Submitted to: Mycological Society of America
Publication Type: Abstract only
Publication Acceptance Date: 4/2/2010
Publication Date: 6/25/2010
Citation: Olarte, R.A., Horn, B.W., Monacell, T., Stone, E., Carbone, I. 2010. Direct genetic evidence to support the presence of sexual recombination within the life cycle of Aspergillus flavus. Mycological Society of America. Interpretive Summary: none required.
Technical Abstract: Aspergillus flavus contaminates many important crops worldwide and is the major producer of aflatoxins, which are cancer-causing secondary metabolites. In the United States, mycotoxins have been estimated to cause agricultural losses totaling upwards of $1.4 billion annually, with aflatoxin contamination in peanut export worldwide potentially accounting for as much as $450 million. We recently described Petromyces flavus, the sexual state of A. flavus, from crosses between strains of the opposite mating type. Sexually compatible strains when crossed with one another varied greatly in their degree of fertility. We demonstrated that sexual reproduction in A. flavus is heterothallic and occurs between individuals belonging to different vegetative compatibility groups, which suggests that the vegetative compatibility system is not a barrier to gene flow. In the present study, we genetically examined the F1 offspring from several successful crosses. Linked loci within the aflatoxin gene cluster on chromosome 3 and unlinked loci on different chromosomes were analyzed to quantify gene flow. We present the first direct genetic evidence to support the occurrence of sexual recombination between compatible strains of A. flavus through the meiotic processes of independent assortment and crossing-over, both of which are likely to contribute to the maintenance and regeneration of the aflatoxigenic phenotype. Crossing-over can repair deleterious mutations in the aflatoxin cluster in recombinant offspring; alternatively, independent assortment of chromosome 3 can potentially restore aflatoxigenicity. Our experimental results are consistent with recent indirect inferences of recombination in nature. The locations of the crossover breakpoints within the aflatoxin cluster of the recombinant F1 progeny from our mating studies corroborate with those deduced from the genetic analysis of natural populations. Implications of recombination on mycotoxin heritability are currently under investigation.