|Kistler, H - Corby|
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 7/10/2014
Publication Date: 7/10/2014
Citation: Wiesenberger, G., Varga, E., Hametner, C., Stuckler, R., Kistler, H.C., Ward, T.J., Schofbeck, D., Krska, R., Schuhmacher, R., Berthiller, F., Adam, G. 2014. A North American isolate of Fusarium graminearum: toxicity and biosynthesis of a new type A trichothecene [abstract]. International Congress on Molecular Plant-Microbe. Interpretive Summary:
Technical Abstract: Fusarium graminearum is one of the economically most important plant pathogens causing diseases such as Fusarium Head Blight (FHB) of small grain cereals and ear rot of maize. The mycotoxin deoxynivalenol (DON) produced by F. graminearum is a virulence factor in wheat and probably also on other host plants. A novel F. graminearum population was discovered in the northern United States during a large-scale survey of F. graminearum (sensu strictu). These strains show normal disease symptoms on wheat, but do not produce any of the known trichothecenes despite the fact that they are able to synthesize the trichothecene precursor trichodiene. We discovered a novel trichothecene specifically produced by these North American (N) strains. This compound was purified and its structure was elucidated. The novel trichothecene, termed NX-2, is identical to 3-ADON with the exception that it lacks the keto group at C-8, which is a hallmark of the typical type B trichothecenes. While the newly discovered strains produced only NX-2 on autoclaved rice, we detected mainly the deacetylated derivative of NX-2 (termed NX-3) after infection of wheat with these strains. The toxicities of the novel mycotoxins were assessed using in vitro translation assays based on rabbit reticulocyte lysate and wheat germ extract. While the toxicity of NX-3 is comparable to that of DON in both assays, NX-2 is non-toxic in the rabbit reticulocyte assay but seemed to inhibit translation by wheat ribosomes. However, we were able show that the apparent toxicity of NX-2 in the wheat germ assay is due to rapid conversion of NX-2 into NX-3. To investigate the molecular basis of NX-2 production in the N strains we sequenced the TRI1 of several isolates. The FgTRI1 gene introduces an oxygen function only at C8 in F. sporotrichoides, while it is is responsible for both the C7 and C8 oxygenation in F. graminearum. We found 14 amino acid changes in the deduced protein sequence of the TRI1 alleles of the N strains compared to the Tri1p of the DON producing PH-1. By swapping the TRI1 coding regions between PH-1 and the NX-2 producing strain WG-9 we were able to show, that the N variant of Tri1p is responsible for specific oxidation at C-7 of the newel discovered trichothcene. Taken together, we discovered a new Type A trichothecene and its deacetylated derivative, which is produced on infected plants. These new mycotoxins, which so far have escaped routine detection techniques, have similarities to A-DON and DON. However, we do not know yet how relevant they are and if their production provides a selective advantage on certain host genotypes.