Comparison of the aflR gene sequences of strains in Aspergillus section Flavi

Abstract

Aflatoxins are polyketide-derived secondary metabolites produced by Aspergillus parasiticus, Aspergillus flavus, Aspergillus nomius and a few other species. The toxic effects of aflatoxins have adverse consequences for human health and agricultural economics. The aflR gene, a regulatory gene for aflatoxin biosynthesis, encodes a protein containing a zinc-finger DNA-binding motif. Although Aspergillus oryzae and Aspergillus sojae, which are used in fermented foods and in ingredient manufacture, have no record of producing aflatoxin, they have been shown to possess an aflR gene. This study examined 34 strains of Aspergillus section Flavi. The aflR gene of 23 of these strains was successfully amplified and sequenced. No aflR PCR products were found in five A. sojae strains or six strains of A. oryzae. These PCR results suggested that the aflR gene is absent or significantly different in some A. sojae and A. oryzae strains. The sequenced aflR genes from the 23 positive strains had greater than 96·6 % similarity, which was particularly conserved in the zinc-finger DNA-binding domain. The aflR gene of A. sojae has two obvious characteristics: an extra CTCATG sequence fragment and a C to T transition that causes premature termination of AFLR protein synthesis. Differences between A. parasiticus/A. sojae and A. flavus/A. oryzae aflR genes were also identified. Some strains of A. flavus as well as A. flavus var. viridis, A. oryzae var. viridis and A. oryzae var. effuses have an A. oryzae-type aflR gene. For all strains with the A. oryzae-type aflR gene, there was no evidence of aflatoxin production. It is suggested that for safety reasons, the aflR gene could be examined to assess possible aflatoxin production by Aspergillus section Flavi strains.

Genetic regulation of aflatoxin biosynthesis: From gene to genome

“…The aflR locus has been compared among strains within section Flavi, especially among isolates of AF producers such as A. parasiticus and A. flavus (Chang et al, 1995;Lee et al, 2006). These comparisons revealed differences in many promoter regulatory elements such as PacC and AreA binding sites (Ehrlich and Cotty, 2002;Lee et al, 2006). The aflR gene is also found in A. nidulans and A. fumigatus (Carbone et al, 2007).…”

“…The gene aflR encodes a sequence-specific DNA-binding binuclear zinc cluster (Zn(II) 2 Cys 6 ) protein, required for transcriptional activation of most, if not all, of the structural genes (Chang et al, 1993(Chang et al, , 1995Chang et al, 1999a,b;Ehrlich et al, 1998;Flaherty and Payne, 1997;Payne et al, 1993;Price et al, 2006;Woloshuk et al, 1994;Yu et al, 1996b). The aflR locus has been compared among strains within section Flavi, especially among isolates of AF producers such as A. parasiticus and A. flavus (Chang et al, 1995;Lee et al, 2006). These comparisons revealed differences in many promoter regulatory elements such as PacC and AreA binding sites (Ehrlich and Cotty, 2002;Lee et al, 2006).…”

Understanding the structure and variation within the genome of the pathogenic ascomycete fungus Leptosphaeria maculans

“…The four putative functional annotations were similar to AflR, similar to TPR domain protein, dicer-like protein 2 and similar to fatty acid synthase beta subunit. The AflR protein in Aspergillus species is involved in the activation of aflatoxin-related genes which are implicated in plant infection (Lee et al, 2006). Aflatoxins are a mycotoxin that can also affect animal and human health (Liu and Chu, 1998).…”

Hematoporphyrin-mediated photosensitization of aflatoxin-producing Aspergillus species isolated from meat products

“…and a final extension at 72 ºC for 5 min in 30 cycles. PCR products were separated and visualized by electrophoresis in 1.5% agarose (W ako, Japan) in Tris-acetate-EDTA (TAE) buffer at 100 V (Lee et al, 2006). aflR gene sequenci ng and anal ysi s:…”

“…3). T he c ons tructi on of the neighbour -joi ning tree of the aflR gene sequence is t he s ame as the amino acid s equenc e tree ( Lee et al, 2006). Strain 1188 1162 1076 1062 1032 1006 846 738 737 672 655 629 592 588 585 581 T Strain 1506 1477 1419 1402 1380 1377 1352 1337 1325 1293 1248 1205 1197 1506 1477 1419 A C A T The s t ud y of phot oi nac tiv ati on eff ec t of diff er ent c onc entr ati ons of hem at op orphyri n on t he gr owt h and afl at oxi n B 1 pr od uc ti on of toxig enic As per gill us is ol at es on Cz ap ek D ox ag ar m edi um ar e s how n i n t abl e 5.…”