Submitted to: Virology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 18, 2012
Publication Date: September 11, 2012
Repository URL: http://handle.nal.usda.gov/10113/55924
Citation: Tatineni, S., Li, R., Qu, F., Morris, J.T., French, R.C. 2012. Triticum mosaic poacevirus enlists P1 rather than HC-Pro to suppress RNA silencing-mediated host defense. Virology. 433: 104-115. Interpretive Summary: Viruses are intracellular obligate parasites and must exploit host molecular mechanisms in order to propagate in hostile environments. Upon virus invasion, the host deploys diverse mechanisms to combat viral infection at both the individual cell as well as whole organism levels. In plants, RNA silencing is one of the most important defense mechanisms employed against viral infections. To counter host RNA silencing, viruses have evolved to encode diverse, yet functionally conserved genes with silencing suppression activity. Triticum mosaic virus (TriMV), the type species of the newly established genus Poacevirus in the family Potyviridae, was reported from the Great Plains region. TriMV is one of the more economically important viruses infecting wheat in this region. In this study, we found that TriMV P1, not HC-Pro as in other potyviruses, was able to effectively suppress host RNA silencing, thus facilitating virus invasion and disease in wheat. The presence of TriMV P1 gene in a heterologous virus induced severe symptoms in Nicotiana benthamiana plants, suggesting that the P1 of TriMV is a pathogenicity determinant by suppressing the host RNA silencing.
Technical Abstract: RNA silencing, or posttranscriptional gene silencing (PTGS) is one of the most important defense mechanisms employed by higher plants and animals to defend against viral infections. Plant viruses evolved by adopting divergent proteins, even within single virus families, to counter this host defense response. In this study we report that the P1 protein of Triticum mosaic virus (TriMV), type species of the newly established Poacevirus genus in the family Potyviridae is a suppressor of RNA silencing. TriMV P1 suppressed local and systemic PTGS induced by single-stranded (ss) or double-stranded (ds) RNAs, and suppressed ssRNA-induced systemic silencing by blocking and/or inhibiting long-distance transport of silencing signals. In contrast to P1/HC-Pro of members of the Potyvirus genus, the presence of HC-Pro with P1 substantially affected the ability of P1 to suppress RNA silencing triggered by ssRNA and dsRNA. TriMV P1 suppressed long-distance movement of RNA silencing signals triggered by dsGFP, while Turnip mosaic potyvirus (TuMV) HC-Pro failed or inefficiently did so, suggesting that TriMV P1 and TuMV HC-Pro differ mechanistically in suppression of systemic PTGS induced by dsRNA. TriMV P1 failed to reverse established silencing, but interrupted initiation of newly induced silencing in systemically silenced plants, implying that P1 interfered with the PTGS initiation stage in systemically silenced plants. TriMV P1 substantially increased Potato virus X pathogenicity in Nicotiana benthamiana. Collectively, our data demonstrate that TriMV P1 is a suppressor of PTGS with functional similarities as well as differences from that of TuMV HC-Pro, indicating that the P1 and HC-Pro cistrons in the family Potyviridae evolved mechanistically as separate lineages to counteract host defense mechanism.