Coexistence, Not Extinction: Tomato bushy stunt virus (TBSV) and its Parasitic Defective Interfering RNA Form a Stable Equilibrium in planta
Research Poster Health & Life Sciences 2025 Graduate ExhibitionPresentation by Anthony Taylor
Exhibition Number 208
Abstract
When a virus’ proteins are translated inside a host, they can be utilized by all replicating genomes within the viral replication complex. Full-length viruses address this by acting as cooperators, producing and consuming these proteins equally. However, defective interfering (DI) RNAs, a subset of the viral population that arises de novo in viral infections, are freeloaders, using the proteins without contributing. According to the most popular theories of cooperation, largely based on Garrett Hardin’s Tragedy of the Commons, this situation should see DIs outcompete the full-length virus, driving it to extinction. The dearth of evidence demonstrating DI existence in non-laboratory passaged infections appears to support this. However, viral proteins, like most things in nature, do not provide additive benefits…they provide non-linear ones. When the situation is modelled non-linearly, we see that there is a potential for coexistence: a polymorphic equilibrium between cooperator and freeloader. This work sets out to provide in planta evidence that plant virus proteins benefit replicating genomes non-linearly, using tomato bushy stunt virus (TBSV), its prototypical DI, and Nicotiana benthamiana plants. Through qPCR data, we deliver evidence that the genome ratio of TBSV to DI settles at an equilibrium around 7 days post inoculation regardless of the starting ratio, concluding that, at least in this system, TBSV and its prototypical DI coexist at a stable equilibrium. We are now seeking evidence that the replicative benefit of TBSV proteins, at least in N. benthamiana protoplasts, is non-linear.
Importance
A “common good” refers to something that everyone in a population can freely consume, but in so doing precludes its consumption by another individual. For microorganisms, common goods are often diffusible molecules that are costly to produce but provide unselective benefit: a situation that makes freeloading and subsequent population collapse seem inevitable. In reality, it rarely occurs, and previous theoretical work has hypothesized that common goods in biology provide benefit(s) that vary non-linearly with the proportion of cooperators in the population, leading to a cooperator/cheater equilibrium and no collapse. Our work showcases an equilibrium between a full-length plant virus and its parasitic RNA, providing evidence supporting this hypothesis as a potential explanation for this common goods paradox.