Movement of hordeivirus hybrids with exchanges in the triple gene block

The barley stripe mosaic virus (BSMV) triple gene block (TGB) coding for mo vement proteins (MPs) was replaced with the respective TGB genes from two o ther hordeiviruses, poa semilatent virus (PSLV) or lychnis ringspot virus ( LRSV). The BSMV/LRSV recombinant did not exhibit infectivity on the plants tested, whereas the infection rate and host range of the BSMV/PSLV hybrid w ere similar to those of BSMV. In particular, the BSMV/PSLV hybrid infected Nicotiana benthamiana, a nonhost plant for PSLV, indicating a contribution of non-MP elements of BSMV genome to host specificity of virus transport. A ssuming that the PSLV TGB was functional in the BSMV genome context, a furt her series of recombinants was constructed, in which smaller portions of th e BSMV TGB were replaced by the corresponding PSLV sequences. Examination o f the infectivity of the hybrid viruses suggested that the TGB-coded protei ns could interact in a host-dependent manner to mediate cell-to-cell moveme nt. Analysis of recombinants with hybrid sequences of the first gene in the TGB (beta b gene) indicated that (i) sequence-independent binding of beta b to viral RNAs could occur during formation of beta b-RNA complexes in viv o, and that (ii) the beta b MP is involved in virus long-distance movement, for which homologous N- and C-terminal beta b domains are required. (C) 19 99 Academic Press.