Pyrrocidines A and B demonstrate synergistic inhibition of Fusarium verticillioides growth

Authors: Lofton, Lily; Read, Quentin; HAMILTON, HAILEY - University Of Georgia; Glenn, Anthony; Hawkins, Jaci; Mitchell, Trevor; Gold, Scott

Submitted to: Frontiers in Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2024
Publication Date: N/A
Citation: N/A

Interpretive Summary: Fusarium verticillioides (Fv) is a fungus that grows in corn seeds and makes toxins (fumonisins) that are harmful to animals. Growing alongside Fv in the seed is another fungus, Sarocladium zeae (Sz), that can protect corn from infection by Fv and other harmful fungi. Sz makes the molecules pyrrocidines A and B, which have been reported to stop Fv growth and block toxin production. Previous work found that a gene, FvZBD1, which was highly induced in response to pyrrocidine challenge, also repressed fumonisin production. Here, we tested the response of Fv strains to pyrrocidines to find which dose was most effective at suppressing Fv growth. We found a powerful synergy between pyrrocidines A and B. When combined they reduced Fv growth significantly. Our results show that Fv requires FvZBD1 to tolerate pyrrocidine A, and that pyrrocidine works through this gene to stop fumonisin production. Additionally, we showed that an efflux pump (FvABC3) is functionally specific to pyrrocidine B. Thus, pyrrocidine A and B have different targets and act synergistically to suppress Fv growth. This information will help us find or develop Sz strains effective at stopping Fv growth and toxin contamination in corn. This study increases our knowledge of competitive relationships between microbes and the role of biological molecules in these interactions.

Technical Abstract: Fusarium verticillioides – a mycotoxigenic fungus and food safety threat – coinhabits maize kernels with Sarocladium zeae. This protective endophyte produces secondary metabolites of interest, pyrrocidines A and B, which inhibit the growth of F. verticillioides and specifically block fumonisin biosynthesis. Previous transcriptomic analyses found FvZBD1 (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 FvZBD1 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 F. verticillioides growth. Further, results provided evidence that FvZBD1 confers partial tolerance to pyrrocidines, particularly pyrrocidine A, and that pyrrocidine functions through FvZBD1 to effectively eliminate fumonisin biosynthesis. Additionally, we showed that the FvABC3 (FVEG_11089) mutant, earlier described as hypersensitive to pyrrocidine, is particularly sensitive to pyrrocidine B. Thus, pyrrocidine A and B show different target specificity (FvZBD1 or FvABC3) and synergistic action. These findings will help inform the optimization of maximally efficacious S. zeae strains for eliminating F. verticillioides 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.