Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 30, 1998
Publication Date: N/A
Interpretive Summary: Botrytis cinerea is an important fungal pathogen of plants. Little is known about the early steps in the infection process exhibited by this pathogen. On such early step is the secretion of a film surrounding the fungal tissue that arises from a newly germinated spore. We had already shown that this film, often referred to as an extracellular matris (ECM), plays a vital role in attaching the fungus to the surface of the host. In the current publication we discuss results of a study in which the composition of the ECM was determined, and in which its enzymatic activity was assessed. The ECM has a surprisingly complex composition, with carbohydrate, protein, and lipid present. Several enzymes were found associated with the ECM, including some thought to be important in the infections process. As we learn more about the infection process, including the role played by the ECM, we are hopeful that it will be possible to develop new disease control measures. For example, it is possible that inhibition of one or more of the enzymes present in the ECM, which is in intimate contact with both the plant host and the fungus, could prevent infection from taking place. We are currently looking into this possibility.
Technical Abstract: Germlings of Botrytis cinerea, an important fungal pathogen of plants, produce an extracellular matrix (ECM), or ensheathing film, that serves, in part, in their attachment (R. P. Doss, et al., Appl. Environ. Microbiol. 61:260-265, 1995). The composition of this film has been ascertained by using samples obtained by growing germlings on a glass surface, removing the fungal mycelium by vigorous washing, and collecting the tightly attached film by scraping the substratum with a razor blade. Slightly over half of the dry weight of the ECM was found to be carbohydrates (about 20%), proteins (about 28%), and lipids (about 6%). Hydrolysis of the carbohydrate portion of the ECM revealed that glucose was the most prominent monosaccharide present, comprising about 60% of the total monosaccharides. Also present were mannose (about 35%) and myo- inositol (about 5%). The proteinaceous fraction of the ECM was made up of a number of polypeptides separable by polyacrylamide gel electrophoresis. The lipid fraction of the ECM, analyzed by thin- layer chromatography, was made up of several simple lipid components, including free fatty acid, mono- and triacylglycerol, wax ester, fatty alcohol, and several unidentified components. No complex lipids were detected. Isolated ECM exhibited polygalacturonase and laccase activity and was able to catalyze the hydrolysis of p-nitrophenyl butyrate, a model substrate for assessing cutinase activity. Cellulase, pectin lyase, and pectin methyl esterase activities were noted with both heated and unheated ECM preparations. Proteinase activity was not detected.