Geosiphon pyriforme, a fungus forming endocytobiosis withNostoc (Cyanobacteria), is an ancestral member of the glomales: Evidence by SSU rRNA Analysis

Abstract

Geosiphon pyriforme inhabiting the surface of humid soils represents the only known example of endocytobiosis between a fungus (Zygomycotina; macrosymbiont) and cyanobacteria (Nostoc; endosymbiont). In order to elucidate the taxonomical and evolutionary relationship of Geosiphon pyriforme to fungi forming arbuscular mycorrhiza (AM fungi), the small-subunit (SSU) ribosomal RNA genes of Geosiphon pyriforme and Glomus versiforme (Glomales; a typical AM fungus) were analyzed and aligned with SSU rRNA sequences of several Basidiomycetes, Ascomycetes, Chytridiomycetes, and Zygomycetes, together with all AM-fungal (Glomales) sequences published yet. The distinct group of the order Glomales, which includes Geosiphon, does not form a clade with any other group of Zygomycetes. Within the Glomales, two main lineages exist. One includes the families Gigasporaceae and Acaulosporaceae; the other one is represented by the genus Glomus, the members of which are very divergent. Glomus etunicatum and Geosiphon pyriforme both form independent lineages ancestral to the Glomales. The data provided by the present paper confirm clearly that Geosiphon represents a fungus belonging to the Glomales. The question remains still open as to whether or not Geosiphon is to be placed within or outside the genus Glomus, since this genus is probably polyphyletic and not well defined yet. Geosiphon shows the ability of a Glomus-like fungus to form a "primitive" symbiosis with a unicellular photoautotrophic organism, in this case a cyanobacterium, leading to the conclusion that a hypothetical association of a Glomus-like fungus with a green alga as a step during the evolution of the land plants appears probable.

Evolutionary relationships among basal fungi (Chytridiomycota and Zygomycota): Insights from molecular phylogenetics

“…The phylogenetic and taxonomic status of the muco-ralean family Mortierellaceae is problematic because it appeared to be distantly related to the other mucoralean fungi, i.e., it rather clusters with Endogone in several nSSU rDNA studies (Gehrig et al, 1996;Jensen et al, 1998). Besides molecular data, Mortierellacean fungi possess several characteristic phenotypic and biochemical properties that are distinct from other mucoralean fungi: hyaline and smooth zygospores, sporangia without a columella (a structure inside the sporangium that is extended from the sporangiophore), and desmosterol and 24,25-methylene cholesterol as the major sterol components (ergosterol in other mucoralean fungi; see Gandhi, 1997, 1999).…”

“…Several nSSU rDNA studies have suggested that the Glomales evolved separately from other basal fungal orders, and that it was related to even higher fungi (Bruns et al, 1992;Gehrig et al, 1996;Jensen et al, 1998;Nagahama et al, 1995;Schüßler et al, 2001). From these results, Schüßler et al (2001) revised the higher-level taxonomy of the Glomales: the Glomales (sensu Morton and Benny, 1990) was elevated to the new phylum Glomeromycota, and the four orders, the Archaeosporales, Diversisporales, Glomerales, and Paraglomales were revised or newly erected within the Glomeromycota.…”

“…Global phylogeny highlighting interordinal relationships of basal Fungi. The tree was proposed taking into account recent results of molecular phylogenetic analyses based on nSSU rDNA (Benny and O'Donnell, 2000;Cafaro, 2005;Gehrig et al, 1996;Tanabe et al, 2000), RPB1 (Tanabe et al, 2004), complete mitochondrial genome (Bullerwell et al, 2003a;Lang et al, 2002) sequences, and the EF-1a indel analysis (Fig. 2).…”

Tansley Review No. 116

“…Difficulties persist in the identification and nomenclature of mycobionts, requiring a combination of morphological, physiological and molecular approaches (Jorgensen, 1991 ;Gargas & Taylor, 1992 ;Bridge & Hawksworth, 1998 ;Nimis, 1998 ;Rambold et al, 1998). †See Schussler et al (1994) and Gehrig et al (1996). ‡See Villareal (1992), Schenk (1992) and Carpenter et al (1999).…”

Enhanced Secondary- and Hormone Metabolism in Leaves of Arbuscular Mycorrhizal Medicago truncatula

“…AM fungi predominantly belong to the phylum Glomeromycota (Gehrig et al, 1996;Schussler et al, 2001). They enhance water uptake and mineral nutrition (mostly inorganic phosphate [P i ]) of the host plant, which, in return, provides photosynthates to the fungus through hyphal structures called arbuscules (Baier et al, 2010;Doidy et al, 2012).…”