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Amino Acid Sequence Motifs Essential for P0-Mediated Suppression of RNA Silencing in an Isolate of Potato leafroll virus from Inner Mongolia

June 2014 , Volume 27 , Number  6
Pages  515 - 527

Tao Zhuo, Yuan-Yuan Li, Hai-Ying Xiang, Zhan-Yu Wu, Xian-Bin Wang, Ying Wang, Yong-Liang Zhang, Da-Wei Li, Jia-Lin Yu, and Cheng-Gui Han

State Key Laboratory for Agro-Biotechnology and Department of Plant Pathology, China Agricultural University, Beijing

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Accepted 14 January 2014.

Polerovirus P0 suppressors of host gene silencing contain a consensus F-box-like motif with Leu/Pro (L/P) requirements for suppressor activity. The Inner Mongolian Potato leafroll virus (PLRV) P0 protein (P0PL-IM) has an unusual F-box-like motif that contains a Trp/Gly (W/G) sequence and an additional GW/WG-like motif (G139/W140/G141) that is lacking in other P0 proteins. We used Agrobacterium infiltration-mediated RNA silencing assays to establish that P0PL-IM has a strong suppressor activity. Mutagenesis experiments demonstrated that the P0PL-IM F-box-like motif encompasses amino acids 76-LPRHLHYECLEWGLLCG THP-95, and that the suppressor activity is abolished by L76A, W87A, or G88A substitution. The suppressor activity is also weakened substantially by mutations within the G139/W140/G141 region and is eliminated by a mutation (F220R) in a C-terminal conserved sequence of P0PL-IM. As has been observed with other P0 proteins, P0PL-IM suppression is correlated with reduced accumulation of the host AGO1-silencing complex protein. However, P0PL-IM fails to bind SKP1, which functions in a proteasome pathway that may be involved in AGO1 degradation. These results suggest that P0PL-IM may suppress RNA silencing by using an alternative pathway to target AGO1 for degradation. Our results help improve our understanding of the molecular mechanisms involved in PLRV infection.

© 2014 The American Phytopathological Society