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Cryptic speciation and recombination in the aflatoxin-producing fungus Aspergillus flavus
D M Geiser1, J I Pitt, J W Taylor
1Department of Plant and Microbial Biology, University of California, Berkeley, CA 94720, USA. dgeiser@nature.bereley.edu
Abstract:
Aspergillus flavus, like approximately one-third of ascomycete fungi, is thought to be cosmopolitan and clonal because it has uniform asexual morphology. A. flavus produces aflatoxin on nuts, grains, and cotton, and assumptions about its life history are being used to develop strategies for its biological control. We tested the assumptions of clonality and conspecificity in a sample of 31 Australian isolates by assaying restriction site polymorphisms from 11 protein encoding genes and DNA sequences from five of those genes. A. flavus isolates fell into two reproductively isolated clades (groups I and II). The lack of concordance among gene genealogies among isolates in one of the clades (group I) was consistent with a history of recombination. Our analysis included five strains of the closely related industrial fungus A. oryzae, all of which proved to be clonally related to group I.
Insights
Aspergillus flavus, a fungus producing aflatoxin, is not entirely clonal. Genetic analysis revealed two distinct groups, one showing evidence of recombination, challenging previous assumptions for biological control strategies.
Area of Science:
- Mycology
- Fungal Genetics
- Population Biology
Background:
- Aspergillus flavus is widely distributed and presumed clonal due to uniform asexual morphology.
- This fungus produces aflatoxins, necessitating effective biological control strategies based on its life history.
- Previous assumptions about A. flavus clonality influence current control method development.
Purpose of the Study:
- To investigate the clonality and conspecificity of Aspergillus flavus isolates.
- To determine the genetic diversity and reproductive history of Australian A. flavus populations.
- To assess the relationship between A. flavus and the industrial fungus Aspergillus oryzae.
Main Methods:
- Analysis of restriction site polymorphisms in 11 protein-encoding genes from 31 A. flavus isolates.
- DNA sequencing of five of these genes to further assess genetic variation.
- Comparative analysis including five strains of Aspergillus oryzae.
Main Results:
- A. flavus isolates were divided into two reproductively isolated clades (Group I and Group II).
- Evidence of recombination was found within Group I, contradicting a purely clonal history.
- All analyzed Aspergillus oryzae strains were found to be clonally related to Group I of A. flavus.
Conclusions:
- The assumption of A. flavus being exclusively clonal is challenged by genetic evidence of recombination.
- Distinct genetic groups within A. flavus may have implications for developing targeted biological control methods.
- The close clonal relationship between A. oryzae and a clade of A. flavus warrants further investigation.