Movement of hordeivirus hybrids with exchanges in the triple gene block.

The barley stripe mosaic virus (BSMV) triple gene block (TGB) coding for movement proteins (MPs) was replaced with the respective TGB genes from two other 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 were 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. Assuming that the PSLV TGB was functional in the BSMV genome context, a further series of recombinants was constructed, in which smaller portions of the BSMV TGB were replaced by the corresponding PSLV sequences. Examination of the infectivity of the hybrid viruses suggested that the TGB-coded proteins could interact in a host-dependent manner to mediate cell-to-cell movement. 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 vivo, 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. Copyright 1999 Academic Press.