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The Mutualist Laccaria bicolor Expresses a Core Gene Regulon During the Colonization of Diverse Host Plants and a Variable Regulon to Counteract Host-Specific Defenses

March 2015 , Volume 28 , Number  3
Pages  261 - 273

Jonathan M. Plett,1,2 Emilie Tisserant,1 Annick Brun,1 Emmanuel Morin,1 Igor V. Grigoriev,3 Alan Kuo,3 Francis Martin,1 and Annegret Kohler1

1Inra, UMR 1136 Inra-Université de Lorraine, Interactions Arbres/Microorganismes, Inra-Nancy, 54280 Champenoux, France; 2Hawkesbury Institute for the Environment, University of Western Sydney, Richmond, NSW, Australia 2753; 3Department of Energy Joint Genome Institute, Walnut Creek, CA 94598, U.S.A.

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Accepted 17 September 2014.

The coordinated transcriptomic responses of both mutualistic ectomycorrhizal (ECM) fungi and their hosts during the establishment of symbiosis are not well-understood. This study characterizes the transcriptomic alterations of the ECM fungus Laccaria bicolor during different colonization stages on two hosts (Populus trichocarpa and Pseudotsuga menziesii) and compares this to the transcriptomic variations of P. trichocarpa across the same timepoints. A large number of L. bicolor genes (≥8,000) were significantly regulated at the transcriptional level in at least one stage of colonization. From our data, we identify 1,249 genes that we hypothesize is the ‘core’ gene regulon necessary for the mutualistic interaction between L. bicolor and its host plants. We further identify a group of 1,210 genes that are regulated in a host-specific manner. This variable regulon encodes a number of genes coding for proteases and xenobiotic efflux transporters that we hypothesize act to counter chemical-based defenses simultaneously activated at the transcriptomic level in P. trichocarpa. The transcriptional response of the host plant P. trichocarpa consisted of differential waves of gene regulation related to signaling perception and transduction, defense response, and the induction of nutrient transfer in P. trichocarpa tissues. This study, therefore, gives fresh insight into the shifting transcriptomic landscape in both the colonizing fungus and its host and the different strategies employed by both partners in orchestrating a mutualistic interaction.

© 2015 The American Phytopathological Society