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SESSION 4: GENETICS OF HOSTS – PLANT RESISTANCE TO FUSARIUM,
VARIETY DEVELOPMENT
In planta inactivation of Fusarium mycotoxins
M. P. Kovalsky-Paris 1 , W. Schweiger 1 , G. Wiesenberger 1 , J. A. Torres-
Acosta 1 , H. Michlmayr 1 , S. Newmister 2 , M. Lemmens 1 , A. Malachova 1 , S.
Shin 3 , G. Muehlbauer 3 , T. Weigl-Pollack 4 , P. Fruhmann 4 , H. Mikula 4 , C.
Hametner 4 , B. Kluger 1 , R. Schuhmacher 1 , R. Krska 1 , J. Fröhlich 4 , I. Rayment 2 ,
F. Berthiller 1 , G. Adam 1
1 University of Natural Resources and Life Sciences, Vienna (BOKU), Konrad Lorenz Str, 20 + 24, A
3430 Tulln Austria; 2 University of Wisconsin, Madison, WI 53706-1544, USA; 3 University of Minnesota,
St. Paul, MN 55108-6026, USA; 4 University of Technology, Institute of Applied Synthetic Chemistry,
A-1060 Vienna, Austria.
E-mail: gerhard.adam@boku.ac.at
Secondary metabolites of plant pathogens are suspected to play a role as
virulence factors, but in many cases their mode of action is unknown. We could
demonstrate that Hsp90 is the plant target for the (estrogenic) Fusarium
mycotoxin zearalenone. ZON is efficiently glycosylated in various plants. We
identified a barley UDP-glucosyltransferase (UGT) which produces a mixture of
the known ZON-4-glucoside and the novel ZON-2-glucoside. In contrast to ZON
and beta-zearalenol their glycosylated forms are not able to inhibit Hsp90 ATPase
activity. DON is known to be required for fungal spread in wheat. It is inactivated
in planta by formation of a glucoside, which is no longer able to interact with the
ribosomal target. We characterized candidate UGTs from barley, Brachypodium,
Sorghum, rice and wheat by heterologous expression in yeast. Some genes
encode enzymes with the ability to detoxify DON, NIV and other trichothecenes.
Surprisingly, the detoxification capability and substrate specificity towards
different toxins was quite different in highly similar genes, which are typically
encoded in clusters of variable gene number in the different genomes. The
Brachypodium genome seemingly has the capacity to encode more than 150
functional UGTs. One rice UGT gene could be expressed in E. coli with a
solubility tag. The availability of affinity purified active enzyme now allows efficient
enzymatic production of DON-3-O-glucoside, and also of still uncharacterized
glucosides of 15-ADON, nivalenol, fusarenone X and HT-2 toxin. They should
become valuable reference substances to study metabolism of mycotoxins in
various plants. Recently a novel detoxification mechanism for DON was
demonstrated, the formation of glutathione adducts and processing products
(Kluger et al., 2012). Chemically synthesized S-methyl-DON (SMD) which is
presumably generated in planta from DON-cysteine by cysteine-S-conjugatebeta-lyase
and methylation was 12-fold less toxic than DON, suggesting that
formation of bulky glutathione adducts is a detoxification reaction.
Keywords: detoxification, glucoside, glutathione, conjugation
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