NX Trichothecenes Are Required for Fusarium graminearum Infection of Wheat

Fusarium graminearum causes Fusarium head blight (FHB) on wheat and barley and contaminates grains with various mycotoxins that are toxic to humans and animals. Deoxynivalenol (DON), a type B trichothecene, is an essential virulence factor that is required for F. graminearum to spread within a wheat head. Recently, novel type A trichothecenes NX-2 and NX-3 (NX) have been found in F. graminearum. NX trichothecenes lack a keto group at the C8 position. To determine if NX trichothecenes play a role similar to that of DON during F. graminearum infection, deletion mutants of TRI5, the first gene for trichothecene biosynthesis, were generated from strains PH-1, NRRL46422, and NRRL44211 (hereafter 44211) representing the 15-acetyl-DON, 3-acetyl-DON, and NX chemotypes. No trichothecene production was detected in any of the ?tri5 mutants in cultures or inoculated wheat heads. FHB symptoms were restricted to the inoculated wheat spikelets when point-inoculated with the ?tri5 mutants, confirming the necessity of NX and DON for FHB spread. Furthermore, whole-head dip inoculations revealed significant reductions in disease and fungal biomass in wheat heads inoculated with 44211?tri5 compared with 44211. Introduction of the native 44211 TRI5 and a Trichoderma arundinaceum TRI5 ortholog in the 44211?tri5 mutant complemented trichothecene production in vitro; however, introducing both TRI5 partially restored wild-type levels of NX in infected heads. Our results demonstrate that NX trichothecenes play an important role in Fusarium graminearum initial infection as well as FHB spread. Thus, TRI5 may serve as an ideal target to control plant infection, FHB spread, and mycotoxin production simultaneously.

Automated summary

Fusarium graminearum causes Fusarium head blight (FHB) on wheat and barley, contaminating grains with toxic mycotoxins. The study found that the newly discovered NX trichothecenes, along with DON, play an important role in FHB infection and spread.