The 5′ untranslated region of Bean pod mottle virus RNA2 tolerates unusually large deletions or insertions
Department of Plant Pathology, Ohio Agricultural Research and Development Center, The Ohio State University, 1680 Madison Ave, Wooster, OH 44691Virus Research (Impact Factor: 2.32). 11/2013; 179(1). DOI: 10.1016/j.virusres.2013.10.024
Bean pod mottle virus (BPMV) is a bipartite, positive-sense (+) RNA virus of Secoviridae. We recently reported that a 137 nucleotide (nt) stretch (#263-399) of the 466 nt 5' untranslated region (5' UTR) of BPMV RNA2 can be deleted without compromising BPMV propagation in host plants [Lin et al., J. Gen. Virol. (2013) 94, 1415-1420]. Here we demonstrate that nonviral insertions of up to 625 nt is tolerated by the same region. Furthermore, one insertion mutant underwent recombination in infected plants, leading to the truncation of nt #250-361, thus extending the dispensable sequence to 150 nt (nt #250-399). We are unaware of any other (+) RNA virus that tolerates insertion/deletion of these sizes (625 nt/150 nt) within its 5' UTR. Importantly, tolerance of large insertions within the RNA2 5' UTR offers a novel, more convenient site for incorporating host gene fragments, making BPMV a more versatile vector of virus-induced gene silencing.
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ABSTRACT: The Potyviridae family relies on a cap-independent translation mechanism to facilitate protein expression. The genomic architecture of the viral RNAs of the Potyviridae family resembles those of the animal picornaviruses. The viral genomes lack a 5' cap structure. Instead, they have the viral protein VPg covalently linked to the 5' end of the RNA. The viral RNAs code for a single large polyprotein, which is then cleaved into several functional subunits. With their common genome organization with the Picornaviridae, it has been largely assumed that the members of the plant Potyviridae family share similar translation mechanism. We will describe the remarkably diverse translational enhancers identified within the family and their unique mechanisms of translation, from internal recruitment of the ribosomes to ribosomal scanning from the 5' end and the recruitment of the VPg in translation, which are unseen in their animal virus counterparts. The divergence among the potyviral translation enhancers is heightened with the recent discovery of Triticum mosaic virus, an atypical member of the Potyviridae family, for which its 5' leader by far exceeds the typical length of plant viral leaders and contains features typically found in animal viruses. Much remains to be learned on how these highly divergent elements enable potyviruses, which include some of the most damaging plant viruses, to take over the host translation apparatus. While no clear consensus sequence, structure or mechanism has been reported yet among the potyviral elements, more thorough studies are need to fill in the gap of knowledge. Copyright © 2015. Published by Elsevier B.V.Virus Research 02/2015; 206. DOI:10.1016/j.virusres.2015.02.005 · 2.32 Impact Factor
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