Sequence comparison of aflR from different Aspergillus species provides evidence for variability in regulation of aflatoxin production

Aflatoxin contamination of foods and feeds is a world-wide agricultural problem. Aflatoxin production requires expression of the biosynthetic pathway regulatory gene, aflR, which encodes a Cys6Zn2-type DNA-binding protein. Homologs of aflR from Aspergillus nomius, bombycis, parasiticus, flavus, and pseudotamarii were compared to investigate the molecular basis for variation among aflatoxin-producing taxa in the regulation of aflatoxin production. Variability was found in putative promoter consensus elements and coding region motifs, including motifs involved in developmental regulation (AbaA, BrlA), regulation of nitrogen source utilization (AreA), and pH regulation (PacC), and in coding region PEST domains. Some of these elements may affect expression of aflJ, a gene divergently transcribed from aflR, that also is required for aflatoxin accumulation. Comparisons of phylogenetic trees obtained with either aligned aflR intergenic region sequence or coding region sequence and the observed divergence in regulatory features among the taxa provide evidence that regulatory signals for aflatoxin production evolved to respond to a variety of environmental stimuli under differential selective pressures. Phylogenetic analyses also suggest that isolates currently assigned to the A. flavus morphotype SBG represent a distinct species and that A. nomius is a diverse paraphyletic assemblage likely to contain several species.