Bases moléculaires de la sensibilité du blé tendre (<em>Triticum aestivum</em>) à la fusariose de l'épi causée par le champignon <em>Fusarium graminearum</em>

Co-encadrant : Ludovic BonhommeFusarium head blight (FHB) is an important disease of cereals, particularly of wheat. It is caused by two fungal genera, the genus Fusarium and genus Microdochium. The species Fusarium graminearum is the principal agent of this disease. This disease affects not only yield and grain quality in wheat, but it causes serious health problem through the production of mycotoxins. The establishment of this disease requires the expression of plant genes (susceptibility factors) that are still unknown. To study the molecular events involved in the development of this disease in the susceptible wheat grain during its development, time course infection of five points corresponding to the main developmental stages of grain was performed. Then two approaches, proteomics and transcriptomics using DNA microarrays were used to answer to this question. Proteomic analysis identified 73 differentially regulated proteins belonging to five major functional groups while the transcriptomics data revealed 1309 genes involved in 16 distinct functional groups. Both approaches have shown that infection does not interrupt grain development, but induces significant changes in primary metabolism, mainly on the synthesis of starch and storage proteins. It also showed a link between FHB response and the grain development. This study provides new evidence necessary to understand the susceptibility response of wheat to FHB. The wheat grain susceptibility is mainly characterized by the induction of detoxifying mechanisms of mycotoxins, the diversion ofcarbon metabolism of the host by the pathogen and control of Programmed Cell Death (PCD) of plant cells. Finally, the study allowed the establishment of a list of at least 100 candidate genes potentially involved in the wheat susceptibility to FHB.La Fusariose de l’épi (FHB) est une maladie importante des céréales et en particulier du blé tendre. Elle est causée par deux genres fongiques, le genre Fusarium et le genre Microdochium. L’espèce Fusarium graminearum est l’agent principal de cette maladie. Elle affecte non seulement les rendements et la qualité des grains chez le blé, mais elle cause un sérieux problème sanitaire via la production des mycotoxines. L’établissement de cette maladie requiert l’expression de gènes végétaux (facteurs de sensibilité) qui restent encore méconnus. Afin d’étudier les événements moléculaires qui participent à la mise en place de cette maladie sur un grain de blé tendre en développement et sensible au FHB, une cinétique d’infection de cinq points correspondant aux principaux stades développementaux du grain a été réalisée. Ensuite, deux approches, la protéomique comparée et la transcriptomique comparée à l’aide de puces à ADN, ont été utilisées pour répondre à ces questions. L’analyse protéomique a permis d’identifier 73 protéines différentiellement régulées appartenant à 5 grands groupes fonctionnels alors que l’approche transcriptomique a mis en évidence 1309 gènes répartis dans 16 groupes fonctionnels différents. Ces deux approches ont montré que l’infection ne bloque pas le développement du grain, mais elle induit des changements importants dans le métabolisme primaire notamment sur la synthèse de l’amidon et des protéines de réserve. Elle a également montré que la réponse du grain au FHB est liée au stade développemental du grain. Cette étude apporte de nouveaux éléments nécessaires à la compréhension de la sensibilité du blé tendre à la Fusariose de l’épi. Cette sensibilité du grain de blé se caractérise principalement par l’induction des mécanismes de détoxification des mycotoxines, la mise en place des mécanismes du détournement du métabolisme carboné de l’hôte par l’agent pathogène et le contrôle de la mort cellulaire programmée des cellules végétales. Enfin, l’étude a permis d’établir une liste d’au moins 100 gènes candidats potentiellement impliqués dans la sensibilité du blé au FHB

In silico prediction of the secretome from the invasive neurotoxic marine dinoflagellate Alexandrium catenella

WOS:000474226700010Alexandrium catenella, a marine dinoflagellate responsible for harmful algal blooms (HABs), proliferates with greater frequency, distribution and intensity, in disturbed marine coastal ecosystems. The proteins secreted into seawater may play a crucial role in maintaining this dinoflagellate in these ecosystems, but this possibility has never been investigated before. In this study, the A. catenella secretome was predicted from its transcriptome by combining several bioinformatics tools. Our results predict a secretome of 2 779 proteins, among which 79% contain less than 500 amino acids, suggesting that most secreted proteins are short in length. The predicted secretome includes 963 proteins (35%) with Pfam domains: 773 proteins with one Pfam domain and 190 proteins with two or more Pfam domains. Their functional annotation showed that they are mainly involved in (i) proteolysis, (ii) stress responses and (iii) primary metabolism. In addition, 47% of the secreted proteins appear to be enzymes, primarily peptidases, known to be biologically active in the extracellular medium during stress responses. Finally, this study provides a wealth of candidates of proteins secreted by A. catenella, which may interact with the marine environment and help this dinoflagellate develop in various environmental conditions

The pathogen Fusarium graminearum manipulates wheat biochemical pathways to favor its development

International audienc

Etude du dialogue moléculaire entre le blé tendre et le champignon mycotoxinogène Fusarium graminearum, principal agent de la fusariose du blé

National audienc

Intraspecific variability in membrane proteome, cell growth, and morphometry of the invasive marine neurotoxic dinoflagellate Alexandrium pacificum grown in metal-contaminated conditions

International audienceOver the past decades, the occurrence, distribution and intensity of harmful algal blooms involving the dinofla-gellate Alexandrium pacificum have increased in marine coastal areas disturbed by anthropogenic inputs. This in-vasive species produces saxitoxin, which causes the paralytic shellfish poisoning syndrome in humans upon consumption of contaminated seafood. Blooms of A. pacificum have been reported in metal-contaminated coastal ecosystems, suggesting some ability of these microorganisms to adapt to and/or resist in metal stress conditions. This study seeks to characterize the modifications in membrane proteomes (by 2-D electrophoresis coupled to LC-MS/MS), cell growth and morphometry (measured with an inverted microscope), in response to metal stress (addition of Zn2+,Pb2+,Cu2+ and Cd2+), in two Mediterranean A pacOcum strains: SG C10-3 and TAR C5-4F, re-spectively isolated from the Santa Giusta Lagoon (Sardinia, Italy) and from the Tarragona seaport (Spain), both metal-contaminated ecosystems. In the SG C10-3 cultures grown in a metal cocktail, cell growth was significantly delayed, and cell size increased (22% of 37.5 mu m cells after 25 days of growth). Conversely, no substantial change was observed for cell growth or cell size in the TAR C5-4F cultures grown in a metal cocktail (P> 0.10), thus in-dicating intraspecific variability in the responses of A. pacificum strains to metal contamination. Regardless of the conditions tested, the total number of proteins constituting the membrane proteome was significantly higher for TAR C5-4F than for SG C10-3, which may help TAR C5-4F to thrive better in contaminated conditions. For both strains, the total number of proteins constituting the membrane proteomes was significantly lower in response to metal stress (29% decrease in the SG C10-3 proteome: 82 +/- 12 proteins for controls, and 58 +/- 12 in metalcontaminated cultures; 17% decrease in the TAR C5-4F proteome: 101 +/- 8 proteins for controls, and 84 +/- 5 in metal-contaminated cultures). Moreover, regardless of the strain, proteins with significantly modified expression in response to stress were mainly down-regulated (representing 45% of the proteome for SG C10-3 and 38% for TAR C5-4F), dearly showing the harmful effects of the metals. Protein down-regulation may affect cell transport (actin and phospholipid scramblase in SG C10-3), photosynthesis (RUBISCO in SG C10-3, light-harvesting protein in TAR C5-4F, and high-CO2-inducing periplasmic protein in both strains), and finally energy metabolism (ATP synthase in both strains). However, other modifications in protein expression may confer to these A. pacificum strains a capacity for adaptation and/or resistance to metal stress conditions, for example by (i) limiting the metal entry through the plasma membrane of the SG C10-3 cells (via the down-regulation of scramblase) and/or (ii) reducing the oxidative stress generated by metals in SG C10-3 and TAR C5-4F cells (due to down-regulation of ATP-synthase)

Deciphering wheat susceptibility factors to Fusarium Head Blight

International audienc

A proteomics survey on wheat susceptibility to Fusarium head blight during grain development.

The mycotoxigenic fungal species Fusarium graminearum is able to attack several important cereal crops, such as wheat and barley. By causing Fusarium Head Blight (FHB) disease, F. graminearum induces yield and quality losses and poses a public health concern due to in planta mycotoxin production. The molecular and physiological plant responses to FHB, and the cellular biochemical pathways used by F. graminearum to complete its infectious process remain still unknown. In this study, a proteomics approach, combining 2D-gel approach and mass spectrometry, has been used to determine the specific protein patterns associated with the development of the fungal infection during grain growth on susceptible wheat. Our results reveal that F. graminearum infection does not deeply alter the grain proteome and does not significantly disturb the first steps of grain ontogeny but impacts molecular changes during the grain filling stage (impact on starch synthesis and storage proteins). The differentially regulated proteins identified were mainly involved in stress and defence mechanisms, primary metabolism, and main cellular processes such as signalling and transport. Our survey suggests that F. graminearum could take advantage of putative susceptibility factors closely related to grain development processes and thus provide new insights into key molecular events controlling the susceptible response to FHB in wheat grains

Physiological and proteomic responses of a mediterranean strain of the marine toxic invasive dinoflagellate Alexandrium catenella exposed to a polymetallic stress

International audienceAlexandrium catenella est un dinoflagellé marin invasif impliqué dans les phénomènes d'efflorescences massives toxiques (Harmful Algal Blooms ou HABs). Les HABs sont notamment observés dans des écosystèmes marins côtiers perturbés par les activités anthropiques, avec des fréquences, des distributions et des intensités croissantes. A. catenella produit des phycotoxines (saxitoxine et dérivés) responsables de graves intoxications, pouvant conduire jusqu'à la mort, chez l'être humain ayant consommé des fruits de mer contaminés (Paralytic Shellfish Poisoning ou PSP). Or, des efflorescences de ce dinoflagellé ont lieu dans des écosystèmes soumis à des contaminations par divers éléments traces métalliques(ETMs) (Étang de Thau : Eric Abadie, communication personnelle ; Rade de Toulon : Jean et al., 2006), ce qui suggère une certaine capacité de résistance et/ou d'adaptation d'A catenella aux stress métalliques, laquelle a peu été étudiée (Jean et al., 2017 ; Jean et al., en préparation). Dans cette étude, la croissance, la morphométrie, les profils toxiniques et les réponses protéomiques de cellules d'A. catenella exposées à un cocktail polymétallique (Cu, Pb, Zn, Cd) ont été analysés. L'approche protéomique permet de comprendre les mécanismes de résistance/d'adaptation développés par des organismes soumis à des stress environnementaux, grâce à des protéines de stress dont ils modifient l'expression au sein de voies métaboliques spécifiques. Cette étude vise donc à (i) identifier les protéines de stress dont l'expression est modifiée par A.catenella en réponse à une contamination polymétallique, (ii) analyser la contribution de ces protéines à des mécanismes cellulaires spécifiques pouvant expliquer le développement/maintien de ce dinoflagellé dans des écosystèmes contaminés par les ETMs, (iii) mettre en évidence des biomarqueursprotéomiques de résistance/d'adaptation d'A. catenella aux conditions de stress métalliques. Les résultats obtenus peuvent contribuer à comprendre la capacité de ce dinoflagellé à coloniser et à se maintenir dans des écosystèmes marins côtiers fortement anthropisés.Mots clés Alexandrium catenella, biomarqueurs, phycotoxines, protéomique, stress métalliqu

Transcriptome dynamics of a susceptible wheat upon Fusarium head blight reveals that molecular responses to Fusarium graminearum infection fit over the grain development processes

In many plant/pathogen interactions, host susceptibility factors are key determinants of disease development promoting pathogen growth and spreading in plant tissues. In the Fusarium head blight (FHB) disease, the molecular basis of wheat susceptibility is still poorly understood while it could provide new insights into the understanding of the wheat/Fusarium graminearum (Fg) interaction and guide future breeding programs to produce cultivars with sustainable resistance. To identify the wheat grain candidate genes, a genome-wide gene expression profiling was performed in the French susceptible wheat cultivar, Recital. Gene-specific two-way ANOVA of about 40 K transcripts at five grain developmental stages identified 1309 differentially expressed genes. Out of these, 536 were impacted by the Fg effect alone. Most of these Fg-responsive genes belonged to biological and molecular functions related to biotic and abiotic stresses indicating the activation of common stress pathways during susceptibility response of wheat grain to FHB. This analysis revealed also 773 other genes displaying either specific Fg-responsive profiles along with grain development stages or synergistic adjustments with the grain development effect. These genes were involved in various molecular pathways including primary metabolism, cell death, and gene expression reprogramming. An increasingly complex host response was revealed, as was the impact of both Fg infection and grain ontogeny on the transcription of wheat genes. This analysis provides a wealth of candidate genes and pathways involved in susceptibility responses to FHB and depicts new clues to the understanding of the susceptibility determinism in plant/pathogen interactions

Isolation of candidates effectors secreted by the fungal pathogen Fusarium graminearum in the early stages of FHB disease on wheat.

National audienc