Adaptation of the geminivirus bean yellow dwarf virus to dicotyledonous hosts involves both virion-sense and complementary-sense genes.

Abstract

Bean yellow dwarf virus (BeYDV) and maize streak virus (MSV) belong to the geminivirus genusMastrevirus and have host ranges confined to dicotyledonous and monocotyledonous species, respectively. To investigate viral determinants of host range specificity, chimeras were constructed by exchanging their coding and non-coding regions. BeYDV chimeras containing MSV ORF V1, ORF V2 or small intergenic region sequences, either individually or in various sequential combinations, replicated and produced virus particles in Nicotiana tabacum protoplasts. BeYDV chimeras containing MSV ORFs C1 and C2 and/or the large intergenic region were unable to replicate. None of the chimeras was able to systemically infect either N. benthamiana or maize. Complementation experiments using BeYDV chimeras containing MSV ORF V1 and/or ORF V2 suggest that expression of MSV movement protein and/or coat protein prevents BeYDV movement. The results demonstrate that factors involved in both viral DNA replication and virus movement are exclusively adapted to either monocotyledonous or dicotyledonous host backgrounds.The majority of members of the Geminiviridae genus Mastrevirus, typified by maize streak virus (MSV), infect monocotyledonous species. However, two members have been described, namely tobacco yellow dwarf virus (Morris et al., 1992) and bean yellow dwarf virus (BeYDV ;, that are adapted to dicotyledonous species. Mutational analysis of open reading frames (ORFs) predicted from the nucleotide sequence, and the identification of a complementary-sense intron has indicated that BeYDV encodes four genes that have functionally conserved homologues in other mastreviruses (Liu et al., a, 1998.

High-Frequency Reversion of Geminivirus Replication Protein Mutants during Infection

“…Although no studies have linked the begomovirus AL1 protein to host range (49,52), the reversion of a tomato yellow leaf curl virus C4 mutant in tomato but not in N. benthamiana has been attributed to different host constraints on systemic movement (29). Mastrevirus replication proteins have also been implicated in host adaptation (33). Interestingly, partial reversion of a three-nucleotide mutation in the RepA coding sequence also occurs at 100% frequency during maize streak virus (MSV) infection (67).…”

Complex Recombination Patterns Arising during Geminivirus Coinfections Preserve and Demarcate Biologically Important Intra-Genome Interaction Networks

“…Functional analyses of recombinant genes [9], [10] and genomes [11]–[13] has indicated that a large proportion (and possibly the vast majority) of recombination events between distantly related genomes probably yield defective progeny.…”

“…Analyses of bacterial [14]–[16] and viral recombination [6], [12], [13], [17] and protein engineering studies utilising DNA-shuffling methodologies [9], [10], [15], [18] have indicated that the probability of a given recombination event being deleterious depends on the modularity of the specific gene(s) or sub-gene module(s) that are transferred and tends to increase with decreasing parental sequence relatedness. This effect is caused, at least in part, by the tendency of recombination to disrupt the networks of genome encoded sequence specific interactions that underpin the biology of all organisms.…”

Recombination hotspots and host susceptibility modulate the adaptive value of recombination during maize streak virus evolution

“…With their small genome size, recombinogenic nature, and high mutation rates, geminiviruses have proved to be excellent models for experimental studies of the evolutionary mechanisms of virus emergence and adaptation. Accordingly, various experiments involving geminiviruses - and MSV in particular - have illuminated genetic factors underpinning important evolutionary processes, including the adaptation of these viruses to specific vector species [34] or hosts [35-37], their mutational dynamics [2,3,38-41], and the biochemical and selective factors constraining their adaptation through recombination [37,42-45]. …”