Action mechanism of a novel agrichemical quinofumelin against Fusarium graminearum

Modern fungicides have made significant contributions to crop disease management, but the development of resistant fungal strains has caused their failure in disease control. Therefore, developing fungicides with novel action mechanisms is the most effective measure to manage resistance. Quinofumelin, a novel quinoline fungicide, exhibits exceptional antifungal activity against phytopathogens. However, there is currently no available information on its mechanism of action. Here, we used transcriptome and metabolome analysis to observe a co-enrichment pattern of differentially expressed genes (DEGs) and differentially accumulated metabolites (DAMs) within pyrimidine biosynthesis pathway (PBP), identifying down-regulation of dihydroorotate dehydrogenase (DHODH). Exogenous uridine monophosphate (UMP), uridine, or uracil (metabolites in PBP) successfully restored quinofumelin-induced inhibition of mycelial growth in <i>Fusarium graminearum</i> and <i>Fusarium asiaticum</i>. Additionally, the deletion of <i>FgDHODHII</i> was determined to be lethal; however, mycelial growth of ΔFgDHODHII mutants could be restored by adding UMP, uridine, or uracil. These findings indicate that the deficiencies in <i>FgDHODHII</i> are functionally equivalent to complete inhibition of its activity by quinofumelin. Finally, molecular docking, surface plasmon resonance (SPR), and microscale thermophoresis (MST) results strongly support the precise interaction between quinofumelin and FgDHODHII. Collectively, these findings provide compelling evidence for the involvement of de novo uracil biosynthesis as a mechanism of action for quinofumelin while identifying FgDHODHII as its specific target.