The 5′ untranslated region of Bean pod mottle virus RNA2 tolerates unusually large deletions or insertions

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. 94 (2013) 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.