Coat Protein-Related Polypeptides from in Vitro Tobacco Mosaic Virus Coat Protein Mutants Do Not Accumulate in the Chloroplasts of Directly Inoculated Leaves. A. G. C. Lindbeck. Departments of Plant Pathology and Botany and Plant Sciences, University of California, Riverside 92521 U.S.A. W. O. Dawson(1), and W. W. Thomson(2). Departments of (1)Plant Pathology and (2)Botany and Plant Sciences, University of California, Riverside 92521 U.S.A. MPMI 4:89-94. Accepted 8 October 1990. Copyright 1991 The American Phytopathological Society.

Chloroplasts from leaves directly inoculated with a series of coat protein deletion mutants of tobacco mosaic virus were examined by electron microscopy. Wild-type tobacco mosaic virus did not cause any ultrastructural changes in fully developed chloroplasts. However, specific mutations in the coat protein gene caused chlorosis on fully expanded leaves by causing significant degradation of the chloroplasts in these tissues. Mutants that caused weak or transient yellowing had no observable effect on the chloroplasts in these tissues. Immunocytochemical localization of the coat protein-related polypeptides from the deletion mutants indicated that the polypeptides do not accumulate in the chloroplasts. The polypeptides accumulate in discrete dark-staining bodies in the cytoplasm of infected cells, which we have termed “coat protein bodies.” The coat protein bodies were often associated with X-bodies. These data suggest that the altered coat protein which was on the outside of the chloroplasts caused the degradation of the chloroplasts in infected cells. Coat protein probably subverts the chloroplasts by interfering with chloroplast protein synthesis and transport in the cytoplasm. A number of possible mechanisms are suggested.