The p29 silencing suppressor of Cryphonectria hypovirus 1 inhibits dcl2 gene transcription by directly binding to the promoter region

Abstract RNA silencing is an innate immune response against viral infections in eukaryotic organisms. Dicer or dicer-like protein (DCL) is a key component of the RNA silencing pathway for the generation of small interfering RNAs, and its expression is often elevated during viral infections. This upregulation reflects the host cell’s attempt to mount an effective antiviral response. However, viruses have evolved diverse strategies to suppress the host’s RNA silencing responses. Previous studies revealed that the p29 silencing suppressor of the mycovirus Cryphonectria hypovirus 1 (CHV1) suppresses the transcriptional upregulation of the dcl2 gene in its fungal host, Cryphonectria parasitica , but the molecular mechanism underlying this suppression remains unclear. In this study, we observed that like dcl2 in C. parasitica , dcl2 in Fusarium graminearum plays a crucial role in combating CHV1 infection. Moreover, p29 inhibits dcl2 expression in F. graminearum . This was further validated by a dcl2 promoter-driven GFP reporter system used to monitor dcl2 promoter activity. Yeast one-hybrid assay, dot blot protein-DNA binding assay, and electrophoretic mobility shift assay indicated that p29 directly binds to the dcl2 promoter region in C. parasitica and F. graminearum to inhibit dcl2 transcription. In particular, the putative MYB cis- regulatory element sequence in the dcl2 promoter is essential for binding with p29 and the repression of promoter activity by p29. Overall, the results of this study provide a novel example in which a viral RNA silencing suppressor operates at the transcriptional level through DNA–protein interactions.