Involvement of the Plant Nucleolus in Virus and Viroid Infections

Abstract

The nucleolus is a dynamic subnuclear body with roles in ribosome subunit biogenesis, mediation of cell-stress responses, and regulation of cell growth. An increasing number of reports reveal that similar to the proteins of animal viruses, many plant virus proteins localize in the nucleolus to divert host nucleolar proteins from their natural functions in order to exert novel role(s) in the virus infection cycle. This chapter will highlight studies showing how plant viruses recruit nucleolar functions to facilitate virus translation and replication, virus movement and assembly of virus-specific ribonucleoprotein (RNP) particles, and to counteract plant host defense responses. Plant viruses also provide a valuable tool to gain new insights into novel nucleolar functions and processes. Investigating the interactions between plant viruses and the nucleolus will facilitate the design of novel strategies to control plant virus infections.

Nucleoli: Composition, Function, and Dynamics

“…The involvement of the nucleolus in infection cycles of animal and human viruses is well established (Hiscox, 2007;Hiscox et al, 2010;Taliansky et al, 2011). In plants, a growing number of viruses show some interaction with the nucleolus (and other nuclear bodies such as CBs) and roles for the nucleolus and nucleolar proteins are now emerging (Taliansky et al, 2011). For example, plant viruses can recruit nucleolar proteins for assembly of viral RNP particles, virus replication and movement, and to counteract hostviral defense systems.…”

“…Other viral proteins are also found in the nucleus/nucleolus (e.g. the P3 protein of Tobacco etch virus and the P6 protein of Cauliflower mosaic virus) but the function of the nucleolar localization is unknown (Taliansky et al, 2011). How different viral proteins target CBs and the nucleolus, their interactions with host proteins like fibrillarin, and the impact of usurping normal functions on nucleolar structure and function are important questions for the future that are likely to provide insights into nucleolar biology.…”

Cajal bodies and their role in plant stress and disease responses

“…The nucleolus plays a crucial role in the infection cycle of numerous DNA and RNA-containing viruses (reviewed in [72][73][74] ). Since DNA viruses tend to replicate within the nucleus it is easier to comprehend their associations with the nucleolus.…”

The Nucleolar Fibrillarin Protein Is Required for Helper Virus-Independent Long-Distance Trafficking of a Subviral Satellite RNA in Plants

“…With the exception of Rubisco, which remained enriched in band 1, the most abundant host protein precipitating with anti-P20 IgG was a nucleolar protein, fibrillarin, which was detected in band 2 in three independent experiments (Table 1). Fibrillarin is known to interact with viral MPs and is important for long-distance trafficking of several RNA viruses (Kim et al, 2007;Taliansky et al, 2010;Semashko et al, 2012;Zheng et al, 2015). The LC-MS/MS results were confirmed by immunoblot analysis, revealing the presence of P20 and fibrillarin in the P20 co-IP complex in the HV coinfected tissues (Figures 4C and 4D).…”

“…Thus, viruses must have evolved various strategies to interact with cellular factors to be loaded into and unloaded from the vascular system (Chen et al, 2000;Kim et al, 2007;Harries et al, 2009;Raffaele et al, 2009;Taliansky et al, 2010;Semashko et al, 2012;Hipper et al, 2013). Host factors such as myosin are required for MP targeting to and virus movement through the PD (Amari et al, 2014;Harries et al, 2009); intercellular and long-distance trafficking of Tobacco mosaic virus (TMV) (Chen et al, 2000) and Groundnut rosette virus (GRV) (Kim et al, 2007;Taliansky et al, 2010;Semashko et al, 2012) were substantially delayed in plants silenced for PECTIN METHYLESTERASE and fibrillarin. However, remorin, a Solanaceae protein resident in membrane rafts and plasmodesmata, can interact physically with the MP from Potato virus X and negatively regulates Potato virus X intercellular and phloem-mediated trafficking (Raffaele et al, 2009).…”