Intron gains and losses in the evolution of fusarium and cryptococcus fungi

Abstract

The presenceof spliceosomal introns in eukaryoticgenes poses a major puzzle for the study ofgenomeevolution. Introndensities vary enormously among distant lineages. However, the mechanisms driving intron gains are poorly understood and very few intron gains and losses have been documented over short evolutionary time spans. Fungi emerged recently as excellent models to study intron evolution and "reverse splicing" was found to be amajor driver of recent intron gains in a clade of ascomycete fungi.Wescreened a total of 38 genomes from twofungal clades important inmedicine and agriculture to identify intron gains and losses both within and between species. We detected 86 and 198 variable intron positions in the Cryptococcus and Fusarium clades, respectively. Some genes underwent extensive changes in their exon-intron structure, with up to six variable intron positions per gene. We identified a very recently gained intron in a group of tomato-infecting strains belonging to the F. oxysporum species complex. In the human pathogen C. gattii, we found recent intron losses in subtypes of the species. The two studied fungal clades provided evidence for extensive changes in their exon-intron structure within and among closely related species. We show that both intronization of previously coding DNA and insertion of exogenous DNA are the major drivers of intron gains. © The Author(s) 2012.