Nonfunctionality of Aspergillus sojae aflR in a Strain of Aspergillus parasiticus with a Disrupted aflR Gene

Abstract

Aspergillus sojae belongs to the Aspergillus section Flavi but does not produce aflatoxins. The functionality of the A. sojae aflR gene (aflRs) was examined by transforming it into an ⌬aflR strain of A. parasiticus, derived from a nitrate-nonutilizing, versicolorin A (VERA)-accumulating strain. The A. parasiticus aflR gene (aflRp) transformants produced VERA, but the aflRs transformants did not. Even when aflRs was placed under the control of the amylase gene (amyB) promoter of Aspergillus oryzae, the amy(p)::aflRs transformants did not produce VERA. A chimeric construct containing the aflRs promoter plus the aflRs N-and aflRp C-terminal coding regions could restore VERA production, but a construct containing the aflRp promoter plus the aflRp N-and aflRs C-terminal coding regions could not. These results show that the A. sojae aflR promoter is functional in A. parasiticus and that the HAHA motif does not affect the function of the resulting hybrid AflR. We conclude that the lack of aflatoxin production by A. sojae can be attributed, at least partially, to the premature termination defect in aflRs, which deletes the C-terminal transcription activation domain that is critical for the expression of aflatoxin biosynthetic genes.

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

“…The premature stop codon in the aflR of A. sojae caused truncation by 62 residues of the C-terminal region. These effects have been found by other workers (Matsushima et al, 2001b;Takahashi et al, 2002). Although the HAHA motif is not important, the missing C terminal of the AFLR protein is essential for aflatoxin production (Matsushima et al, 2001a;Takahashi et al, 2002).…”

“…These effects have been found by other workers (Matsushima et al, 2001b;Takahashi et al, 2002). Although the HAHA motif is not important, the missing C terminal of the AFLR protein is essential for aflatoxin production (Matsushima et al, 2001a;Takahashi et al, 2002). It is believed that an acidic amino acid region of GAL4, AFLR and some other proteins constitutes the activation function of these DNA-binding regulators.…”

Mycotoxins

“…Although these food fungi have never been shown to produce aflatoxin (276), they contain homologues of several aflatoxin biosynthesis pathway genes (140). Deletions and other genetic defects have led to silencing of the aflatoxin pathway in both Aspergillus oryzae and Aspergillus sojae (254,274).…”

Genomics ofAspergillus oryzae

“…However, A. oryzae and A. sojae, used in the fermentation industry, does not produce aflatoxin, since the aflR gene is not expressed and/or AflR is nonfunctional in these strains. [62][63][64][65] 2. C2H2 transcription factors C2H2 transcription factors are found in both prokaryotic and eukaryotic organisms, and they constitute the second-largest family in the filamentous fungus N. crassa.…”