The intraspecific variability of mitochondrial genes of Agaricus bisporus reveals an extensive group I intron mobility combined with low nucleotide substitution rates
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Intraspecific mitochondrial variability was studied in ten strains of A. bisporus var. bisporus, in a strain representative of A. bisporus var. eurotetrasporus and in a strain of the closely related species Agaricus devoniensis. In A. bisporus, the cox1 gene is the richest in group I introns harboring homing endonuclease genes (heg). This study led to identify group I introns as the main source of cox1 gene polymorphism. Among the studied introns, two groups were distinguished according to the heg they contained. One group harbored heg maintained putatively functional. The other group was composed of eroded heg sequences that appeared to evolve toward their elimination. Low nucleotide substitution rates were found in both types of intronic sequences. This feature was also shared by all types of studied mitochondrial sequences, not only intronic but also genic and intergenic ones, when compared with nuclear sequences. Hence, the intraspecific evolution of A. bisporus mitochondrial genome appears characterized by both an important mobility (presence/absence) of large group I introns and by low nt substitution rates. This stringent conservation of mitochondrial sequences, when compared with their nuclear counterparts, appears irrespective of their apparent functionality and contrasts to what is widely accepted in fungal sequence evolution. This strengthens the usefulness of mtDNA sequences to get clues on intraspecific evolution.
KeywordsBasidiomycota cox1 gene heg Mobile ORF SNP (single-nucleotide polymorphism)
The authors thank the cultural service of French Embassy in Iran for the attribution of a research grant to Banafsheh Jalalzadeh. The authors also thank the French embassy in Senegal for the research grant U3E to Idy Carras Saré and the “Ministère de la recherche scientifique du Sénégal” as part of a “Program FIRST”.
Conflict of interest
The authors declare that they have no conflict of interest.
The authors declare that the experiments comply with the current laws of the countries, in which they were performed.
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