Cauliflower mosaic virus protein P6 is a multivalent node for RNA granule proteins and interferes with stress granule responses during plant infection

Cauliflower mosaic virus intersects with components of the stress granule pathway within its replication factories and has a global capacity to suppress stress granule assembly in plants. Biomolecular condensation is a multipurpose cellular process that viruses use ubiquitously during their multiplication. Cauliflower mosaic virus replication complexes are condensates that differ from those of most viruses, as they are nonmembranous assemblies that consist of RNA and protein, mainly the viral protein P6. Although these viral factories (VFs) were described half a century ago, with many observations that followed since, functional details of the condensation process and the properties and relevance of VFs have remained enigmatic. Here, we studied these issues in Arabidopsis thaliana and Nicotiana benthamiana. We observed a large dynamic mobility range of host proteins within VFs, while the viral matrix protein P6 is immobile, as it represents the central node of these condensates. We identified the stress granule (SG) nucleating factors G3BP7 and UBP1 family members as components of VFs. Similarly, as SG components localize to VFs during infection, ectopic P6 localizes to SGs and reduces their assembly after stress. Intriguingly, it appears that soluble rather than condensed P6 suppresses SG formation and mediates other essential P6 functions, suggesting that the increased condensation over the infection time-course may accompany a progressive shift in selected P6 functions. Together, this study highlights VFs as dynamic condensates and P6 as a complex modulator of SG responses.

Automated summary

The Cauliflower mosaic virus can suppress stress granule assembly in plants by intersecting with components of the stress granule pathway. The virus forms condensates called viral factories, which consist of RNA and protein. The viral protein P6 plays a central role in these condensates, while host proteins show dynamic mobility within them. The study also found that components of stress granules localize to viral factories during infection, and the viral protein P6 can localize to stress granules and reduce their assembly.