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Proc Natl Acad Sci U S A. 2015 Jun 23;112(25):7791-6. doi: 10.1073/pnas.1501676112. Epub 2015 May 11.

Minimal genomes of mycoplasma-related endobacteria are plastic and contain host-derived genes for sustained life within Glomeromycota.

Author information

1
Graduate Field of Microbiology, Cornell University, Ithaca, NY 14853;
2
Division of Plant and Soil Sciences, West Virginia University, Morgantown, WV 26506; and.
3
Plant Pathology and Plant-Microbe Biology, School of Integrative Plant Science, Cornell University, Ithaca, NY 14853 tep8@cornell.edu.

Abstract

Arbuscular mycorrhizal fungi (AMF, Glomeromycota) colonize roots of the majority of terrestrial plants. They provide essential minerals to their plant hosts and receive photosynthates in return. All major lineages of AMF harbor endobacteria classified as Mollicutes, and known as mycoplasma-related endobacteria (MRE). Except for their substantial intrahost genetic diversity and ability to transmit vertically, virtually nothing is known about the life history of these endobacteria. To understand MRE biology, we sequenced metagenomes of three MRE populations, each associated with divergent AMF hosts. We found that each AMF species harbored a genetically distinct group of MRE. Despite vertical transmission, all MRE populations showed extensive chromosomal rearrangements, which we attributed to genetic recombination, activity of mobile elements, and a history of plectroviral invasion. The MRE genomes are characterized by a highly reduced gene content, indicating metabolic dependence on the fungal host, with the mechanism of energy production remaining unclear. Several MRE genes encode proteins with domains involved in protein-protein interactions with eukaryotic hosts. In addition, the MRE genomes harbor genes horizontally acquired from AMF. Some of these genes encode small ubiquitin-like modifier (SUMO) proteases specific to the SUMOylation systems of eukaryotes, which MRE likely use to manipulate their fungal host. The extent of MRE genome plasticity and reduction, along with the large number of horizontally acquired host genes, suggests a high degree of adaptation to the fungal host. These features, together with the ubiquity of the MRE-Glomeromycota associations, emphasize the significance of MRE in the biology of Glomeromycota.

KEYWORDS:

genome contraction; genome plasticity; horizontal gene transfer; vertical transmission

Comment in

PMID:
25964324
PMCID:
PMC4485128
DOI:
10.1073/pnas.1501676112
[Indexed for MEDLINE]
Free PMC Article

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