Sexuality Generates Diversity in the Aflatoxin Gene Cluster: Evidence on a Global Scale

PLoS Pathogens

Eric A. Stone¹  Rakhi Singh²  Jacalyn L. Elliott²  Manjunath K. Naik³  German G. Barros³  Sofia N. Chulze⁴  Graeme C. Wright⁵  Kerstin Hell⁶  Ignazio Carbone⁷  Bruce W. Horn⁸  Joe W. Dorner⁸  Geromy G. Moore⁹ 

[1] Bioinformatics Research Center, North Carolina State University, Raleigh, North Carolina, United States of America;Center for Integrated Fungal Research, Department of Plant Pathology, North Carolina State University, Raleigh, North Carolina, United States of America;Departamento de Microbiología e Inmunología, Universidad Nacional de Río Cuarto, Córdoba, Argentina;Department of Genetics, North Carolina State University, Raleigh, North Carolina, United States of America;Department of Plant Pathology, College of Agriculture, Karnataka, India;Department of Primary Industries, Kingaroy, Queensland, Australia;International Institute of Tropical Agriculture, Cotonou, Republic of Benin;National Peanut Research Laboratory, Agricultural Research Service, United States Department of Agriculture, Dawson, Georgia, United States of America;Southern Regional Research Center, Agricultural Research Service, United States Department of Agriculture, New Orleans, Louisiana, United States of America

关键词: Aspergillus flavus;    Argentina;    Toxins;    Australia;    Haplotypes;    Benin;    India;    Population genetics;   

DOI  :  10.1371/journal.ppat.1003574

学科分类：生物科学（综合）

来源: Public Library of Science

【 摘 要 】

Aflatoxins are produced by Aspergillus flavus and A. parasiticus in oil-rich seed and grain crops and are a serious problem in agriculture, with aflatoxin B1 being the most carcinogenic natural compound known. Sexual reproduction in these species occurs between individuals belonging to different vegetative compatibility groups (VCGs). We examined natural genetic variation in 758 isolates of A. flavus, A. parasiticus and A. minisclerotigenes sampled from single peanut fields in the United States (Georgia), Africa (Benin), Argentina (Córdoba), Australia (Queensland) and India (Karnataka). Analysis of DNA sequence variation across multiple intergenic regions in the aflatoxin gene clusters of A. flavus, A. parasiticus and A. minisclerotigenes revealed significant linkage disequilibrium (LD) organized into distinct blocks that are conserved across different localities, suggesting that genetic recombination is nonrandom and a global occurrence. To assess the contributions of asexual and sexual reproduction to fixation and maintenance of toxin chemotype diversity in populations from each locality/species, we tested the null hypothesis of an equal number of MAT1-1 and MAT1-2 mating-type individuals, which is indicative of a sexually recombining population. All samples were clone-corrected using multi-locus sequence typing which associates closely with VCG. For both A. flavus and A. parasiticus, when the proportions of MAT1-1 and MAT1-2 were significantly different, there was more extensive LD in the aflatoxin cluster and populations were fixed for specific toxin chemotype classes, either the non-aflatoxigenic class in A. flavus or the B1-dominant and G1-dominant classes in A. parasiticus. A mating type ratio close to 1∶1 in A. flavus, A. parasiticus and A. minisclerotigenes was associated with higher recombination rates in the aflatoxin cluster and less pronounced chemotype differences in populations. This work shows that the reproductive nature of the population (more sexual versus more asexual) is predictive of aflatoxin chemotype diversity in these agriculturally important fungi.

【 授权许可】

CC BY