Functional characterization of a C-4 sterol methyl oxidase from the endomycorrhizal fungus Glomus intraradices

Fungicides With Contrasting Mode of Action Differentially Affect Hyphal Healing Mechanism in Gigaspora sp. and Rhizophagus irregularis

Fungicides are widely used in conventional agriculture to control fungal diseases, but may also affect non-target microorganisms such as arbuscular mycorrhizal (AM) fungi. These root symbionts develop extended mycelial networks within the soil via mechanisms such as anastomosis that indistinctly concerns intact and damaged hyphae, the latter being named hyphal healing mechanism (HHM). The HHM differs between Glomeraceae and Gigasporaceae. However, the effects of fungicides on this mechanism in unknown. Here, the impact of azoxystrobin, pencycuron, flutolanil, and fenpropimorph at 0.02 and 2 mg L-1 were tested in vitro on the HHM of Gigaspora sp. MUCL 52331 and Rhizophagus irregularis MUCL 41833, and repair events visualized carefully under a dissecting bright-field light microscope. Azoxystrobin was the more detrimental for both AM fungi at 2 mg L-1, while fenpropimorph impacted only R. irregularis (stimulating at low and inhibiting at high concentration). Conversely, flutolanil and pencycuron did not impact any of the two AM fungi. The mechanisms involved remains to be elucidated, but perturbation in the still-to-be firmly demonstrated spitzenkörper or in sterols content as well as a process of hormesis are possible avenues that deserve to be explored in view of a rationale management of chemicals to control fungal pathogens without harming the beneficial AM fungi.

Integrated multi-omics analysis supports role of lysophosphatidylcholine and related glycerophospholipids in the Lotus japonicus-Glomus intraradices mycorrhizal symbiosis

Interaction of plant roots with arbuscular mycorrhizal fungi (AMF) is a complex trait resulting in cooperative interactions among the two symbionts including bidirectional exchange of resources. To study arbuscular mycorrhizal symbiosis (AMS) trait variation in the model plant Lotus japonicus, we performed an integrated multi-omics analysis with a focus on plant and fungal phospholipid (PL) metabolism and biological significance of lysophosphatidylcholine (LPC). Our results support the role of LPC as a bioactive compound eliciting cellular and molecular response mechanisms in Lotus. Evidence is provided for large interspecific chemical diversity of LPC species among mycorrhizae with related AMF species. Lipid, gene expression and elemental profiling emphasize the Lotus-Glomus intraradices interaction as distinct from other arbuscular mycorrhizal (AM) interactions. In G. intraradices, genes involved in fatty acid (FA) elongation and biosynthesis of unsaturated FAs were enhanced, while in Lotus, FA synthesis genes were up-regulated during AMS. Furthermore, FAS protein localization to mitochondria suggests FA biosynthesis and elongation may also occur in AMF. Our results suggest the existence of interspecific partitioning of PL resources for generation of LPC and novel candidate bioactive PLs in the Lotus-G. intraradices symbiosis. Moreover, the data advocate research with phylogenetically diverse Glomeromycota species for a broader understanding of the molecular underpinnings of AMS.

The arbuscular mycorrhizal Rhizophagus irregularis activates storage lipid biosynthesis to cope with the benzo[a]pyrene oxidative stress

The phytoremediation assisted by arbuscular mycorrhizal fungi (AMF) could constitute an ecological and economic method to restore polycyclic aromatic hydrocarbon (PAH) polluted soils. Unfortunately, little is known about the PAH impact on the beneficial symbiotic AMF. Using radiolabelling experiments, our work aims to understand how benzo[a]pyrene (B[a]P), a representative of high molecular weight PAH, acts on the AMF lipid metabolism. Our results showed decreases in the sterol precursors as well as in total phospholipid quantities, in link with the [1-(14)C]acetate incorporation decreases in these lipids. Interestingly, a concomitant increase of [1-(14)C]acetate incorporation by 29.5% into phosphatidylcholine with its content decrease in Rhizophagus irregularis extraradical mycelium was observed, suggesting a membrane regeneration. A second concomitant increase (estimated to 69%) of [1-(14)C]acetate incorporation into triacylglycerols (TAG) with the content decrease was also observed. This suggests a fungal TAG biosynthesis activation probably to offset the decrease in storage lipid content when the fungus was grown under B[a]P pollution. In addition, our findings showed that lipase activity was induced by more than 3 fold in the presence of B[a]P in comparison to the control indicating that the drop in TAG content could be a consequence of their active degradation. Taken together, our data suggest the involvement of the fungal TAG metabolism to cope B[a]P toxicity through two means: (i) by providing carbon skeletons and energy necessary for membrane regeneration and/or for B[a]P translocation and degradation as well as (ii) by activating the phosphatidic acid and hexose metabolisms which may be involved in cellular stress defence.

The expression of GintPT, the phosphate transporter of Rhizophagus irregularis, depends on the symbiotic status and phosphate availability

The development of mutualistic interactions with arbuscular mycorrhizal (AM) fungi is one of the most important adaptation of terrestrial plants to face mineral nutrition requirements. As an essential plant nutrient, phosphorus uptake is acknowledged as a major benefit of the AM symbiosis, but the molecular mechanisms of its transport as inorganic phosphate (Pi) from the soil to root cells via AM fungi remain poorly known. Here we monitored the expression profile of the high-affinity phosphate transporter (PT) gene (GintPT) of Rhizophagus irregularis (DAOM 197198) in fungal structures (spores, extraradical mycelium and arbuscules), under different Pi availability, and in respect to plant connection. GintPT resulted constitutively expressed along the major steps of the fungal life cycle and the connection with the host plant was crucial to warrant GintPT high expression levels in the extraradical mycelium. The influence of Pi availability on gene expression of the fungal GintPT and the Medicago truncatula symbiosis-specific Pi transporter (MtPT4) was examined by qRT-PCR assay on microdissected arbusculated cells. The expression profiles of both genes revealed that these transporters are sensitive to changing Pi conditions: we observed that MtPT4 mRNA abundance is higher at 320 than at 32 μM suggesting that the flow towards the plant requires high concentrations. Taken on the whole, the findings highlight novel traits for the functioning of the GintPT gene and offer a molecular scenario to the models describing nutrient transfers as a cooperation between the mycorrhizal partners.

Propiconazole inhibits the sterol 14α-demethylase in Glomus irregulare like in phytopathogenic fungi

The increasing concentrations impact (0.02, 0.2 and 2 mg L(-1)) of a Sterol Biosynthesis Inhibitor (SBI) fungicide, propiconazole, was evaluated on development and sterol metabolism of two non-target organisms: mycorrhizal or non-mycorrhizal transformed chicory roots and the arbuscular mycorrhizal fungus (AMF) Glomus irregulare using monoxenic cultures. In this work, we provide the first evidence of a direct impact of propiconazole on the AMF by disturbing its sterol metabolism. A significant decrease in end-products sterols contents (24-methylcholesterol and in 24-ethylcholesterol) was observed concomitantly to a 24-methylenedihydrolanosterol accumulation indicating the inhibition of a key enzyme in sterol biosynthesis pathway, the sterol 14α-demethylase like in phytopathogenic fungi. A decrease in end-product sterol contents in propiconazole-treated roots was also observed suggesting a slowing down of the sterol metabolism in plant. Taken together, our findings suggest that the inhibition of the both AM symbiotic partners development by propiconazole results from their sterol metabolism alterations.

The induction of epigenetic regulation of PROS1 gene in lung fibroblasts by gold nanoparticles and implications for potential lung injury

Advances in nanotechnology have given rise to the rapid development of novel applications in biomedicine. However, our understanding in the risks and health safety of nanomaterials is still not complete and various investigations are ongoing. Here, we show that gold nanoparticles (AuNPs) significantly altered the expression of 19 genes in human fetal lung fibroblasts (using the Affymetrix Human Gene 1.0 ST Array). Among the differentially expressed genes, up-regulation of microRNA-155 (miR-155) was observed concomitant with down-regulation of the PROS1 gene. Silencing of miR-155 established PROS1 as its possible target gene. DNA methylation profiling analysis of the PROS1 gene revealed no changes in the methylation status of this gene in AuNP-treated fibroblasts. At the ultrastructural level, chromatin condensation and reorganization was observed in the nucleus of fibroblasts exposed to AuNPs. The findings provide further insights into the molecular mechanisms underlying toxicity of AuNPs and their impact on epigenetic processes.

Fenpropimorph and fenhexamid impact phosphorus translocation by arbuscular mycorrhizal fungi

Fenpropimorph and fenhexamid are sterol biosynthesis inhibitor (SBI) molecules widely used to control diseases in agriculture. Both molecules, at increasing concentrations, have been shown to impact on the non-target arbuscular mycorrhizal (AM) fungi. Root colonization, spore production and mycelium architecture, including the branched absorbing structures which are thought to be involved in phosphorus (P) uptake, were affected. In the present study, we investigated the capacity of Glomus sp. MUCL 43204 to take up, transfer and translocate labelled P to Medicago truncatula in the presence of these SBI molecules. We used a strict in vitro cultivation system associating an autotrophic plant of M. truncatula with the AM fungus. In addition, the effects of both SBI molecules on the proportion of hyphae with alkaline phosphatases (ALP), succinate dehydrogenase (SDH) activity and on the expression of the mycorrhiza-specific plant phosphate transporter MtPT4 gene were examined. We demonstrated that the two SBI molecules impacted the AM fungus. This was particularly evidenced for fenpropimorph. A decrease in P transport and ALP and SDH activities associated with the extraradical mycelium and MtPT4 expression level was noted. These three factors were closely related to the development of the AM fungus, suggesting a direct impact not only on the AM fungal growth but also on the physiology and metabolic activities of the AM fungus. These results further emphasized the interest on the autotrophic in vitro culture system as an alternative to pot experiments to investigate the mechanisms behind the impact of disease control molecules on the non-target AM fungal symbionts.

Characterization of a CuZn superoxide dismutase gene in the arbuscular mycorrhizal fungus Glomus intraradices

To gain further insights into the mechanisms of redox homeostasis in arbuscular mycorrhizal fungi, we characterized a Glomus intraradices gene (GintSOD1) showing high similarity to previously described genes encoding CuZn superoxide dismutases (SODs). The GintSOD1 gene consists of an open reading frame of 471 bp, predicted to encode a protein of 157 amino acids with an estimated molecular mass of 16.3 kDa. Functional complementation assays in a CuZnSOD-defective yeast mutant showed that GintSOD1 protects the yeast cells from oxygen toxicity and that it, therefore, encodes a protein that scavenges reactive oxygen species (ROS). GintSOD1 transcripts differentially accumulate during the fungal life cycle, reaching the highest expression levels in the intraradical mycelium. GintSOD1 expression is induced by the well known ROS-inducing agents paraquat and copper, and also by fenpropimorph, a sterol biosynthesis inhibitor (SBI) fungicide. These results suggest that GintSOD1 is involved in the detoxification of ROS generated from metabolic processes and by external agents. In particular, our data indicate that the antifungal effects of fenpropimorph might not be only due to the interference with sterol metabolism but also to the perturbation of other biological processes and that ROS production and scavenging systems are involved in the response to SBI fungicides.