Submitted to: American Society of Sugarbeet Technologists
Publication Type: Proceedings
Publication Acceptance Date: 3/17/2003
Publication Date: 7/15/2003
Citation: WEILAND, J.J. PROTEASE SECRETION IN APHANOMYCES COCHLIOIDES. PROCEEDINGS OF THE 1ST JOINT INTERNATIONAL INSTITUTE FOR BEET RESEARCH AND THE AMERICAN SOCIETY OF SUGAR BEET TECHNOLOGISTS CONGRESS. 2003. P. 415-417.
Interpretive Summary: Pathogenic fungi utilize a range of mechanisms to gain access to plant tissues. A major means by which these fungi penetrate the plant surface is be the secretion of enzymes that degrade the external barrier of the plant. Since proteins are involved in giving the surface of the plant exterior its form and strength, it is possible the fungi might produce enzyme that degrade this protein in order to gain access to the plant cells. The data found in this work confirm that an important fungal pathogen of sugarbeet, Aphanomyces cochlioides, does indeed produce large amounts of enzyme capable of protein degredation (protease) both during growth in nutirent mixtures in the laboratory and in diseased plants. Characterization of these enzymes will enable researchers and agriculturalists to design rational strategies for pathogen control that is based on protease inhibition. This in turn will help protect the sugarbeet crop from this important and costly disease.
Technical Abstract: Protease activities have been implicated in the infection of fish and crayfish by Aphanomyces astaci, a pathogen of these host organisms. In an effort to characterize protease activities produced by the sugarbeet pathogen A. cochlioides, culture supernatants of this oomycete were tested for bulk enzyme activity and examined for protease isozyme complement. Bulk protease activity was readily detected using azocoll as a colorimetric substrate. At least 8 distinct isoforms of protease secreted by A. cochlioides were detected after electrophoretic fractionation in native polyacrylamide gels containing co-polymerized gelatin. A subset of the protease activities was sensitive to inhibitors of trypsin, including the proteinacious trypsin inhibitors from lima bean. Co-culture of sugarbeet seedlings in the presence of A. cochlioides and lima bean trypsin inhibitor resulted in increased seedling survival relative to control inoculations. The data suggest that protease activities secreted by A. cochlioides may be virulence determinants in the infection of sugarbeet by this pathogen.