Mutations introduced to a highly variable region in HCpro reduced HCpro-HIP2 interactions and virulence of PVA, and induced novel types of necrotic symptoms in the systemically infected leaves of Nicotiana species. Microarray-based analysis of gene expression revealed induction of large numbers of defence-related genes including jasmonic acid and ethylene inducible pathways in the leaves systemically infected by the mutated PVA. Three treaments: infection with wild type PVA (WT), infection with mutated PVA (MUT), and mock-inoculation (Mock). Six plants were treated for each treatment. Experiment was repeated three times. WT and MUT samples from all three experiments were hybridised on microarray. Mock samples from experiments 1 and 2 were hybridised as healthy controls.