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Ectomycorrhiza-mediated repression of the high-affinity ammonium importer gene AmAMT2 in Amanita muscaria

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Abstract

A main function of ectomycorrhizas, a symbiosis between certain soil fungi and fine roots of woody plants, is the exchange of plant-derived carbohydrates for fungus-derived nutrients. As it is required in large amounts, nitrogen is of special interest. A gene (AmAMT2) coding for a putative fungal ammonium importer was identified in an EST project of functional Amanita muscaria/poplar ectomycorrhizas. Heterologous expression of the entire AmAMT2 coding region in yeast revealed the corresponding protein to be a high-affinity ammonium importer. In axenically grown Amanita hyphae AmAMT2 expression was strongly repressed by nitrogen, independent of whether the offered nitrogen source was transported by AmAMT2 or not. In functional ectomycorrhizas the AmAMT2 transcript level was further decreased in both hyphal networks (sheath and Hartig net), while extraradical hyphae revealed strong gene expression. Together our data suggest that (1) AmAMT2 expression is regulated by the endogenous nitrogen content of hyphae and (2) fungal hyphae in ectomycorrhizas are well supported with nitrogen even when the extraradical mycelium is nitrogen limited. As a consequence of AmAMT2 repression in mycorrhizas, ammonium can be suggested as a potential nitrogen source delivered by fungal hyphae in symbiosis.

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Abbreviations

UTR:

Untranslated region

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Acknowledgments

We are indebted to Margret Ecke and Andrea Bock for excellent technical assistance and to Dr. Nina Grunze for critical reading of the manuscript. This work was financed by the Deutsche Forschungsgemeinschaft (Ne 332/9).

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Authors and Affiliations

  1. Physiologische Ökologie der Pflanzen, Eberhard Karls Universität, Auf der Morgenstelle 1, 72076, Tübingen, Germany

    Anita Willmann & Uwe Nehls

  2. Spezielle Botanik und Mykologie, Eberhard Karls Universität, Auf der Morgenstelle 1, 72076, Tübingen, Germany

    Michael Weiß

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  1. Anita Willmann
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  2. Michael Weiß
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  3. Uwe Nehls
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Correspondence to Uwe Nehls.

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Communicated by U. Kües.

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Willmann, A., Weiß, M. & Nehls, U. Ectomycorrhiza-mediated repression of the high-affinity ammonium importer gene AmAMT2 in Amanita muscaria . Curr Genet 51, 71–78 (2007). https://doi.org/10.1007/s00294-006-0106-x

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  • DOI: https://doi.org/10.1007/s00294-006-0106-x

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