EXTRACELLULAR PROTEASES OF THE RUST FUNGUS UROMYCES-VICIAE-FABAE

On thigmo-inductive membranes the broad bean rust fungus Uromyces vici ae-fabae differentiates complex infection structures including haustor ial mother cells. Using this in vitro system, formation of extracellul ar proteases of the obligately biotrophic fungus was studied during in fection structure differentiation. Enzyme activities occur when appres soria are formed, and extracellular washing fluids of substomatal vesi cles, infection hyphae, and haustorial mother cells show complex prote ase patterns on polyacrylamide gels containing gelatin as substrate. T he majority of the rust proteases can be classified as metallo-, inclu ding Ca2+-stabilized proteases. The presence of substrate is not requi red for synthesis of the enzymes. The extracellular proteases, in cont rast to intracellular enzymes of this fungus, specifically degrade fib rous, hydroxyproline-rich proteins. Since such proteins are important in plants for cell wall stability and play a role in defense against f ungal pathogens, the extracellular proteases of U. viciae-fabae may be involved in localized breaching of the host cell wall. (C) 1995 Acade mic Press, Inc.