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Mechanisms of interaction between ectomycorrhizal fungi and the mycorrhiza helper bacterium Pseudomonas fluorescens BBc6R8

ABSTRACT: Mycorrhiza helper bacteria (MHB) promote the formation of ectomycorrhizae between tree roots and ectomycorrhizal fungi. Despite the high relevance of MHB for forestry and for sustainable tree production in tree nurseries, little is known about the properties of the bacteria that contribute to their helper abilities. The MHB strain Pseudomonas fluorescens BBc6R8 is used as a model to study the mechanisms of the helper effect. We took advantage of new technologies to obtain, for the first time, the whole genome sequence of an MHB. Analyses reveal an important plasticity of the genome with numerous functions acquired by horizontal gene tranfer. Genome mining was combined with transcriptomic and mutagenesis approaches to reveal molecular determinants of the helper effect. The data suggest that the production of helper molecules is likely to be constitutive in vitro. The helper effect appears to be pleiotropic and to rely, for a substantial part, on trophic interactions. Despite its helper abilities, the bacterium is also able in specific conditions to outcompete ectomycorrhizal fungi and inhibit their growth. We conclude that the helper bacterium possess a broad range of properties whose expression depending on the biotic and abiotic conditions can result in either a beneficial, neutral or antagonistic interaction between the plant, the ectomycorrhizal fungus and the bacterium.

ORGANISM(S): Pseudomonas fluorescens BBc6R8

PROVIDER: GSE38243 | GEO | 2014/06/12

SECONDARY ACCESSION(S): PRJNA171402

REPOSITORIES: GEO

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Mechanisms of interaction between ectomycorrhizal fungi and the mycorrhiza helper bacterium Pseudomonas fluorescens BBc6R8

Project description:Mycorrhiza helper bacteria (MHB) promote the formation of ectomycorrhizae between tree roots and ectomycorrhizal fungi. Despite the high relevance of MHB for forestry and for sustainable tree production in tree nurseries, little is known about the properties of the bacteria that contribute to their helper abilities. The MHB strain Pseudomonas fluorescens BBc6R8 is used as a model to study the mechanisms of the helper effect. We took advantage of new technologies to obtain, for the first time, the whole genome sequence of an MHB. Analyses reveal an important plasticity of the genome with numerous functions acquired by horizontal gene tranfer. Genome mining was combined with transcriptomic and mutagenesis approaches to reveal molecular determinants of the helper effect. The data suggest that the production of helper molecules is likely to be constitutive in vitro. The helper effect appears to be pleiotropic and to rely, for a substantial part, on trophic interactions. Despite its helper abilities, the bacterium is also able in specific conditions to outcompete ectomycorrhizal fungi and inhibit their growth. We conclude that the helper bacterium possess a broad range of properties whose expression depending on the biotic and abiotic conditions can result in either a beneficial, neutral or antagonistic interaction between the plant, the ectomycorrhizal fungus and the bacterium. The study was performed along a kinetic with three sampling times: before contact between the bacterial colonies and the fungus (14 days after inoculation), at the time of contact (16 days after inoculation) and after an extended period of contact (21 days). For each time, three independent replicates were performed. A control treatment without the fungus was performed in triplicate and sampled at 14 days.

2014-06-12 | E-GEOD-38243 | biostudies-arrayexpress

The soil organic matter decomposition mechanisms in ectomycorrhizal fungi are tuned for liberating soil organic nitrogen

Project description:Many trees form ectomycorrhizal symbiosis with fungi. During symbiosis, the tree roots supply sugar to the fungi in exchange for nitrogen, and this process is critical for the nitrogen and carbon cycles in forest ecosystems. However, the extents to which ectomycorrhizal fungi can liberate nitrogen and modify the soil organic matter and the mechanisms by which they do so remain unclear since they have lost many enzymes for litter decomposition that were present in their free-living, saprotrophic ancestors. Using time-series spectroscopy and transcriptomics, we examined the ability of two ectomycorrhizal fungi from two independently evolved ectomycorrhizal lineages to mobilize soil organic nitrogen. Both species oxidized the organic matter and accessed the organic nitrogen. The expression of those events was controlled by the availability of glucose and inorganic nitrogen. Despite those similarities, the decomposition mechanisms, including the type of genes involved as well as the patterns of their expression, differed markedly between the two species. Our results suggest that in agreement with their diverse evolutionary origins, ectomycorrhizal fungi use different decomposition mechanisms to access organic nitrogen entrapped in soil organic matter. The timing and magnitude of the expression of the decomposition activity can be controlled by the below-ground nitrogen quality and the above-ground carbon supply.

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Dual transcriptomic analysis of the interaction between the ectomycorrhizal fungus Laccaria bicolor S238N and soil Pseudomonas fluorescens Pf29Arp

Project description:In order to get insights into the ability of ectomycorrhizal fungi to perceive their biotic environment as well as into the mechanisms of the interactions between ectomycorrhizal fungi and soil bacteria, we analysed the transcriptomic response of the ectomycorrhizal fungus L. bicolor and the strain Pseudomonas fluorescens Pf29Arp during their interactions in vitro.

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Project description:In order to get insights into the ability of ectomycorrhizal fungi to perceive their biotic environment as well as into the mechanisms of the interactions between ectomycorrhizal fungi and soil bacteria, we analysed the transcriptomic response of the ectomycorrhizal fungus L. bicolor and one detrimental bacterial strain during their interactions in vitro.

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Dual transcriptomic analysis of the interaction between the ectomycorrhizal fungus Laccaria bicolor S238N and soil bacterium Collimonas fungivorans Ter331

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2014-06-12 | GSE53609 | GEO

Dual transcriptomic analysis of the interaction between the ectomycorrhizal fungus Laccaria bicolor S238N and soil bacteria Pseudomonas fluorescens BB6cR8 and Pf29Arp

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2014-06-12 | GSE53608 | GEO

Ectomycorrhizal fungi decompose humus-rich litter material using oxidative mechanisms adapted from saprotrophic ancestors

Project description:Decomposition of soil organic matter in forest soils is thought to be controlled by the activity of saprotrophic fungi, while biotrophic fungi including ectomycorrhizal fungi act as vectors for input of plant carbon. The limited decomposing ability of ectomycorrhizal fungi is supported by recent findings showing that they have lost many of the genes that encode hydrolytic plant cell-wall degrading enzymes in their saprophytic ancestors. Nevertheless, here we demonstrate that ectomycorrhizal fungi representing at least four origins of symbiosis have retained significant capacity to degrade humus-rich litter amended with glucose. Spectroscopy showed that this decomposition involves an oxidative mechanism and that the extent of oxidation varies with the phylogeny and ecology of the species. RNA-Seq analyses revealed that the genome-wide set of expressed transcripts during litter decomposition has diverged over evolutionary time. Each species expressed a unique set of enzymes that are involved in oxidative lignocellulose degradation by saprotrophic fungi. A comparison of closely related species within the Boletales showed that ectomycorrhizal fungi oxidized litter material as efficiently as brown-rot saprotrophs. The ectomycorrhizal species within this clade exhibited more similar decomposing mechanisms than expected from the species phylogeny in concordance with adaptive evolution occurring as a result of similar selection pressures. Our data shows that ectomycorrhizal fungi are potential organic matter decomposers, yet not saprotrophs. We suggest that the primary function of this decomposing activity is to mobilize nutrients embedded in organic matter complexes and that the activity is driven by host carbon supply. Comparative transcriptomics of ectomycorrhizal (ECM) versus brown-rot (BR) fungi while degrading soil-organic matter

2015-09-24 | E-GEOD-64897 | biostudies-arrayexpress

Ectomycorrhizal fungi decompose humus-rich litter material using oxidative mechanisms adapted from saprotrophic ancestors

2015-09-24 | GSE64897 | GEO

Pseudomonas fluorescens BBc6R8

Project description:Mycorrhizal helper bacterium that enhances ectomycorrhizal establishment

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Carbon starvation induces autophagy and recycling of nutrients in the ectomycorrhizal fungus Paxillus involutus

Project description:Ectomycorrhizal fungi are dependent on host trees for carbon supply. In return ectomycorrhizal fungi supply trees with water and nutrients. It is known that when ectomycorrhizal fungi have exploited a nutrient rich patch in soil, the carbon allocation to mycelia in that patch is reduced, with the consequence of mycelia dying, but less is known of the dynamics of this senescence. We cultivated the ectomycorrhizal fungus Paxillus involutus in an axenic system. We collected growth and transcriptome data at different stages of carbon starvation during fungal growth. Carbon starvation induced a decrease in fungal biomass, which coincided with the release of NH4+ and the expression of genes connected with autophagy as well as protease and chitinase activity. Monoaromatic compounds, chitin and protease activity was detected in the liquid growth media during carbon starvation. The exudation of NH4+ and increase of monoaromatic compound during C starvation suggests senescence and autolysis of P. involutus. Together with the upregulation of genes involved in autophagy, chitinase and endopeptidase activity this points towards a controlled senescence including recycling of compounds originating from the fungi. Reduced C allocation to ectomycorrhizal mycelia in recently depleted nutrient patches in forest soils must be of ubiquitous nature. Understanding the mechanisms during exploitation of nutrients by ectomycorrhizal fungi is of great importance for understanding carbon and nutrient dynamics in forest soils. This is to our knowledge the first study describing the carbon starvation response in an ectomycorrhizal fungus.

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