Molecular mechanism of Arabidopsis thaliana profilins as antifungal proteins

Background: It remains an open question whether plant phloem sap proteins are functionally involved in plant defense mechanisms. Methods: The antifungal effects of two profilin proteins from Arabidopsis thaliana, AtPFN1 and AtPFN2, were tested against 11 molds and 4 yeast fungal strains. Fluorescence profiling, biophysical, and biochemical analyses were employed to investigate their antifungal mechanism. Results: Recombinant AtPFN1 and AtPFN2 proteins, expressed in Escherichia coli, inhibited the cell growth of various pathogenic fungal strains at concentrations ranging from 10 to 160 mu g/mL. The proteins showed significant intracellular accumulation and cell-binding affinity for fungal cells. Interestingly, the AtPFN proteins could penetrate the fungal cell wall and membrane and act as inhibitors of fungal growth via generation of cellular reactive oxygen species and mitochondrial superoxide. This triggered the AtPFN variant-induced cell apoptosis, resulting in morphological changes in the cells. Conclusion: PFNs may play a critical role as antifungal proteins in the Arabidopsis defense system against fungal pathogen attacks. General significance: The present study indicates that two profilin proteins, AtPFN1 and AtPFN2, can act as natural antimicrobial agents in the plant defense system.