Virus-specific adaptations for the production of a pseudorecombinant virusformed by two distinct bipartite geminiviruses from central America

Most whitefly-transmitted geminiviruses possess bipartite genomes comprisin g DNAs A and B. The production of viable pseudorecombinants by reassortment of infectious cloned components is generally limited to isolates/strains o f a particular virus. Following exchange of cloned genomic components of Si da golden mosaic virus from Costa Rica (SiGMV/Co) and Sida golden mosaic vi rus from Honduras (SiGMV/Ho-yv), the pseudorecombinant viruses were infecti ous in various plant species. Three DNA B components (B-1, B-2, B-3), diffe rent in a few nucleotides, were isolated from Sida rhombifolia naturally in fected with SiGMV/Ho-yv. Only SiGMV/Ho-yv DNA B-2 was able to form a viable pseudorecombinant with SiGMV/Co DNA A. In protoplasts, as well as in inocu lated leaves, SiGMV/Co DNA A trans-replicated the heterogenomic SiGMV/Ho-yv DNA B-1 component, indicating that impaired movement is involved in the de ficiency of SiGMV/Ho-yv DNA B-2 to form a pseudorecombinant virus with SiGM V/Co DNA A. Even after extensive mutation analysis of SiGMV/Ho-yv DNA B-1 a nd B-2, we were unable to pinpoint differences in SiGMV/Ho-yv DNA B-2 that allowed the formation of a pseudorecombinant virus with SiGMV/Co DNA A. We observed a gradual increase of infectivity from noninfectious SiGMV/Co DNA A/SiGMV/Ho-yv DNA B-1 and B-3 pseudorecombinant virus to pseudorecombinant viruses showing normal systemic spread of both genomic components associate d with symptomatic plants. (C) 2000 Academic Press.