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

Abstract

Gibberella zeae causes wheat ear blight and produces trichothecene toxins in infected grain. In previous studies, trichothecene production in this fungus was disabled by specific disruption of the trichodiene synthase gene (Tri5) and was restored by two methods : gene reversion and transformation-mediated mutant complementation. In previous field tests of wheat ear blight, trichothecene-nonproducing mutants were less virulent than the wild-type progenitor strain from which they were derived. Trichothecene-producing revertants also were restored to wild-type levels of virulence. In contrast, in the field test of wheat ear blight reported here, trichothecene-producing strains obtained by Tri5 mutant complementation were not restored to wildtype levels of virulence. The complemented mutants showed a slightly reduced radial growth compared to the wild-type strain, but otherwise appeared normal in morphology, pigmentation and sexual fertility. Genetic analysis indicated that the aberrant virulence of a complemented mutant was likely due to non-target effects that occurred during the process of transforming the trichothecene-nonproducing mutant with Tri5. These results confirm previous findings that trichothecenes contribute to the virulence of G. zeae, but also demonstrate that manipulating this fungus in the laboratory may cause it to undergo subtle changes that reduce its virulence.

Deletion and Complementation of the Mating Type ( MAT ) Locus of the Wheat Head Blight Pathogen Gibberella zeae

“…Although some MAT deletion strains and other transformants were less virulent than the wild-type strain from which they were derived, the reduced virulence of these transformants was linked to the source of protoplasts and not to the transforming DNA. Thus, it is likely that procedures used for protoplast production and transformation reduced virulence by causing alterations at loci other than the targeted gene, a phenomenon previously observed in transformationmediated gene disruption in G. zeae (11).…”

“…Virulence tests were conducted on cultivar Wheaton as previously described (11). Heads were inoculated by injecting a drop of macroconidium suspension containing approximately 10 3 macroconidia into one floret of a central spikelet of each head.…”

Global Carbon Utilization Profiles of Wild-Type, Mutant, and Transformant Strains of Hypocrea jecorina

“…Thus, our data demonstrate that indirect mutagenesis and transformation events alter central carbon metabolism in H. jecorina in similar manners. Desjardins et al (6) also observed that Gibberella zeae can undergo spontaneous or transformation-induced mutations that significantly altered its virulence.…”

The CID1 cyclin C-like gene is important for plant infection in Fusarium graminearum

“…In addition to genes related to well conserved signal transduction pathways (Hou et al, 2002;Jenczmionka et al, 2003;Jenczmionka and Schafer, 2005;Urban et al, 2003;Yu et al, 2008), a number of pathogenicity genes with diverse biological or biochemical functions have been characterized (Han et al, 2007;Lee et al, 2005;Lu et al, 2003;Seong et al, 2005Seong et al, , 2006Shim et al, 2006). The first pathogenicity factor most thoroughly characterized by molecular studies in F. graminearum is the trichodiene synthase gene TRI5 (Desjardins et al, 2000;Proctor et al, 1995). Although trichothecene mycotoxins are not necessary for the initial infection, they are important for the spread of the fungus within colonized spikes (Bai et al, 2002;Desjardins et al, 2000;Harris et al, 1999;Proctor et al, 1995).…”

“…The first pathogenicity factor most thoroughly characterized by molecular studies in F. graminearum is the trichodiene synthase gene TRI5 (Desjardins et al, 2000;Proctor et al, 1995). Although trichothecene mycotoxins are not necessary for the initial infection, they are important for the spread of the fungus within colonized spikes (Bai et al, 2002;Desjardins et al, 2000;Harris et al, 1999;Proctor et al, 1995). In the past decade, the trichothecene biosynthetic gene cluster and biosynthesis pathway have been extensively studied.…”