Single mutation converts mild pathotype of the Pepino mosaic virus into necrotic one

Pepino mosaic virus (PepMV) is a member of the Flexiviridae family, genus Potexvirus. PepMV isolates from the same genotype differ in the symptoms they induce in Datura inoxia and Solanum lycopersicum. Necrotic isolates cause necrosis on these plants whereas mild isolates are very often asymptomatic or induce mild mosaic. Sequence analysis of the genomes of mild (PepMV-P22) and necrotic (PepMV-P19) strains revealed that they differ by several nonsynonymous mutations. Eleven mutations are located in the RdRp coding region and one mutation is placed in the TGB3 coding region. To investigate whether these mutations affect the symptom induction, both PepMV-P22 and PepMV-P19 were mutagenized. As a result we found that the genetic determinant responsible for necrosis induction was amino acid 67 of TGB3. This showed that one point mutation is sufficient to alter the virus from mild to aggressive in tomato and D. inoxia.