Enhanced activity of strobilurin and fludioxonil by using berberine and phenolic compounds to target fungal antioxidative stress response

Aims: Identify natural products that effectively target antioxidative signal transduction/stress response systems [i.e., mitogen-activated protein kinase (MAPK) pathway, mitochondrial superoxide dismutase (Mn-SOD)] of fungi. Enhance activity of strobilurin or fludioxonil with discovered compounds. Methods and Results: Enhancement of antifungal activity of strobilurins, inhibitors of complex III of the mitochondrial respiratory chain, was tested using berberine hemisulfate and different phenolic compounds. The Saccharomyces cerevisiae sod2Δ, a deletion mutant lacking Mn-SOD gene, was highly sensitive to berberine and veratraldehyde. Functional complementation analysis verified these compounds target Mn-SOD. Activity of strobilurin (25-50 μmol l^-1) was elevated on most aspergilli and Penicillium expansum by co-application with berberine or veratraldehyde (2-4 mmol l^-1). These compounds also prevented Aspergillus fumigatus MAPK mutants (sakAΔ and mpkCΔ) from escaping toxicity of fludioxonil (a phenylpyrrole fungicide potentiated by the MAPK pathway), a typical phenotype of fungal MAPK mutants. Conclusions: Strobilurin activity or prevention of fungal escape from fludioxonil toxicity can be enhanced by co-application of certain alkaloids or phenolics. Significance and Impact of the Study: Natural products can be used to target cellular stress response systems in fungal pathogens and serve as alternatives/additives to commercial antifungal agents.