Repressor-AFLR interaction modulates aflatoxin biosynthesis in Aspergillus parasiticus.
Regulation of aflatoxin (AF) biosynthesis likely involves a complex interplay of positive- and negative-acting factors that are affected by physiological cues responsive to internal and external stimuli. These factors, presumably, modulate the expression of the AF pathway-specific regulatory gene, aflR, whose product, AFLR, a zinc cluster transcription factor, then turns on or off the transcription of other AF genes. To determine if the AFLR carboxyl region (AFLRC) interacts with positive- or negative-acting proteins, we fused the Aspergillus parasiticus aflR carboxyl coding region (aflRC) to the promoter of A. parasiticus nitrite reductase gene (niiA(p)::aflRC), and transformed it into A. parasiticus SRRC 2043. Transformants that contained two copies of niiA(p)::aflRC, one at the niaD locus and another at the aflR locus, overproduced AF precursors independent of the nitrogen source. The higher copy number of the integrated niiA(p)::aflRC correlated with increased production of AF precursors by the transformants as well as increased expression of both aflRC and native aflR in potato dextrose broth and A&M medium. Since aflRC does not encode a DNA-binding domain, the expressed AFLRC should not bind to the promoters of AF pathway genes and affect transcription directly. The results are consistent with AFLRC titrating out a putative repressor that interacts with AFLR under different growth conditions and modulates AF biosynthesis. This interaction also indirectly affects sclerotial development.
Chang
P K
PK
Southern Regional Research Center, U.S. Department of Agriculture, New Orleans, Louisiana 70124, USA. pkchang@nola.srrc.usda.gov
Yu
J
J
Bhatnagar
D
D
Cleveland
T E
TE
D000348:Aflatoxins / Q000096:biosynthesis*; D001230:Aspergillus / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005656:Fungal Proteins; D009572:Nitrite Reductases / Q000235:genetics; D009573:Nitrites / Q000378:metabolism; D009584:Nitrogen / Q000378:metabolism; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012097:Repressor Proteins / Q000378:metabolism*; D014157:Transcription Factors; D014170:Transformation, Genetic
C113837:AFLR protein, Aspergillus; D000348:Aflatoxins; D017931:DNA Primers; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D009573:Nitrites; D000644:Quaternary Ammonium Compounds; D012097:Repressor Proteins; D014157:Transcription Factors; D009572:Nitrite Reductases; D009584:Nitrogen