Le biocontrôle de la sclérotiniose par des Pseudomonas spp. phytobénéfiques chez la laitue

Le champignon pathogène Sclerotinia sclerotiorum s’attaque à une grande variété d’hôtes, dont la laitue. Cette grande variété d’hôtes limite les méthodes de contrôle et de répression du champignon et donc engendre de grandes pertes économiques chaque année en affectant le rendement et la qualité des plantes agricoles. L'utilisation de fongicides synthétiques pour lutter contre cet agent pathogène devient moins efficace en raison du développement de la résistance de S. sclerotiorum, et c’est pourquoi des méthodes de lutte biologiques plus respectueuses de l’environnement sont recherchées. Les travaux de recherche présentés dans ce mémoire s’intéressent à l’utilisation d’agents de biocontrôle, tels que des Pseudomonas spp. phytobénéfiques, pour lutter contre l’infection de la sclérotiniose chez la laitue. Les Pseudomonas spp. ont plusieurs traits qui les rendent performants en tant qu’agents de biocontrôle, tels que la production d’une multitude de métabolites bioactifs comme des antibiotiques et des lipopeptides. Dans ce projet, nous avons donc sélectionné et caractérisé des souches de Pseudomonas spp. capables d’inhiber la croissance du champignon S. sclerotiorum in vitro (objectif 1), validé leur capacité à inhiber le dévelopement de la scérotiniose en conditions in planta, et identifié des gènes ou groupe de gènes potentiellement impliqués dans le biocontrôle observé (objectif 2). Le premier objectif a permis à d’isoler des souches de Pseudomonas spp. prélevées de champs agricoles sous régie biologique situées dans la région de la Montérégie (Québec, Canada). Ces souches ont ensuite été caractérisées, ce qui a permis de construire une phylogénie grâce au séquençage des génomes des souches les plus performantes. Neuf souches de Pseudomonas spp.ont démontré une forte inhibition in vitro dans des essais de confrontation en double culture. Le séquençage du génome entier de ces souches a révélé leur affiliation à quatre sous-groupes phylogénétiques, à savoir P. corrugata, P. asplenii, P. mandelii et P. protegens. x Le deuxième objectif visait une démonstration de la capacité des neuf souches à contrôler la sclérotiniose de la laitue sur des feuilles de laitues détachées. Une réduction significative des symptômes de la maladie (p < 0,05) a été observée lorsque des feuilles de laitue ont été inoculées avec deux souches appartenant au sous-groupe P. corrugata et par une souche appartenant au sous-groupe P. asplenii. Ensuite, l’utilisation d’outils de génomique comparative avec les souches de Pseudomonas ayant démontré une inhibition et des souches de Pseudomonas non-antagonistes, a permis d’identifier des déterminants géniques potentiellement impliqués dans leur capacité de biocontrôle. Des gènes et groupes de gènes impliqués dans la production de lipopeptides de type mycine et peptine, et d'antibiotiques tels que la brabantamide, qui peuvent être potentiellement impliqués dans l'activité antagoniste contre S. sclerotiorum, ont été identifiés. Ces résultats ouvrent une voie de biocontrôle contre S. sclerotiorum par au moins trois souches de Pseudomonas spp. qui présentent une importante activité antagoniste in vitro et in planta. L'identification de gènes et groupes de gènes liés au biocontrôle dans ces souches qui sont potentiellement impliqués dans l'inhibition de S. sclerotiorum a reçu une attention particulière. L'utilisation d'approches de génétique inverse et de chimie analytique, ainsi que des expériences plus complexes sur des systèmes végétaux complets, représenteront les prochaines étapes vers une meilleure compréhension de la capacité de biocontrôle de ces souches, et ainsi, vers un moyen de contrôler la sclérotiniose de la laitue

Identification and genomic characterization of Pseudomonas spp. displaying biocontrol activity against Sclerotinia sclerotiorum in lettuce

Lettuce is an economically major leafy vegetable that is affected by numerous diseases. One of the most devastating diseases of lettuce is white mold caused by Sclerotinia sclerotiorum. Control methods for this fungus are limited due to the development of genetic resistance to commonly used fungicides, the large number of hosts and the long-term survival of sclerotia in soil. To elaborate a new and more sustainable approach to contain this pathogen, 1,210 Pseudomonas strains previously isolated from agricultural soils in Canada were screened for their antagonistic activity against S. sclerotiorum. Nine Pseudomonas strains showed strong in vitro inhibition in dual-culture confrontational assays. Whole genome sequencing of these strains revealed their affiliation with four phylogenomic subgroups within the Pseudomonas fluorescens group, namely Pseudomonas corrugata, Pseudomonas asplenii, Pseudomonas mandelii, and Pseudomonas protegens. The antagonistic strains harbor several genes and gene clusters involved in the production of secondary metabolites, including mycin-type and peptin-type lipopeptides, and antibiotics such as brabantamide, which may be involved in the inhibitory activity observed against S. sclerotiorum. Three strains also demonstrated significant in planta biocontrol abilities against the pathogen when either inoculated on lettuce leaves or in the growing substrate of lettuce plants grown in pots. They however did not impact S. sclerotiorum populations in the rhizosphere, suggesting that they protect lettuce plants by altering the fitness and the virulence of the pathogen rather than by directly impeding its growth. These results mark a step forward in the development of biocontrol products against S. sclerotiorum

Combining Desirable Traits for a Good Biocontrol Strategy against Sclerotinia sclerotiorum

The fungal pathogen Sclerotinia sclerotiorum (Helotiales: Sclerotiniaceae) causes white mold, a disease that leads to substantial losses on a wide variety of hosts throughout the world. This economically important fungus affects yield and seed quality, and its control mostly relies on the use of environmentally damaging fungicides. This review aimed to present the latest discoveries on microorganisms and the biocontrol mechanisms used against white mold. A special focus is put on the identification of biocontrol desirable traits required for efficient disease control. A better understanding of the mechanisms involved and the conditions required for their action is also essential to ensure a successful implementation of biocontrol under commercial field conditions. In this review, a brief introduction on the pathogen, its disease cycle, and its main pathogenicity factors is presented, followed by a thorough description of the microorganisms that have so far demonstrated biocontrol potential against white mold and the mechanisms they use to achieve control. Antibiosis, induced systemic resistance, mycoparasitism, and hypovirulence are discussed. Finally, based on our actual knowledge, the best control strategies against S. sclerotiorum that are likely to succeed commercially are discussed, including combining biocontrol desirable traits of particular interest

Sulfolipid Is a Potential Candidate for Annexin Binding to the Outer Surface of Chloroplast

International audienceUsing a subcellular-specific proteomic approach, we have identified by protein microsequencing, a putative 35-kDa annexin from among the chloroplast envelope polypeptides. To confirm this identification, we demonstrate that (a) a 35-kDa protein, identified as annexin by antibody cross-reactivity, co-purifies with Percoll-purified chloroplasts and their envelope membranes when extracted in the presence of Ca(2+) and (b) the native spinach annexin protein binds to chloroplast-specific lipids in a Ca(2+)-dependent manner. The binding of the spinach annexin to these glycerolipids occurs at similar Ca(2+) concentrations as those, which promote the interaction of annexins to phospholipids in other membranes. Among chloroplast glycerolipids known to be accessible on the cytosolic face (outer leaflet) of the outer envelope membrane, sulfolipid, and probably phosphatidylinositol, would be the sole candidates for a putative Ca(2+)-dependent interaction of annexin with the chloroplast surface

Isolation and characterization of Chlamydomonas mutants deficient in the plastid ycf10 open reading frame

International audienceThe complete DNA sequences of a dozen plastid genomes have been determined and they have revealed the existence of approximately 120 genes that can be divided in three major groups. The first group (approximately 50 genes) corresponds to sequences required for plastid transcription and translation. The second group (approximately 40 genes) codes for components of the photosynthetic apparatus. The last group contains many open reading frames of unknown function (for review, see [1]). Some of these are species-specific and designated as ORFs. Those that are conserved in algae and in higher and lower plants have been designated ycf for “hypothetical chloroplast open reading frame”. Chloroplast reverse genetics coupled with biophysical and biochemical analysis has become a powerful tool for analyzing the function of chloroplast-encoded proteins. Several of these ORFs of unknown function have been inactivated in Chlamydomonas reinhardtii and tobacco by biolistic transformation (for review, see [2]). This paper summarizes the characterization of a Chlamydomonas ycf10-deficient mutant. An unusual feature of this chloroplast gene is that it encodes a plastid envelope protei

The Biochemical Machinery of Plastid Envelope Membranes

International audienc

Low levels of genetic differentiation and structure in red fox populations in Eastern Canada and implications for Arctic fox rabies propagation potential

Rabies is a lethal zoonosis present in most parts of the world which can be transmitted to humans through the bite from an infected mammalian reservoir host. The Arctic rabies virus variant (ARVV) persists mainly in populations of Arctic foxes (Vulpes lagopus), and to a lesser extent in red fox populations (Vulpes vulpes). Red foxes are thought to be responsible for sporadic southward movement waves of the ARVV outside the enzootic area of northern Canada. In this study, we wanted to investigate whether red foxes displayed notable levels of genetic structure across the Quebec-Labrador Peninsula, which includes portions of the provinces of Quebec and Newfoundland-Labrador in Canada, and is a region with a history of southward ARVV movement waves. We combined two datasets that were collected and genotyped using different protocols, totalling 675 red fox individuals across the whole region and genotyped across 13 microsatellite markers. We found two genetic clusters across the region, reflecting a latitudinal gradient, and characterized by low genetic differentiation. We also observed weak but significant isolation by distance, which seems to be marginally more important for females than for males. These findings suggest a general lack of resistance to movement in red fox populations across the Quebec-Labrador Peninsula, regardless of sex. Implications of these findings include additional support for the hypothesis of long-distance southward ARVV propagation through its red fox reservoir host