Signaling pathways driving the development of ectomycorrhizal symbiosis

Yohann Daguerre, Jonathan M. Plett, Claire Veneault-Fourrey

Research output: Chapter in Book / Conference PaperChapter

20 Citations (Scopus)

Abstract

In forest ecosystems, the roots of trees are continously in contact with beneficial, commensal and pathogenic soil microbes. These belowground microbial communities, called the microbiome, are also responsible for nutrient (C, N, P) recycling and nutrient exchanges, and have an impact on soil fertility and carbon sequestration. Consequently, the root microbiome drives forest health, productivity and sustainability. Within the rhizospheric zoo, the mutualistic ectomycorrhizal (ECM) fungi occupy a unique niche, with a shift from extramatrical or free‐living mycelium in soil to hyphae in intimate con­ tact with the apoplast of root cells. ECM interactions contribute to better tree growth and health via improving mineral nutrition, strengthening plant defenses and direct contribution to the exclusion of competitive microbes (Smith and Read, 2008). Despite their ecological importance, ECM symbiosis is still not well understood at the molecular level, partly because of the complexity of eukaryotic cells and their multi‐cellularity. During ECM establishment, soil‐borne fungal hyphae first grow towards host root cells and encompass short lateral roots to form the mantle. Mycelia then colonize the apoplastic space forming the Hartig net – the symbiotic interface where a molecular dialogue and an efficient nutrient exchanges take place (Peterson and Massicote, 2004; Martin, 2007). The tree supplies the ECM fungus with up to 20% of its photosynthesis‐derived carbohydrates, in return for up to 70% of its nitrogen and phosphorus needs, received from the ECM hyphal net­ works that extend deep within the soil. During the course of root colonization by an ECM fungus, the plant root undergoes a number of morphological changes, from the cessation of growth, to the alteration of plant cell wall properties and, finally, the alternate control of membrane‐bound trans­ porters to accommodate the new paradigm of nutrient fluxes inherent in mutualistic interactions. Therefore, establishment of a mutualistic interaction firstly requires recognition between both partners, and secondly a coordination of microbial and plant responses. Thanks to enormous efforts in fungal genome sequencing and, in particular, ECM fungal genomes, molecular mechanisms driving ECM development and functioning are receiving renewed attention (Kuo et al., 2014; Martin et al., 2008, 2010). In this chapter, we will first present our current knowledge on signal molecules and putative receptors that promote and mediate the very early steps of ECM establishment. We will then emphasize both the hormone‐based and symbiosis effector‐based dialogues, partly explaining how ECM hyphae can proliferate in host roots without eliciting plant defenses. Metabolic responses of colonized ECM roots will be also presented.
Original languageEnglish
Title of host publicationMolecular Mycorrhizal Symbiosis
EditorsFrancis Martin
Place of PublicationU.S.
PublisherWiley-Blackwell
Pages141-157
Number of pages17
ISBN (Electronic)9781118951422
ISBN (Print)9781118951415
DOIs
Publication statusPublished - 2017

Keywords

  • ectomycorrhizal fungi
  • forests and forestry
  • microbial communities
  • symbiosis

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