The filamentous fungus Aspergillus nidulans produces the mycotoxin sterigmatocystin (ST). This polyketide compound is the penultimate precursor in the aflatoxin biosynthetic pathway found in related species such as A. parasiticus, A. flavus, and A. nomius. In A. nidulans the genes involved in ST biosynthesis are clustered in chromosome IV. This gene cluster is regulated by the aflR, encoding a specific transcription factor that binds to the promoters of ST genes activating their transcription. Expression of aflR is positively regulated by the veA gene, encoding a global regulatory protein that controls secondary metabolism and morphogenesis. In order to find additional regulatory genetic elements controlling ST production downstream veA, we carried out a chemical mutagenesis in a veA deletion strain, unable to express ST genes or produce toxin, and search for revertant mutants that regained the capacity to produce it. The strain used in this mutagenesis also has a mutation in the stcE gene, which in the wild type leads to the accumulation of the orange norsonolinic acid (NOR) ST intermediate, facilitating a visual screen. From this mutagenesis we isolated several revertant mutants able to produce NOR, indicating restoration of the ST biosynthetic pathway. Some of these mutations also affected fungal morphogenesis. Several of these revertants, corresponding to different linkage groups, are currently being characterized. Complementation with the A. nidulans genomic library followed by sequencing will reveal the identity of these genetic regulatory elements downstream veA that are involved in the control of ST biosynthesis.
Full conference title:
26th Fungal Genetics Conference
- Fungal Genetics Conference 26th (2005)