CO-PRODUCTION OF 3ADON AND 15ADON BY CULTURES OF FUSARIUM GRAMINEARUM 15ADON STRAINS, BUT NOT 3ADON STRAINS, IS DUE TO DIFFERENCES IN ACETYLTRANSFERASE ACTIVITY AND SUBSTRATE SPECIFICITY

摘要

Fusarium graminearum strains can be assigned to chemotypes, e.g. 3ADON or 15ADON, on the basis of PCR analysis using polymorphisms in the trichothecene biosynthetic genes TRI3 and TRI12. Trichothecene production in liquid culture is consistent with the chemotype predicted with PCR analyses, i.e., acetylated DON (3ADON or 15ADON) is produced but no DON is detected. In contrast, grain infected with 3ADON or 15ADON strains are predominantly contaminated with DON with small amounts of 3ADON or 15 ADON, or sometimes both, detected. A mixture of acetylated deoxynivalenols is also sometimes found in rice cultures. Although F. graminearum 70E1, a 3ADON strain, produced DON and 3ADON, F. graminearum GZ3639, a 15 ADON strain, produced a mixture of DON, 15ADON, 3ADON and 3,15-diADON. We have previously shown that differences in the TRI8 esterase gene determine the 3 A DON or 15ADON chemotype. Disruption of Tri8 in either 3ADON or 15ADON strains results in the accumulation of 3,15-diADON, the common precursorof 3 ADON and 15 ADON. Yeast expressing TRI8 from a 3ADON strain removed the C-15 acetyl group from 3,15-diADON while yeast expressing TRI8 from a 15ADON strain removed the C-3 acetyl group from 3,15-diADON. In order to determine if differences in trichothecene acetyltransferase genes might contribute to the production of both acetylated forms in the cultures of one chemotype, TRI3 and TRI101 from 3 ADON and 15ADON chemotypes were expressed in yeast. In trichothecene biosynthesis, TrilOl acetylates at C-3, converting isotrichodermol into isotrichodermin, and Tri3 acetylates at C-15, converting 15-decalonectrin into calonectrin. Feeding experiments with yeast expressing Tril0l from a 3ADON or a 15ADON strain indicated that TrilOl can convert DON into 3ADON. Feeding experiments with yeast expressing Tri3 indicated that Tri3 from 3ADON or 15ADON strains were functional, i.e. able to convert 15-decalonectrin into calonectrin. Tri3 from a 15ADON strain was also able to convert DON into 15ADON but Tri3 from a 3ADON strain did not convert DON into 15ADON. These differences in Tri3 activity and substrate specificity can account for both 3ADON and 15ADON being produced in a 15ADON strain but not a 3ADON strain.