Plants live under the constant threat of pathogen attacks. The interaction between host, pathogen and environment is complex. The general notion assumes that RNA silencing is the main antiviral defense strategy in plants, although recent discoveries suggest that innate immunity also plays a role in the antiviral defense. Plant viruses use silencing suppressor proteins to counteract the effect of silencing in a manner analogous to how microbial effectors suppress pattern-triggered immune(PTI) responses. These viral effectors can be recognised directly or indirectly by intracellular R receptors to trigger a cell death response that confines the virus to the site of infection. The Tobacco Rattle Virus (TRV) 16 kDa protein (16K) is a silencing suppressor that inhibits the formation of plant silencing complexes, preventing target RNA degradation. However, the information concerning the mode of action of the protein, its contribution to the infective cycle,as well as its interactions with plant proviral and defence factors is still incomplete. This issue is central to better understand the mechanisms of infection and antiviral defense, since the net outcome of infection in a susceptible host will depend on the joint and balanced action of proviral factors necessary for viral proliferation and defence factors that restrict infection. Protein-protein interactions between the viral proteins and cellular proteins are crucial for the outcome of the infection. In this study, we aimed to identify host factors associated with the viral protein 16K. To this end, we used immunoprecipitation followed by mass spectrometry, to find direct protein interactors of 16K in N. benthamiana plants. Additionally, to understand the mode of action of 16K during the infection of the cell, we studied its subcellular localisation via confocal microscopy in transitory expression assays of constructions fused with GFP. 16K-GFP appears to be localised in the cytoplasm, somewhat in the endoplasmic reticulum and, interestingly, also in chloroplasts, which play key roles in defence responses against biotic pathogens.

This work was supported by National Research grants PID2021 127982NB-I00 to CL from Ministerio de Ciencia e Innovación (Spain) and UE-FEDER, and grant iLINKA20415 to CL from CSIC (Spain).

Peer reviewed

1 p.-4 fig.