Bacterial endosymbionts of arbuscular mycorrhizal fungi: ecology and evolution*

The goal of this project is to understand the interaction between arbuscular mycorrhizal (AM) fungi (phylum Glomeromycota) and endosymbiotic bacteria that reside in their hyphae and spores.  AM fungi and their endobacteria are components of a three-partite symbiotic association that also includes the majority of terrestrial plants, and may be one of the most common multipartner symbioses on the planet.  AM fungi colonize roots of land plants, and assist in the uptake of mineral nutrients to the plant in exchange for plant-assimilated carbon.  As a consequence, arbuscular mycorrhiza is a pivotal interaction that shapes the structure and function of terrestrial ecosystems.  Endobacteria of AM fungi associated with dune vegetation of the North Atlantic coast of the U. S. were selected as a focal system for the study.   


Experimental plan

(i) A survey of endobacteria distribution among AM fungal lineages combined with reconstruction of phylogenies of the interacting partners will enable inferences about the evolutionary origin, the age of the association, and the phylogentic relationships of endobacteria with their free-living relatives. 

(ii) A reconstruction of the population structure of endobacteria will clarify their reproductive and transmission mode. 

(iii) An assessment of the effects that harboring endobacteria has on the fungal host fitness as well as on the plant host fitness will reveal whether endobacteria are parasites or mutualists of AM fungi and, as a result, of arbuscular mycorrhiza.


Publications

Mondo, S.J., K.H. Toomer, J.B. Morton, Y. Lekberg and T.E. Pawlowska.  2012.  Evolutionary stability in a 400-million-year-old heritable facultative mutualism.  Evolution 66: 2564-2576. Abstract

Castillo, D.M. and T.E. Pawlowska.  2010. Molecular evolution in bacterial endosymbionts of fungi. Molecular Biology and Evolution 27(3): 622–636. Abstract

*Funded by NSF DEB-0918880

1Background image: bacterial endosymbionts in Gigaspora margarita spore cytoplasm visualized by cytological staining with the LIVE/DEAD® BacLight™ Bacterial Viability Kit; live bacteria are pseudo-colored green; dead bacteria are red. Photo Kara Pivarski.

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