Study of nitrogen and carbon transfer from soil organic matter to Tuber melanosporum mycorrhizas and ascocarps using 15N and 13C soil labelling and whole-genome oligoarrays
Background and aims
We previously showed by 13CO2 host labelling that almost all of the constitutive carbon allocated to the truffles originated from the host. The objective of this present work was to determine the putative capacity of T. melanosporum ectomycorrhizas and ascocarps to use soil carbon and to uptake or assimilate soil nitrate.
The current investigation involved 13C and 15N soil labelling by incorporating labelled leaf litter and expression of genes involved in carbon and nitrogen metabolism in ascocarps and ectomycorrhizas.
The ascocarps harvested in the labelled plots were highly enriched in 15N but were almost never enriched in 13C. The main source of soil mineral nitrogen was nitrate. A nitrate transporter, one nitrate reductase and a nitrite reductase were well expressed in ectomycorrhizas. Several genes involved in aminoacid synthesis or in transamination processes were also well expressed in ectomycorrhizas. No nitrate transporter was expressed in ascocarps where the CAZyme genes upregulated were mainly Glycosyltransferases involved in saccharide transfer.
Ascocarps did not exhibit saprotrophic capacity for C, supporting previous results from 13CO2 host labelling showing that C is provided by the host tree. The 15N present in the ascocarps after soil labelling is supplied as ammonium or aminoacids by the ectomycorrhizas, which are able to uptake, reduce and metabolize nitrate.
KeywordsTruffle 13C 15N Ectomycorrhizas Ascocarps Gene expression
All of our thanks to the CEA/Cadarache-DSV-DEVM for growing the labelled seedlings. We utilized the online continuous flow CN analyzer (Carlo Erba NA1500) coupled with an isotope ratio mass spectrometer (Finnigan delta S) and DNA sequencing facilities at INRA-Nancy Lorraine financed by INRA and the Regional Council of Lorraine.
The labelling experiment and the gene expression study were supported by the SYSTRUF program (An integrated approach for sustainable management of ecosystems producing Black Truffle, Tuber melanosporum) financed by the French ANR (Agence Nationale de la Recherche; programme SYSTERRA, ANR-09-STRA-10-02).
This work was also supported by a grant overseen by the French National Research Agency (ANR) as part of the “Investissements d’Avenir” program (ANR-11-LABX-0002-01, Laboratory of Excellence ARBRE).
We would like to thank the two anonymous reviewers for their interest in our work and for their comments or suggestions, which allowed us to greatly improve the first version of the manuscript. We are thankful to Aimee Orsini for having corrected the English of this manuscript.
We also would like to thank Alain and René Sourdon, the owners of the Pierre Blanche truffle orchard, for their help and the AGRI-TRUFFE Company for providing seedlings mycorrhizal with T. melanosporum.
We also thank the dogs Biela for hunting the truffles in Rollainville and Louna and Diane, who hunted truffles in Pierre Blanche.
Conflict of interest
This work received financial support exclusively for the purposes of research and there exists no conflict of interest (financial or otherwise).
François Le Tacon: conceived and supervised the work, wrote the first draft and edited the manuscript. Christophe Robin: provided the truffle orchard, harvested the truffles and contributed to correct, to rewrite and to edit the manuscript. Bernd Zeller: conducted the soil labelling experiment and contributed to the correction of the manuscript. Annegret Keller and Francis Martin: conducted the study on gene expression and contributed to correct or to rewrite this part of the work. Caroline Plain: conducted the soil respiration measurements and contributed to the correction of the manuscript. Christian Hossann and Claude Bréchet conducted the isotopic analyses and contributed to the correction of the manuscript. Jean Villerd: designed the statistic analyses and contributed to correct and to rewrite parts of the manuscript.
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