Citrus Exocortis Viroid Infection Alters the in Vitro Pattern of Protein Phosphorylation of Tomato Leaf Proteins. Pablo Vera. Departamento de Biotecnología, Universidad Politécnica de Valencia, 46020-Valencia, Spain. Vicente Conejero. Departamento de Biotecnología, Universidad Politécnica de Valencia, 46020-Valencia, Spain.. MPMI 3:28-32. Accepted 30 August 1989. Copyright 1990 The American Phytopathological Society.

The involvement of protein phosphorylation in the pathogenesis of citrus exocortis viroid (CEV) in tomato (Lycopersicon esculentum) plants was investigated by determining the pattern of protein phosphorylation after labeling with (γ-³²P)ATP.³²P incorporation into proteins was determined by autoradiography after fractionation of proteins by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. CEV infection markedly and consistently enhanced the phosphorylation of several proteins with molecular masses of 68, 40, 30, 27, and a triplet of 22-24 kDa. Also, a reduction in the phosphorylation of other proteins, normally phosphorylated in mock-inoculated tomato plants, was found. The expression of this differential phosphorylation of proteins was Mn²⁺ -dependent. These viroid-induced effects on protein phosphorylation could only be observed after disease symptoms had emerged in the plant.