A Large Genomic Deletion in Gibberella zeae Causes a Defect in the Production of Two Polyketides but not in Sexual Development or Virulence

Abstract

Gibberella zeae (anamorph: Fusarium graminearum) is an important pathogen of cereal crops. This fungus produces a broad range of secondary metabolites, including polyketides such as aurofusarin (a red pigment) and zearalenone (an estrogenic mycotoxin), which are important mycological characteristics of this species. A screen of G. zeae insertional mutants, generated using a restriction enzyme-mediated integration (REMI) procedure, led to the isolation of a mutant (Z43R606) that produced neither aurofusarin nor zearalenone yet showed normal female fertility and virulence on host plants. Outcrossing analysis confirmed that both the albino and zearalenone-deficient mutations are linked to the insertional vector in Z43R606. Molecular characterization of Z43R606 revealed a deletion of at least 220 kb of the genome at the vector insertion site, including the gene clusters required for the biosynthesis of aurofusarin and zearalenone, respectively. A re-creation of the insertional event of Z43R606 in the wild-type strain demonstrated that the 220-kb deletion is responsible for the phenotypic changes in Z43R606 and that a large region of genomic DNA can be efficiently deleted in G. zeae by double homologous recombination. The results showed that 52 putative genes located in the deleted genomic region are not essential for phenotypes other than the production of both aurofusarin and zearalenone. This is the first report of the molecular characterization of a large genomic deletion in G. zeae mediated by the REMI procedure.