No Plant Is an Island

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Science  09 Apr 2010:
Vol. 328, Issue 5975, pp. 141
DOI: 10.1126/science.328.5975.141-b
CREDIT: NAUMANN ET AL., ISME J. 10.1038/ISMEJ.2010.21 (2010)

Most land plants form mutualistic associations with fungi, in which the partners rely on each other for mineral and nutrient exchange, as well as for the endowment of beneficial properties such as heat tolerance and protection from pests. These arbuscular mycorrhizal fungi (AMFs) in turn host at least two types of endosymbiotic prokaryotes: a β-proteobacterium and a distinctive coccoid Gram-positive entity. Naumann et al. have found the latter in the cytoplasm of many AMF lineages, and sequence analysis shows that despite possessing a cell wall, these bacterium-like organisms cluster with the Mollicutes. These bacteria appear to have been associated with AMFs since the Devonian, 400 million years ago; for this partnership to have persisted so long, there must be significant fitness benefits. Furthermore, this association is an intimate one as the bacteria live in the fungal cytoplasm with no discernable membrane enclosing them. This discovery raises several questions about the evolution of key bacterial and fungal lineages, as well as the evolution of plants and the functional nature of this ecologically key suite of symbioses.

ISME J. 10.1038/ismej.2010.21 (2010).

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