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Fungal metabolism and free amino acid content may predict nitrogen transfer to the host plant in the ectomycorrhizal relationship between Pisolithus spp. and Eucalyptus grandis

ABSTRACT: Ectomycorrhizal (ECM) fungi are crucial for tree nitrogen (N) nutrition, however, mechanisms governing N transfer from fungal tissues to the host plant are not well understood. ECM fungal isolates, even from the same species, vary considerably in their ability to support tree N nutrition resulting in a range of often unpredictable symbiotic outcomes. In this study, we used isotopic labelling to quantify the transfer of N to the plant host by isolates from the ECM genus Pisolithus known to have significant variability in colonisation and transfer of nutrients to a host. We considered the metabolic fate of N acquired by the fungi and found that the percentage of plant N acquired through symbiosis significantly correlated to the concentration of free amino acids present in the ECM extra-radical mycelium. Transcriptomic analyses complemented these findings with isolates having high amino acid content and N transfer showing increased expression of genes in amino acid transport and catabolic pathways. These results suggest that fungal N metabolism drives transfer to the host plant in this interaction and that relative N transfer may be possible to predict through basic biochemical analyses.

ORGANISM(S): Pisolithus microcarpus Eucalyptus grandis

PROVIDER: GSE235669 | GEO | 2023/10/27

REPOSITORIES: GEO

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Project description:Around two-thirds of all plant species form arbuscular mycorrhizasa symbiosis between plant roots and glomalean fungi that leads to the formation of intraradical organs of nutrient exchange and an extraradical network of fungal hyphae effectively extending the plant root system. The mycorrhiza plays a key role in plant nutrition and in enhancing plant resistance against pathogens and improving drought resistance. At present very little is known about the molecular basis of arbuscular mycorrhiza formation. Arabidopsis thaliana (as with all Brassicaceae) does not form arbuscular mycorrhizas (AM). Arabidopsis may either have lost essential gene functions or acquired new ones that prevent a successful symbiotic interaction. However given that mycorrhizal symbiosis developed very early during the evolution of land plants and that many ectomycorrhizal plant species can be colonised by AM fungi it is likely that important components of AM signalling pathways are conserved in all plants including Arabidopsis. Possibly the lack of AM development is a multigenic trait and this would make it difficult to isolate mutants that (re-)gain the ability to interact with AM fungi. What can be done however is firstly to test which parts of one or several putative AM signalling pathways are still functional and which ones are not. Secondly we can test whether negatively acting pathways such as those involved in defence against pathogenic microorganisms are induced upon inoculation with AM fungi. Together this work is likely to give important information of why Arabidopsis (and Brassicaceae) are behaving as non-hosts for AM fungi. In other words Arabidopsis will be an ideal system to study mechanisms of non-host "resistance" to AM colonisation. Elucidating these mechanisms will obviously make a great contribution to understanding the basis of the mycorrhizal interaction. Moreover using Arabidopsis as a tool it will be possible at the end to integrate the information obtained for AM signalling with that obtained for other developmental and environmentally triggered signalling pathways such as plant hormone signalling or plant defence responses. To produce an inventory of which Arabidopsis genes respond at all to inoculation with AM fungi a genome-wide screen for AM-controlled genes is proposed. RNA will be prepared from Arabidopsis roots treated with AM fungus and mock-inoculated control plants. Arabidopsis (Col-0) will be grown in pot culture (1:1 sand/Terra-Green) at low concentrations of phosphate. Three week-old plants will be inoculated with surface-sterilised spores of Gigaspora rosea. RNA will be isolated 3 days post inoculation. Experimenter name: Hsiu-Ling Yap; Experimenter phone: 01904 434 302/304; Experimenter fax: 01904 434 312; Experimenter institute: University of York; Experimenter address: Department of Biology; University of York; P.O.Box 373; York!Series_summary = Experimenter zip/postal_code: YO10 5YW; Experimenter country: UK Experiment Overall Design: 4 samples were used in this experiment