Microbial Antagonism at the Root Level Is Involved in the Suppression of Fusarium Wilt by the Combination of Nonpathogenic Fusarium oxysporum Fo47 and Pseudomonas putida WCS358

Two biological control agents, nonpathogenic Fusarium oxysporum Fo47 and Pseudomonas putida WCS358, were evaluated for suppression of Fusarium wilt of flax grown in nutrient solution and for suppression of the population density and metabolic activity of the causal organism F. oxysporum f. sp. lini strain Foln3GUS on root surfaces. Due to the presence of an introduced gusA reporter gene construct in Foln3GUS, the pathogen expressed b-glucuronidase activity that was related to its carbon metabolism. At a Fo47 to Foln3GUS inoculum ratio of 100:1, both the population density of the pathogen and the b-glucuronidase activity on and in flax roots were reduced by the nonpathogenic strain, and Fusarium wilt was suppressed. At a Fo47 to Foln3GUS inoculum ratio of 10:1, Fo47 decreased the severity of Fusarium wilt to a smaller extent and it also reduced b-glucuronidase activity without reducing the density of Foln3GUS on flax roots. At a nonpathogenic to pathogenic Fusarium strains ratio of 10:1, the addition of P. putida WCS358 further suppressed Fusarium wilt and the density of the pathogen at the root level, whereas a mutant of WCS358 deficient in pseudobactin production had no significant effect. Iron availability to WCS358 on flax roots, assessed by ice-nucleation activity conferred from a transcriptional fusion (pvd-inaZ) of an ice-nucleation reporter gene to an iron-regulated promoter, was sufficiently low to allow pseudobactin production. P. putida WCS358 did not reduce the severity of Fusarium wilt of flax when inoculated without Fo47, and it did not improve disease suppression achieved by high inoculum doses of Fo47 (a Fo47 to Foln3GUS ratio of 100:1). Together, these data provide evidence that (i) suppression of Fusarium wilt of flax by Fo47 is related to reductions in the population density and metabolic activity of the pathogen on the root surface; (ii) WCS358 can enhance the biological control activity of Fo47, but this enhancement depends on the population of Fo47 relative to the pathogen; and (iii) pseudobactin contributes to suppression of Fusarium wilt by the combination of Fo47 and WCS358 on roots in which conditions are conducive to pseudobactin production by the bacterium

Evidence that a common arbuscular mycorrhizal network alleviates phosphate shortage in interconnected walnut sapling and maize plants

Under agroforestry practices, inter-specific facilitation between tree rows and cultivated alleys occurs when plants increase the growth of their neighbors especially under nutrient limitation. Owing to a coarse root architecture limiting soil inorganic phosphate (Pi) uptake, walnut trees (Juglans spp.) exhibit dependency on soil-borne symbiotic arbuscular mycorrhizal fungi that extend extra-radical hyphae beyond the root Pi depletion zone. To investigate the benefits of mycorrhizal walnuts in alley cropping, we experimentally simulated an agroforestry system in which walnut rootstocks RX1 (J. regia x J. microcarpa) were connected or not by a common mycelial network (CMN) to maize plants grown under two contrasting Pi levels. Mycorrhizal colonization parameters showed that the inoculum reservoir formed by inoculated walnut donor saplings allowed the mycorrhization of maize recipient roots. Relative to non-mycorrhizal plants and whatever the Pi supply, CMN enabled walnut saplings to access maize Pi fertilization residues according to significant increases in biomass, stem diameter, and expression of JrPHT1;1 and JrPHT1;2, two mycorrhiza-inducible phosphate transporter candidates here identified by phylogenic inference of orthologs. In the lowest Pi supply, stem height, leaf Pi concentration, and biomass of RX1 were significantly higher than in non-mycorrhizal controls, showing that mycorrhizal connections between walnut and maize roots alleviated Pi deficiency in the mycorrhizal RX1 donor plant. Under Pi limitation, maize recipient plants also benefited from mycorrhization relative to controls, as inferred from larger stem diameter and height, biomass, leaf number, N content, and Pi concentration. Mycorrhization-induced Pi uptake generated a higher carbon cost for donor walnut plants than for maize plants by increasing walnut plant photosynthesis to provide the AM fungus with carbon assimilate. Here, we show that CMN alleviates Pi deficiency in co-cultivated walnut and maize plants, and may therefore contribute to limit the use of chemical P fertilizers in agroforestry systems

Arbuscular mycorrhizal symbiosis elicits shoot proteome changes that are modified during cadmium stress alleviation in Medicago truncatula

Background : Arbuscular mycorrhizal (AM) fungi, which engage a mutualistic symbiosis with the roots of most plant species, have received much attention for their ability to alleviate heavy metal stress in plants, including cadmium (Cd). While the molecular bases of Cd tolerance displayed by mycorrhizal plants have been extensively analysed in roots, very little is known regarding the mechanisms by which legume aboveground organs can escape metal toxicity upon AM symbiosis. As a model system to address this question, we used Glomus irregulare-colonised Medicago truncatula plants, which were previously shown to accumulate and tolerate heavy metal in their shoots when grown in a substrate spiked with 2 mg Cd kg-1.[br/] Results : The measurement of three indicators for metal phytoextraction showed that shoots of mycorrhizal M. truncatula plants have a capacity for extracting Cd that is not related to an increase in root-to-shoot translocation rate, but to a high level of allocation plasticity. When analysing the photosynthetic performance in metal-treated mycorrhizal plants relative to those only Cd-supplied, it turned out that the presence of G. irregulare partially alleviated the negative effects of Cd on photosynthesis. To test the mechanisms by which shoots of Cd-treated mycorrhizal plants avoid metal toxicity, we performed a 2-DE/MALDI/TOF-based comparative proteomic analysis of the M. truncatula shoot responses upon mycorrhization and Cd exposure. Whereas the metalresponsive shoot proteins currently identified in non-mycorrhizal M. truncatula indicated that Cd impaired CO2 assimilation, the mycorrhiza-responsive shoot proteome was characterised by an increase in photosynthesisrelated proteins coupled to a reduction in glugoneogenesis/glycolysis and antioxidant processes. By contrast, Cd was found to trigger the opposite response coupled the up-accumulation of molecular chaperones in shoot of mycorrhizal plants relative to those metal-free.[br/] Conclusion : Besides drawing a first picture of shoot proteome modifications upon AM symbiosis and/or heavy metal stress in legume plants, the current work argues for allocation plasticity as the main driving force for Cd extraction in aboveground tissues of M. truncatula upon mycorrhization. Additionally, according to the retrieved proteomic data, we propose that shoots of mycorrhizal legume plants escape Cd toxicity through a metabolic shift implying the glycolysis-mediated mobilization of defence mechanisms at the expense of the photosynthesis-dependent symbiotic sucrose sink

S. Declerck, D.G. Strullu and J.A. Fortin (eds) (2005) In Vitro culture of mycorrhizas

International audienc

Protein Profiling Analyses in Arbuscular Mycorrhizal Symbiosis

International audienceBecause proteins are well known as key effectors of plant responses to environmental cues including recognition, signaling, transport, and defense reactions, interest has been paid to characterize those involved in the establishment and functioning of arbuscular mycorrhizal (AM) symbiosis. The recent development of high throughput techniques has enabled large-scale analyses of symbiosis-related proteins. Different proteomic strategies have been established depending on the symbiotic stage targeted and on the abundance of mycorrhizal material. In mature mycorrhiza, sub-cellular proteomic approaches have been developed in the model legume Medicago truncatula to target symbiosis-related membrane proteins eligible for nutrient transport and signaling between symbionts upon arbuscule formation. Modifications in the M. truncatula root proteome during early stages of AM symbiosis have also been investigated by comparing protein patterns of non-inoculated roots and roots synchronized for appressorium formation. Concomitantly, proteomic approaches have been developed on in vitro-grown mycorrhiza to identify extraradical fungal proteins along with endomycorrhizins. The genome sequencing programs launched for M. truncatula and Glomus intraradices are likely to provide additional knowledge about AM symbiosis-related proteins. © 2009 Springer-Verlag Berlin Heidelberg

Pouvoir contre-sélectionner une population bactérienne: application à l'étude des transferts génétiques

International audienc

Adhesion of Fusarium oxysporum conidia to tomato roots

International audienc

Proteomics of Biotrophic Plant–Microbe Interactions: Symbioses Lead the March

International audienc