Identification and Regulation offusA, the Polyketide Synthase Gene Responsible for Fusarin Production in Fusarium fujikuroi

Abstract

ABSTRACTFusarins are a class of mycotoxins of the polyketide family produced by differentFusariumspecies, including the gibberellin-producing fungusFusarium fujikuroi. Based on sequence comparisons between polyketide synthase (PKS) enzymes for fusarin production in otherFusariumstrains, we have identified theF. fujikuroiorthologue, calledfusA. The participation offusAin fusarin biosynthesis was demonstrated by targeted mutagenesis. Fusarin production is transiently stimulated by nitrogen availability in this fungus, a regulation paralleled by thefusAmRNA levels in the cell. Illumination of the cultures results in a reduction of the fusarin content, an effect partially explained by a high sensitivity of these compounds to light. Mutants of thefusAgene exhibit no external phenotypic alterations, including morphology and conidiation, except for a lack of the characteristic yellow and/or orange pigmentation of fusarins. Moreover, thefusAmutants are less efficient than the wild type at degrading cellophane on agar cultures, a trait associated with pathogenesis functions inFusarium oxysporum. ThefusAmutants, however, are not affected in their capacities to grow on plant tissues.