Selosse, Marc-Andre , Weiß, Michael .
Evolution of mycorrhizal associations in Ericaceae shaped host ecology: an overview.
With 2700 species, Ericaceae colonized widely distributed geographical regions, mainly at high latitudes and altitudes, and various ecological niches. Their mycorrhizae (i.e., the associations of their roots with soil fungi) display a morphological diversity that correlates with the involved fungi. Mycorrhizae of Ericaceae greatly contributed to their ecological and evolutionary success, as exemplified in our recent works on Ericaceae mycorrhizae. Ericaceae phylogeny supports that two mycorrhizal evolutionary transitions occurred during evolution of this taxon.
First, ancestral arbuscular mycorhizae (retained in Enkianthoideae) were replaced by Asco- and Basidiomycetes, that occur in the basal clades Arbutoideae (e.g. on Mediterranean Arbutus unedo) and Monotropoideae. The fungi involved usually form ectomycorrhizae on forest trees co-occurring with these species. In Monotropoideae, fungal sharing with surrounding trees likely allowed adaptation to low-light forests by indirect exploitation of tree carbon. The case for heterotrophic, achlorophyllous plants such as Monotropa spp. is long reported, but we found this strategy in closely related, green Monotropoideae species (Pyroleae: Pyrola and Orthilia spp.). Our investigations on stable carbon and nitrogen isotopes support a partial heterotrophy (called mixotrophy) for Pyroleae, contributing to their adaptation to shaded forests. Phylogenies suggest that mixotrophy likely arose in Monotropoideae ancestor and predisposed to the rise of fully heterotrophic species.
A second shift established the typical ericoid endomycorrhizae known in the Ericoideae / Styphelioideae / Vaccinioideae clades, where the fungi form intracellular hyphal coils in fine roots. The fungal partners were assumed to be exclusively Helotiales, a group of Ascomycetes. Our molecular and electron microscopy investigations showed that Sebacinales (an order of Basidiomycetes) commonly form ericoid endomycorrhizae worldwide. Our recent investigations show that these Sebacinales and Helotiales usually grow endophytically in many plants. Thus, at the rise of the typical ericoid endomycorrhizae, common endophytes were likely recruited as exclusive mycorrhizal fungi.
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1 - Centre d'Ecologie Fonctionnelle et Evolutive, CNRS, UMR 5175, Equipe Interactions Biotiques , 1919 Route de Mende, Montpellier, 34000, France
2 - Universitaet Tuebingen, Spezielle Botanik und Mykologie, Auf der Morgenstelle 1, Tuebingen, 72076, Germany
Presentation Type: Oral Paper:Papers for BSA Sections
Location: Wasatch A/Cliff Lodge - Level C
Date: Wednesday, July 29th, 2009
Time: 4:00 PM