New tricks of an old enemy: isolates of F usarium graminearum produce a type A trichothecene mycotoxin

Abstract

Summary The ubiquitous filamentous fungus F usarium graminearum causes the important disease F usarium 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 N orth A merica 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 3α‐acetoxy‐7α,15‐dihydroxy‐12,13‐epoxytrichothec‐9‐ene. Compared with the well‐known 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 C hlamydomonas 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 TRI 1 allele in the N ‐isolates, which was verified to be responsible for the difference in hydroxylation at C ‐8.

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