High resolution mapping of the recombination landscape of the phytopathogen Fusarium graminearum suggests two-speed genome evolution

Recombination is a major evolutionary force, increasing genetic diversity and permitting efficient coevolution of fungal pathogen(s) with their host(s). The ascomycete Fusarium graminearum is a devastating pathogen of cereal crops, and can contaminate food and feed with harmful mycotoxins. Previous studies suggest a high-adaptive potential of this pathogen, illustrated by an increase of pathogenicity and resistance to fungicides. In this study, we provide the first detailed picture of the crossovers events occurring during meiosis and discuss the role of recombination may play for pathogen evolution. An experimental recombinant population (n=88) was created and genotyped using 1,306 polymorphic markers obtained from Restriction site Associated DNA sequencing (RAD-seq) and aligned to the reference genome. The construction of a high-density linkage map, anchoring 99% of the total length of the reference genome, allowed the identification of 1,451 putative crossovers, positioned at a median resolution of 24 kilobases. The majority of crossovers (87.2%) occurred in a relatively small portion of the genome (30%). All chromosomes demonstrated recombination-active sections which had a near 15-fold higher crossover rate than non-active recombinant ones. Recombination rate had a strong positive correlation with nucleotide diversity, and recombinant active regions were enriched for genes with a putative role in host-pathogen interaction, as well as putative diversifying genes. Our results confirm preliminary analysis observed in other F. graminearum strains and suggest a conserved 'two-speed' recombination landscape. The consequences on the evolutionary potential of this major fungal pathogen are also discussed. This article is protected by copyright. All rights reserved.