Abstract
Fusarium culmorum is a fungal pathogen causing economically important diseases on a variety of crops. Fungicides can be applied to control this species with triazoles being the most efficient molecules. F. culmorum strains resistant to these molecules have been reported, but the underlying resistance mechanisms remain unknown. In this study, a tebuconazole-adapted F. culmorum strain was developed with a level of fitness similar to its parental strain. The adapted strain showed cross-resistance to all demethylation inhibitors (DMIs), but not to other classes of fungicides tested. RNA-Seq analysis revealed high transcriptomic differences between the resistant strain and its parental strain after tebuconazole treatment. Among these changes, FcABC1 (FCUL_06717), a pleiotropic drug resistance transporter, had a 30-fold higher expression level upon tebuconazole treatment in the adapted strains as compared to the wild-type strain. The implication of this transporter in triazole resistance was subsequently confirmed in field strains harboring distinct levels of sensitivity to triazoles. FcABC1 is present in other species/genera, including F. graminearum in which it is known to be necessary for azole resistance. No difference in FcABC1 sequences, including the surrounding regions, were found when comparing the resistant strain to the wild-type strain. Fusarium culmorum is therefore capable to adapt to triazole pressure by overexpressing a drug resistance transporter when submitted to triazoles and the same mechanism is anticipated to occur in other species.
Highlights
IntroductionSmith] Saccardo) is a fungal pathogen responsible for multiple diseases on a variety of crops and weeds
The baseline sensitivity of F. culmorum to triazoles has been previously shown to be quite stable over time, more resistant strains could be observed in the field
Their common mode of action enable fungi to develop cross-resistance to these molecules and this phenomenon has been often reported for Fusarium spp. (Yin et al, 2009; Becher et al, 2010; Serfling and Ordon, 2014; Spolti et al, 2014) as well as for other fungi such as Ustilago maydis (DC.) Corda, Sclerotinia homoeocarpa
Summary
Smith] Saccardo) is a fungal pathogen responsible for multiple diseases on a variety of crops and weeds Among these diseases, Fusarium head blight (FHB) is one of the major small-grain cereal diseases. Fusarium culmorum and F. graminearum (Schwabe), a closely related species, are among the most common species found in Europe, but with high variations between years and locations (Parry et al, 1995; Xu et al, 2005; Hellin et al, 2016a). These species can produce the type B trichothecenes deoxynivalenol (DON) or nivalenol (NIV), depending on the strain. Type B trichothecenes were shown to contribute to virulence on wheat and were demonstrated to inhibit protein translation threatening human and animal health (Desjardins, 2006)
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