Title: Tri3, Which Controls Trichothecene C-15 Acetylation, is Functional in 3ADON Chemotype Authors
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: December 7, 2009
Publication Date: December 7, 2009
Citation: Mccormick, S.P., Alexander, N.J. 2009. Tri3, Which Controls Trichothecene C-15 Acetylation, is Functional in 3ADON Chemotype. Meeting Abstract. Technical Abstract: Three different trichothecene chemotypes have been identified in U.S. strains of Fusarium graminearum: 3-acetyldeoxynivalenol (3ADON), 15-acetyldeoxynivalenol (15ADON), and nivalenol (NIV), although grain is typically contaminated with deoxynivalenol (DON) or nivalenol rather than the acetylated derivatives. In DON-producing strains of F. graminearum, two of the trichothecene cluster genes, TRI7 and TRI13, are nonfunctional as a result of multiple insertions and deletions within their coding regions, whereas in NIV-producing strains, TRI7 and TRI13 are functional (Lee et al., 2002). These differences, combined with the finding that TRI13 is responsible for trichothecene C-4 hydroxylation, identified the basis for NIV versus DON chemotypes in F. graminearum. Differences in TRI7 and TRI13 were used to develop PCR markers to predict DON and NIV chemotypes (Chandler et al., 2003). PCR markers for TRI3 and TRI12 have been used to predict 3ADON and 15ADON chemotypes in Fusarium graminearum (Ward et al., 2008). In order to determine the genetic basis for these chemotypes, we looked at differences in the function of TRI3 in 3ADON, 15ADON and NIV strains. TRI3 controls the addition of an acetyl group at the C-15 of trichothecenes in Fusarium sporotrichioides (McCormick et al. 1996, Garvey et al. 2009). A group of sixty Fusarium strains were analyzed for production of trichothecenes in liquid culture and on rice to confirm the chemotype predicted with PCR markers for TRI3 and TRI12 (Ward et al., 2008). TRI3 from representative strains of each chemotype were expressed in yeast and the transformants were fed possible Tri3 substrates (15-decalonectrin, DON). Tri3 from all three chemotypes converted 15-decalonectrin to calonectrin indicating that Tri3 is functional, even in the 3ADON chemotype. DON was not a good substrate for Tri3 which supports the addition of the C-15 acetyl group earlier in the biosynthesis of 3ADON. Cell free extracts were also prepared from representative strains of each chemotype and fed 3,15-diADON. Cell-free extracts of 15-ADON and NIV strains converted 3,15-diADON to 15-ADON; cell-free extracts of 3ADON strains converted 3,15-diADON to 3ADON. The Tri8esterase removes the acetyl group from the C-3 position in 15ADON strains (McCormick and Alexander, 2003). The results indicates that a C-15 esterase is required to produce 3ADON. Efforts to characterize this esterase are ongoing.