Tobacco Rattle Virus Coat Protein Targets Ferredoxin 1 for Degradation.

Plant virus infections commonly inhibit leaf photosynthesis, leading to characteristic symptoms such as chlorosis. However, whether a conserved mechanism underpins this phenomenon remains unclear. Here, we demonstrate that the coat protein (CP) of tobacco rattle virus (TRV) interacts with Nicotiana benthamiana ferredoxin (NbFd1) in chloroplasts, recruiting the 26S proteasome to promote NbFd1 degradation. This degradation reduces the net photosynthetic rate facilitated by NbFd1, ultimately causing leaf chlorosis. Notably, this interaction is not unique to TRV CP, as other viral proteins also recognise Fd1, suggesting a conserved mechanism among plant viruses. Evolutionary analyses indicate that Fd1 originated from prokaryotic photosynthetic bacteria and was maintained in plants through endosymbiosis under strong selective pressure. Notably, Fd1 from Selaginella moellendorffii, an early-diverging vascular plant, is also recognised by TRV CP, suggesting an ancient origin of this interaction. In addition, Solanum lycopersicum Fd1 interacts with TRV CP, and its overexpression suppresses TRV-GFP infection, supporting a defensive role. Together, these findings show that TRV CP targets Fd1 to impair host photosynthesis and promote symptom development, whereas highlighting the evolutionary significance of this interaction.