Finally: A Biochemical Function for the pathogenesis–related protein 1
J. GAMIR (1), P. van't Hof (2), R. Darwiche (2), R. Schneiter (2), F. Mauch (2) (1) Department of Biology/University of Fribourg, Switzerland; (2) Department of Biology/University of Fribourg, Switzerland

The pathogenesis–related protein 1 (PR-1) was discovered more than fifty years ago as the most prominent of several pathogenesis-related proteins that accumulated in the apoplastic space of pathogen-challenged tobacco plant. In support of an immune related function, PR-1 proteins from different plant species were shown to possess in vitro antimicrobial activity. However, in contrast to other groups of PR-proteins, the biochemical activity and mode of action of PR-1 proteins remained a mystery. We have made a new effort to solve this longstanding puzzle. We show here a) that PR-proteins of tobacco and tomato can rescue the sterol export defect of a yeast mutant suggesting that PR-1 binds sterols in the secretory pathway to mediate their export, b) that PR-1 proteins have an in vitro sterol binding activity and c) that the sterol binding capacity is the cause of the antimicrobial activity as addition of sterols titrates the inhibitory activity. In summary, we provide genetic and biochemical evidence for the capacity of PR-1 proteins to bind sterols and demonstrate that the sterol-binding activity is the mode of action of the antimicrobial activity.

Abstract Number: C20-3, P6-149
Session Type: Concurrent