|VARGA, ELISABETH - University Of Natural Resources & Applied Life Sciences - Austria|
|WIESENBERGER, GERLINDE - University Of Natural Resources & Applied Life Sciences - Austria|
|HAMETNER, CHRISTIAN - Vienna University Of Technology|
|DONG, YANHONG - University Of Minnesota|
|SCHOFBECK, DENISE - University Of Natural Resources & Applied Life Sciences - Austria|
|STUCKLER, ROMANA - University Of Natural Resources & Applied Life Sciences - Austria|
|SCHUHMACHER, RAINER - University Of Natural Resources & Applied Life Sciences - Austria|
|KRSKA, RUDOLF - University Of Natural Resources & Applied Life Sciences - Austria|
|BERTHILLER, FRANZ - University Of Natural Resources & Applied Life Sciences - Austria|
|ADAM, GERHARD - University Of Natural Resources & Applied Life Sciences - Austria|
Submitted to: Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2014
Publication Date: 1/30/2015
Publication URL: https://handle.nal.usda.gov/10113/62928
Citation: Varga, E., Wiesenberger, G., Hametner, C., Ward, T.J., Dong, Y., Schofbeck, D., McCormick, S.P., Broz, K.L., Stuckler, R., Schuhmacher, R., Krska, R., Kistler, H.C., Berthiller, F., Adam, G. 2015. New tricks of an old enemy: isolates of Fusarium graminearum produce a type A trichothecene mycotoxin. Environmental Microbiology. 17(8):2588-2600.
Interpretive Summary: Fusarium graminearum and related fungi are responsible for Fusarium head blight (FHB) and other economically destructive diseases of wheat, barley, and other cereals world-wide. In addition, these fungi contaminate grain with trichothecene mycotoxins that pose a significant threat to food safety and animal health. This leads to enormous losses of food and feed worldwide as well as to high costs for monitoring and mycotoxin management to protect consumers. In this research, we describe strains of F. graminearum from the Upper Midwest of the United States that produce two previously unknown trichothecene toxins, termed NX toxins. We determined the chemical structure of these novel toxins and describe why they are not detectable by analytical methods that are widely used for mycotoxin monitoring. In addition, we demonstrated that this novel compound has nearly the same toxicity to plants and animals as deoxynivalenol (DON), which is regulated in many countries. Finally, the gene responsible for the difference between DON and NX toxins was identified, and a genetic test was developed to rapidly identify fungi capable of producing the novel NX toxins. As such, the results reported here are critical to promoting food safety and cereal production through improved mycotoxin monitoring and improved understanding of fungal diversity that can inform efforts to breed cereals with broad resistance to FHB.
Technical Abstract: The ubiquitous filamentous fungus Fusarium graminearum causes the important disease Fusarium head blight on various species of cereals, leading to contamination of grains with mycotoxins. In a survey of F. graminearum (sensu stricto) on wheat in North America several novel strains were isolated, which produced none of the known trichothecene mycotoxins despite causing normal disease symptoms. In rice cultures, a new trichothecene mycotoxin (named NX-2) was characterized by liquid chromatography-tandem mass spectrometry. Nuclear magnetic resonance measurements identified NX-2 as 3a-acetoxy-7a,15-dihydroxy-12, 13-epoxytrichothec-9-ene. Compared with the wellknown 3-acetyl-deoxynivalenol (3-ADON), it lacks the keto group at C-8 and hence is a type A trichothecene. Wheat ears inoculated with the isolated strains revealed a 10-fold higher contamination with its deacetylated form, named NX-3, (up to 540 mg kg-1) compared with NX-2. The toxicities of the novel mycotoxins were evaluated utilizing two in vitro translation assays and the alga Chlamydomonas reinhardtii. NX-3 inhibits protein biosynthesis to almost the same extent as the prominent mycotoxin deoxynivalenol, while NX-2 is far less toxic, similar to 3-ADON. Genetic analysis revealed a different TRI1 allele in the N-isolates, which was verified to be responsible for the difference in hydroxylation at C-8.