A P-type Pentatricopeptide Repeat-Containing Protein Interacts with the Japanese Soil-Borne Wheat Mosaic Virus Movement Protein and Modulates Susceptibility to Infection

As obligate intracellular pathogens, plant viruses interact with host factors to achieve efficient replication and spread. Host factors also play important roles in virus detection and antiviral defence. Furoviruses cause substantial losses in cereals and efficient control measures are lacking. We therefore used Japanese soil-borne wheat mosaic furovirus movement protein (MP JSBWMV ) in immunoprecipitation experiments to identify host interaction partners in the model host plant Nicotiana benthamiana . We identified a P-type pentatricopeptide repeat-containing protein (NbPPR) as the interaction partner of the MP JSBWMV . Fluorescent protein-tagged NbPPR localized to chloroplasts and to the cytosol and plasmodesmata (PD) depending on the location of the fluorescent protein tag, suggesting that the protein may be dually localized to these cellular compartments. MP JSBWMV :RFP and GFP:NbPPR colocalized and interacted at PD as shown by fluorescence resonance energy transfer fluorescence lifetime imaging and co-immunoprecipitation. To functionally characterize the MP JSBWMV -interacting NbPPR, we immunoprecipitated GFP:NbPPR-interacting RNAs and identified a motif overrepresented in the GFP:NbPPR-bound RNAs. The motif is consistent with the PPR target sequence predicted using PPR code. While most of the RNA targets encode subunits of the organellar NADH-dehydrogenase complex, we also identified RNAs encoding cell wall proteins. Downregulation of NbPPR, using virus-induced gene silencing and subsequent infection with fluorescent protein-tagged viruses, resulted in increased numbers of infection sites for JSBWMV in plants silenced for NbPPR compared to controls. We propose a model to explain how virus infection may affect NbPPR function and how NbPPR may regulate the infection cycle. As PPRs are increasingly explored for the modulation of gene expression, virus-targeting PPRs may be developed into tools for virus control in future.