Argonaute 5-mediated antiviral defense and viral counter-defense in Nicotiana benthamiana

• Published in: Virus research Vol. 334; p. 199179
• Main Authors: Tu, Chin-Wei, Huang, Ying-Wen, Lee, Chin-Wei, Kuo, Song-Yi, Lin, Na-Sheng, Hsu, Yau-Heiu, Hu, Chung-Chi
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.09.2023; Elsevier
• Subjects: 26S proteasome; AGO5; Antiviral Agents - metabolism; Autophagy; Cucumovirus - genetics; Cytomegalovirus Infections; Nicotiana; Plant antiviral defense; Plant Diseases; RNA - metabolism; RNA Interference; RNA silencing; Viral suppressors of RNA silencing (VSR); Viral suppressors of RNA silencing (VSR); AGO5; 26S proteasome; RNA silencing; Plant antiviral defense; Autophagy
• ISSN: 0168-1702; 1872-7492
• DOI: 10.1016/j.virusres.2023.199179

•NbAGO5 expression is ubiquitously stimulated upon viral infections.•NbAGO5 confers defense against diverse viruses by binding to vsiRNAs.•CMV and TuMV counteract plant defense by degrading NbAGO5 protein.•CMV 2b and TuMV HC-Pro drive NbAGO5 degradation by 26S proteasome and autophagy.•TuMV HC-Pro provides additional counter-defense by interfering with vsiRNA loading. The argonaute (AGO) family proteins play a crucial role in preventing viral invasions through the plant antiviral RNA silencing pathway, with distinct AGO proteins recruited for specific antiviral mechanisms. Our previous study revealed that Nicotiana benthamiana AGO5 (NbAGO5) expression was significantly upregulated in response to bamboo mosaic virus (BaMV) infection. However, the roles of NbAGO5 in antiviral mechanisms remained to be explored. In this research, we examined the antiviral functions of NbAGO5 in the infections of different viruses. It was found that the accumulation of NbAGO5 was induced not only at the RNA but also at the protein level following the infections of BaMV, potato virus X (PVX), tobacco mosaic virus (TMV), and cucumber mosaic virus (CMV) in N. benthamiana. To explore the antiviral mechanism and regulatory function of NbAGO5, we generated NbAGO5 overexpression (OE-NbAGO5) and knockout (nbago5) transgenic N. benthamiana lines. Our findings reveal that NbAGO5 provides defense against BaMV, PVX, TMV, and a mutant CMV deficient in 2b gene, but not against the wild-type CMV and turnip mosaic virus (TuMV). Through affinity purification and small RNA northern blotting, we demonstrated that NbAGO5 exerts its antiviral function by binding to viral small interfering RNAs (vsiRNAs). Moreover, we observed that CMV 2b and TuMV HC-Pro interact with NbAGO5, triggering its degradation via the 26S proteasome and autophagy pathways, thereby allowing these viruses to overcome NbAGO5-mediated defense. In addition, TuMV HC-Pro provides another line of counter-defense by interfering with vsiRNA binding by NbAGO5. Our study provides further insights into the antiviral RNA interference mechanism and the complex interplay between NbAGO5 and plant viruses. [Display omitted]