Molecular Mechanisms of Chromosomal Rearrangement in Fungi

Abstract

Both sexual and asexual fungi undergo chromosomal rearrangements, which are the main cause of karyotype variability among the populations. Different recombination processes can produce chromosomal reorganizations, both during mitosis and meiosis, but other mechanisms operate to limit the extent of the rearrangements; some of these mechanisms, such as the RIP (repeat-induced point mutations) of Neurospora crassa, have been well established for sexual fungi. In laboratory strains, treatments such as mutation and transformation enhance the appearance of chromosomal rearrangements. Different DNA sequences present in fungal genomes are able to promote these reorganizations; some of these sequences are involved in well-regulated processes (e.g., site-specific recombination) but most of them act simply as substrates for recombination events leading to DNA rearrangements. In Penicillium chrysogenum we have found that short specific DNA sequences are involved in tandem reiterations leading to amplification of the cluster of the penicillin biosynthesis genes. In some cases, specific chromosomal rearrangements have been associated with particular phenotypes (as occurs in adaptive-like mutants of Candida albicans and Candida stellatoidea), and they may play a role in genetic variability for environmental adaptation.

Recombination and Annealing Pathways Compete for Substrates in Making rrn Duplications in Salmonella enterica

“…While standard conversion events would be expected to require canonical recombination functions, the rate of rDNA copy-number increase is not reduced by lack of Rad51, Rad52, or Rad59 (Houseley and Tollervey 2011). Although the process of yeast rDNA copy-number control is complex (Fierro 1999;Pâques and Haber 1999), it may resemble the process described here in that copy-number changes are caused by homologous recombination, but can also arise by alternative annealing pathways that are activated when recombination is prevented. In addition, the copy-number changes in yeast rDNA copies may be more similar to the second step of amplification (e.g., increasing from a tandem duplication to three tandem copies).…”

Potential Role of Transposable Elements in the Rapid Reorganization of the Fusarium oxysporum Genome

“…With the development of pulsed-field gradient gel electrophoresis (PFGE), first done for molecular karyotyping in yeast (Schwartz and Cantor, 1984), the study of the small size of the chromosomes was transformed since almost all the chromosomes of fungi could be separated electrophoretically. This approach has led to the discovery that chromosome length polymorphism (CLP) is a very common feature in natural isolates of fungi (reviewed in Kistler and Miao, 1992;Zolan, 1995;Fierro and Martin, 1999), thus revealing the flexibility of the fungal genome. Previous karyotyping studies on F. oxysporum isolates revealed differences between formae speciales (Migheli et al, 1993) but also among individual strains of a forma specialis, exemplified by f. sp.…”

Fine-Resolution Physical Mapping of Genomic Diversity in Candida albicans

“…However, in a population that undergoes clonal propagation, the diversification of karyotype will be acceptable if the progeny are viable (reviewed in Zolan 1995). Karyotypic variation has been reported in species that undergo clonal propagation (Mills and McCluskey 1990;Zolan 1995;Fierro and Martin 1999). However, the molecular mechanisms for karyotypic variation have not yet been clarified.…”