Gehrig H, Schüssler A, Kluge M
Institut für Botanik, der Technischen Hochschule Darmstadt, Germany.
J Mol Evol. 1996 Jul;43(1):71-81. doi: 10.1007/BF02352301.
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.
栖息于潮湿土壤表面的梨形地管菌是已知唯一的真菌（接合菌亚门；大共生体）与蓝细菌（念珠藻属；内共生体）之间内共生现象的例子。为了阐明梨形地管菌与形成丛枝菌根的真菌（丛枝菌根真菌）之间的分类学和进化关系，对梨形地管菌和多样硬囊霉（球囊霉目；一种典型的丛枝菌根真菌）的小亚基（SSU）核糖体RNA基因进行了分析，并与几种担子菌纲、子囊菌纲、壶菌纲和接合菌纲真菌的SSU rRNA序列以及所有已发表的丛枝菌根真菌（球囊霉目）序列进行了比对。包括地管菌在内的球囊霉目这一独特类群并不与任何其他接合菌纲类群形成一个进化枝。在球囊霉目内，存在两个主要谱系。一个包括巨孢囊霉科和无梗囊霉科；另一个以硬囊霉属为代表，该属成员差异很大。地表球囊霉和梨形地管菌都形成了球囊霉目的祖先独立谱系。本文提供的数据清楚地证实，地管菌是属于球囊霉目的一种真菌。地管菌是否应归入硬囊霉属仍悬而未决，因为该属可能是多系的且尚未得到很好的界定。地管菌表现出类似硬囊霉属真菌与单细胞光合自养生物（在这种情况下是蓝细菌）形成“原始”共生关系的能力，由此得出结论，在陆地植物进化过程中，类似硬囊霉属真菌与绿藻的假设关联似乎是可能的。
