Different RNA Elements Control Viral Protein Synthesis in Polerovirus Isolates Evolved in Separate Geographical Regions

Most plant viruses lack the 5'-cap and 3'-poly(A) structures, which are common in their host mRNAs, and are crucial for translation initiation. Thus, alternative translation initiation mechanisms were identified for viral mRNAs, one of these being controlled by an RNA element in their 3'-ends that is able to enhance mRNA cap-independent translation (3'-CITE). The 3'-CITEs are modular and transferable RNA elements. In the case of poleroviruses, the mechanism of translation initiation of their RNAs in the host cell is still unclear; thus, it was studied for one of its members, cucurbit aphid-borne yellows virus (CABYV). We determined that efficient CABYV RNA translation requires the presence of a 3'-CITE in its 3'-UTR. We showed that this 3'-CITE requires the presence of the 5'-UTR in cis for its eIF4E-independent activity. Efficient virus multiplication depended on 3'-CITE activity. In CABYV isolates belonging to the three phylogenetic groups identified so far, the 3'-CITEs differ, and recombination prediction analyses suggest that these 3'-CITEs have been acquired through recombination with an unknown donor. Since these isolates have evolved in different geographical regions, this may suggest that their respective 3'-CITEs are possibly better adapted to each region. We propose that translation of other polerovirus genomes may also be 3'-CITE-dependent.

Automated summary

Most plant viruses lack the 5'-cap and 3'-poly(A) structures found in their host mRNAs and have developed alternative translation initiation mechanisms. In this study, the translation initiation mechanism of cucurbit aphid-borne yellows virus (CABYV), a member of poleroviruses, was investigated. The presence of a 3'-CITE in the 3'-UTR of CABYV was found to be necessary for efficient translation. Additionally, it was demonstrated that the 3'-CITE's activity is dependent on the presence of the 5'-UTR in cis. The 3'-CITEs of different CABYV isolates have evolved through recombination, potentially adapting to specific geographical regions.