Pn-AMP1, a Plant Defense Protein, Induces Actin Depolarization in Yeasts

Pn-AMP1, Pharbitis nil antimicrobial peptide 1, is a small cysteine-rich peptide implicated in host-plant defense. We show here that Pn-AMP1 causes depolarization of the actin cytoskeleton in Saccharomyces cerevisiae and Candida albicans. Pn-AMP1 induces rapid depolarization of actin cables and patches within 15 min. Increased osmolarity or temperature induces transient actin depolarization and results in increased sensitivity to Pn-AMP1, while cells conditioned to these stresses show less sensitivity. Mutations in components of a cell wall integrity pathway (Wsc1p, Rom2p, Bck1p and Mpk1p), which regulate actin repolarization, result in increased sensitivity to Pn-AMP1. A genetic screen reveals that mutations in components of the alpha-1,6-mannosyltransferase complex (Mnn10p, Mnn11p and Och1p), which regulate mannosylation of cell wall proteins, confer resistance to Pn-AMP1. FITC-conjugated Pn-AMP1 localizes to the outer surface of the cell with no significant staining observed in spheroplasts. Taken together, these results indicate that cell wall proteins are determinants of resistance to Pn-AMP1, and the ability of a plant defense protein to induce actin depolarization is important for its antifungal activity.