Antimicrobial peptides (AMPs) constitute an essential part of the plant immune system. They are regarded as alternatives to conventional antibiotics and pesticides. In this study, we have identified the γ-core motifs, which are associated with antimicrobial activity, in 18 AMPs from grasses and assayed their antimicrobial properties against nine pathogens, including yeasts affecting humans, as well as plant pathogenic bacteria and fungi. All the tested peptides displayed antimicrobial properties. We discovered a number of short AMP-derived peptides with high antimicrobial activity both against human and plant pathogens. For the first time, antimicrobial activity was revealed in the peptides designed from the 4-Cys-containing defensin-like peptides, whose role in plant immunity has remained unknown, as well as the knottin-like peptide and the C-terminal prodomain of the thionin, which points to the direct involvement of these peptides in defense mechanisms. Studies of the mode of action of the eight most active γ-core motif peptides on yeast cells using staining with propidium iodide showed that all of them induced membrane permeabilization leading to cell lysis. In addition to identification of the antimicrobial determinants in plant AMPs, this work provides short candidate peptide molecules for the development of novel drugs effective against opportunistic fungal infections and biopesticides to control plant pathogens.
Keywords: Fusarium species; antimicrobial activity; human pathogenic yeasts; novel antimicrobials; plant antimicrobial peptides; plant pathogenic bacteria; γ-core.