Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: December 9, 2010
Publication Date: December 9, 2010
Citation: Mccormick, S.P., Alexander, N.J., Proctor, R. 2010. Fusarium TRI8 determines 3-acetyldeoxynivalenol (3ADON) or 15ADON production. Meeting Abstract. Technical Abstract: Trichothecene mycotoxins produced by Fusarium species can promote disease in small grain crops such as wheat and barley. Two main trichothecene production phenotypes (chemotypes) have been identified among strains of Fusarium graminearum and closely related species: strains produce either deoxynivalenol (DON) or nivalenol (NIV) trichothecenes. The DON phenotype can be further subdivided into the 3-acetyldeoxynivalenol (3ADON) chemotype and the 15-acetyldeoxynivalenol (15ADON) chemotype. However, grain infected by strains with either the 3ADON or 15ADON chemotype is typically contaminated with DON rather than the acetylated derivatives. DON and NIV are identical in structure except for the presence (NIV) and absence (DON) of a hydroxyl function at carbon atom 4 (C-4) of the trichothecene molecule. The basis for DON and NIV chemotypes resides in the trichothecene C-4 hydroxylase gene TRI13. In DON-producing strains of F. graminearum, TRI13 is nonfunctional because of multiple insertions and deletions within its protein coding region. As a result DON-producing strains are unable to hydroxylate trichothecenes at C-4. In contrast, NIV-producing strains have a functional TRI13 and, therefore, can hydroxylate trichothecenes at C-4. For greater efficiency in chemotype classification, differences in TRI13, as well as the C-4 acetyl transferase gene (TRI7), sequences have been used to develop PCR markers to predict DON and NIV chemotypes. During the last several years, PCR markers for TRI3 and TRI12 have been used to predict 3ADON and 15ADON chemotypes in Fusarium graminearum. In order to determine the genetic basis for these chemotypes, we examined differences in the sequences and functions of TRI3 and TRI8, two trichothecene biosynthetic genes that have been proposed to play a role in production of 3ADON versus 15ADON in Fusarium. TRI3 was functional in both 3ADON and 15ADON strains and had the same function, namely trichothecene C-15 acetyltransferase, in strains with either chemotype. TRI8 was also functional in strains with both chemotypes; however, its function differed in the two types of strains. In 15ADON-producing strains, the TRI8 enzyme is a trichothecene C-3 esterase; it catalyzes removal of an acetyl group from the C-3 position. In contrast, in 3ADON strains, the TRI8 enzyme homolog is a C-15 esterase; it catalyzes removal of an acetyl group from the C-15 position. These results indicate that TRI8, but not TRI3, determines whether Fusarium produces 3ADON or 15ADON. Furthermore, expression studies with TRI8 chimeras containing a portion of TRI8 from a 3ADON strain and a portion from a 15ADON strain indicated that sequence differences in the middle of the coding region are responsible for determining the 3ADON versus 15ADON chemotype. These results should contribute to understanding the role of the 3ADON and 15ADON chemotypes in the ecology of Fusarium species that cause wheat head blight.