Molecular differentiation in the extrahaustorial membrane of pea powdery mildew haustoria at early and late stages of development

Abstract

Two new monoclonal antibodies (MAbs) are described which recognise glycoprotein components of the extrahaustorial membrane ( ehm) which surrounds the haustorium formed during the infection of pea leaves by the powdery mildew fungus Erysiphe pisi. One of the MAbs, UB9, raised against enriched pea leaf plasma membranes, recognises a large (200 kDa) glycoprotein in this membrane within infected and uninfected epidermal cells. It does not label haustoria at early stages of development showing that at least one plasma membrane glycoprotein is excluded from the ehm. However, UB9 binds to the ehm of a subpopulation (approx 20%) of HCs late in the infection process and it is possible that the insertion of this glycoprotein into the ehm may represent a breakdown of biotrophy during senescence of haustoria or could be a late defence response by the plant. A second MAb, UB11, was raised against isolated haustorial complexes derived from the pea powdery mildew system. This antibody recognises a glycoprotein (250 kDa) which is present in the ehm of the haustorial complex and is expressed very early in haustorial development. UB11 does not bind to plant membranes of infected or uninfected plants and does not cross-react with other fungal components. This antibody therefore identifies a glycoprotein specifically located to the ehm of haustorial complexes and shows that there is molecular differentiation of this key interface between the biotrophic partners.