Autoregulation of ZEB 2 expression for zearalenone production in F usarium graminearum

Summary Several F usarium species produce the polyketide mycotoxin zearalenone ( ZEA ), a causative agent of hyperestrogenic syndrome in animals that is often found in F . graminearum –infected cereals in temperate regions. The ZEA biosynthetic cluster genes PKS 4 , PKS 13 , ZEB 1 and   ZEB 2 encode a reducing polyketide synthase, a non‐reducing polyketide synthase, an isoamyl alcohol oxidase and a transcription factor respectively. In this study, the production of two isoforms ( ZEB 2 L and ZEB 2 S ) from the ZEB 2 gene in F . graminearum via an alternative promoter was characterized. ZEB 2 L contains a basic leucine zipper (b ZIP ) DNA ‐binding domain at the N ‐terminus, whereas ZEB 2 S is an N ‐terminally truncated form of ZEB 2 L that lacks the b ZIP domain. Interestingly, ZEA triggers the induction of both ZEB 2 L and ZEB 2 S transcription. ZEB 2 L and ZEB 2 S interact with each other to form a heterodimer that regulates ZEA production by reducing the binding affinity of ZEB2L for the ZEB2 L gene promoter. Our study provides insight into the autoregulation of ZEB 2 expression by alternative promoter usage and a feedback loop during ZEA production; this regulatory mechanism is similar to that observed in higher eukaryotes.