Tomato geminivirus encoded RNAi suppressor protein, AC4 interacts with host AGO4 and precludes viral DNA methylation.

Abstract Plant RNA silencing systems are organized as a network, regulating plant developmental pathways and restraining invading viruses, by sharing cellular components with overlapping functions. Host regulatory networks operate either at the transcriptional level via RNA-directed DNA methylation, or at the post-transcriptional stage interfering with mRNA to restrict viral infection. However, viral-derived proteins, including suppressors of RNA silencing, favour virus establishment, and also affect plant developmental processes. In this investigation, we report that Tomato leaf curl New Delhi virus-derived AC4 protein suppresses RNA silencing activity and mutational analysis of AC4 showed that Asn-50 in the SKNT-51 motif, in the C-terminal region, is a critical determinant of its RNA silencing suppressor activity. AC4 showed interaction with host AGO4 but not with AGO1, aggregated around the nucleus, and influenced cytosine methylation of the viral genome. The possible molecular mechanism by which AC4 interferes in the RNA silencing network, helps virus establishment, and affects plant development is discussed. Highlights • Expression or silencing status of AC4 influences viral DNA cytosine methylation. • AC4 is an RNA silencing suppressor and Asn-50 in the SKNT-51 motif is crucial for suppressor activity. • Interaction with AGO4 and sub-cellular localization imply AC4 regulates PTGS and TGS. • Molecular evidence for the role of AC4 in silencing suppression [ABSTRACT FROM AUTHOR]