive expression, suggesting a strong natural polymorphism for constitutive expression of defense. Constitutive levels of hormones like salicylic acid and ethylene cannot explain constitutive expression of defense. We could identify an area of the genome that contributes to explain both preformed defense and partial resistance. Conclusion These results indicate that constitutive expression of defense-related genes is likely responsible for a large part of partial resistance in rice. The finding of this preformed defense system should help guide future breeding programs and open the possibility to identify the molecular mechanisms behind partial resistance.</p