Isolation and ultrastructural localization of a soluble protein from Ophiostoma ulmi

Abstract

Two-dimensional polyacrylamide gel electrophoresis was used to identify and isolate a soluble polypeptide, the QP1 protein, which is characteristic of the vegetative hyphae of nonaggressive isolate Q412 of Ophiostoma ulmi. Individual QP1 spots were excised from 16 two-dimensional gels. Polypeptides were eluted from the gel spots by electroelution and lyophilized. The protein was injected into rabbits for the production of polyclonal antibodies. Antiserum specificity was tested by transferring polypeptides from a two-dimensional gel onto nitrocellulose and treating with QP1 serum. The resulting immunoblot contained a single spot that corresponded in shape and location to that of the QP1 polypeptide. Thin sections of fungal mycelia, from nonaggressive isolate Q412 and the aggressive isolate VA of O. ulmi, were treated with QP1 antibodies and protein A – gold. The gold label was localized in thin sections over conidial and hyphal cell walls of the nonaggressive isolate. The aggressive isolate was nonreactive. Mycelia from nonaggressive isolates Q412 and Q311 and aggressive isolates VA and CESS16K of O. ulmi were grown on solid medium, treated with QP1 antibodies, labelled with protein A – gold, and prepared for scanning electron microscopy. The gold-labelled QP1 polypeptide was detected on the leading edge of a small number of hyphae from nonaggressive isolates Q412 and Q311. Key words: immunogold labelling, Ophiostoma ulmi, soluble proteins.