Time course of expression of genes identified in this study and pathogenesis-related (PR) genes in ClYVV-infected plants. mRNA accumulation was investigated by Northern blot analysis with DIG-labeled RNA probes. (A, B, C) RNAs were extracted from tip leaves of ClYVV- or ClYVV/CN-NdB-inoculated broad beans for Northern blot analysis (Figure 1). Hybridized probes were chemiluminescently detected with CDP-star reagent (New England Biolabs, Beverly, MA, USA). (D) The same experiment as in A, B, and C was performed with a pea line, PI 343958. (E) The same experiment as in D was performed with BYMV, which did not cause necrotic symptoms, but did result in mosaic symptoms in inoculated pea PI 343958.