Comparative genomics ofCryptococcusandKwoniellareveals pathogenesis evolution and contrasting karyotype dynamics via intercentromeric recombination or chromosome fusion

Abstract

AbstractA large-scale comparative genomic analysis was conducted for the global human fungal pathogens within theCryptococcusgenus, compared to non-pathogenicCryptococcusspecies, and related species from the sister genusKwoniella. Chromosome-level genome assemblies were generated for multiple species of both genera, resulting in a dataset encompassing virtually all of their known diversity. AlthoughCryptococcusandKwoniellahave comparable genome sizes (about 19.2 and 22.9 Mb) and similar gene content, hinting at pre-adaptive pathogenic potential, our analysis found evidence in pathogenicCryptococcusspecies of specific examples of gene gain (via horizontal gene transfer) and gene loss, which might represent evolutionary signatures of pathogenic development. Genome analysis also revealed a significant variation in chromosome number and structure between the two genera. By combining synteny analysis and experimental centromere validation, we found that mostCryptococcusspecies have 14 chromosomes, whereas mostKwoniellaspecies have fewer (11, 8, 5 or even as few as 3). Reduced chromosome number inKwoniellais associated with formation of giant chromosomes (up to 18 Mb) through repeated chromosome fusion events, each marked by a pericentric inversion and centromere loss. While similar chromosome inversion-fusion patterns were observed in allKwoniellaspecies with fewer than 14 chromosomes, no such pattern was detected inCryptococcus. Instead,Cryptococcusspecies with less than 14 chromosomes, underwent chromosome reductions primarily through rearrangements associated with the loss of repeat-rich centromeres. Additionally,Cryptococcusgenomes exhibited frequent interchromosomal translocations, including intercentromeric recombination facilitated by transposons shared between centromeres. Taken together, our findings advance our understanding of genomic changes possibly associated with pathogenicity inCryptococcusand provide a foundation to elucidate mechanisms of centromere loss and chromosome fusion driving distinct karyotypes in closely related fungal species, including prominent global human pathogens.