Tri13 and Tri7 Determine Deoxynivalenol- and Nivalenol-Producing Chemotypes of Gibberella zeae

Abstract

Gibberella zeae , a major cause of cereal scab, can be divided into two chemotypes based on production of the 8-ketotrichothecenes deoxynivalenol (DON) and nivalenol (NIV). We cloned and sequenced a Tri13 homolog from each chemotype. The Tri13 from a NIV chemotype strain (88-1) is located in the trichothecene gene cluster and carries an open reading frame similar to that of Fusarium sporotrichioides , whereas the Tri13 from a DON chemotype strain (H-11) carries several mutations. To confirm the roles of the Tri13 and Tri7 genes in trichothecene production by G. zeae , we genetically altered toxin production in 88-1 and H-11. In transgenic strains, the targeted deletion of Tri13 from the genome of 88-1 caused production of DON rather than NIV. Heterologous expression of the 88-1 Tri13 gene alone or in combination with the 88-1 Tri7 gene conferred on H-11 the ability to synthesize NIV; in the latter case, 4-acetylnivalenol (4-ANIV) also was produced. These results suggest that Tri13 and Tri7 are required for oxygenation and acetylation of the oxygen at C-4 during synthesis of NIV and 4-ANIV in G. zeae . These functional analyses of the Tri13 and Tri7 genes provide the first clear evidence for the genetic basis of the DON and NIV chemotypes in G. zeae .