In vivo and in vitro activity of truncated osmotin that is secreted into the extracellular matrix

Abstract

Osmotin is a basic pathogenesis-related protein of group 5 (PR-5) that displays antifungal activity in vitro and in vivo. Basic, vacuolar forms of PR-5 proteins have a C-terminal extension compared to the acidic forms which are secreted extracellularly. To demonstrate that the C-terminal 20-amino acids extension of osmotin is responsible for intracellular targeting, we made transgenic tobacco and potato plants overexpressing osmotin with or without the 20 C-terminal amino acids. Plants overexpressing an osmotin gene with a complete open reading frame accumulated osmotin mostly in an intracellular compartment, probably the vacuole. In contrast, in plants overexpressing a C-terminal 20 amino acid truncated osmotin gene, osmotin was totally secreted into the extracellular matrix. Truncated osmotin purified from transgenic tobacco plants retained antifungal activity. Potato plants that overexpressed the truncated osmotin protein exhibited resistance to Phytophthora infestans.