P-262 - Tobamovirus fructirugosum protein synthesis control in the host cell

Viral mRNAs have evolved numerous mechanisms to recruit the host protein translational machinery. Thus, most positive single stranded RNA plant viruses lack one or both of the canonical 5´-cap or 3’-poly(A) at their genome ends. This is also the case for the tobamovirus genomes that have a 5’-cap, but no 3’-poly(A)-tail. We have studied the role of the 5’- and 3’-untranslated regions (UTRs) of tomato brown rugose fruit virus (ToBRFV) (Tobamovirus fructirugosum) genome on protein translation. Our results showed that, while the 5´-UTR is important for efficient cap-independent translation, both UTRs are important for efficient cap-dependent translation. The 3’-UTR contains two structural RNA elements, a region including three pseudoknots followed by a tRNA-like structure that are both involved in efficient cap-dependent translation. We showed that while the positive effect of the tRNA-like structure on translation efficiency is the consequence of RNA stability increase, the 5´-UTR and PK elements have additional important roles. To deepen in their mechanisms, we are trying to identify the proteins that bind to these RNA elements. Additional results on the host mechanism against aberrant RNAs (nonsense-mediated decay, NMD, acting on RNAs with long 3’-UTRs) suggest that the ToBRFV genomic and subgenomic RNAs are resistant to NMD. One of the factors avoiding RNA degradation by NMD is the presence of the viral 3´-UTR at its 3´-terminus.