Mutant Coat Protein of Tobacco Mosaic Virus Induces Acute Chlorosis in Expanded and Developing Tobacco Leaves. Alwyn G. C. Lindbeck. Departments of Plant Pathology Botany and Plant Sciences, University of California, Riverside 92521 U.S.A. Dennis J. Lewandowski(1), James N. Culver(1), William W. Thomson(2), and William O. Dawson(1). Departments of (1)Plant Pathology and (2)Botany and Plant Sciences, University of California, Riverside 92521 U.S.A. MPMI 5:235-241. Accepted 20 January 1992. Copyright 1992 The American Phytopathological Society.

The production of a mutated coat protein of tobacco mosaic virus caused acute (bright yellow) chlorosis in both expanded and developing tobacco leaves. In systemically infected tobacco leaves, synthesis of coat protein was not necessary for induction of the classic light green/dark green mosaic symptoms. However, the appearance of a bright yellow mosaic in leaves systemically infected with the mutant virus was due to synthesis of the mutant coat protein. This symptom resulted from the addition of bright yellow chlorosis, associated with the synthesis of mutant coat protein, to the normal light green/dark green mosaic symptoms that were caused by some viral product other than the coat protein. Electron microscopy of tissue from the yellowed areas in systemically infected leaves showed that normal chloroplast development was disrupted. These chlorotic areas contained only immature chloroplasts. Protein aggregates similar to the coat protein bodies previously seen in expanded leaves inoculated with chlorosis-causing coat protein mutants were also observed in acute chlorotic tissue of systemically infected leaves. These findings show that the combination of bright yellow chlorosis and normal mosaic symptoms on nascent leaves result from two separate virus-host interactions.