NX toxins: New threat posed by Fusarium graminearum species complex

Background: Trichothecenes are the most common toxins found in grains and mainly produced by Fusarium graminearum species complex (FGSC). However, a population of FGSC strain was found to produce a group of type A trichothecenes, NX toxins. Studies on this toxigenic Fusarium population and the emerging NX toxins are crucial for grain production and food safety.Scope and approach: In this review, we systematically introduced the diagnostic techniques, population distribution and frequency of the NX-producing strains. The structure elucidation, stability, and toxicology of NX toxins were summarized. The molecular mechanisms of NX toxins biosynthesis were discussed.Key findings and conclusions: The available information showed that NX-producing strains endemic to the border of Canada and United States, and TRI1 gene is the key determinant of NX production in FGSC. Structure elucidation results showed that NX toxins are similar in structure to type B trichothecenes but lack the keto group at C-8. In vitro experiments indicated that NX toxins can inhibit the eukaryotic protein synthesis and comparable toxic effects of NX-3 toxin were observed compared with DON on plant and mammalian cells. Nevertheless, significant stability difference is observed between NX-3 and DON in bread baking process, the stability of NX toxins reduced strongly compared with DON. Potential impacts of global warming on NX strains and mycotoxin production are discussed. Furthermore, genes involved in NX biosynthesis, and their functions are discussed, and potential pathways of NX toxins biosynthesis are proposed in our knowledge of trichothecene biosynthesis. This review should contribute to the current situation and future trends of the toxigenic Fusarium population and the emerging trichothecenes.