Proliferating cell nuclear antigen suppresses RNA replication of through an interaction with the viral genome.

(BaMV), a member of the genus, has a monopartite positive-strand RNA genome, on which five open reading frames (ORFs) are organized. ORF1 encodes a 155-kDa non-structural protein (REP) that plays a core function in replication/transcription of the viral genome. To find out cellular factors modulating the replication efficiency of BaMV, a putative REP-associated protein complex from leaf was isolated on a SDS-PAGE gel and a handful of proteins preferentially associated with REP were identified by tandem mass spectrometry. Among them, proliferating cell nuclear antigen (PCNA) was particularly noted. Overexpression of PCNA strongly suppressed the accumulation of BaMV coat protein and RNAs in leaf protoplasts. In addition, PCNA exhibited an inhibitory effect on BaMV polymerase activity. A pull-down assay confirmed a binding capability of PCNA toward BaMV genomic RNA. Mutations at D41 or F114 residues, which are critical for PCNA to function in nuclear DNA replication and repair, disabled PCNA from binding BaMV genomic RNA as well as suppressing BaMV replication. This suggests that PCNA bound to the viral RNA may interfere with the formation of a potent replication complex or block the replication process. Interestingly, BaMV is almost invisible in the newly emerging leaves where PCNA is actively expressed. Accordingly, PCNA is probably one of the factors restricting the proliferation of BaMV in young leaves. and were also suppressed by PCNA in the protoplast experiment, suggesting a general inhibitory effect of PCNA on the replication of potexviruses. Knowing the dynamic interplay between plant RNA viruses and their host is a basic step toward firstly understanding how the viruses survive the plant defense mechanisms, and secondly gaining knowledge of pathogenic control in the field. This study found that plant proliferating cell nuclear antigen (PCNA) imposes a strong inhibition on the replication of several potexviruses including , and Based on the tests on , PCNA is able to bind the viral genomic RNA and this binding is a prerequisite for the protein to suppress the virus replication. This study also suggests that PCNA plays an important role in restricting the proliferation of potexviruses in the rapidly dividing tissues of plants.