Submitted to: Physiological and Molecular Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2005
Publication Date: 5/1/2005
Citation: Weiland, J.J. 2004. Production of protease isozymes by Aphanomyces cochlioides and Aphanomyces euteiches. Physiological and Molecular Plant Pathology. 65:225-233.
Interpretive Summary: Fungi that infect sugarbeet use many mechanisms, some known and some unknown, to gain entry into the host plant. In this study, the enzyme protease was examined as a potential means by which the sugarbeet root rot pathogen Aphanomyces cochlioides enters sugarbeet seedlings in the field. Protease activity was found in liquid in which Aphanomyces was grown and these same activities were found in plants that were infected with the fungus. Chemical inhibitors were found that block the activity of some of the proteases examined. It is proposed that protease activity may be important for the fungus to chew up proteins that help the sugarbeet plant fend off attack by the fungus. This will be investigated in future experiments designed to protect sugarbeet seedlings from infection by this devastating pathogen of beet sugar production.
Technical Abstract: The production of protease activity by the sugarbeet pathogen Aphanomyces cochlioides, the legume pathogen A. euteiches, and the fish pathogen Saprolegnia parasitica was examined. Protease activity was found to be readily detected in supernatants of water cultures of each organism using autoclaved host tissue as a nutrient source. Protease isozymes extracted from sugarbeet and pea seedlings infected with A. cochlioides and A. euteiches, respectively, co-migrated with enzymes produced by the pathogens in culture. Use of class-specific inhibitors indicated that a portion of the protease activity was of the trypsin-class. Trypsin-like isozymes that possessed a relatively fast electrophoretic migration were detected in the A. cochlioides, A. euteiches, and S. parasitica protease complements, whereas the remaining isozymes were not affected by any of the inhibitors tested. Proteinacious trypsin inhibitors from the legumes lima bean (Phaseolus lunatus) and soybean (Glycine max) were able to inhibit the trypsin-like isozymes from A. cochlioides, but not A. euteiches, whereas low molecular weight, synthetic trypsin inhibitors inhibited these isozymes from both pathogen sources. The potential role of protease inhibition in host range determination in the phytopathogenic Aphanomyces is discussed.