Molecular Phylogenetics and Evolution
Ancestral Lineages of Arbuscular Mycorrhizal Fungi (Glomales)
J. B. Morton2 and
T. D. Bruns1
Department of Plant and Microbial Biology, 321 Koshland Hall,
University of California, Berkeley, California, 94720, USA
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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