Validation of an in vitro system to trigger changes in the gene expression of effectors of Sclerotinia sclerotiorum.

AIMS: Sclerotinia sclerotiorum, the causal agent of white mold, can infect several host species, including economically important crops. In this study, we propose and validate a new in vitro system able to mimic the conditions of interaction with the host and promote the induction of S. sclerotiorum effectors. METHODS AND RESULTS: For culture media production, we selected three plant species, common bean (Phaseolus vulgaris L, cv. Requinte.), maize (Zea mays, cv. BRS1030) and beggarticks (Bidens pilosa). To validate this system as an in vitro inducer of effectors, the qRT-PCR technique was used to investigate the expression profile of some S. sclerotiorum effector genes in each growth medium at different times after inoculation. CONCLUSION: The results obtained in this study provide a validation of a new method to study S. sclerotiorum during mimetic interaction with different hosts. Although leaf extract does not fully represent the plant environment, the presence of plant components in the culture medium seems to induce effector genes, mimicking in planta conditions. The use of MEVM is simpler than in planta growth, bypasses problems such as the amount of mycelium produced, as well as contamination of host cells during transcriptomic and proteomic analyses. SIGNIFICANCE AND IMPACT OF THE STUDY: We have devised MEVM media as a model mimicking the interaction of S. sclerotiorum and its hosts and used it to evaluate in vitro expression of effectors normally expressed only in planta.

Soil lead pollution modifies the structure of arbuscular mycorrhizal fungal communities.

The impact of lead (Pb) pollution on native communities of arbuscular mycorrhizal fungi (AMF) was assessed in soil samples from the surroundings of an abandoned Pb smelting factory. To consider the influence of host identity, bulk soil surrounding plant roots soil samples of predominant plant species (Sorghum halepense, Bidens pilosa, and Tagetes minuta) growing in Pb-polluted soils and in an uncontaminated site were selected. Molecular diversity was assessed by sequencing the 18S rDNA region with primers specific to AMF (AMV4.5NF/AMDGR) using Illumina MiSeq. A total of 115 virtual taxa (VT) of AMF were identified in this survey. Plant species did not affect AMF diversity patterns. However, soil Pb content was negatively correlated with VT richness per sample. Paraglomeraceae and Glomeraceae were the predominant families while Acaulosporaceae, Ambisporaceae, Archaeosporaceae, Claroideoglomeraceae, Diversisporaceae, and Gigasporaceae were less abundant. Acaulosporaceae and Glomeraceae were negatively affected by soil Pb, but Paraglomeraceae relative abundance increased under increasing soil Pb content. Overall, 26 indicator taxa were identified; four of them were previously reported in Pb-polluted soils (VT060; VT222; VT004; VT380); and five corresponded to cultured spores of Scutellospora castaneae (VT041), Diversispora spp. and Tricispora nevadensis (VT060), Diversispora epigaea (VT061), Glomus proliferum (VT099), and Gl. indicum (VT222). Even though AMF were present in Pb-polluted soils, community structure was strongly altered via the differential responses of taxonomic groups of AMF to Pb pollution. These taxon-specific differences in tolerance to soil Pb content should be considered for future phytoremediation strategies based on the selection and utilization of native Glomeromycota.

Differential growth response to arbuscular mycorrhizal fungi and plant density in two wild plants belonging to contrasting functional types.

The effect of arbuscular mycorrhizal fungi (AMF) on plant growth was examined in two wild plant species belonging to contrasting functional types: an annual forb (Bidens pilosa, Asteraceae) and a deciduous shrub (Acacia caven, Fabaceae) at three contrasting plant densities (one, two, and three individuals per pot). AMF had a slightly negative effect on B. pilosa when the species grew in isolation while they positively affected A. caven. Positive effects of AMF on shoot mass of A. caven decreased at higher plant densities, while shoot mass of individuals of B. pilosa showed less marked differences between plant densities. When considering total biomass per pot, AMF positively affected A. caven growth while negatively affecting B. pilosa, at all three plant densities. Root/shoot ratio per pot was negatively affected by AMF but not plant density in both species. These findings highlight the importance of including plants belonging to different life forms and/or traits in research regarding the interaction between AMF and intraspecific plant competition.