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F-box like motif of the brassica yellows virus silencing suppressor P0 protein facilitates its stability in vivo

Yuanyuan Li: China Agricultural University

<div>Several studies have shown that P0 of some poleroviruses can target Argonaute 1 (AGO1) to suppress RNA silencing. Although P0 harbor F-box like motif reported to be essential for RNA silencing suppression activity, it is the autophagy pathway that was shown to contribute to the AGO1 degradation. Therefore, the role of P0 F-box like motif in silencing suppression remains unclear. Here, global mutagenesis and comparative functional analysis of the P0 encoded by Brassica yellows virus genotype A (P0<sup>BrA</sup>) revealed different residues within P0<sup>BrA</sup> are required for local and systemic silencing suppression activities. Furthermore, P0<sup>BrA</sup>-mediated<sup> </sup>destabilization of AGO1 is only required for the suppression of local but not systemic silencing. Remarkably, the F-box like motif mutant of P0<sup>BrA</sup> is destabilized <em>in vivo</em>. Inhibitor treatment assay indicated involvement of both 26S proteasome system and autophagy pathway in this process. Genetic analyses indicated that, although P0<sup>BrA</sup> F-box like motif is required for its interaction with SKP1, it is not required for its silencing suppression activity. Therefore, the F-box like motif is required for the stability of P0<sup>BrA</sup> protein to assure efficient RNA silencing suppression. Consistent with these findings, efficient systemic infection of BrYV requires P0<sup>BrA</sup>. Results presented here provide a novel insight into the polerovirus P0 protein stability and RNA silencing suppression activities and the function of P0 F-box like motif.</div>