Molecular Phylogenetics and Evolution
2000: 14:276-284

Ancestral Lineages of Arbuscular Mycorrhizal Fungi (Glomales)

D. Redecker1, J. B. Morton2 and T. D. Bruns1
1 Department of Plant and Microbial Biology, 321 Koshland Hall, University of California, Berkeley, California, 94720, USA
2 International Collectioon of Vesicular-Arbuscular and Arbuscular Mycorrhizal Fungi, Division of Plant and Soil Sciences, 401 Brooks Hall, P.O. Box 6057, West Virginia University, Morgantown, West Virginia 26506

Using new and existing 18S rRNA sequence data, we show that at least five species of glomalean fungi lie outside the previously defined families and diverged very early in the evolution of that group. These five fungi would have been missed by many previous ecological studies because their sequences are not well matched to available taxon-specific primers and they do not stain well with the standard reagents used for morphological analysis. Based upon spore morphology, these species are currently assigned to Glomus and Acaulospora, and two of the species are dimorphic, exhibiting spore stages of both genera. This suggests that dimorphic spores are the ancestral state for the order and that one or the other morphology was lost in various lineages. Our analyses also show that Geosiphon pyriforme, a symbiont with cyanobacteria, is not necessarily a sister group of the Glomales; instead, it may be derived from mycorrhizal ancestors.

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