Two different polyketide synthase genes are required for synthesis of zearalenone in Gibberella zeae.

Zearalenone (ZEA) is a polyketide mycotoxin produced by some species of Gibberella/Fusarium and causes hyperestrogenic syndrome in animals. ZEA occurs naturally in cereals infected by Gibberella zeae in temperate regions and threatens animal health. In this study, we report on a set of genes that participate in the biosynthesis of ZEA in G. zeae. Focusing on the non-reducing polyketide synthase (PKS) genes of the G. zeae genome, we demonstrated that PKS13 is required for ZEA production. Subsequent analyses revealed that a continuous, 50 kb segment of DNA carrying PKS13 consisted of three additional open reading frames that were coexpressed as a cluster during the condition for ZEA biosynthesis. These genes, in addition to PKS13, were essential for the ZEA biosynthesis. They include another PKS gene (PKS4) encoding a fungal reducing PKS; zearalenone biosynthesis gene 1 (ZEB1), which shows a high similarity to putative isoamyl alcohol oxidase genes; and ZEB2 whose deduced product carries a conserved, basic-region leucine zipper domain. ZEB1 is responsible for the chemical conversion of beta-zearalenonol (beta-ZOL) to ZEA in the biosynthetic pathway, and ZEB2 controls transcription of the cluster members. Transcription of these genes was strongly influenced by different culture conditions such as nutrient starvations and ambient pH. Furthermore, the same set of genes regulated by ZEB2 was dramatically repressed in the transgenic G. zeae strain with the deletion of PKS13 or PKS4 but not in the ZEB1 deletion strain, suggesting that ZEA or beta-ZOL may be involved in transcriptional activation of the gene cluster required for ZEA biosynthesis in G. zeae. This is the first published report on the molecular characterization of genes required for ZEA biosynthesis.