The human fungal pathogen Aspergillus fumigatus can produce the highest known number of meiotic crossovers

Sexual reproduction involving meiosis is essential in most eukaryotes. This produces offspring with novel genotypes, both by segregation of parental chromosomes as well as crossovers between homologous chromosomes. A sexual cycle for the opportunistic human pathogenic fungus Aspergillus fumigatus is known, but the genetic consequences of meiosis have remained unknown. Among other Aspergilli, it is known that A. flavus has a moderately high recombination rate with an average of 4.2 crossovers per chromosome pair, whereas A. nidulans has in contrast a higher rate with 9.3 crossovers per chromosome pair. Here, we show in a cross between A. fumigatus strains that they produce an average of 29.9 crossovers per chromosome pair and large variation in total map length across additional strain crosses. This rate of crossovers per chromosome is more than twice that seen for any known organism, which we discuss in relation to other genetic model systems. We validate this high rate of crossovers through mapping of resistance to the laboratory antifungal acriflavine by using standing variation in an undescribed ABC efflux transporter. We then demonstrate that this rate of crossovers is sufficient to produce one of the common multidrug resistant haplotypes found in the cyp51A gene (TR34/L98H) in crosses among parents harboring either of 2 nearby genetic variants, possibly explaining the early spread of such haplotypes. Our results suggest that genomic studies in this species should reassess common assumptions about linkage between genetic regions. The finding of an unparalleled crossover rate in A. fumigatus provides opportunities to understand why these rates are not generally higher in other eukaryotes

Identification of a mitotic recombination hotspot on chromosome III of the asexual fungus Aspergillus niger and its possible correlation elevated basal transcription

Genetic recombination is an important tool in strain breeding in many organisms. We studied the possibilities of mitotic recombination in strain breeding of the asexual fungus Aspergillus niger. By identifying genes that complemented mapped auxotrophic mutations, the physical map was compared to the genetic map of chromosome III using the genome sequence. In a program to construct a chromosome III-specific marker strain by selecting mitotic crossing-over in diploids, a mitotic recombination hotspot was identified. Analysis of the mitotic recombination hotspot revealed some physical features, elevated basal transcription and a possible correlation with purine stretches