Amino Acid Sequence Motifs Essential for P0-Mediated Suppression of RNA Silencing in an Isolate of Potato leafroll virus from Inner Mongolia
Zhuo, Tao | Li, Yuan-Yuan | Xiang, Hai-Ying | Wu, Zhan-Yu | Wang, Xian-Bin | Wang, Ying | Zhang, Yong-Liang | Li, Da-Wei | Yu, Jia-Lin | Han, Cheng-Gui
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.
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