IMMUNOGOLD LOCALIZATION OF THRGP-LIKE EPITOPES IN THE HAUSTORIAL INTERFACE OF OBLIGATE, BIOTROPHIC FUNGI ON MONOCOTS

Immunoelectron microscopy was used to determine the subcellular distri bution of threonine-hydroxyproline-rich glycoprotein (THRGP) epitopes in host-parasite interactions between obligate, biotrophic fungi and c ereals. Infection sires of stem rust (Puccinia grarniizis f. sp. triti ci) and leaf rust (Puccinia recondita) on primary leaves of wheat (Tri ticum aestivum), as well as of powdery mildew (Erysiphe graminis f. sp . hordei) on coleoptiles of barley (Hordeum vulgare),were probed with a polyclonal antiserum to maize THRGP. A few immunogold particles were found over the cell walls of wheal mesophyll tissue and barley coleop tile epidermis. Unlike previous examples in dicot plants, no enhanced accumulation of THRGP was observed in cereal cell walls adjacent to si tes of pathogen ingress. Instead, the most pronounced accumulation of THRGP-like molecules occurred over the extrahaustorial matrix in both incompatible and compatible plant-pathogen interactions. For powdery m ildew of barley, immunogold staining was distinctly increased over the center of the penetration sites; however, no labeling was found over papillae that formed during incompatible and compatible interactions. In addition, no cross-reactivity of the anti-THRGP antiserum with inte rcellularly growing rust pathogens was observed. The highly localized deposition of THRGP-like molecules in the extrahaustorial matrix sugge sts that the host plant establishes a modified barrier between itself and the pathogen.