Functional analysis of all succinate dehydrogenase subunits in Fusarium fujikuroi

Abstract

AbstractFusarium fujikuroi, the causal agent of rice bakanae disease (RBD), contains five succinate dehydrogenase (Sdh) subunits: FfSdhA, FfSdhB, FfSdhC1, FfSdhC2, and FfSdhD. However, the role of these subunits in regulating sensitivity to succinate dehydrogenase inhibitors (SDHIs) is largely unknown. Here, we conducted targeted gene disruption and phenotypic assays for all Sdh subunits and found that the deletion mutants of FfSdhA, FfSdhB, and FfSdhD exhibited severe defects in hyphal growth, conidiation, virulence, and sensitivity to CaCl2 and oxidative stresses. To a lesser extent, the mycelial growth rate and conidial production of ΔFfSdhC1 were also decreased as compared to those of the wild-type strain JS16. In addition, fungicide sensitivity assays showed that deletion of FfSdhA, B, C1, or D led to decreased sensitivity to all SDHIs tested. Unexpectedly, we were unable to obtain a FfSdhC1 + C2 double mutant and further found significant up-regulation of FfSdhC2 in ∆FfSdhC1, indicating that FfSdhC1 and -C2 might be essential for fungal growth although the FfSdhC2 deletion mutant was indistinguishable from the wild-type strain. These findings provide useful information for enhancing our understanding of the biological functions of the Sdh subunits in pathogenic fungi.