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Applied and Environmental Microbiology, April 2009, p. 1970-1978, Vol. 75, No. 7
0099-2240/09/$08.00+0     doi:10.1128/AEM.01974-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

High-Level Molecular Diversity of Copper-Zinc Superoxide Dismutase Genes among and within Species of Arbuscular Mycorrhizal Fungi ^,

Nicolas Corradi,^1,2, Beat Ruffner,^1, Daniel Croll,¹ Alexandre Colard,¹ Ales Horák,² and Ian R. Sanders^1*

Department of Ecology and Evolution, Biophore Building, University of Lausanne, CH-1015 Lausanne, Switzerland,¹ Department of Botany, University of British Columbia, 3529-6270 University Boulevard, Vancouver, British Columbia V6T 1Z4, Canada²

Received 25 August 2008/ Accepted 21 January 2009

In the ecologically important arbuscular mycorrhizal fungi (AMF), Sod1 encodes a functional polypeptide that confers increased tolerance to oxidative stress and that is upregulated inside the roots during early steps of the symbiosis with host plants. It is still unclear whether its expression is directed at scavenging reactive oxygen species (ROS) produced by the host, if it plays a role in the fungus-host dialogue, or if it is a consequence of oxidative stress from the surrounding environment. All these possibilities are equally likely, and molecular variation at the Sod1 locus can possibly have adaptive implications for one or all of the three mentioned functions. In this paper, we analyzed the diversity of the Sod1 gene in six AMF species, as well as 14 Glomus intraradices isolates from a single natural population. By sequencing this locus, we identified a large amount of nucleotide and amino acid molecular diversity both among AMF species and individuals, suggesting a rapid divergence of its codons. The Sod1 gene was monomorphic within each isolate we analyzed, and quantitative PCR strongly suggest this locus is present as a single copy in G. intraradices. Maximum-likelihood analyses performed using a variety of models for codon evolution indicated that a number of amino acid sites most likely evolved under the regime of positive selection among AMF species. In addition, we found that some isolates of G. intraradices from a natural population harbor very divergent orthologous Sod1 sequences, and our analysis suggested that diversifying selection, rather than recombination, was responsible for the persistence of this molecular diversity within the AMF population.

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* Corresponding author. Mailing address: Department of Ecology and Evolution, Biophore Building, University of Lausanne, CH-1015 Lausanne, Switzerland. Phone: 41 21 692 4261. Fax: 41 21 692 4265. E-mail: Ian.Sanders{at}unil.ch

Published ahead of print on 6 February 2009.

Supplemental material for this article may be found at http://aem.asm.org/.

N.C. and B.R. contributed equally to this work.

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Applied and Environmental Microbiology, April 2009, p. 1970-1978, Vol. 75, No. 7
0099-2240/09/$08.00+0     doi:10.1128/AEM.01974-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.