Analysis of the effects of the mutation of selected genes of pedilanthus leaf curl virus on infectivity, symptoms and the maintenance of tobacco leaf curl betasatellite

Pedilanthus leaf curl virus (PeLCV) is a widely encountered monopartite begomovirus with a wide host range that usually associates with a betasatellite. The cloned PeLCV used was highly infectious to Nicotiana benthamiana plants by agroinoculation and symptoms were enhanced by co-inoculation with tobacco leaf curl betasatellite (TbLCB). The study investigated the effects of the mutation of the coat protein (CP), V2, C2 and C4 genes of PeLCV on infectivity, symptoms and maintenance of TbLCB in N. benthamiana. Mutation of the CP abolished infectivity of PeLCV, which was not rescued by co-inoculation with TbLCB. Mutation of the V2 gene severely reduced infectivity that, in a small number of plants, was rescued by TbLCB, resulting in plants with very mild symptoms. Mutation of the C2 or V4 genes led to a significant reduction in virus infectivity, but also to non-symptomatic infections. Co-inoculation of either mutant with TbLCB led to a greater number of plants infected but fewer plants ultimately maintained the betasatellite, compared with inoculation of the betasatellite with the wild-type virus, indicating that the C2 and C4 proteins play a role in the maintenance of the betasatellite. For the C2 mutation, but not the C4 mutation, the presence of the betasatellite also resulted in mild symptoms. The results here, in conjunction with earlier studies, highlight commonalities as well as differences for the effects of gene mutations and interactions with betasatellites of different begomoviruses, indicating that begomovirus--betasatellite interaction is highly nuanced.