Pyrrocidines A and B demonstrate synergistic inhibition of Fusarium verticillioides growth

<i>Fusarium verticillioides</i>-a mycotoxigenic fungus and food safety threat-coinhabits maize kernels with <i>Sarocladium zeae</i>. This protective endophyte produces secondary metabolites of interest, pyrrocidines A and B, which inhibit the growth of <i>F. verticillioides</i> and specifically block fumonisin biosynthesis. Previous transcriptomic analyses found <i>FvZBD1</i> (FVEG_00314), a gene adjacent to the fumonisin biosynthetic gene cluster, to be induced over 4,000-fold in response to pyrrocidine challenge. Deletion of <i>FvZBD1</i> resulted in dramatic increases in fumonisin production (FB₁ >30-fold). Here, using pyrrocidine dose-response assays, we discovered a potent synergy between pyrrocidines A and B, where they functioned powerfully together to inhibit <i>F. verticillioides</i> growth. Further, results provided evidence that <i>FvZBD1</i> confers partial tolerance to pyrrocidines, particularly pyrrocidine A, and that pyrrocidine functions through <i>FvZBD1</i> to effectively eliminate fumonisin biosynthesis. Additionally, we showed that the <i>FvABC3</i> (FVEG_11089) mutant, earlier described as hypersensitive to pyrrocidine, is particularly sensitive to pyrrocidine B. Thus, pyrrocidine A and B show different target specificity (<i>FvZBD1</i> or <i>FvABC3</i>) and synergistic action. These findings will help inform the optimization of maximally efficacious <i>S. zeae</i> strains for eliminating <i>F. verticillioides</i> colonization and fumonisin contamination in maize cropping systems. This novel study contributes significantly to our knowledge of competitive microorganism relationships and the role of secondary metabolites in antagonistic fungal-fungal interactions.