Mycelium

About: Mycelium is a research topic. Over the lifetime, 8923 publications have been published within this topic receiving 170993 citations.

Expression profiles of a phosphate transporter gene (GmosPT) from the endomycorrhizal fungus Glomus mosseae

Abstract: Arbuscular mycorrhizal (AM) fungi have long been shown to successfully contribute to phosphate uptake by plant roots. The first step of the fungus-mediated uptake is carried out by fungal membrane Pi transporters (PT) that transfer Pi from the soil into the extraradical hyphae. In the present work we report the identification and characterisation of a PT gene from Glomus mosseae, an AM fungus important for natural and agricultural ecosystems. Degenerate primers and rapid amplification of cDNA ends-polymerase chain reaction (PCR) allowed us to obtain a sequence (GmosPT) showing a highly significant similarity with GiPT and GvPT, the only two other PT genes already isolated from AM fungi. Reverse transcriptase-PCR experiments were carried out to study GmosPT expression profiles in structures corresponding to different fungal life stages (quiescent and germinated sporocarps, intraradical and extraradical hyphae) and in extra- and intraradical hyphae exposed to high and low Pi concentrations. GmosPT showed an expression pattern similar to GiPT, the Glomus intraradices PT gene, since its transcript was more abundant in the extraradical mycelium treated with micromolar Pi levels. In addition, the intraradical mycelium also showed a significant GmosPT expression level that was independent from external Pi concentrations. This finding opens new questions about the role and functioning of high-affinity PT in AM fungi.

Rates and quantities of carbon flux to ectomycorrhizal mycelium following 14C pulse labeling of Pinus sylvestris seedlings: effects of litter patches and interaction with a wood-decomposer fungus.

Abstract: We used a novel digital autoradiographic technique that enabled, for the first time, simultaneous visualization and quantification of spatial and temporal changes in carbon allocation patterns in ectomycorrhizal mycelia. Mycorrhizal plants of Pinus sylvestris L. were grown in microcosms containing non-sterile peat. The time course and spatial distribution of carbon allocation by P. sylvestris to mycelia of its mycorrhizal partners, Paxillus involutus (Batsch) Fr. and Suillus bovinus (L.): Kuntze, were quantified following 14C pulse labeling of the plants. Litter patches were used to investigate the effects of nutrient resource quality on carbon allocation. The wood-decomposer fungus Phanerochaete velutina (D.C.: Pers.) Parmasto was introduced to evaluate competitive and territorial interactions between its mycelial cords and the mycelial system of S. bovinus. Growth of ectomycorrhizal mycelium was stimulated in the litter patches. Nearly 60% of the C transferred from host plant to external mycorrhizal mycelium (> 2 mm from root surfaces) was allocated to mycelium in the patches, which comprised only 12% of the soil area available for mycelial colonization. Mycelia in the litter patch most recently colonized by mycorrhizal mycelium received the largest investment of carbon, amounting to 27 to 50% of the total 14C in external mycorrhizal mycelium. The amount of C transfer to external mycelium of S. bovinus following pulse labeling was reduced from a maximum of 167 nmol in systems with no saprotroph to a maximum of 61 nmol in systems interacting with P. velutina. The 14C content of S. bovinus mycelium reached a maximum 24-36 h after labeling in control microcosms, but allocation did not reach a peak until 56 h after labeling, when S. bovinus interacted with mycelium of P. velutina. The mycelium of S. bovinus contained 9% of the total 14C in the plants (including mycorrhizae) at the end of the experiment, but this was reduced to 4% in the presence of P. velutina. The results demonstrate the dynamic manner in which mycorrhizal mycelia deploy C when foraging for nutrients. The inhibitory effect of the wood-decomposer fungus P. velutina on C allocation to external mycorrhizal mycelium has important implications for nutrient cycling in forest ecosystems.

Ultrastructural localization of heavy metals in the extraradical mycelium and spores of the arbuscular mycorrhizal fungus Glomus intraradices

Abstract: Arbuscular mycorrhizal fungi, obligate symbionts of most plant species, are able to accumulate heavy metals, thereby, protecting plants from metal toxicity. In this study, the ultrastructural local...

TasHyd1, a new hydrophobin gene from the biocontrol agent Trichoderma asperellum, is involved in plant root colonization

Abstract: SUMMARY A hydrophobin-like clone (TasHyd1) was isolated during a PCR differential mRNA display analysis conducted on Trichoderma asperellum mycelia interacting with plant roots. The open reading frame encodes a 145-amino-acid protein showing similarity to Pbhyd1, a Class I hydrophobin from the dimorphic fungus Paracoccidioides brasiliensis. TasHyd1 expression was detected in planta up to 5 days after Trichoderma root inoculation. TasHyd1 is constitutively expressed at low levels in mycelia in young cultures but gene expression is not detected in sporulating hyphae or in non-germinating spores. Carbon limitation stimulates expression of TasHyd1 whereas nitrogen or phosphate starvation down-regulate expression. TasHyd1 fused to an HA tag was over-expressed in Trichoderma and the protein was detected with an anti-HA antibody in the trifluoroacetic-acid-soluble fraction of mycelial cell walls. Over-expressor mutants were not affected in their mycoparasitic activity when tested in vitro against the plant pathogen Rhizoctonia solani and retained root colonization capacity comparable with that of the wild-type. TasHyd1 deletion mutants had no significant reduction in in vitro mycoparasitic activity but were altered in their wettability and were severely impaired in root attachment and colonization. These phenotypes were recovered by complementation of TasHyd1, indicating that the protein is a new hydrophobin that contributes to Trichoderma interaction with the plant.

Soil conditions and the take‐all disease of wheat

Abstract: SUMMARY A study has been made of the decline in viability of Ophiobolus graminis as resting mycelium in artXcialIy infected wheat straw buried in the soil. The pieces of straw were buried in variously treated soils set up in glass tumblers, and were examined at intervals for the presence of still viable Ophiobolus mycelium by means of a wheat seem test. The experimental results suggest that the disappearance of Ophiobolus from the straws was due to natural decomposition by the other soil microorganisms since, in its resting phase, the fungus tolerated adverse physical conditions of the soil better than conditions optimum for microbiological activity. Decline in viability of the fungus appeared to be indefinitely postponed in air-dry soil, in soil at 2–3°C., and under sterile conditions in the culture flask; it was less rapid in a waterlogged soil than in one maintained at medium moisture content. The soil conditions least favourable for the advance of Ophiobolus along the host roots in its parasitic phase (Garrett, 1936) may best preserve it during its resting phase because they are also unfavourable for general microbiological activity. Loss of viability was hastened by the addition of energy materials poor or entirely lacking in nitrogen, such as glucose, starch, and rye-grass meal, to the soil; it was more rapid in a partially sterilized and reinoculated soil than in an untreated soil. These results may be attributed to the rise in numbers and activity of soil micro-organisms following upon the treatments. The rate of decline of the fungus varied with soil type, being more rapid in rich and heavy soils than in poor, light soils. Rate of decline was apparently not directly affected by soil reaction, nor appreciably by moisture content of the soil over the range 30–80% saturation. Decline of the fungus was more rapid under conditions of fluctuating soil moisture and improved aeration in unglazed flower-pots than under more uniform conditions in glass tumblers; it was slowest in soil maintained under still and uniform conditions in a small closed incubator. The most rapid disappearance of the Ophiobolus resting mycelium, therefore, seems to have been secured by conditions favouring maximum microbiological activity in the soil. The decline in viability of the fungus did not necessarily proceed parallel with gross decomposition of the infected straw as a whole. It was delayed by the addition of dried blood, containing 13% nitrogen, to the soil, whereas this treatment accelerated decomposition of the straw. Decline of the fungus was accelerated by addition of rye-grass meal, which delayed decomposition of the straw by taking up the available nitrogen. It is suggested that the Ophiobolus mycelium may itself serve as a source of nitrogen for the decomposition of the straw, and that the rapidity of its disappearance may be related directly to the degree of nitrogen scarcity in the soil and straw medium. I have much pleasure in thanking Dr A. G. Norman for various useful suggestions, and for all the nitrogen determinations. I am especially indebted to Miss L. Cunow and to Miss M. M. Browne for help in the carrying out of the experiments.