Characterization of a new closterovirus infecting Ficus carica

Figs (Ficus carica L.) are economically important worldwide, valued for both fruit production and ornamental purposes. Due to the widespread use of vegetative propagation, diverse viruses have accumulated in fig germplasm. To date, more than 14 viruses have been described associated to fig trees, including eight members of the family Closteroviridae, although their role in the etiology of fig mosaic disease (FMD) is unclear. Characteristic symptoms of FMD include mosaic and chlorotic spots on the leaves, along with deformation of fruits and leaves. Fig mosaic virus (FMV) is the causal agent of FMD, although at least five closteroviruses have also been associated with FMD, with unclear roles. In this study, leaf samples displaying typical FMD symptoms, including yellow mosaic and mottling, were collected from a fig tree in Iowa, United States. Total RNA was extracted and subjected to high-throughput sequencing (HTS). Analysis of HTS data revealed contigs corresponding to FMV and a putative new member of the family Closteroviridae, tentatively named fig virus C (FiVC). Based on the HTS-derived sequence, we obtained the full-length genome of the putative new closterovirus using RT-PCR and RACE. The complete genome is approximately 17.8 kb long with open reading frames consistent with the genomic organization of closteroviruses. Sequence comparisons and phylogenetic analysis of the RNA-dependent RNA polymerase, heat shock protein 70-like protein, and capsid protein corroborates that FiVC is a new member of the genus Closterovirus, closely related to other fig-infecting viruses. The discovery of this novel closterovirus in a symptomatic fig tree highlights the need for further studies to clarify the roles of multiple viruses in disease development.