Nuclear populations of the multinucleate fungus of leafcutter ants can be dekaryotized and recombined to manipulate growth of nutritive hyphal nodules harvested by the ants

ABSTRACT

We dekaryotized the multinucleate fungus Leucocoprinus gongylophorus, a symbiotic fungus cultivated vegetatively by leafcutter ants as their food. To track genetic changes resulting from dekaryotization (elimination of some nuclei from the multinuclear population), we developed two multiplex microsatellite fingerprinting panels (15 loci total), then characterized the allele profiles of 129 accessions generated by dekaryotization treatment. Genotype profiles of the 129 accessions confirmed allele loss expected by dekaryotization of the multinucleate fungus. We found no evidence for haploid and single-nucleus strains among the 129 accessions. Microscopy of fluorescently stained dekaryotized accessions revealed great variation in nuclei number between cells of the same vegetative mycelium, with cells containing typically between 3 and 15 nuclei/cell (average = 9.4 nuclei/cell; mode = 8). We distinguish four mycelial morphotypes among the dekaryotized accessions; some of these morphotypes had lost the full competence to produce gongylidia (nutritive hyphal-tip swellings consumed by leafcutter ants as food). In mycelial growth confrontations between different gongylidia-incompetent accessions, allele profiles suggest exchange of nuclei between dekaryotized accessions, restoring full gongylidia competence in some of these strains. The restoration of gongylidia competence after genetic exchange between dekaryotized strains suggests the hypothesis that complementary nuclei interact, or nuclear and cytoplasmic factors interact, to promote or enable gongylidia competence.

KEYWORDS:

• Attamyces bromatificus
• Attini
• fungus-growing ant
• Leucoagaricus gongylophorus
• Leucocoprinus gongylophorus
• multinucleate
• multiplex microsatellite markers
• polyploidy

ACKNOWLEDGMENTS

We thank J. Miller and J. Peña for help with maintenance of fungal isolates; Duur Aanen, Eric Bastiaans, Alex Grum-Grzhimaylo, Mathijs Nieuwenhuis, Lennart van de Peppel, Sabine Vreeburg, and Margo Wisselink for constructive comments on the manuscript; and Timothy James for advice on interpretation of microscopy images and comments to improve the manuscript.

FUNDING

The work was supported by the National Science Foundation (DEB-0639879, IOS-0920138, and DEB-1354666 to U.G.M.); an Undergraduate Research Fellowship to I.G. from the College of Natural Science of the University of Texas at Austin; and the W. M. Wheeler Lost Pines Endowment.

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