The Induction of Succinate Dehydrogenase of “C1” Conformation and the Difference in Its Binding to Fungicides Lead to the Variation in Toxicity of SDHI Fungicides Against <i>Fusarium pseudograminearum</i>

Genetic differentiation of the succinate dehydrogenase (SDH) subunit C in <i>Fusarium</i> spp. contributes to significant variations in the efficacy of succinate dehydrogenase inhibitor (SDHI) fungicides against these pathogens. However, the structural states of the two SDH conformations in mitochondria and their binding modes with SDHI fungicides are still unknown. Based on SDH activity and qRT-PCR assay, we confirmed that the SDH of "C2" conformation in <i>Fusarium pseudograminearum</i> is a constitutively expressed type, while that of "C1" conformation is an inducibly expressed type.Through molecular docking, the difference in binding affinity between SDHI fungicides and the two conformations also proves to be a key factor contributing to the variations in toxicity of SDHI fungicides against <i>F. pseudograminearum</i>. These results established that SDHI fungicides induce the expression of SDH of "C1" conformation, which leads to weak binding between SDHI fungicides and the target, thereby resulting in variations in the toxicity of SDHI fungicides.