The first phlebo-like virus infecting plants: a case study on the adaptation of negative-stranded RNA viruses to new hosts

"Backgrounds Concave gum (CG) is a virus-like disease of citrus first described in the early 1930s, the etiology of which is still unknown. Objectives Identification of viruses associated with CG disease Methods Next generation sequencing of cDNA libraries from symptomatic and non-symptomatic citrus plants, field surveys and phylogenetic analyses Conclusions A novel negative-stranded RNA virus has been identified and shown to be closely associated with CG disease. The new virus, tentatively named citrus concave gum-associated virus (CCGaV), has a bipartite genome composed of a negative-sense RNA1 coding for the RNA-dependent RNA polymerase (RdRp), and an ambisense RNA2 encoding the nucleocapside (N) and a putative movement protein (MP). RNA signatures in viral RNAs and phylogenetic analyses of RdRP and N proteins highlighted the close relationships of CCGaV with members of the genus Phlebovirus, which are arthropod-transmitted viruses infecting mammals, and with some phlebo-like viruses exclusively infecting arthropods. The putative CCGaV MP has the typical features of MPs grouped in the 30K superfamily and is phylogenetically related to the MPs of the plant-infecting viruses of the family Ophioviridae. Based on these data, CCGaV can be considered the first phlebo-like virus infecting plants. Implications of these findings in the evolutionary events that allowed the adaptation of the ancestor negativestranded RNA virus(es), likely infecting arthropods, to plant hosts will be examined. The need of creating a new genus for classifying this bipartite negative-stranded RNA virus, and the impact of specific detection methods developed in the frame of this study on sanitation and certification programs of citrus will be also discussed"