Submitted to: International Congress of Mycology Proceedings and Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: March 15, 2005
Publication Date: April 1, 2005
Citation: Chang, P.-K., Horn, B.W., Dorner, J.W. 2005. Determination of chromosomal breakpoints in the aflatoxin biosynthesis gene cluster of nonaflatoxigenic Aspergillus flavus isolates. XIthe International Congress of Mycology Proceedings and Abstracts. p. 10. Technical Abstract: Aspergillus flavus isolates produce either, neither, or both aflatoxin (AF) and cyclopiazonic acid (CPA). A 66-kb gene cluster is responsible for the synthesis of AF. To investigate if defects are present in the AF gene cluster of 40 AF-negative A. flavus isolates collected from agricultural soils of the southern United States, we performed PCR assays using AF-gene specific primers. The 16 CPA-positive and 24 CPA-negative isolates were grouped into four (A to D) and five (E to I) deletion patterns, respectively. Using PCR techniques, we determined the chromosomal breakpoints of the patterns C, F, and I. One breakpoint of the 3 isolates of pattern C is in the 3’ non-translated region of the cypA gene, 217 nucleotides downstream of the TGA stop codon. Another breakpoint is in the coding region of the verA gene, at the first nucleotide encoding the amino acid residue #378 of VerA. The size of the deleted region is 40 kb. Pattern F, two isolates of different vegetative compatibility groups, has a breakpoint at the #300 nucleotide upstream of the start codon of the ver1 gene. The breakpoints of the two isolates at the other end are identical, though the position in the chromosome is not known. Pattern I consists of 18 isolates belonging to different vegetative compatibility groups and includes the active ingredient of the biopesticide Afla-Guard®, A. flavus NRRL 21882. For pattern I in which the entire AF gene cluster is deleted, the breakpoint at the hypA end is in the hexA gene of the sugar utilization gene cluster, at the first nucleotide encoding the amino acid residue #62 of HexA. The breakpoint beyond the norB gene extends to an end of the chromosome as suggested by the presence of the 12 repeats of the telomeric sequence, CCCTAATGTTGA reported for Aspergillus oryzae. Deletions in the AF gene cluster among A. flavus isolates thus are not rare and the patterns appear to be diverse.