Analysis of aberrant virulence of Gibberella zeae following transformation-mediated complementation of a trichothecene-deficient (Tri5) mutant

Gibberella zeae causes wheat ear blight and produces trichothecene toxins i n infected grain. In previous studies, trichothecene production in this fun gus was disabled by specific disruption of the trichodiene synthase gene (T ri5) and was restored by two methods: gene reversion and transformation-med iated mutant complementation. In previous field tests of wheat ear blight, trichothecene-nonproducing mutants were less virulent than the wild-type pr ogenitor strain from which they were derived. Trichothecene-producing rever tants also were restored to wild-type levels of virulence. In contrast, in the field test of wheat ear blight reported here, trichothecene-producing s trains obtained by Tri5 mutant complementation were not restored to wildtyp e levels of virulence. The complemented mutants showed a slightly reduced r adial growth compared to the wild-type strain, but otherwise appeared norma l in morphology, pigmentation and sexual fertility. Genetic analysis indica ted that the aberrant virulence of a complemented mutant was likely due to non-target effects that occurred during the process of transforming the tri chothecene-nonproducing mutant with Tri5. These results confirm previous fi ndings that trichothecenes contribute to the virulence of G. zeae, but also demonstrate that manipulating this fungus in the laboratory may cause it t o undergo subtle changes that reduce its virulence.