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In Situ Localization of Barley Yellow Dwarf Virus Coat Protein in Oats. Petra H. Nass, University of Illinois, Department of Plant Pathology, Urbana 61801; Birute P. Jakstys(2), and Cleora J. D'Arcy(3). (2)University of Illinois, Center for Electron Microscopy, Urbana 61801; (3)University of Illinois, Department of Plant Pathology, Urbana 61801. Phytopathology 85:556-560. Accepted for publication 6 January 1995. Copyright 1995 The American Phytopathological Society. DOI: 10.1094/Phyto-85-556.

The expression of barley yellow dwarf virus (BYDV) coat protein was followed in situ by immunogold labeling of ultrathin sections. Samples of BYDV-PAV-IL–infected oat seedlings were taken 1–10 days postinoculation (dpi) and prepared for electron microscopy. Gold labeling was first detected in the host cytoplasm at 2 dpi. At 3 dpi, labeling had increased and was found mostly around or within regions that contained ribosome-associated filamentous material. No labeling was found over densely compressed filaments. By 4–5 dpi, viral coat protein also was detected in the nucleus. Viral coat protein was not associated with any other cellular components. The results suggest that viral coat protein is first expressed in the cytoplasm of the infected host cell. Since labeling was mostly found in or around regions of ribosome-associated filaments, it is proposed that coat protein is expressed by cytoplasmic ribosomes from viral RNA. Coat protein found in the nucleus during later stages of infection probably diffused into the nucleoplasm after disruption of the nuclear membrane.