Isolation and analysis of fluP, a gene associated with hyphal growth and sporulation in Aspergillus parasiticus

Aflatoxins (AF) are polyketide-derived mycotoxins that frequently contamina te food and feed crops, causing health risks to animals and humans. The flu P gene was cloned by screening an Aspergillus parasiticus genomic DNA libra ry with a cDNA probe encoding part of a polyketide synthase (PKS), the 6-me thylsalicylic acid synthase (MSAS) from Penicillium patulum. FluP was hypot hesized to function as a PKS in AF biosynthesis. The predicted amino acid s equence of FluP demonstrated a high degree of identity to MSAS (55%), moder ate identity to another fungal PKS protein encoded by wA from A. nidulans ( 22%) and low identity (<5%) to fungal fatty acid synthase (FAS) proteins. D isruption of fluP in A. parasiticus resulted in the loss of fluP transcript , a 3- to 4-fold reduction in hyphal growth rate, the appearance of a fluff y, cotton-like hyphal morphology, reduction or elimination of asexual spore s and spore-bearing structures, and a twofold reduction in aflatoxin accumu lation. Removal of selective pressure on fluP knockout transformants result ed in frequent reversion (10%) to the wild-type genotype and phenotype, est ablishing a direct link between gene disruption and the associated phenotyp e. The data suggest that fluP encodes a novel PKS associated with hyphal gr owth and cell development (sporulation). whose activity indirectly influenc es aflatoxin accumulation in A. parasiticus.