A PUTATIVE IGG-BINDING 65-KDA ADHESIN INVOLVED IN ADHESION AND INFECTION OF SOYBEANS BY PHYTOPHTHORA-MEGASPERMA F SP GLYCINEA

Using an in vivo adhesion test and a newly developed leaf-disc infection assay we demonstrate that antibodies against mammalian substrate adhesion molecules, and also pre-immune IgG and D-mannose, inhibit (1) adhesion of the pathogen Phytophthora megasperma f.sp. glycinea (Kuan and Erwin) to the walls of soybean mesophyll cells, and (2) infection and colonization of the host through open wounds. Concanavalin A inhibited adhesion and infection in the infection assay but net adhesion in the adhesion test described previously. In control experiments, these compounds had no significant influence on cyst germination rates, or on germ tube growth of the pathogen. D-glucose was able to partially reverse the inhibitory effect of ConA and IgG. Intercellular washing fluids of soybean leaf tissue and surface (glyco)proteins from the pathogen were screened for putative IgG-binding adhesins. From both sources a major 65 kDa IgG-binding band was localized on SDS-PAGE gels. Based on ConA and IgG binding, the putative adhesins are (manno) glycoproteins. The study shows that adhesion of the fungal pathogen to the host cell wall is a prerequisite for colonization of the host tissue and that an IgG-binding 65 kDa glycoprotein appears to be instrumental in adhesion.