facilitative and synergistic interactions between fungal and plant viruses plants and fungi are closely associated through parasitic or symbiotic relationships in which bidirectional exchanges of cellular contents occur recently a plant virus was shown to be transmitted from a plant to a fungus but it is unknown whether fungal viruses can also cross host barriers and spread to plants in this study we investigated the infectivity of cryphonectria hypovirus 1 chv1 family hypoviridae a capsidless positivesense singlestranded rna ssrna fungal virus in a model plant nicotiana tabacum chv1 replicated in mechanically inoculated leaves but did not spread systemically but coinoculation with an unrelated plant ssrna virus tobacco mosaic virus tmv family virgaviridae or other plant rna viruses enabled chv1 to systemically infect the plant likewise chv1 systemically infected transgenic plants expressing the tmv movement protein and coinfection with tmv further enhanced chv1 accumulation in these plants conversely chv1 infection increased tmv accumulation when tmv was introduced into a plant pathogenic fungus fusarium graminearum in the in planta f graminearum inoculation experiment we demonstrated that tmv infection of either the plant or the fungus enabled the horizontal transfer of chv1 from the fungus to the plant whereas chv1 infection enhanced fungal acquisition of tmv our results demonstrate twoway facilitative interactions between the plant and fungal viruses that promote crosskingdom virus infections and suggest the presence of plantfungalmediated routes for dissemination of fungal and plant viruses in nature