Une analyse histopathologique et génomique d'une interaction in vitro entre Ulmus americana et Ophiostoma novo-ulmi

Les interactions entre les plantes et les agents pathogènes fongiques conduisent habituellement à la mise en place par l’hôte de différents mécanismes de défense. Des exemples de ces mécanismes sont le renforcement de la paroi cellulaire par la subérine, la lignine et les composés phénoliques pariétaux, ainsi que l’accumulation de protéines PR et la production de phytoalexines qui peuvent être toxiques pour l’agent pathogène. Chez les plantes susceptibles, ces mécanismes ne réussissent pas à empêcher le développement de la maladie. La maladie hollandaise de l’orme est une maladie à caractère épidémique qui a causé la mort de millions d’ormes en Europe et en Amérique du Nord. Les bases moléculaires de cette maladie sont encore peu connues. Afin d’identifier des gènes impliqués dans l’interaction entre l’espèce susceptible Ulmus americana L. et son champignon pathogène Ophiostoma novo-ulmi Brasier, un système in vitro a été mis au point, celui-ci utilisant des cultures de cals auxquelles des cellules levuriformes du champignon ont été inoculées. Afin de valider son utilisation pour l’analyse génomique, ce système a d’abord fait l’objet d’une analyse histopathologique en microscopie photonique et électronique. Le développement du champignon dans les cals et les réactions de défenses de ces derniers face à la présence du champignon ont été observés à 4, 24 48, 72 et 96 heures post-inoculation (hpi). Le champignon a été détecté sous forme de réseau d’hyphes dans toutes les parties du cal à partir de 48 hpi. Les tests histochimiques ont montré l’importance de certaines réactions telles que l’accumulation de phénols, de lignine et de subérine dans les cellules des cals. Le pourcentage de cellules subérisées était 4,6 fois plus élevé à 96 hpi dans les cals infectés que dans les cals témoins. Une banque d’ADN complémentaire a été construite à partir de cals infectés (72 hpi) en utilisant la technique des hybridations suppressives et soustractives (SSH). Un total de 535 étiquettes de séquences exprimées (EST) a été obtenu et déposé dans la banque de données Genbank suite au séquençage partiel des clones. Ces étiquettes ont été regroupées en 314 uniséquences dont la majorité correspondait à des gènes d’orme identifiés durant l’interaction. Cinquante-trois uniséquences représentant des gènes impliqués dans différentes voies métaboliques associées à la défense ont été sélectionnées par un criblage différentiel et considérées comme étant induites durant l’interaction. Les profils d’expression à différents temps après inoculation ont été établis par PCR quantitative chez 18 uniséquences provenant de cals infectés ainsi que de cals traités à l’eau stérile. Ils confirment l’induction ou l’expression constitutive des gènes correspondants durant le processus de l’infection. Cette étude fournit pour la première fois une ressource génomique pour l’orme et révèle des mécanismes moléculaires impliqués dans l’interaction entre l’orme américain et l’agent pathogène responsable de la maladie hollandaise de l’orme.Interactions between plants and fungal pathogens usually lead to the induction of different host defense mechanisms. Some of these mechanisms are the reinforcement of the plant cell wall by suberin, lignin and wall bound-phenolics, the accumulation of pathogenesis-related proteins, and the production of phytoalexins that could be toxic to the pathogen. Yet in susceptible plants, these mechanisms are not effective to produce resistance and disease develops. Dutch elm disease (DED) is a pandemic tree disease that killed millions of elm trees, especially in North America and Europe. The molecular bases of this disease are still poorly understood. With the objective of identifying genes involved in the interaction between the susceptible Ulmus americana L. and the pathogen Ophiostoma novo-ulmi Brasier, an in vitro system was developed using callus cultures inoculated with budding cells of the fungus. In order to validate the use of this system for genomic analyses of the interaction, a histopathological analysis was carried out using light and electron microscopy. Fungal colonization of the callus tissue and reactions of callus cells to the presence of the pathogen were observed at 4, 24, 48, 72 and 96 hours post-inoculation (hpi). The fungus was seen in its hyphal form by 48 hpi in all parts of the callus. Histochemical tests showed the importance of host reactions such as the accumulation of phenols, lignin, and suberin. The percentage of suberized cells was 4.6 times higher at 96 hpi in infected calli than in mock-inoculated control calli. A cDNA library using suppression subtractive hybridization (SSH) was constructed from infected elm callus tissue harvested at 72 hpi. A total of 535 expressed sequence tags were generated through partial sequencing and submitted to Genbank. These were grouped into 314 unisequences, the majority corresponding to elm genes identified during the interaction. Fifty-three unisequences representing genes involved in different pathways associated with plant defense were selected by differential screening and considered upregulated in the infected tissues. The expression profiles in mock and infected elm callus cultures of a subset of 18 elm genes were analyzed in more detail by quantitative reverse transcriptase polymerase chain reaction. These confirmed upregulation and constitutive expression of selected genes during the infection process. This study provides, for the first time, a genome-wide resource for the elm, and furthermore identifies molecular mechanisms likely involved during the interaction between U. americana and the DED pathogen

Unlocking heirloom diversity: a pathway to bridging global challenges in modern apple cultivation

Reports indicate that climate changes will result in the extinction of a significant percentage of plant species even though many of these species contributed to crucial genetic traits that led to the development of domestic crops. In the past, the diversified range of plant species, varieties, and agricultural practices allowed agriculture production and local food systems to tolerate moderate climate variability. Today, industrial farming relies on very limited genetic diversity for commercial production. Narrowing the genetic base leads to higher susceptibility to environmental changes and diseases.Heirloom cultivars survived climate variations and extreme conditions but were abandoned in favor of a handful of commercial cultivars that dominate the food industry and fit the standards of the global food system. From a climate change perspective, it would be important to conserve heirloom cultivars to preserve biodiversity and make greater genetic diversity available to farming, which will lead to resilience and adaptation

Finite volume scheme and renormalized solutions for nonlinear elliptic Neumann problem with L1 data

In this paper we study the convergence of a finite volume approximation of a convective diffusive elliptic problem with Neumann boundary conditions and L 1 data. To deal with the non-coercive character of the equation and the low regularity of the right hand-side we mix the finite volume tools and the renormalized techniques. To handle the Neumann boundary conditions we choose solutions having a null median and we prove a convergence result

Finite volume scheme and renormalized solutions for nonlinear elliptic Neumann problem with L1 data

In this paper we study the convergence of a finite volume approximation of a convective diffusive elliptic problem with Neumann boundary conditions and L 1 data. To deal with the non-coercive character of the equation and the low regularity of the right hand-side we mix the finite volume tools and the renormalized techniques. To handle the Neumann boundary conditions we choose solutions having a null median and we prove a convergence result

Characterization of the fluctuations of an ultrasonic wave passing through a complex environment in order to simplify the modeling

Ultrasonic nondestructive testing, also called ultrasonic NDT, is a method for characterizing the thickness or internal structure of material using high-frequency acoustic waves. This technique consists in emitting an ultrasound within the object and detecting the echoes produced by the possible defects. In complex environments, in particular for certain metals, composite materials and concretes, ultrasonic waves are strongly disturbed by the material through which they propagate, which can distort measurements. Modeling these phenomena can help designing control procedures and improving their signal to noise ratio. Because simulation using finite-element methods can be computationally prohibitive, it is important to develop alternative and lighter approaches. In this report, we model these fluctuations in the same manner as dynamic speckle sequences, using stochastic processes. These methods have parameters that we fit with respect to the simulations generated by the CEA

Characterization of the fluctuations of an ultrasonic wave passing through a complex environment in order to simplify the modeling

Ultrasonic nondestructive testing, also called ultrasonic NDT, is a method for characterizing the thickness or internal structure of material using high-frequency acoustic waves. This technique consists in emitting an ultrasound within the object and detecting the echoes produced by the possible defects. In complex environments, in particular for certain metals, composite materials and concretes, ultrasonic waves are strongly disturbed by the material through which they propagate, which can distort measurements. Modeling these phenomena can help designing control procedures and improving their signal to noise ratio. Because simulation using finite-element methods can be computationally prohibitive, it is important to develop alternative and lighter approaches. In this report, we model these fluctuations in the same manner as dynamic speckle sequences, using stochastic processes. These methods have parameters that we fit with respect to the simulations generated by the CEA

Characterization of the fluctuations of an ultrasonic wave passing through a complex environment in order to simplify the modeling

Ultrasonic nondestructive testing, also called ultrasonic NDT, is a method for characterizing the thickness or internal structure of material using high-frequency acoustic waves. This technique consists in emitting an ultrasound within the object and detecting the echoes produced by the possible defects. In complex environments, in particular for certain metals, composite materials and concretes, ultrasonic waves are strongly disturbed by the material through which they propagate, which can distort measurements. Modeling these phenomena can help designing control procedures and improving their signal to noise ratio. Because simulation using finite-element methods can be computationally prohibitive, it is important to develop alternative and lighter approaches. In this report, we model these fluctuations in the same manner as dynamic speckle sequences, using stochastic processes. These methods have parameters that we fit with respect to the simulations generated by the CEA

Characterization of the fluctuations of an ultrasonic wave passing through a complex environment in order to simplify the modeling

Ultrasonic nondestructive testing, also called ultrasonic NDT, is a method for characterizing the thickness or internal structure of material using high-frequency acoustic waves. This technique consists in emitting an ultrasound within the object and detecting the echoes produced by the possible defects. In complex environments, in particular for certain metals, composite materials and concretes, ultrasonic waves are strongly disturbed by the material through which they propagate, which can distort measurements. Modeling these phenomena can help designing control procedures and improving their signal to noise ratio. Because simulation using finite-element methods can be computationally prohibitive, it is important to develop alternative and lighter approaches. In this report, we model these fluctuations in the same manner as dynamic speckle sequences, using stochastic processes. These methods have parameters that we fit with respect to the simulations generated by the CEA

Low incidence of SARS-CoV-2, risk factors of mortality and the course of illness in the French national cohort of dialysis patients

International audienceThe aim of this study was to estimate the incidence of COVID-19 disease in the French national population of dialysis patients, their course of illness and to identify the risk factors associated with mortality. Our study included all patients on dialysis recorded in the French REIN Registry in April 2020. Clinical characteristics at last follow-up and the evolution of COVID-19 illness severity over time were recorded for diagnosed cases (either suspicious clinical symptoms, characteristic signs on the chest scan or a positive reverse transcription polymerase chain reaction) for SARS-CoV-2. A total of 1,621 infected patients were reported on the REIN registry from March 16th, 2020 to May 4th, 2020. Of these, 344 died. The prevalence of COVID-19 patients varied from less than 1% to 10% between regions. The probability of being a case was higher in males, patients with diabetes, those in need of assistance for transfer or treated at a self-care unit. Dialysis at home was associated with a lower probability of being infected as was being a smoker, a former smoker, having an active malignancy, or peripheral vascular disease. Mortality in diagnosed cases (21%) was associated with the same causes as in the general population. Higher age, hypoalbuminemia and the presence of an ischemic heart disease were statistically independently associated with a higher risk of death. Being treated at a selfcare unit was associated with a lower risk. Thus, our study showed a relatively low frequency of COVID-19 among dialysis patients contrary to what might have been assumed