Host-Pathogen Interactions

Abstract

The effect of a number of physiological variables on the secretion of polysaccharide-degrading enzymes by culturegrown Colletotrichum lindemuthianum (Saccardo and Magnus) Scribner was determined. The number of spores used to inoculate cultures grown on isolated bean hypocotyl cell walls affects the time after inoculation at which enzyme secretion occurs, but has no significant effect on the maximal amount of enzyme ultimately secreted. Cell walls isolated from bean leaves, first internodes, or hypocotyls (susceptible to C. lindemuthianum infection), when used as carbon source for C. lindemuthianum growth, stimulate the fungus to secrete more a-galactosidase than do cell walls isolated from roots (resistant to infection). The concentration of carbon source used for fungal growth determines the final level of enzyme activity in the culture fluid. The level of enzyme secretion is not proportional to fungal growth; rather, enzyme secretion is induced. Maximal a-galactosidase activity in the culture medium is found when the concentratioii of cell walls used as carbon source is 1% or greater. A higher concentration of cell walls is necessary for maximal a-arabinosidase activity. Galactose, when used as the carbon source, stimulates a-galactosidase secretion but, at comparable concentrations, is less effective in doing so than are cell walls. Polysaccharide-degrading enzymes are secreted by C. lindemuthianum at different times during growth of the pathogen on isolated cell walls. Pectinase and a-arabinosidase are secreted first, followed by ,6-xylosidase and cellulase, then fl-glucosidase, and.finally, a-galactosidase.An important aspect of the role of polysaccharide-degrading enzymes in plant pathogenesis is the control of the production of such enzymes (1). The variety and concentration of mono-and polysaccharides in the environment in which a pathogen is growing affect both quantitatively and qualitatively the array of polysaccharide-degrading enzymes secreted by the pathogen (1).The in a medium containing, as the sole carbon source, cell wall material isolated from the hypocotyls of young bean plants (4). The secretion of these enzymes is apparently regulated both by the pathogen and by the host plant, since enzyme secretion can be correlated with the strain of the fungus and with the origin of the cell wall material on which the fungus is grown (4). Additional studies have been carried out with this system, and this report describes the effects of several parameters on the production of polysaccharide-degrading enzymes by C. lindemuthianum grown in culture. MATERIAILS AND METHODSPlant Material and Isolation of Cell Walls. Cell walls isolated from the various anatomical parts of the common bean (Phaseolus vulgaris L. cv. Red Kidney) were used throughout this study. The growth conditions and method of cell wall preparation are modifications of those described previously (10, 11). Seeds were surface sterilized by immersion for 2 min in a 0.5c%o sodium hypochlorite (10%, Clorox) solution. The sterilized seeds ...

A Cell Wall-degrading Endopolygalacturonase Secreted by Colletotrichum lindemuthianum

“…These are the first detectable enzymes secreted by C. lindemuthianum (9) the purified C. lindemuthianum endopolygalacturonase. The dissociation constant of this complex is 2 x 10' M or less (1).…”

“…The a strain of Colletotrichum lindemuthianum was cultured as reported (9). The endopolygalacturonase secreted by this fungus was induced by growing the fungus in shake culture on minimal salts media containing 1% citrus pectin (the gift of Sunkist Growers, Inc.).…”

“…The mixture of enzymes secreted by C. lindemuthianum, when this fungus is grown on isolated cell walls as the carbon source, has been shown to degrade isolated cell walls (8 grown under these conditions is an endopolygalacturonase (9). The present paper describes the production, purification, and partial characterization of this enzyme and demonstrates the ability of this purified enzyme to degrade isolated cell walls.…”

Proteins from Plant Cell Walls Inhibit Polygalacturonases Secreted by Plant Pathogens

“…The fungal pathogen Colletotrichum lindenuthianum secretes different enzymes in a temporal sequence with regard to culture age. The first enzyme secreted is an endopolygalacturonase (7). This enzyme has been purified to what is believed to be a homogeneous state (English, P. D., A. Maglothin, and P. Albersheim, in preparation), and the pure enzyme retains the ability to remove most of the galacturonic acid from the isolated cell walls of a number of plants.…”

Cloning and characterization of a rhamnogalacturonan hydrolase gene from Botrytis cinerea

“…It is generally accepted, however, that cell wall degrading hydrolases secreted from fungi are important factors in pathogenesis (1,2,3,4,5). During the infection process, pectolytic hydrolases are secreted earlier than other wall degrading enzymes (6,7,8,9), suggesting that pectolytic hydrolases may be early determinants of the decay process.…”