Submitted to: Keystone Symposia
Publication Type: Abstract Only
Publication Acceptance Date: 11/4/2011
Publication Date: 1/10/2012
Citation: Olarte, R.A., Horn, B.W., Monacell, J.T., Singh, R., Carbone, I. 2012. Evidence of aneuploidy modulating aflatoxigenicity in Aspergillus flavus. Keystone Symposia. Interpretive Summary: None required.
Technical Abstract: Aspergillus flavus is a well-known pathogen of many important agricultural commodities and is a major producer of aflatoxins, which are carcinogenic polyketides that pose a serious health risk to humans and animals. Aflatoxin contamination in peanut exports worldwide accounts for as much as $450 million in losses. A. flavus is also an emerging human pathogen and is second only to A. fumigatus in reported aspergillosis outbreaks. Comparative genome analyses between A. flavus and its domesticated nontoxigenic relative A. oryzae have revealed large chromosomal inversions and duplications. Similar genome rearrangements and aneuploidies are observed in natural A. flavus strains and in progeny strains derived from intra-specific matings. We recently described Petromyces flavus, the sexual state of A. flavus, from crosses between strains of opposite mating type. In the present study, we genetically examined the F1 offspring from several sexual crosses. We observed non-Mendelian inheritance of extra-genomic aflatoxin cluster alleles in crosses with partial aflatoxin cluster parents. The specific function of cryptic alleles and the mechanisms for their transmission are currently under investigation. Because A. flavus has multinucleate mycelium and conidia, we cannot rule out the possibility of cryptic heterokaryosis in which the parental strains harbor a small proportion of aneuploid nuclei that sort out in progeny in a non-Mendelian-like fashion. Preliminary evidence indicates that aneuploidy can be maintained to varying degrees in natural isolates but may be accelerated in strains that are serially transferred under adverse culture conditions. For example, A. flavus lineage IB appears to be more prone to segmental aneuploidy, resulting in a large 300-kb deletion from the right arm of chromosome 3, which harbors the aflatoxin gene cluster. This is advantageous from a screening perspective since the frequency of segmental aneuploids in progeny populations can be easily determined by assaying for aflatoxin production. Further characterization of aneuploidies and their frequency in A. flavus populations will be important in understanding the role of genome plasticity in modulating toxicity and the adaptation of these fungi to changing environmental conditions.