Changes in Turnip Leaf Messenger RNA Populations During Systemic Infection by Severe and Mild Strains of Cauliflower Mosaic Virus. Rebecca Stratford. Department of Virus Research, John Innes Institute and AFRC Institute of Plant Science Research, Coloney Lane, Norwich NR4 7UH, U.K.. Simon N. Covey. Department of Virus Research, John Innes Institute and AFRC Institute of Plant Science Research, Coloney Lane, Norwich NR4 7UH, U.K.. MPMI 1:243-249. Accepted 17 August 1988. Copyright 1988 The American Phytopathological Society.

Host gene expression in turnip leaves systemically infected with two strains of cauliflower mosaic virus (CaMV) was examined by 2-D polyacrylamide gel analysis of polypeptides synthesized by in vitro translation of cellular mRNAs. We observed a greater number of changes in the level of specific translatable mRNAs in response to infection by a severe CaMV strain, Cabb B-JI (16 changes), which induces leaf chlorosis (yellowing), than to a mild strain, Bari 1 (11 changes), which does not. Six changes were common to infections by both CaMV strains. By using northern blot analysis, we identified one of the mRNAs that decreased markedly in level during Cabb B-JI infection as that encoding the precursor to the small subunit of ribulose bisphosphate carboxylase (rbcS). In contrast, the level of the rbcS mRNA was usually only slightly reduced in Bari 1-infected leaves. We also compared the translatable mRNA population of senescing and nonsenescing leaves to assess the degree of similarity to infection-induced chlorosis. Of the seven major changes in cellular mRNAs occurring during senescence, only three were common to those seen during infection by the severe CaMV strain; one of these changes was to the rbcS. We conclude that plants respond at the molecular level in different ways to systemic infection by mild and severe strains of the same virus and that changes in gene expression occurring during infection resulting in leaf chlorosis are not simply due to premature induction of senescence.