Roy, Melanie , Selosse, Marc-Andre .
Plasticity in ectomycorrhizal fungi: the amazing shift from ectomycorrhizae to orchid mycorrhizae.
Most orchids are mycorrhizal with rhizoctonias, basidiomycetes that are saprobic. They colonize orchid roots and form intracellular hyphal coils (pelotons) in root cells; this is considered as the typical orchid mycorrhiza. Nevertheless, recent investigations on some partly or fully heterotrophic forest orchid, including our new findings on Thailand species, revealed that their mycorrhizae involve fungi such as Russulaceae, Thelephoraceae, Inocybe, Sebacinaceae, or even ascomycetes such as Tuber. These fungal species are known to form ectomycorrhizae on tree roots, and the same individual can be found both on orchids and on surrounding tree ectomycorrhizae. This demonstrates the ability of a fungal species, and even of an individual fungus, to form two morphologically different types of mycorrhizae.
Three main differences can be underlined between orchid- and ecto-mycorrhizae formed by these fungi. (i) The mycorrhizal morphology differs since the fungal colonization occurs within or between the host cells, respectively. This raises questions about the recognition process and suggests that the host plant critically controls to the morphogenesis. (ii) The physiology of these symbioses differs as the carbon flow is reversed in orchid mycorrhizae, raising questions on how carbon is transferred. Noteworthy, fungi are digested in orchid cells after some time, implying a higher turnover than in ectomycorrhizae. (iii) The specificity differs, being often (but not always) higher in orchids, whereas ectomycorrhizae are often unspecific. Conversely, different fungi can be found on the same orchid mycorrhizal root, whereas ectomycorrhizae are more exclusive.
We review ectomycorrhizal fungal species colonizing orchid roots, in temperate and tropical species, insisting on the symbiosis functioning and specificity in partly to fully heterotrophic orchids. For example, Russulaceae are associated to orchid roots all over the world, and illustrate the plasticity of association in a mainly ectomycorrhizal fungal family.
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1 - Centre d'Ecologie Fonctionnelle et Evolutive, CNRS, UMR 5175, Equipe Interactions Biotiques , 1919 Route de Mende, Montpellier, 34000, France
Presentation Type: Poster:Posters for BSA Sections
Location: Event Tent/Cliff Lodge
Date: Tuesday, July 28th, 2009
Time: 5:30 PM