Facilitative and synergistic interactions between fungal and plant viruses

Significance Unlike other eukaryotic viruses, fungal viruses generally lack an extracellular phase in their life cycle. It thus remains unclear whether fungal viruses can spread beyond their native hosts. Herein, we investigated the infectivity of a fungal virus, Cryphonectria hypovirus 1 (CHV1) in Nicotiana tabacum plants. CHV1 is able to systemically infect plants after mechanical coinoculations with plant viruses such as tobacco mosaic virus (TMV) or when inoculated to transgenic plants expressing the TMV movement protein. In the fungal inoculation experiment, we demonstrated that plant virus infections in plants enable horizontal transfer of CHV1 from fungi to plants and to other heterologous fungal species. Hence, our results reveal a facilitative effect of plant viruses in spreading fungal viruses.