title: Lower prevalence but similar fitness in a parasitic fungus at higher radiation levels near Chernobyl.
abstract: Nuclear disasters at Chernobyl and Fukushima provide examples of effects of acute ionizing radiation on mutations that can affect the fitness and distribution of species. Here, we investigated the prevalence of Microbotryum lychnidis-dioicae, a pollinator-transmitted fungal pathogen of plants causing anther-smut disease in Chernobyl, its viability, fertility and karyotype variation, and the accumulation of nonsynonymous mutations in its genome. We collected diseased flowers of Silene latifolia from locations ranging by more than two orders of magnitude in background radiation, from 0.05 to 21.03 μGy/h. Disease prevalence decreased significantly with increasing radiation level, possibly due to lower pollinator abundance and altered pollinator behaviour. Viability and fertility, measured as the budding rate of haploid sporidia following meiosis from the diploid teliospores, did not vary with increasing radiation levels and neither did karyotype overall structure and level of chromosomal size heterozygosity. We sequenced the genomes of twelve samples from Chernobyl and of four samples collected from uncontaminated areas and analysed alignments of 6068 predicted genes, corresponding to 1.04 × 10(7)  base pairs. We found no dose-dependent differences in substitution rates (neither dN, dS, nor dN/dS). Thus, we found no significant evidence of increased deleterious mutation rates at higher levels of background radiation in this plant pathogen. We even found lower levels of nonsynonymous substitution rates in contaminated areas compared to control regions, suggesting that purifying selection was stronger in contaminated than uncontaminated areas. We briefly discuss the possibilities for a mechanistic basis of radio resistance in this nonmelanized fungus.
authors.affiliation: Ecologie Systématique Evolution, CNRS, Univ. Paris-Sud, AgroParisTech, Université Paris-Saclay, 91400, Orsay, France.
authors.forename: Gabriela
authors.initials: G
authors.lastname: Aguileta
authors.affiliation: Ecologie Systématique Evolution, CNRS, Univ. Paris-Sud, AgroParisTech, Université Paris-Saclay, 91400, Orsay, France.
authors.forename: Helene
authors.initials: H
authors.lastname: Badouin
authors.affiliation: Biology Department, Amherst College, Amherst, MA 01002, USA.
authors.forename: Michael E
authors.initials: ME
authors.lastname: Hood
authors.affiliation: Ecologie Systématique Evolution, CNRS, Univ. Paris-Sud, AgroParisTech, Université Paris-Saclay, 91400, Orsay, France.
authors.forename: Anders P
authors.initials: AP
authors.lastname: Møller
authors.affiliation: Ecologie Systématique Evolution, CNRS, Univ. Paris-Sud, AgroParisTech, Université Paris-Saclay, 91400, Orsay, France.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Le Prieur
authors.affiliation: Ecologie Systématique Evolution, CNRS, Univ. Paris-Sud, AgroParisTech, Université Paris-Saclay, 91400, Orsay, France.
authors.forename: Alodie
authors.initials: A
authors.lastname: Snirc
authors.affiliation: INRA, Laboratoire des Interactions Plantes-Microorganismes (LIPM), UMR441, Castanet-Tolosan, F-31326, France.|CNRS, Laboratoire des Interactions Plantes-Microorganismes (LIPM), UMR2594, Castanet-Tolosan, F-31326, France.
authors.forename: Sophie
authors.initials: S
authors.lastname: Siguenza
authors.affiliation: Department of Biological Sciences, University of South Carolina, Columbia, SC, 29208, USA.
authors.forename: Timothy A
authors.initials: TA
authors.lastname: Mousseau
authors.affiliation: Ecologie Systématique Evolution, CNRS, Univ. Paris-Sud, AgroParisTech, Université Paris-Saclay, 91400, Orsay, France.
authors.forename: Jacqui A
authors.initials: JA
authors.lastname: Shykoff
authors.affiliation: Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA.
authors.forename: Christina A
authors.initials: CA
authors.lastname: Cuomo
authors.affiliation: Ecologie Systématique Evolution, CNRS, Univ. Paris-Sud, AgroParisTech, Université Paris-Saclay, 91400, Orsay, France.
authors.forename: Tatiana
authors.initials: T
authors.lastname: Giraud
mesh_terms: D000818:Animals; D001487:Basidiomycota / Q000235:genetics* / Q000472:pathogenicity / Q000528:radiation effects*; D002080:Butterflies; D047852:Chernobyl Nuclear Accident; D004271:DNA, Fungal / Q000235:genetics; D035264:Flowers / Q000382:microbiology; D056084:Genetic Fitness; D016681:Genome, Fungal; D007303:Insect Vectors; D059785:Karyotype; D059645:Mutation Rate; D010935:Plant Diseases / Q000382:microbiology; D011839:Radiation, Ionizing; D012100:Reproduction, Asexual; D012641:Selection, Genetic; D017422:Sequence Analysis, DNA; D029751:Silene / Q000382:microbiology*; D014455:Ukraine
chemical_list: D004271:DNA, Fungal
keywords: Microbotryum violaceum; bumblebees; butterflies; genomic degeneration; melanin; positive selection; red pigment