Differential toxicity of antifungal protein AFP against mutants of Fusarium oxysporum

Antifungal protein (AFP) from Aspergillus giganteus was assayed for toxicity against the Fusarium oxysporum wild-type strain and mutants in genes involved in cell signaling (ΔpacC, pacCc Δfmk1) or cell-wall biogenesis (ΔchsV, Δchs7, Δgas1). The mutants were classified into two groups according to their sensitivity to AFP: ΔpacC, Δgas1 and Δchs7, which were significantly more resistant to AFP than the wild-type, and pacCC, Δfmk1 and ΔchsV, which were more sensitive. Western blot analysis revealed increased binding of AFP to the three resistant mutants, ΔpacC, Δgas1 and Δchs7, but also to ΔchsV, indicating that differential binding may not be a key determinant for sensitivity. Addition of Ca2+ or K+ dramatically reduced antifungal activity and binding of AFP, suggesting that these cations compete for the same targets as AFP at the surface of the fungal cell. [Int Microbiol 2009; 12(2):115-121