PNNL

Abstract

In the indeterminate nodules of the model legume Medicago truncatula, ~700 nodule-specific cysteine-rich (NCR) peptides with a conserved cysteine-signature are expressed. NCR peptides are highly diverse in sequence and some of these cationic peptides exhibit antimicrobial activity in vitro and in vivo. However, there is a lack of knowledge regarding their structural architecture, antifungal activity, and modes of action against plant fungal pathogens. Here, the three-dimensional NMR structure of a 36-amino acid NCR peptide, NCR044, was solved. Aside from one four-residue a-helix and one three-residue anti-parallel ß-sheet stabilized by two disulfide bonds, the peptide was otherwise disordered. NCR044 exhibited potent fungicidal activity against multiple plant fungal pathogens including Botrytis cinerea and three Fusarium species. It also inhibited germination in quiescent spores of B. cinerea. In germlings, NCR044 breached the fungal plasma membrane and induced reactive oxygen species generation. NCR044 bound to multiple bioactive phosphoinositides in vitro. In vivo, time-lapse confocal and super-resolution microscopy with NCR044 revealed strong fungal cell wall binding, penetration of the cell membrane at discrete foci followed by gradual loss of turgor, accumulation in the cytoplasm, and elevated levels in nucleoli of germlings. Spray-applied NCR044 significantly reduced gray mold disease symptoms caused by the fungal pathogen B. cinerea in tomato and tobacco plants and post-harvest products. This study highlights a novel structurally unique fungal cell penetrating NCR peptide which localized to multiple compartments in a fungal pathogen. Antifungal properties of the peptide reported here warrant further validation of its potential as a peptide-based fungistat/fungicide.