Monoclonal antibodies to surface and extracellular antigens of a fungal plant pathogen, Phytophthora megasperma f.sp. glycinea, recognize specific carbohydrate epitopes

Abstract

A library of monoclonal antibodies was produced to both extracellular glycoproteins and purified mycelial walls from the fungus Phytophthora megasperma f.sp. glycinea, the causal agent of root rot in soybeans ( Glycine max L. Merr.). More than 44 independent monoclonal antibodies were characterized for binding to antigens from several races of P. megasperma f.sp. glycinea. The monoclonal antibodies fell into 11 epitope groups based on pairwise antibody competitions. Competitive binding assays revealed dramatic differences between races and between different isolates of the same race, however none of the 11 immunodominant epitopes could be correlated with particular avirulence genes. The same immunodominant epitopes are found on both extracellular glycoproteins and mycelial walls from P. megasperma f.sp. glycinea. Chemical and enzymatic treatment of fungal antigens indicate that most of the monoclonal antibodies recognize carbohydrate epitopes. Competition analysis with carbohydrates of known structure revealed that monoclonal antibody VIII was specific for β-1,3 linked terminal glucosyl residues. Monoclonal antibody X was shown to recognize non-terminal stretches of β-1,3 linked glucosyl residues. Two of the monoclonal antibodies bound to elicitor preparations from walls of P. megasperma f.sp. glycinea, but not to an elicitor preparation from yeast.